Tag Archives: limbic system

The Male Brain: Demystifying the Divinely Devised Differences

Male Brain. While women don’t often understand or agree, men have—since the dawn of time—had different instincts, emotions, and approaches to situations. Although these approaches can (arguably) be questionable, the varying innate reactions are simply different than those of women: not better, not worse. While both sexes come with their own strengths and weaknesses, we have to wonder: what biological structures underlie the instincts and actions of the male brain? Why are there differences between the male brain and the female brain? And how do the neurophysiological structures within the male brain attribute to the behavior we see in everyday life? Find out more below. 

Male Brain

The Male Brain

Historically, social differences between men and women centralized around physical characteristics and social constructs that defined each gender. As our modern society has progressed to challenge the social roles and labels that have, for centuries, defined men and women, research over the past twenty years has zeroed in on sex-based differences that classify neurological differences between the sexes. While the emerging biological discoveries underline the strengths and weaknesses of both the male and female brain, the overarching goal of research aims to emphasize the divine differences that distinguish sexes—rather than imply inferiority—to better understand how anatomical differences influence behavioral differences between sexes.

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While the natural behavioral tendencies of both males and females seem to be unpredictable and bewildering, understanding the neurophysiological dissimilarities between sexes links behavioral differences to a structural root. Although, at times, it seems as though the men and women are from two entirely different planets—as the saying goes:

“men are from Mars, women are from Venus”

Understanding the male brain is fundamental for discovering the neurological and behavioral differences that distinguish the innate tendencies people have based on their biology.

The Male Brain: How It All Started

As a trailblazer in the investigation of behavioral differences between sexes, Nirao Shah, spearheaded research to biological differences in 1998 as he began his postdoctoral fellowship.  While Shah observed the behaviors essential for the survival of each sex, he investigated how this innate behavior is biologically wired in the brain. He hoped to find the root of behaviors by identifying neuronal circuitry unique to each sex, he has since inspired researchers to unearth the inherent differences that distinguish the male brain from its female counterpart.

The Male Brain: Structural and Functional Differences

A Question of Grey Matter and White Matter in the Male Brain

The most obvious difference between the male and female brain is the distinctly larger crania of males. Due to the proportionally larger body size of males, larger craniums allow for a larger brain to develop amongst male brains. While the presence of a larger brains lacks correlation for heightened intelligence, a fundamental size difference is present between the male and female brain.

As research has found that the male and female brain are wired differently, it has been determined that the male brain operates on intrahemispheric communication, contrasting that of the female brain which optimally operates through inter-hemispheric communication. This insinuates that the male brain has stronger connections within a single region of the brain, whereas females have stronger connections between the left and right hemispheres. While this puzzling difference seems to be without reason, the cellular composition of brain tissue accounts for the wiring that makes the male brain unique.

As a result of an MRI study at the University of Pennsylvania, it has been confirmed that male brains have higher percentages of white matter. Found within the cerebellum, which is split into the right and left hemisphere, two types of tissue of the central nervous system are found: grey matter and white matter. The outer layer of the cerebellum, composed of grey matter folds, is made up of tightly packed dendrites, cell bodies, and axon terminals.

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These tightly folded regions are specialized to regulate memory, language, perceptual awareness, and attention—ultimately containing the synapses that communicate messages. White matter, in contrast, is made up of axons—connecting grey matter to one another—creating a fast communication network, like a metro system. White matter makes up important structures, like the thalamus and hypothalamus, which ultimately relay information from the body to the cerebellum.

Together, these tissues work to allow the white matter to communicate between grey matter areas, and for the grey matter to communicate with the rest of the body. While the researchers at the University of Pennsylvania speculated that the higher volumes of white matter are found amongst larger brains because of the further distance for information transference, the research team concluded that the greater amounts of grey matter amongst the female brain facilitates inter-hemispherical computation of information in a smaller amount of space (e.g. a smaller brain).

During development, the male brain is structured to increase activity and connectivity within each hemisphere by creating communication networks that are modular and direct. While this within-hemispheric processing allows linkage of perception to action along the posterior tract of the cerebellum, it also allows the mediation of motor action ipsilaterally. By way of strong within-hemispheric processing and connectivity, the divinely designed male brain allows for strong coordination of actions in males.

As research and functional imaging have suggested, white matter tracts are activated while working memory is in use. Because of the high percentage of white matter within the male brain, it comes as no surprise that men are better equipped to juggle items within their working memory.

The Male Brain and the Corpus Callosum

The Bridge of the Brain

Extending from the University of Pennsylvania study in 2014, the corpus callosum—a white matter cable that connects the right and left hemisphere—is smaller in the male brain. This also led to the observation of heightened bilateral symmetry amongst the brain in females compared to males: as communication between hemispheres increases, greater symmetry in muscle tissue arises. From these observations, the larger corpus callosum in the female brain can account for the greater inter-hemispherical communication observed in females, and why, biologically, the male brain tends to reflect the success of intrahemispheric communication. This anatomical explanation helps debunk why men are easily frustrated when asked to multitask: because the female brain allows multiple tasks and an abundance of information to flow simultaneously, the smaller corpus callosum in men inhibits the same task juggling ability that the female brain facilitates.

The Male Brain and the Limbic System

The Emotions of a Man

Areas of the Brain

Comprised of the hypothalamus, hippocampus, amygdala, and various other surrounding areas, the limbic system is heavily involved in emotional regulation. In an issue of the Journal of Neuroscience, which was solely dedicated to sex differences within the nervous system, Larry Cahill discussed how the amygdala in the male brain—which experiences and recalls emotional events—is larger than the amygdala in the female brain. Even as infants, MRI research shows that the male brain has higher activity within the limbic system than the female brain. While men are often stereotyped as “unemotional creatures,” this natural, anatomical difference supports the idea that men are, in fact, more emotional than women, but nurture leads to the masking of emotional expression.

Thought to attribute to learning differences between sexes, neurochemical and anatomical differences between the hippocampi of men and women have also been discovered. Contrasting the left hippocampus activation in females, the right hippocampus has increased activation in the male brain; these findings suggest that when presented tasks that require cognitive thinking, males use fewer verbal strategies than women.

Additionally, despite the stereotype that men think about sex more than women, the limbic system— specifically, the hypothalamus—is responsible for this biological drive for sexual pursuit. While the hypothalamus within the male brain is nearly two and a half times larger than the female brain’s hypothalamus, testosterone fertilizing the Y gene (aka the male gene) attributes to this size discrepancy. This is why males report thinking about sex three times more often than females. While this research serves as a biological basis of male behavior, it does not negate an ability to learn to be civil and controlled. (Just because a man has an urge to act, it doesn’t mean he can’t control it!)

The Male Brain and Visuospatial Skills

The male brain tends to surpass the skills of the female brain when it comes to visuospatial skills that allow them to analyze and mentally manipulate objects. Seen from early stages of development, the superior visuospatial abilities of the male brain exceeds the female brain’s ability when it comes time to track moving objects, aim projectiles at targets, and visualize the rotation of two- or three-dimensional objects. While females exceed at other tasks, such as recalling word lists, the differing brain development between sexes explains the heightened accuracy of males in certain skills, such as spatial tasks and motor skills. In everyday life, these surpassing abilities can be seen in navigational skills: males better calculate their position by direction and relative distance traveled, whereas the female brain relies on landmarks to distinguish location.

The Male Brain and Chemical Differences

While we often attribute the prominence of aggression amongst males with their increased levels of testosterone, there are a variety of uses of testosterone throughout the body. Notably, testosterone, in the male brain, impairs impulse-control and ignites libido. While so many questions where they stand with their partner when they see him checking out the supermodel walking by, rest assure that it is just biology at play! Because of the dampened impulse control and revved libido, it makes it harder for men to suppress their impulse to scope the gorgeous woman walking by.

Questionably unfaithful behavior can also be attributed to the presence of the hormone vasopressin. In a study of mole rats, a species containing the vasopressin gene were more monogamous and committed than their cousin species: the cousin species of mole rats that lacked the vasopressin gene were more promiscuous. When the vasopressin gene was injected into the brain of the promiscuous mole rat, the transient tendencies subsided and the mole rats became monogamous. While we are not claiming that men are (always) like rats, a higher presence of vasopressin in the male brain is attributed to more committed, faithful relationships.

While it often seems that male behavior is dominated by their natural abundance of testosterone, the male brain changes when they become a dad-to-be. Similar to the changing chemicals of an expecting mother’s brain, the male brain decreases testosterone and increases bonding hormones, such as prolactin and oxytocin, ultimately equipping them with more bonding hormones to make them better dads.

In terms of stressful situations, male brains have a unique increase of dopamine, serotonin, and norepinephrine in the basolateral amygdala, while female brains don’t. In the onset of stress exposure, chemical levels change within the male brain, particularly influencing the prefrontal cortex and hippocampus, which are associated with spatial and nonspatial memory. This helps to explain why the onset of stressful situations impairs the male brain’s ability of object recognition.

The Male Brain is Different From the Female Brain: Why?

Biologically speaking, the male brain has different sex-steroid hormones than women’s. While females have high levels of estrogen and progesterone, males are dominated by testosterone and androgens. During in-utero development, the male brain becomes heavily influenced by the high levels of testosterone, which are responsible for their masculine body plan; while this naturally attributes to physical characteristics, the surging testosterone naturally shapes the brain, too. Regions, like the amygdala and hippocampus, have an abundance of receptors specific for sex hormones, explaining why these regions differ in size between the male brain and the female brain.

In terms of evolution, researchers break down the neural differences as a result of adaptation to the actions of neurotransmitters and hormones that appease our sense organs and brain. As the female brain has adapted to childbearing and education, the female brain is better adapted for verbal sharing and communication. Evolutionarily, the male brain, in contrast, is adapted for hunting and fighting; as men roamed the land for hunting, their silent pursuits and navigational skills required heightened visuospatial skills and a decreased need for verbal sharing.

Although some behaviors of men are confusing and, at times, unforgivable, nature has equipped men with biological predispositions that are simply different from those of females. Debunking the differences between the biological structures of the male and female brain helps to understand what motivates behaviors. Although testosterone fuels the male brain to strive for sexual pursuit, differing structures between the male and female brain attribute to functional and behavioral differences. While subtle deviations are seen anatomically between the male and female brain, the emerging research of sex-based neurological differences attempts to explain how the male brain approaches life.

Consider checking out an in-depth look at the female brain and how the structural differences result in different behaviors.

Feel free to comment below!

References

Madhura, l., Alex, S., Drew, P., Theodore D., S., Mark A., E., Kosha, R., & … Ragini, V. (2014). Sex differences in the structural connectome of the human brain. Proceedings Of The National Academy Of Sciences Of The United States Of America, (2), 823.

Goldman, Bruce, and Gérard DuBois. “Two Minds: How Men’s and Women’s Brains Are Different.” Stanford Medicine, stanmed.stanford.edu/2017spring/how-mens-and-women’s-brains-are-different.html.

Amygdala: The powerhouse of emotions

Our brain is a palace of structures. It dictates everything we do, how we think, how we behave and how we feel. In this article, we will focus only on the amygdala (sounds like a character out of a Star Wars movie): From what it is, functions, neurophysiological aspects of the amygdala, what happens if it gets damaged, and its relationship with other brain areas.  

Amygdala

What is the amygdala?

The amygdala is a structure in the limbic system that is involved directly with motivation: Particularly related to survival and our emotions. It is also responsible for processing emotions such as fear, pleasure, and anger.

The amygdala is the house where all of our emotions are stored. One of its main functions is to help us to recognize potential threats when we encounter them. When doing this, it revs the body up in preparation for a fight or flight response by increasing our breathing and heart rates. It is also responsible for evaluating the emotional intensity of various situations. This is especially important because since we encounter certain situations repeatedly, from emotional memory, our amygdala wouldn’t need to fire up… unless our brains say otherwise.

The word ‘amygdala’ was derived from the Greek word for “almond” since this part of our brain is shaped like one. Like most other structures in our brain and in other animals, we have two amygdalae. Each amygdala is located on each of the left and right temporal lobe. Since it’s in very close proximity to the hippocampus, the amygdala is involved with the influence of memory consolidation. Memory consolidation is the process that stabilizes a memory trace right when it has been obtained.

Amygdala: The limbic system

To understand the amygdala a little bit better, this article is going to give a swift review of the limbic system and why it’s important.

The limbic system is not a separate system, but a system composed of several key structures in the brain including the diencephalon, mesencephalon, and telencephalon. The limbic system specifically includes the amygdala, thalamus, hippocampus, hypothalamus, basal ganglia, and cingulate gyrus.

You can find the limbic system nuzzled immediately underneath the cerebrum. The limbic system is important because it is responsible for the formation of memories, and our emotional lives are stored in this area of the brain. The components of the limbic system regulate endocrine and autonomic function in response to any sort of emotional stimuli. In short, the three key functions it is known to deal with are arousal (stimulation), memory, and emotions.

Hemispherical differences

Since we possess two amygdalae, it has been noted that the left and right amygdala serve a different purpose in how we process our emotions. Even though the left and right amygdala have independent memory systems, they still work as a team to encode, store and interpret our emotions.

Studies have reported that electrical stimulations to the right amygdala provoke negative emotions of sadness and fear. When looking at the left side, electrical stimulations induce unpleasant (anxiety, sadness, and fear) feelings, yet also has the ability to induce positive emotions such as happiness.

The right hemisphere is commonly associated with declarative memory. Declarative memory stores various information and facts from previously experienced events which need to be consciously recalled. The right amygdala is also responsible for the retention of episodic memory. Episodic memory stores the autobiographical memory, which allows you to recall sensory and emotional experiences of a particular event.

Development of the amygdala

The development of the amygdalae is an interesting tale that consists of developmental differences between the right and left amygdala, as well as sex differences.

When looking at this area of the brain, there are some observable differences in the growth of the amygdalae. The left is the first to develop, reaching its peak 1.5-2 years before the right. Looking aside from the early growth of the left, the right has a continuous increase in volume for a longer period of time. The right side of the amygdala is often associated with face recognition and fear stimuli. As for the left, it is said that its early development provides infants with the capability of being able to detect danger.

There are also considerable differences in the development of the amygdalae between male and females. In the early stages of development of the brain, it is seen that the limbic system in females grows much more quickly than in males. For males, the structural development of the amygdalae occurs over a longer period of time, while females reach their full growth potential 1.5 years before their counterparts. It is noted that reasoning behind the slower development of the male amygdalae is due to relatively larger sizing.

Sex distinction

In regards to the differences in sexes, this area of the brain is one of the best understood. As briefly described above, we see that the amygdala is larger in male adults and in adult rats.

Adding to size, the functioning of the amygdalae differs in males and females. In one study, participants amygdala activation was looked at by watching a horror movie. Results of this study showed a completely different lateralization in the amygdalae between males and females. They showed that enhanced memory of the film was related to more activity occurring in the left amygdala and not the right. For males, it showed that the memory of the film was related to the right and not the left.

The left is responsible for the recollection of details, which results in more thought than action in response to emotionally stressful stimuli. This can be used to attribute why we see less of a physical response in women than in men. The right has been linked to taking action and has been linked to negative emotions. In this scenario, this is why we see males respond to emotionally stressful stimuli in a physical manner.

Functions of the amygdala

  • Memory – This area of our brain has been linked to the storage of our emotional memory. The amygdala is heavily involved in calculating the emotional significance of events that occur in our lives. Since the amygdala has connections to other regions of the brain, it also has an influence on emotional perception. What this means, is that the amygdala alerts us to notice significant events even when we are not paying attention.
  • Arousal – Sexual desire is largely mediated by the limbic system. Activation of our amygdala can cause sexual feelings, memories of sexual intercourse, penile erections, orgasms, uterine contractions, and ovulation.
  • Hormonal secretions  When experiencing stressful events, our amygdala sounds the alarm by sending a distress signal to our hypothalamus. When this happens, the hypothalamus activates the SNS (sympathetic nervous system) by sending signals through autonomic nerves to the adrenal glands. Then, the glands will respond by pumping out epinephrine, also known as adrenaline. The amygdala is also strongly modulated by serotonin, norepinephrine, epinephrine, and dopamine.

What happens if the amygdala is damaged?

Because there are two amygdalae, if there is a bilateral lesion, there is a reduction in aggression and fear. This may mean you may adopt a superman complex and feel like nothing can hurt you or scare you… unless it’s kryptonite. A study was done on monkeys who had bilateral lesions of their amygdala and researchers reported a huge drop in fear and aggression, just as we see in our human counterparts.

Don’t hold your breath there though. Even though the monkeys showed a significant drop in fear and aggression, humans are faced with a lot more when the amygdala is destroyed. A bilateral lesion can cause an individual to have an impaired ability to interpret emotional facial expression. Kind of sounds like Autism. This type of lesion has actually been linked to autism, with MRI scans detecting an increase in amygdala volume.

Neuropsychological correlates of the amygdala

Advancements in neuroimaging technology have made it possible for neuroscientists to make significant findings related it. Data has shown that the size of an individual’s amygdala can be linked to anxiety, and how size may fluctuate due to antidepressant medication consumption (left). Certain studies have also shown children with anxiety tend to have smaller amygdalae.

Aside from those two interesting facts, data has shown that the amygdala plays a large role in particular mental disorders as well as other mental states.

Fear

A very rare genetic disease known as Urbach-Wiethe disease is responsible for focal bilateral lesions of the amygdala in people. Such a disease results in individual’s showing no signs of fear. This finding of the disease continues to prove that the amygdala plays a large role in triggering the state of fear.

Aggression

Several studies that have looked at animals have repeatedly shown that stimulating the amygdala induces sexual and aggressive behavior. 

Schizophrenia 

Schizophrenic patients are known to have enlarged ventricles, as well as enlarged amygdalae.

Social interaction

It has been said that there is a positive correlation between amygdala volume and the size and complexity of social networks. Size, in this case, means the number of contacts an individual may have, while complexity stands for the number of different groups an individual belongs to.

Data reveals that the larger a person’s amygdalae are the larger amount of social networks an individual has.

It has also been shown that the amygdalae are responsible for processing the violations of personal space. It has been observed in fMRI scans that this region of our brain is activated when it is sensed that a person is standing very close to them. For example, the person who is being scanned is aware when the observer is physically close to them, then when the observer is standing at a distance.

Sexual orientation

In recent studies, it has been suggested that there may be possible correlations between connection patterns in the amygdala, and sexual orientation. It has been reported that homosexual males have a tendency to show more feminine patterns in the amygdala than heterosexual males do. Homosexual females tended to show more masculine patterns in the amygdala than heterosexual females.

Bipolar Disorder

It is well documented that in bipolar disorder, there is great amygdala dysfunction during facial emotion processing. Those who have bipolar disorder have also displayed increased activity in their amygdala.

Post-Traumatic Stress Disorder (PTSD)

Patients who suffer from PTSD typically have a hyperactive amygdala in response to various stimuli that are in some way connected to trauma.

Depression

It is also overactive in those who suffer from depression, especially when you present them with sad stimuli. However, when presented with “happy” stimuli, their amygdala is under-active.

Anxiety

It is responsible for setting off a chain reaction for this disorder. It begins to react because some environmental stressor has convinced this area of the brain that you are in danger. However, this is only an issue to worry about when the amygdala is regularly triggered.

Amygdala and other brain regions

It holds some very special connections with other areas of the brain. It is known to make reciprocal connections with the hypothalamus, thalamus, septal nuclei, hippocampus, parahippocampal gyrus, orbital frontal cortex, the brain stem, and the cingulate gyrus.

The amygdala receives input from all senses as well as visceral inputs. Visceral inputs derive from the hypothalamus, parabrachial nucleus, septal area, and orbital cortex. Visual, auditory, and somatosensory information comes through via the temporal and anterior cingulate cortices. Olfactory sensory information is received from the olfactory bulb.

Some output pathways of the amygdala include:

  1. Stria terminals
  2. Ventral amygdalofugal pathway
  3. Directly to the hippocampus
  4. Directly to the dorsomedial nucleus of the thalamus
  5. Directly to the entorhinal cortex

Amygdala/emotional hijacking 

Emotional hijacking is an event that occurs when an individual’s cognitions are overpowered by their emotions. You normally see emotional hijacking occur in the context of fear and aggression. A perfect example of emotional hijacking to kick off this section is when Mike Tyson bit Evander Holyfield’s ear. According to Daniel Goleman who coined the term amygdala hijacking, this bad decision on Tyson’s behalf is the perfect example of it.

The neocortex – the “thinking” brain, has been completely overridden, and the amygdala fires up taking over total control of the brain; Thus the name “amygdala hijacking.” Hijacking can cause a person to perform irrationally, making decisions that are destructive. Not only does this take a toll on an individual (people who experience emotional hijacking are very remorseful after they realize and reflect on what they have done), their social relationships also take a huge hit. Emotional hijacking can lead to verbal or physical attacks, and such a surge of rage can easily cause an individual to severely harm a person, giving them the capacity to kill.

Something to keep in mind is that emotional hijacking is a phenomenon that requires build up. Troubling past experiences that are crippling an individual can be the direct link to why someone will have an outburst like this. When a person has an outburst, they don’t last long, but the consequences can be quite damaging as a result.

However, there is no need to worry. Not all emotional hijacks are distressing. Goleman states that there are positive hijacks. He gives an example that if a joke strikes a person as funny, and their laughter is explosive, that is a limbic response.

There are three signs you can look out for if you happen to experience an emotional hijack:

  • Strong emotional reaction
  • Sudden onset
  • Post-episode realization if the reaction was appropriate or not/regret

Areas of the brain are especially fascinating, especially when looking at them in more depth. Learning about them gives us an idea of what’s going on within ourselves, and we are able to give a reason for our behavior.

Is this your favorite part of the brain after reading the article? Do you have a favorite area of the brain? Please let us know in the comments below! We hoped you enjoyed this article. 🙂

Synesthesia: Can You Hear Colors?

What is it like to hear colors and see sounds – people who have synesthesia might be able to give a little insight into that. Imagine the world full of new possibilities, sounds, images, and tastes. The way you are able to perceive and sense nature is so different from everybody else. You can say that the sky tastes like plums. When you hear Vivaldi’s four seasons on the piano, vibrant colors appear from every possible direction, representing spring, summer, fall, and winter. You are able to differentiate months of the year by colors and different smells by taste. Some of these are just examples. If you are able to relate to any of them, you might have synesthesia.

What is synesthesia?

Synesthesia

Scientists consider synesthesia to be a neurological and perceptual condition. It comes from Greek words that represent ‘togetherness and sensation’.  It is quite extraordinary and brings a whole different understanding to what surrounds us. In fact, people who have synesthesia most often than not, embrace it. They do not want to ‘cure’ the condition, per say. To them, the world is full of tastes and colors and sounds, depending on their particular type of synesthesia, of course. That’s how they’ve always experienced the world. They understand that Monday to have a green color, but Saturday more of a purple one and it makes sense to them.

Imagine looking at the sun each and every day and seeing that it’s yellow and one day wakes up and realize it’s a bland gray. That’s what it would be like for a synesthetic to lose their sense and understanding of the world. They would not only be very confused for a long period of time. No, despite that, they’d probably also feel sadness and grief for the loss of all of the beautiful imagery, sounds smell and touch that they will never experience again.

It’s quite difficult to understand synesthesia without experiencing it. A sky that tastes like blueberries or colors appearing when you hear music? That sounds crazy to anybody who has not experienced it themselves. Synesthesia, however, is not limited to just these people though. A lot of researchers looked into synesthetic occurrences in the regular population. These studies found that many are actually able to experience synesthesia. Sometimes they don’t even realize they are doing it.

Perhaps, in order to understand it better, you should experience a little touch of what synesthesia can be. This is what scientists call the McGurk effect

The McGurk effect

For a very long time, researchers understood speech as an auditory perception only. Now know the McGurk effect where there is an interplay between auditory and visual stimuli in the perception of speech. It is somewhat an illusion. Scientists, Harry McGurk and John Macdonald coined the effect in their 1976 study. It seems to be that when speech is paired with visual stimuli, a very extraordinary multi-sensory illusion happens.

They achieved this surprising effect by making a recording of a person voicing a consonant. After that they put the recording with a face, however, that face was expressing a different consonant. When the voice recording was heard by itself, the participants recognized it for what it was. However, when McGurk and Macdonald paired the voice recording along with a face expressing an incongruent sound – the participants heard a different sound. That sound ended up being the combination of the voice recording and the visual face articulation. The McGurk effect shows an absolutely astounding example of multisensory integration and how both, visual and auditory information can integrate and result in a unified experience.

If you can imagine, a lot of researchers found the illusion quite interesting and attempted to replicate it with different populations and conditions. What they found was quite astounding. Summerfield & McGrath found in their 1984 study that the effect happens with the use of vowels and not just consonants. The McGurk effect is present in pre linguistic infants according to the 1997 study by Rosenblum, Schmuckler & Johnson. Astonishingly enough, the effect even worked across a variety of languages which Massaro, Cohen, Gesi and Heredia showed in their 1992 study.

Synesthesia and the McGurk effect

It seems that even people who do not have the condition fall for the McGurk effect. The effect is very strong. Even when you know what to expect from it, you still cannot change it. When you think about it, it makes sense. The world we live in is full of senses and a variety of experiences. We do not just perceive sound by itself, or cannot look at something in a complete silence. There is always an ongoing integration of senses that happens all around us. It is no wonder that sometimes in our lives we are able to experience a synesthetic episode.

Types of Synesthesia

Synesthesia can appear in a variety of forms and types. In fact, researchers have been able to find over seventy types of synesthesia. We characterize the different varieties by what type of sensation they are able to cause and where that sensation came from. Here are some of the more common ones:

  • Number-Form Synesthesia: those who have this type of synesthesia are able to perceive numbers as mental maps. That means that these people will put the numbers in certain positions in space that will form a mental map. Whenever a person thinks of a number, a mental map will appear in their mind. Francis Galton introduced this type in his ‘The visions of sane persons’ work.
  • Lexical-Gustatory Synesthesia: people with this type will experience different tastes that correspond to specific words or phonemes. Badminton could taste like mashed potatoes but suitcase will taste like a chocolate cake. Quite a fun type, this one!
  • Grapheme Synesthesia: this one emerges with perceiving numbers and letters as different colors. This is one of the most common types of synesthesia. Interestingly enough, different people experience different colors in association with numbers and letters. Some commonalities occur. Letter ‘A’ often appears red for some reason.
  • Personification: A variety of ordered sequences will show up as different personalities. For example, Friday can be a happy go-lucky girl who enjoys dancing while Monday is an angry and bitter old man. Do you see any connection with real life?
  • Chromesthesia: people perceive sounds as a variety of colors. There is a variety of different experiences within this type with some people only perceiving colors during spoken speech and others seeing them during musical pieces. This type is quite common among musicians.
  • Misophonia: this one is not a particularly nice type of synesthesia. People who have this type experience very negative emotions when it comes to sounds. Examples of experienced emotions can be anger, disgust, sadness etc. Fortunately, this is one of the rarer types and it happens due to a disturbance between the limbic system and the auditory cortex.
  • Mirror-touch-pain Synesthesia: these people will experience a sensation of touch when they see somebody else being touched. The pain type can experience pain in a similar way when they see somebody else in pain. Researchers have linked this particular type of synesthesia with mirror neurons and regions responsible for empathy in the brain.

There are many other types of synesthesia. If you think you might be experiencing synesthesia but did not find your specific type above, you can type in your symptoms into google search, and sure enough, there will be somebody else with similar symptoms.

Synesthesia: Diagnostic Criteria

Synesthesia

Up to this date, there is no clear cut method for diagnosing synesthesia. Certain criteria exist that specialists adopt in order to help with the diagnosis. Keep in mind, however, that some of the leading scientists and researchers do not follow these criteria. Despite that, it gives at least a little bit of guidance in diagnosing synesthesia.

Symptoms

  • Projection: people will see the sensations outside of their body (hearing sounds outside during a musical piece)
  • Memory: associations that the synesthetic has will stick with him and will often overpower new associations that he or she might experience in the course of a lifetime.
  • Involuntary: sensations happen without the control of these people
  • Emotion: sensations can be perceived either positively or negatively.
  • Duration: the perceptions have to be stable and unchangeable.

Synesthesia and the Brain

Synesthesia

The original cause for synesthesia is still unknown. Due to such a variation in types of synesthesia, it is quite difficult to generalize brain studies to all of the different types. The brain uses different parts of the brain for the processing of different senses, therefore, with such a large variety of synesthesia types, an involvement of different brain parts happens. Researchers have to study each type separately and see whether there are some similarities between them. Some studies reported the activity in the superior posterior parietal cortex in relation with the grapheme-color synesthesia. Both visual cortex and the auditory cortex are activated during the McGurk effect because we are both listening and seeing at the same time.

The consensus among scientists is that depending on the type of synesthesia, the brain regions responsible for that sense will activate. What we speculate is that the uniqueness of synesthesia comes from a different way of network connections within the brain. Baron-Cohen and colleagues mention the excessive quantity of neuronal connections in the brain of synesthetics. According to him, during normal perceptual experiences, we have different brain areas for different senses and a different perception. The connection between those areas is present but is restricted. However, when you have synesthesia, your brain develops more connections between different neurons. This makes the restrictions between the areas to disappear and leads to synesthesia.

Peter Grossenbacher, on the other hand, says that the feedback communications are not subdued in a way that it happens in normal perception. The information that is processed from areas responsible for high-level of processing is not able to come back to each signified area. Instead of different senses going back to areas responsible for single senses, they mix together, allowing synesthesia.

Ramachandran and Hubbard support the increase in neural connection theory, but they also add that it happens due to the fact that the pruning between different sensory modalities is decreased.

Pruning is the removal process of the synaptic connections and more neurons in order to enhance the work of already existing neural transmissions.

Synesthesia and Genetics

Some studies have found a genetic link with the development of synesthesia. Asher and colleagues claim there is a link between auditory-visual synesthesia and certain chromosomes. Due to previous research suggesting a familial trend and a genetic factor helping in the development of synesthesia, they decided to look at 43 different families who had it. They found four different types of loci that could cause the variation in brain development in the brain of those who have the condition. What is interesting is that one of the genes that they identified, might be important for pruning.

Thomsen and colleagues focused on different genetic components. This leads to a variety of scientists to believe that synesthesia occurs due to a combination of a variety of genes.

Famous people throughout history with Synesthesia

Synesthesia is more common than some people believe. In fact, a variety of famous people are believed to have had this condition.

  • Vincent Van Gogh: chromesthesia
  • Lorde: music –> color
  • Vladimir Nabokov: grapheme -> color
  • Pharrell Williams: chromesthesia
  • Stevie Wonder: chromesthesia
  • Billy Joel: chromesthesia, grapheme-> color
  • Duke Ellington: chromesthesia

Prevalence

As mentioned before, diagnosis synesthesia is quite difficult so knowing its prevalence can bring some challenges as well. Before people used to think that the condition is quite rare, however, nowadays we know that it is a lot more common. Simner and colleagues in their 2006 study investigated the overall population. They found that around 1% of the population have the grapheme-color type. Around 5% have some sort of type of synesthesia. Due to the difficulty of diagnosis, this could be a very low account of the overall numbers, however.

Synesthesia is very common and a lot of people might have it. Family members, friends, co-workers, and classmates. Even you might have some sort of type of synesthesia and not know about it!

Limbic System Functions: Limbo With Your Limbic System

Your limbic system functions range from regulating your emotions to storing your memories to even helping you to learn new information. Your limbic system is one of the most essential parts of the brain that help you live your daily life. The primary structures that work together in your limbic system are the amygdala, the hippocampus, the thalamus and hypothalamus, the cingulate gyrus, and the basal ganglia. All these parts help you to be active in society, engage in social relationships, and be a well-rounded person. To learn more about the interesting ways your limbic system impacts your life, sit back and get in-tuned with all of its hard-working employees!

Limbic System Functions

1. What is another name for your amygdala?
  • Your amygdala is essential for controlling the emotions that you express. That is why it is called ''the emotional center of the brain.''

2. What is your basal ganglia involved with?
  • Your basal ganglia is the main structure that controls all of the voluntary movements your body performs

3. Where do hormones originate in the brain?
  • Your hypothalamus is controlled by the pituitary gland which regulates how many and what hormones are released throughout your body (this is all under the endocrine system)

Limbic System Functions

Limbic System Functions

Interconnected nuclei and cortical structures located in the telencephalon and diencephalon have different functions that are related to the limbic system. These nuclei main functions are of self-preservation. They regulate our autonomic and endocrine function especially as a response to emotional stimuli.

Many of the areas are related to memory and with arousal levels involved in motivation and reinforcing behaviors. Since it’s related to self-preservation, many of the areas are related to the sense of smell, since it is critical for survival.

The areas critical for functions in the limbic system are two:

  • Subcortical structures include the olfactory bulb, hypothalamus, amygdala, septal nuclei and thalamic nuclei.
  • Cerebral Cortex also is known as the limbic lobe it includes the hippocampus, insular cortex, subcallosal gyrus, cingulate gyrus and parahippocampal gyrus.

Here are some of the different parts of the limbic system and how they affect you:

Limbic System Functions: The Amygdala

Shaped like a small almond, the amygdala is located in each of the left and right temporal lobes. It’s known as  “the emotional center of the brain,” because it is involved in evaluating the emotional intake of different situations or emotional intelligence (for example, when you feel happy because you received an awesome grade on your math exam or when you might be frustrated because the heavy traffic is making you late for work). The amygdala is what makes the brain recognize potential threats (like if you are hiking in the lone woods and suddenly you hear the loud footsteps of a bear coming toward you). It helps your body prepare for fight-or-flight reactions by increasing your heart and breathing rate. The amygdala is also responsible for understanding rewards or punishments, a psychological concept known as reinforcement coined by the classical and operant conditioning experiments of Ivan Pavlov.

The amygdala works by being stimulated through the electrical forces of neurotransmitters (understand the different types of neurotransmitters). Many times, when this stimulation is very high, we show physical acts of aggression, like throwing tantrums, screaming, or hitting objects. If the amygdala was removed from the human brain, then we would all become extremely tame and no longer respond to things that previously caused us frustration or annoyance. Also, we would become indifferent to all forms of external stimuli, especially those related to fear and sexual responses.

Limbic System Functions: The Hippocampus

This part of the brain is found deep within the temporal lobe and is shaped like a seahorse. The exact role of the hippocampus is disputed between psychologists and neuroscientists, but we generally know that it is essential in forming new memories about past experiences. The three major stages of memory forming in the brain are:

1. Sensory input from your peripheral nervous system sending neurotransmitters to your brain

2. Your brain storing those stimuli in its “short-term memory,” which holds the information for about 3-5 minutes

3. If 5 minutes has elapsed and you are still thinking about that memory, then it will enter into your long-term memory, where it will stay for virtually an endless period of time.

Your hippocampus is the main brain portion responsible for going from stage 2 to stage 3, or converting short-term memories to long-term memories.

Researchers suggest that the hippocampus is responsible for “declarative memory,” which is the ability for one to explicitly verbalize their memories (i.e. episodic memories and semantic memories).

Limbic System Functions

If the hippocampus is damaged, then a person will not be able to build new memories (known in neuropsychology terms as anterograde amnesia) although he or she might be able to hold onto older memories. This individual would instead live in a very strange world where everything they experience and everyone knew whom they meet just fades away. A classic example of this is seen in the movie 50 First Dates, where Drew Barrymore plays the lead role of a girl with short-term memory who loses memory every night being with her beloved during the day.

Limbic System Functions: The Thalamus

These structures are both associated with changes in emotional reactions. The thalamus is known as the “way-station” of the limbic system because it aids in communicating what is going on in the system with the rest of the brain. It connects areas of the cerebral cortex that are involved in sensory perception and movement with other parts of the body associated with sensation and movement. It has control over your peripheral nervous system, which moves sensations from the body through the spinal cord into the brain. Specifically, it works alongside these major lobes in the brain:

  1. The parietal lobes – it sends sensory touch information to the somatosensory cortex located here
  2. The occipital lobes – it sends visual information to the visual cortex here
  3. The temporal lobes – auditory signals are sent to the auditory cortex here

The thalamus has other functions for your body as well, like controlling your sleep and awake states of consciousness. It sends signals from the brain to the rest of the body to reduce your perception of sensory information while sleeping, which is why you wouldn’t necessarily feel if an ant was crawling on you or someone put their hand on your arm gently while you were sleeping. The thalamus also is involved in motor controls, relaying sensory signals to the cerebral cortex, forming memories and expressing emotions, and perceiving pain.

Limbic System Functions: The Hypothalamus

The hypothalamus is a small piece located just below the thalamus and has lesions on it that are the driving forces behind our major unconscious activities, like respiration and metabolism. One of its central functions is homeostasis for the body, which is returning it from either too much excitement or too little pleasure to a calm “set-point” from which we behave “normally.” It is one of the busiest parts of the brain because it also helps drive other motivated behaviors like hunger, sexuality, and aggression. The lower side of the hypothalamus seems to be involved with pleasure and rage, while the middle section is associated with displeasure, aversion, and uncontrollable and loud laughter. Because the hypothalamus also regulates the functions of your autonomic nervous system, it controls things like your pulse, blood pressure, breathing, and arousal response to emotional circumstances.

Recent biological studies have shown that when we overeat, a protein called leptin is released by fat cells in our bodies. The hypothalamus is the first part of the brain to sense these high levels of leptin in the bloodstream so it will respond by decreasing our appetites. Some research suggests that some people have a mutation in the gene which produces leptin, so their hypothalamus is unable to recognize that they are overeating. However, there are many overweight individuals studied who do not have this mutation, so work is still being done in this research idea.

The hypothalamus also works in coordination with the pituitary gland, known as the “master gland.” It is chemically and neurally related to the pituitary gland, which as a result of its control, pumps hormones called releasing factors into the bloodstream. The pituitary gland has the central control over your endocrine system, so it releases hormones that are essentially important to regulating growth and metabolism for you.

 Limbic System Functions: The Cingulate Gyrus

This part is located in the middle of your brain next to the corpus callosum. Not much is known about the cingulate gyrus, but researchers suggest that this is the area that links smell and sight with pleasurable memories of previous experiences and emotions because it provides a pathway from the thalamus to the hippocampus. This area is involved with your emotional reaction to pain and how well you regulate aggressive behavior.

The anterior cingulate gyrus deals with the vocalization of emotions. It has connections with speech and vocalization areas of the frontal lobe, which includes Broca’s area, a brain piece that controls motor functions involved with speech production. People with Broca’s aphasia, or an impairment in their Broca’s area, are unable to fluently produce speech to convey what exactly is in their mind but they are able to fully comprehend the speech and writing of others.

The cingulate gyrus also is involved in the emotional bonding and attachment between a mother and her child because of the frequent vocalization that takes place between mothers and their infants, so children feel deeply attached to the voices of their mothers. Because the cingulate gyrus is connected with the amygdala, it processes emotions and is responsible for fear conditioning and relating memories to sensory information received from the thalamus.

Limbic System Functions: The Basal Ganglia

This area is an entire system within itself located deep in the frontal lobes. It organizes motor behavior by controlling your physical movements and inhibiting your potential movements until it gets the instructions to carry them out, based on the circumstances that you are in. The basal ganglia also participate in rule-based habit learning; choosing from a list of potential actions; stopping yourself from undesired movements and permitting acceptable ones; sequencing; motor planning; prediction of future movements; working memory; and attention.

In general terms the limbic system functions are as follows:

  • The sense of smell: the amygdala directly intervenes in the process of olfactory sensation.
  • Appetite and eating behaviors: The amygdala and the hypothalamus both act in this behavior. The amygdala helps in food choice and emotional modulation of food intake. Meanwhile, the hypothalamus controls the intake of these foods.
  • Sleep and dreams: While dreaming, the limbic system is one of the most active brain areas according to different neuroimaging techniques. The hypothalamus also intervenes in this case particularly the suprachiasmatic nucleus of the hypothalamus that controls the sleep-wake cycle through circadian rhythms.
  • Emotional Responses: Limbic system functions include modulating emotional responses of fear, rage and endocrine responses of fight or flight responses. In these responses, the amygdala, the hypothalamus, the cingulate gyrus and even the basal ganglia’s motor tasks work together.
  • Sexual Behavior: The limbic system also takes part in the sexual behavior through the hypothalamus and different neurotransmitters, specifically dopamine.
  • Addiction and motivation: Addiction is highly related to your reward system which in part is controlled by the amygdala. Therefore it’s important to know this when treating addicts. Relapse is usually related to the release of excitatory neurotransmitters in brain areas such as the hippocampus and the amygdala.
  • Memory: As we mentioned before emotional responses are related to the limbic system. Emotions are is also involved in the retrieval and consolidation of memory, therefore one of the limbic system functions is the emotional memory. Other memories that have influence from the limbic system are medial temporal lobe memory system in charge of making and storing new memories. As well as, Diencephalic memory system related to the storage of a recent memory, a dysfunction of this circuit results in Korsakoff’s Syndrome.
  • Social Cognition: This refers to thought processes involved in understanding and dealing with other people. Social cognition involves regions that mediate face perception, communication skills, emotional processing, and working memory. They help the complex behaviors necessary for social interactions. Limbic structures involved are the cingulate gyrus and amygdala.

To end this fantastic article we leave a video with a song to learn the limbic system functions. Hope you enjoyed the article and feel free to leave a comment below.

https://www.youtube.com/watch?v=B-RLFEWTqsY

Hypothalamus: the importance of hormones in the brain

What is the hypothalamus? Let’s start by painting a picture: Your stomach starts churning. It’s been hours since you last ate and you can feel the hunger intensely. You start craving every food available and it starts to become difficult to concentrate. The only thing you can think about is food and it becomes too uncomfortable to bear so you decide to eat. Does this sound familiar?

If you want to learn in depth about the hypothalamus don’t miss “the extend further” section at the end of this article!

The responsible of this whole process is the hypothalamus, a small sub-cortical structure located in the center of the brain. Being only the size of a pea, the hypothalamus is in charge of regulating different functions that are essential to our day to day life, such as eating and homeostasis. If it weren’t for the hypothalamus, we wouldn’t know when we needed to eat and we would end up dying of hunger.

It modules the food intake by increasing or decreasing hunger and satiation awareness. – Ali Inay on Unsplash

What is the Hypothalamus?

The hypothalamus and the thalamus are part of the diencephalon. They are part of the limbic system and contain the main diversity in neurons of the whole brain. It’s in charge of the autonomic nervous system and the endocrine system. It’s an endocrine gland that releases hormones in charge of modulating behaviors relating to species maintenance. It also regulates hormone secretion of the hypophysis (pituitary gland) with whom it shares the hypothalamic-pituitary-adrenal axis. It’s made of two different secreting neurons: The parvocellular (who secrete peptidic hormones) and the magnocellular (which secrete neurohypophysial hormones).

Where is the Hypothalamus located?

Having a perfect spot in the brain is important. It is located in a brain part just beneath the thalamus (from there the name) and right above the brainstem. It connects with the hypophysis through the pituitary stalk. The hypothalamus central position allows it to communicate perfectly, receiving information from different body structures and sending information to others.

What does the Hypothalamus do? How does it keep us alive?

Its functions are essential to our daily life. It is responsible for maintaining the body’s systems, including body temperature, body weight, sleep, mating, levels of aggression and even emotional regulation. Most of these functions are regulated by a chain of hormones that inhibit or release between themselves.

  • Hunger: when our body detects that we have don’t have enough energy saved, it sends Ghrelin (hunger hormone) to the hypothalamus, telling us we need to eat. It then releases a neuropeptide that produces the hunger feeling in our body. In the painted picture above our body is producing so many neuropeptides that we feel overwhelmed by hunger.
  • Satiation: when we have eaten enough, our body has to tell our brain that we don’t need any more food and that we need to stop eating. While we are eating our body produces insulin which in turn increases the production of a hormone called Leptin. Leptin travels through our blood until it reaches the ventromedial nucleus of the hypothalamus. This inhibits the production of neuropeptides, therefore, stopping the hunger sensation.
  • Thirstiness: Similar to hunger, when the body is thirsty it releases an antidiuretic hormone (vasopressin) that allows for the body not to lose water and stimulate drinking more.
  • Temperature: The blood temperature when it arrives at the hypothalamus will determine if we need to reduce or increment our body temperature. If the temperature is too high, we need to lose heat, therefore, the anterior portion with inhibit the posterior, producing certain events such as sweating, in order to lower heat. On the other hand, when the temperature is too low, the posterior portion will inhibit the anterior. This will enable the release of a thyroid stimulating hormone (TSH) and the adrenocorticotropic hormone (ACTH), both helping heat conservation.
  • Sleep: The reason why it’s so difficult to sleep with the light on is because of the hypothalamus. The sleep cycle is regulated by circadian rhythms, which in turn are managed by a set of neurons in the medial hypothalamus called the suprachiasmatic nucleus. This nucleus receives information from ganglion cells in the retina through the optic nerve tract. This way the retina is capable of detecting a change in lighting and sends the information back to the hypothalamus. The set of neurons process the information and then it is sent to the pineal gland. If there is no light, the pineal gland will secrete melatonin (sleep hormone). If there is light, the gland reduces melatonin levels which promotes wakefulness.
  • Mating and Aggression: Even though these behaviors are opposites they are highly related in the animal world and are also regulated by the hypothalamus. Some neurons are stimulated when there is mating behavior present while others when there is aggression. However, there are other neurons that happen to respond to both scenarios. The amygdala sends in information related to the aggressive area in the hypothalamus so that it can release important and pertinent hormones depending on the situation.
  • Emotions: when we experience an emotion this comes with many physiological changes. For example, when walking in a dark alley by yourself the natural response is to feel fear. Therefore the body has to prepare to respond appropriately given the circumstance. So, the hypothalamus sends information to the different parts of the body (increasing our breathing rate, contraction of the blood vessels, pupil dilation and muscle contraction). This way, the hypothalamus allows us to detect threats and run if necessary away from it. That being so, it enables the physical response to the emotion.

What relationship does the hypothalamus have with love?

One of the most important brain functions is processing emotions. These emotions are processed in the limbic system. The hypothalamus is a big part of this system since it’s in charge of letting the whole body know what emotion the brain is feeling. How emotions work in the brain is a complex task, nevertheless, the hypothalamus is responsible for how we feel love. The hypothalamus produces phenylethylamine, a type of neurotransmitter with similar effects to amphetamines. This is the reason why when we fall in love we feel happy and euphoric. This neurotransmitter also leads to an increase in adrenaline and noradrenaline, which rises the heartbeat, oxygen levels and blood pressure (triggering the sensation of your “heart skipping a beat”).

On the other hand, the brain also produces dopamine and serotonin, which allows us to focus our attention on the person that makes us feel these emotions and regulate our emotions accordingly. Consequently, the hypothalamus is very important since without it, we wouldn’t be able to fall in love.

Without the it, we wouldn’t be capable of falling in love.

What link is there between the hypothalamus and the hypophysis (pituitary gland)?

The hypothalamus regulates the emission of hormones from the hypophysis. The hypophysis is also an endocrine gland and its under the hypothalamus, protected by the sella turcica (bone structure in the base of the cranium). The pituitary gland function is to secrete hormones, under the hypothalamus command, through the blood that our body needs to maintain homeostasis (level our temperature or balance different hormones). Their relationship is so close that they form the hypothalamic-pituitary-adrenal axis and they couldn’t work separately. The hypophysis allows for the hypothalamus to extends its effects to the rest of the body.

What happens when the hypothalamus is disturbed? In what disorders o diseases is the hypothalamus involved?

Given the relevance of the hypothalamus, an injury in any of the hypothalamus’ nuclei can be fatal. For example, if the satiation center is damaged (not being capable of being satiated), we wouldn’t stop eating and therefore eat non-stop with a high risk to what this conveys. Some of the most frequent pathologies are:

  • Diabetes insipidus: It is when the supraoptic, paraventricular and the supraoptic hypophysial fasciculus nuclei are injured. Due to low production of ADH, there is more liquid intake and more urine output.
  • Injury in the caudolateral hypothalamus: If this region is damaged all sympathetic activity of the nervous system will diminish including body temperature.
  • Injury in the medial hypothalamus: all parasympathetic activity of the nervous system will be damaged but the body temperature will rise.
  • Korsakoff Syndrome: with the mammillary nucleus (related to the hippocampus) altered, there will be anterograde amnesia, the person will have difficulty remembering new information in long-term memory. Since remembering is difficult, people with this syndrome tend to use fabrications to fill the gaps. This disorder is usually associated with chronic alcoholism it can also happen as an alteration in the mammillary tubers and their connections.

To extend further…

What hormones are produced in the hypothalamus?

The hypothalamus function is through hormone release. Some of the hormones are:

  • Neurohormones: Antidiuretic hormone and oxytocin.
  • Hypothalamic factors: The hypothalamus uses corticotropin-releasing hormone (CRH or corticoliberin), thyrotropin-releasing hormone (TRH), gonadotropin-releasing hormone (GnRH or gonadoliberin), growth hormone–releasing hormone (GHRH or somatoliberin).

Of what nuclei is the hypothalamus made of and what is their purpose?

Each nuclei has a main purpose:

  • Arcuate nucleus: it’s part of the emotional function of the hypothalamus. Its endocrine function consists of synthesizing hypothalamic peptides and neurotransmitters. In charge of liberating the gonadotropin hormone.
  • Anterior hypothalamic nucleus: it’s in charge of releasing the heat when sweating. It’s also in charge of liberating thyrotropin in the hypophysis.
  • Posterior hypothalamic nucleus: Its function is to keep the heat inside the body when it’s cold.
  • Lateral hypothalamic nucleus: it regulates thirst and hunger. When it detects a lack of sugar or water it tries to find homeostasis.
  • Mammillary nucleus: given its connections with the hippocampus, it’s related to the memory.
  • Paraventricular hypothalamic nucleus: It regulates hormone release from the hypophysis (oxytocin, vasopressin, and corticotropin).
  • Preoptic Nucleus: it influences functions such as nutrition, locomotion, and mating.
  • Supraoptic nucleus: It regulates arterial pressure and liquid equilibrium through the antidiuretic hormone.
  • Suprachiasmatic nucleus: In charge of hormones relating to circadian rhythms.
  • Ventromedial nucleus: its role consists of regulating satiation.

From where does the hypothalamus receive information? Where does it send it?

The hypothalamus has great different connections due to the brain area where it’s located. On one side, it receives information from other structures (afferent) and then sends information to other parts of the brain (efferent).

Afferents

  • Reticular cephalic flexure: From the cephalic flexure to the lateral mammillary nucleus.
  • Median prosencephalic fasciculus: from the olfactory region, septal nuclei and amygdala region to the preoptic lateral and lateral hypothalamus.
  • Stria terminalis: from the hippocampus to the septum and mammillary nucleus.
  • Precommissural fornix fibers: connect with the dorsal hypothalamic area, septal nuclei and preoptic lateral nucleus.
  • Postcommissural fornix fibers: takes the information to the medial mammillary nucleus.
  • Retinohypothalamic fibers: Take information from the amount of light in the retina and sends it to the suprachiasmatic nucleus for circadian rhythm regulation.
  • Cortical projections: receives information from the cerebral cortex and sends it to the hypothalamus.

Efferents

  • Dorsal longitudinal fasciculus: from the medial and periventricular regions of the hypothalamus to the grey matter.
  • Mammillary efferent fibers: From the medial mammillary nucleus to the anterior thalamic nuclei, and also from the mesencephalon to the ventral nuclei.
  • Supraoptic nucleus: from the supraoptic nuclei to the posterior lobe of the hypophysis.
  • Tuberohypophyseal: from the nuclei arcuati to the infundibular stalk.
  • Descendent projections to the brainstem and spinal cord: from the paraventricular nucleus to the solitary nucleus and the ventrolateral regions of the medulla oblongata.
  • Efferent projections to the suprachiasmatic nucleus: it connects directly with the pineal gland.

Questions? Leave a comment below 🙂

This article was originally written in Spanish by David Asensio Benito, translated by Alejandra Salazar.