Brain Reward System: A complete guide to our pleasure center
Our brain reward system is incredible in how it functions! But what is it and how does it function? How does the brain reward system affect our bodies? How does it affect addiction, depression, and motivation? What happens when we crave something or our reward system is damaged? Find out this and more in this article!
What is the brain reward system?
The brain reward system (BRA) is the reward system that is made up of a group of neural structures that are responsible for incentive salience (our desire and craving for a reward), associative learning, and positive emotions that involve pleasure, such as joy, ecstasy, and euphoria.
Our first clue into the existence of a brain reward system happened by accident in Skinner Boxes during the 1950’s by researchers James Olds and Peter Milner. Scientists put electrodes into the limbic system of rats brains and sent a teeny tiny shock to the area when the rat entered a particular corner of the box. In theory, the shock would be unpleasant enough to make the rat want to stay away from that corner. This is because, with enough shocks, the rat’s brain would rewire itself to think of the corner as bad with aversive stimuli. However, when the electrodes were placed in the nucleus accumbens (a dopamine route that is part of the limbic system), the rats did the opposite as expected. Rather than avoiding the corner, the rats kept going back to the corner to get the shock over and over again… to the point that some rats opted for getting shocked over getting food. Some rats went back up 700 times within an hour. One rat went 7,500 times within a 12-hour period.
The brain reward system pathway: How does it work?
When the brain is exposed to something rewarding, it responds to the rewarding stimulus by increasing the release of dopamine. This is why the structures that are associated with the brain reward system are found along the major dopamine pathways in the brain. The mesolimbic dopamine pathway is the big player in our brain reward system and it connects the ventral tegmental area (VTA) (one of the main dopamine producers in the brain) with the nucleus accumbens (the area of the brain associated with reward and motivation). The mesocortical pathway is another dopamine pathway that connects the ventral tegmental area to the cerebral cortex. Essentially, the brain reward system is connected by dopamine pathways, chiefly the mesolimbic pathway, and neural structures, like the VTA, to help dopamine travel and ‘reward us”.
Many neuroscience studies on the brain reward system show that the more dopamine that is released by the reward, the more effective the reward is. This big dopamine release is known as the hedonic impact, which can change by the effort for the reward and the reward itself.
The brain reward system contains hedonistic hotspots, also known as pleasure centers, that bring about pleasure from intrinsic rewards. Our pleasure centers react to two types of stimuli. One that is naturally pleasurable and attractive (by naturally liking). These stimuli are known as intrinsic rewards. The other that is not inherently pleasurable and motivate behavior (by wanting) are called extrinsic rewards. Our brains react to intrinsic rewards in our pleasure center. Things like money, for example, are extrinsic rewards but have been taught by learned association that it’s an intrinsic reward. Therefore, the extrinsic rewards motivate a wanting, not a liking towards something.
These hedonistic hotspots are found within the nucleus accumbens shell, the ventral pallidum, the parabrachial nucleus in the pons. It’s thought that the insular cortex and the orbitofrontal cortex also contain some hotspots, as well. It’s also thought that in order to get a complete sensation of euphoria, simultaneous activation of every single hedonistic hotspot within the brain is necessary.
Our “wanting center” is located in the nucleus accumbens shell. This center is where our desires and wants comes from, also known as incentive salience. The amount of dopamine that travels through our mesolimbic pathway is correlated with the magnitude of want that we have. When the dorsorostral region of the nucleus accumbens is activated, our wanting for something increases without our actual liking of it. For example, some people who smoke may not actually like smoking, but they have a certain want to do it anyway.
One theory, the incentive-sensitization theory, proposes that wanting (an incentive) and liking (a pleasure) are two different branches of the same tree. For example, if our stimulus is activated by chocolate, it’s because we have the desire to have chocolate (the want) and the pleasurable effect of the chocolate (the liking). Rewards are usually liked and wanted to the same degree. However, each can change under certain circumstances. For example, rats that don’t eat after getting a dose of dopamine experience a loss desire to eat, although they act that they still like food. The wanting element is thought to be controlled by our dopaminergic pathways, while the liking element is theorized to be controlled by opiate-benzodiazepine systems.
Animals vs. Humans
Just like humans can, animals can also learn rather quickly to do something specific in order to obtain something rewarding. For example, rats can learn to press on a bar in order to get an injection of opiates into the brain. Also like humans, these animals won’t try to get the rewarding thing if the dopaminergic neurons of the mesolimbic pathway are inactivated. These means that animals and humans both engage in specific behaviors in order to increase the release of dopamine in their brain.
One study showed that sweet (something good, something liked) and bitter (something bad, something disliked) tastes produced similar facial expressions in human newborns, rats, and orangutans. This proves that pleasure, something good and liked, has objective features that are shared across various animal species.
How does the brain reward system affect our body?
Our reward system plays an obviously essential role in our brain. It helps play part in the executive functions, motor control, motivation, arousal, reward, reinforcement, nausea, sexual gratification, and lactation.
Regarding our organs, the rewarding release of dopamine plays an essential role in the immune system because dopamine acts upon certain cells in our immune system called lymphocytes. Mainly, dopamine reduces their activation level. Dopamine is also important in the spleen, bone marrow, and the circulatory system. Within our kidneys, dopamine is synthesized and discharged into a tubular fluid in order to increase blood supply to the kidneys, and increase the discharge of sodium in urine. This is a cause of development in hypertension. The role of dopamine in our pancreas is a more complex role. It’s theorized that dopamine protects out intestinal mucosa from damage and reduces gastrointestinal motility.
Hormonally, dopamine is the main dude when it comes to our brain reward system. It is a neurotransmitter that feeds our brain’s reward system and increases our motivation, pleasure, and addiction. High levels of dopamine involve a loss of reality, delusions, and a lack of emotion. Low levels of dopamine are associated with risk-taking and addictive behavior. It’s been proven that within the pancreas, dopamine also synthesizes and secretes hormones like insulin into the bloodstream. When dopamine is released, the stress-reducing hormones like cortisol and oxytocin are also released from our hypothalamus. Serotonin, the “happiness hormone” is released as part of the reward. Dopamine is the precursor to noradrenaline. Part of the job of noradrenaline is to help the brain make decisions by enhancing alertness and cognition.
The brain reward system and addiction
Addictive drugs and behaviors- such as smoking, drinking, and gambling- are rewarding to us (our brains) and are therefore reinforced because of their effects on our dopamine reward pathway- also known as our brain reward system. Within studies of addiction and our reward system, the lateral hypothalamus and the medial forebrain bundle are the most frequently studied. The system that has been most identified with the habit-forming actions of addiction is the mesolimbic dopamine system because its neurotransmitters target the nucleus accumbens- where our reward system is placed in the brain. However, those who have been studied, rats included, with amphetamine and cocaine addictions also have shown signs of dopaminergic synapses in the medial prefrontal cortex. One study that infused nicotine directly into the nucleus accumbens showed that there is a huge dopamine release within the medial prefrontal cortex. ΔFosB (Delta FosB) is a gene that is a common factor among those who have all different forms of addictions.
The brain reward system and depression
Having depression can be exhausting on your body. Well, it’s exhausting on the brain, too. Studies show that depressed people exhaust the areas of the brain that are related to positive emotions- like the reward system. People who suffer from depression have the same activity levels in positive emotions as someone without depression- they simply have an inability to sustain these emotions over time. The inability to experience pleasure in things that are normally rewarding is a classic sign of depression and is known as Anhedonia.
The brain reward system and motivation
When we are motivated to do something, it begins because our brain wants to because it’ll get a dopamine reward. Scientists have found that the stimuli that light up when we are motivated come from our ventral striatum, essentially the shell of the nucleus accumbens. Our motivation is regulated by a neurotransmission of dopamine in the mesocorticolimbic projection, but there are hedonic hotspots that also help regulate and bump up our motivation.
How does the brain reward system affect us when we crave something?
We all know that a craving isn’t just something we want- but something we need. It’s being thought nowadays that cravings originate in the brain, not the body. Cravings originate from two systems: our brain reward-processing activity and the release of hormones. The reward-processing system becomes intertwined with a feeling of longing. Later, conscious thoughts that include motivated reasoning as to why it’s a good idea to please the craving.
To take it step-by-step, our brain reward system first finds a target. This target causes the brain to release dopamine with the hopes that the brain receives happiness or pleasure from the craving. This desire for immediate satisfaction blocks our prefrontal cortex from considering the long-term goals against the craving. To understand better, think about the angel and the devil on the shoulder image. The angel is our prefrontal cortex who wants to consider the long-term consequences while the devil is the craving who only things about the short-term reward and perk. Once we don’t get our craving, our body releases stress hormones to make us feel discomfort or even pain in some cases. This stress is meant to trick the body into believing that the only way to feel better is to surrender to the craving.
Our brain can learn to connect the promise of a reward to anything. If our brain thinks that something will make us happy or better, our brain will begin the craving response to it.
What happens when the brain reward system is damaged?
When the brain reward system is damaged, meaning there aren’t enough dopamine receptors to cause our brains to release and receive the dopamine, it can be bad. This is known as reward deficiency syndrome (RDS). Pleasure comes from the anticipation and approach to rewarding stimuli. However, those with RDS get their dopamine “muted” in these events. People can become unmotivated because the receptors that give rise to our motivations don’t work as well. Sometimes, this damage can lead to drug addiction because the only way to feel a dopamine release is through drugs. A dopamine/neurological problem with becoming addicted to drugs in order to get a dopamine release is that drugs also dull the dopamine pathways and dopamine receptors. So, in reality, our lack of dopamine and current will be damaged further.
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