Neuromodulation: Find out more about nerve activity

Neuromodulation—it sounds complex, yet neuromodulation is simply a fancy term for the alternation of nerve activity. Through magnetic or electrical forces, this medical therapy normalizes nervous tissue function by applying electromagnetic currents or medications into the nerves. Neuromodulation stimulates the nerves to release neurotransmitters like dopamine to reduce pain, improve dementia, and even treat mental illness symptoms.

Neuromodulation
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What is Neuromodulation?

Neuromodulation describes highly developed biotechnology which modifies the nervous system for medical treatment. The human nervous system is comprised of the central nervous system, the peripheral nervous system, and the autonomic nervous system—all connected by the brain and spinal cord. Neuromodulation controls these nerves by delivering electromagnetic impulses or medications to specific areas of the body. This is frequently accomplished through implanted devices to a target area, but less invasive neuromodulation options outside of the body do exist. The overall purpose of neuromodulation is to reduce troubling chronic pain symptoms or to treat symptoms of an underlying disease. Neuromodulation methods either stimulate or depress nerve signals using the natural processes that regularly occur within the nervous system.

Neuromodulation and the Brain

The effects of neuromodulation are exerted in the nerves, but must first be processed by the brain. The central nervous system—the brain and spinal cord—has nerve cells called neurons. Neurons release substances like serotonin, dopamine, norepinephrine, histamine, acetylcholine, and many others. These neurotransmitters and hormones regulate the functions of the body and are considered neuromodulators because they are not broken down, remaining in the cerebrospinal fluid for long periods while they influence the neurons in the brain. Neuromodulation devices and pharmaceuticals control the neurons through the application of natural neuromodulators to treat various symptoms.

What Conditions Does Neuromodulation Treat?

Neuromodulation treats a variety of both physical and mental medical conditions. Because the nervous system is involved in a variety of bodily processes, neuromodulation is beneficial for almost any symptom ranging from migraine headaches to extensive diseases of the nervous system such as Parkinson’s disease.

Other conditions include:

  • Chronic pain
  • Epilepsy
  • Stroke
  • Movement disorders (dystonia, seizures, Tourette’s, etc.)
  • Ischemic disorders
  • Parkinson’s disease
  • Bowel and bladder dysfunction (i.e. incontinence, constipation)
  • Spinal injury
  • Cardiac disorders
  • Psychiatric disorders (i.e. depression, obsessive-compulsive disorder)
  • Hearing loss
  • Visual impairment

Invasive Neuromodulation Methods

Invasive methods of neuromodulation require a surgeon to place a battery-operated device inside of the body. The device resembles a pacemaker. Leads are placed in the targeted area of the body such as the brain or spinal cord, and they attach to a stimulator that delivers electromagnetic fields. The stimulator can also be implanted in a pocket near the internal leads or it can stay outside of the body.

Deep Brain Stimulation

Deep brain stimulation is a neuromodulation method in which a neurosurgeon places electrodes in the brain through small holes in the skull. The location may range from the right side to the left side of the brain in the areas that regulate movement. Those electrodes lie under the skin with insulated wires extending to the stimulator in the chest. Once activated, electrical pulses block the nerve signals causing symptoms.

A programmed controller allows the physician to adjust the settings based on the patient’s symptoms. The main conditions deep brain stimulation treats are essential tremor, dyskinesias, and rigidity associated with Parkinson’s disease, dystonia, and uncontrolled movements derived from medication side effects.

Spinal Cord Stimulation

Spinal cord stimulation sends electrical pulses to the spinal cord to manage chronic pain. Small leads lead to the spine from a device implanted in the patient’s abdomen. Spinal cord stimulation is optimal for patients with treatment-refractory chronic pain. The mild electrical pulses decrease the need for large amounts of pain medication. Due to the invasive nature of the therapy, physicians require patients to undergo intense physical and psychological testing.

Vagus Nerve Stimulation

The vagus nerve is one of the cranial nerves connecting the brainstem to the body. It is an accessory to the autonomic nervous system and communicates the motor and sensory activities of the major organs—the heart, lungs, gastrointestinal tract, and the neck.

Therefore, vagus nerve stimulation is a neuromodulation technique that stimulates the vagus nerve. The electrical impulses travel through a lead running from the vagus nerve to the stimulator implanted into the chest. The impulses are transmitted in intervals to prevent seizures and even treat depression. Side effects include difficulty speaking, sore throat, shortness of breath, coughing, and possible cardiac arrest.  

Auditory Brainstem Implant

In some cases, someone suffering from profound hearing loss is missing a hearing nerve or has an extensive inner ear abnormality that renders hearing aids or cochlear implants ineffective for restoring their hearing. An auditory brainstem implant is an option for those individuals. It stimulates hearing pathways by bypassing the hearing nerve and the inner ear. The auditory brainstem implant has three parts. The electrodes are connected to the brainstem, but rather than a large implanted stimulator, a microphone is situated behind the ear. Sound information is then transmitted by a decoding chip under the skin.

Functional Electrical Stimulation

Functional electrical stimulation targets the muscles. This type of neuromodulation sends electrical charges to weakened or paralyzed muscles originating from damage to the brain or spinal cord. The placement of the device varies depending on the patient’s symptoms. Electrodes are applied to the nerve controlling the dysfunctional muscle, while the stimulator is worn outside of the body. For example, functional electrical stimulation corrects a foot drop with the device worn in a cuff below the knee.

Sacral Nerve Stimulation

In sacral nerve stimulation, a surgeon creates a pocket in the left buttock where the battery stimulator rests. It connects to a lead on the sacral nerve. This neuromodulation treatment is for patients with urinary incontinence, overactive bladder, and constipation that is unresponsive to medication or physical therapy. Patients and their doctors to adjust the settings of the stimulator according to the severity of their symptoms through a pre-programmed remote.

Occipital Nerve Stimulation

Occipital nerve stimulation targets a pair of nerves (called the occipital nerve) in the back of the neck. Electrodes of the device go into the subcutaneous tissues at the back of the neck. The wires are concealed under the skin to a surgical pocket containing the stimulator in the chest, back, or abdomen. Stimulating the occipital nerve relieves migraine headaches and craniofacial pain disorders.

Trials of occipital nerve stimulation in migraine headache patients have proven to be promising. Physicians in Boston (2008) claim there is an “excellent outcome” in over half of the patients in the trial with “50% improvement in one or more aspects of headache severity, frequency, or disability.”

Hypoglossal Nerve Stimulation

If symptoms are not adequately managed through continuous positive airway pressure (CPAP), hypoglossal nerve stimulation regulates breathing for those with obstructive sleep apnea, which is the repeated obstruction of the airway while sleeping. An ENT specialist surgical implants the stimulator into the right side of the chest. It has two wires. The first is fixed on the hypoglossal nerve and the second on the lower chest to monitor breathing. Hypoglossal nerve stimulation keeps the patient’s airway open during sleep because it triggers the nerve that moves the tongue muscles out of the way. A remote control allows patients to turn on the device at bedtime.

Noninvasive Neuromodulation Methods

Noninvasive neuromodulation methods do not require a surgical operation to alter the function of the nervous system. The electrodes and the device reside outside of the body to deliver electrical or magnetic fields to the desired area.

Transcranial Magnetic Stimulation (TMS)

Transcranial magnetic stimulation is a non-invasive neuromodulation treatment for patients with severe depression who have not responded to medication. The magnetic pulses of transcranial magnetic stimulation travel through the skull and into the brain through an insulated coil on the patient’s scalp. The pulses are similar to those of magnetic resonance imaging (MRI) and target the areas of the brain that control mood regulation. Up to 70% of depressive patients noticed lasting changes in brain activity.

Transcutaneous Electrical Nerve Stimulation (TENS)

There are non-invasive neuromodulation options for chronic pain like that of transcutaneous electrical nerve stimulation (TENS). The electrodes of a TENS unit are applied to the skin at varying frequencies and intensities. According to DeSantana and colleagues (2009), TENS activates sites in the spinal cord and brain that rely on neuromodulators for pain relief. Its currents block signals from pain receptors from reaching the brain. A convenient aspect of transcutaneous electrical nerve stimulation is that the small device can be used at home. Common chronic and acute pain conditions TENS treats are fibromyalgia, cancer pain, osteoporosis, neck pain, tendinitis, and more.

Electroconvulsive Therapy (ECT)

Electroconvulsive therapy is unique in comparison to the other neuromodulation options. Electrodes sit on the scalp delivering electrical currents to alter brain chemistry while the patient is under general anesthesia. This induces a medically controlled seizure. Contrary to the negative associates of electroconvulsive therapy, no structural damage is inflicted on the brain. The changes in neuromodulators treat severe mental disorders. Physicians prescribe electroconvulsive therapy for severe depression, psychosis, and bipolar disorder.

Chemical Methods of Neuromodulation

Chemical methods of neuromodulation are invasive, as medications are delivered directly into a specific location inside of the body. This differs from pharmacotherapy because absorption is increased in comparison to swallowing a prescribed pill. Controlled by a pump, chemical neuromodulation requires an intrathecal drug delivery system surgically implanted into the spinal cord where pain signals travel. The most common form of chemical neuromodulation is the administration of pain medication. Through an intrathecal drug delivery system, patients use significantly less medication and pain is managed more effectively.

Neuromodulation
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Possible Risks To Neuromodulation

Although minimal, neuromodulation carries risks like any medical therapy. The majority of the potential complications arise from invasive implanted neuromodulation devices. Studies reflect that 38% of patients experienced the device-related complications of migration of the leads into unwanted areas of the body, failed lead connections, or the breakage of leads (Mehta, 2016). Serious injuries from neuromodulation rarely occur. However, injury to a nerve or the spinal cord by the implanted device resulting in permanent neurological damage is a possibility. The remaining risks are related to surgical procedures to place the neuromodulation device. Examples include pain from insertion, infections at the implant site, and hemorrhage.

Finding a Neuromodulation Specialist

Only a trained physician who specializes in pain, movement, or spasticity disorders is capable of performing neuromodulation techniques. The first step in beginning neuromodulation is to discuss your symptom concerns with your doctor. They will refer you to a neuromodulation specialist best suited for your needs. Organizations like the North American Neuromodulation Society can connect you with over 1,000 passionate specialists who have the goal of improving the quality of life of their patients using neuromodulation.

References

DeSantana, J. M., Walsh, D. M., Vance, C., Rakel, B. A., & Sluka, K. A. (2008). Effectiveness of transcutaneous electrical nerve stimulation for treatment of hyperalgesia and pain. Current rheumatology reports, 10(6), 492–499. doi:10.1007/s11926-008-0080-z

Occipital Nerve Stimulation for Headache. (2008). Neurology Reviews, 16(10). Retrieved from https://www.mdedge.com/neurology/article/72982/headache-migraine/occipital-nerve-stimulation-headache