Non-Invasive Brain Stimulation[NIBS] in 2024: How It works

Introduction to Non-Invasive Brain Stimulation:

What is Non-Invasive Brain Stimulation?

When you hear Non-invasive brain stimulation, you might be thinking of large machines and wires attached to your brain…and a probability of electrocution.

But do not worry, it is not as daunting as it sounds.

Brain stimulation is a technique commonly used to treat mental disorders and other brain-related disorders. It holds promise for people who have not tried other therapies or want an effective solution with minimal side effects.

The factual term for brain stimulation is neurostimulation. In simple terms, it is the deliberate rectification of the nervous system either through invasive techniques like microelectrodes or non-invasive techniques that use transcranial magnetic stimulation or transcranial electric stimulation.

Non-invasive brain stimulation simply means a set of techniques that can alter the brain activity from the surface itself. This technique doesn’t involve the introduction of any instruments in the head and hence is considered safe.

History of Brain Stimulation:

The oldest record of brain stimulation has been dated back to the stone carvings from the Fifth Dynasty of Egypt in which an electric fish was used to treat pain; and later, during the time of Socrates, when electric fish were used to treat headaches and arthritis.

This is, of course, really old proof that states the use of neurostimulation.

Cut to the 19th century, when Michael Faraday discovered the law of induction. Researchers on the other side studied the electrical impulses sent by the neurons (brain cells). In the 1940s, electroconvulsive therapy was used on people by passing electric currents to treat severe depression. Since then, there have been modifications in the technique. The researchers achieved a breakthrough in 1985 when they discovered transcranial magnetic stimulation. This eventually led to the discovery of transcranial direct current stimulation which gained massive popularity due to its safety and potential to deliver effective results.

Importance in Modern Neuroscience:

NIBS is extremely safe and painless and has minimal side effects. It helps to restore the functions of the brain that had been affected because of depression. It compensates for the loss of function of the brain and improves the cognition of an individual. NIBS are known to induce neuroplastic changes (alterations that last longer than the stimulation) thus making it an effective tool to treat depression.

How does Non-invasive brain stimulation work?

Basic Principle of Non-Invasive Brain Stimulation:

NIBS involves neurostimulation in parts of the brain by the application of electric current. A passage of weak electric current passes through the skull and excites the neurons (brain cells). It strengthens the neural network (the brain network through which the information is passed). The affected area of the brain is targeted for stimulation. It excites the neurons that have been affected because of mental health disorders or physiological injuries.

Fundamentals of Brain Stimulation:

Brain stimulation works to modulate the brain behavior. It is of two types, invasive and non-invasive. Invasive techniques include deep brain stimulation while non-invasive techniques include electrostimulation by tDCS, TMS, etc. These techniques help to excite the neurons in the brain. In simple terms, imagine NIBS as an alarm that helps your brain wake up. This excitation can effectively reverse the symptoms of certain mental health conditions. The primary basis is the excitation of the neurons by the application of electricity.

While deep brain stimulation was used in the past, non-invasive techniques are now becoming more prevalent due to their safety and efficiency.

Modalities Used for Non-Invasive Brain Stimulation Techniques:

TRANSCRANIAL MAGNETIC STIMULATION (TMS):

The transcranial magnetic stimulation uses a magnetic field to target electric currents to specific cortical regions of the brain. The electric current’s intensity must be enough to activate the action potential of the neurons in the stimulated regions of the brain.

This technique uses Faraday’s law to generate electric current. An electromagnet (circular and figure-of-8 or butterfly coil are most commonly used) is placed on the scalp to generate magnetic field pulses. There are two types of magnetic brain stimulation. Single pulse and repetitive pulse TMS (rTMS).

TMS is an effective tool because of its precision to target the cortical areas accurately. Modifications in this technique also include rhythmic TMS. This technique uses short patterns of signals resulting in activation of the neurons over a specific area.

MECHANISM OF ACTION OF TRANSCRANIAL MAGNETIC STIMULATION :

When the electric current passes through this, the formed electromagnetic field passes in a perpendicular axon to the coil and produces a current, reverse and parallel to the coil.

MRI is performed before using TMS to determine the area of the cortical region to be stimulated. The circular coil covers more area while the 8-figure butterfly focuses on the midpoint and the stimulation is stronger. By activating the neurons, it is easy to determine the neural networks as well as the cognitive functions of the targeted brain area.

TRANSCRANIAL DIRECT CURRENT STIMULATION (tDCS):

tDCS is a portable and convenient technique used for brain stimulation. It is portable and hence is easier to use as compared to TMS. In this technique, the electrodes are placed on the scalp and an electric current is applied directly through the electrodes.

The electrodes are of two types: anode and cathode. One electrode is placed on the cortical region of the scalp while the other is placed on the right or the left side of the scalp, right above the eyes.

The electric current flows and directly reaches the neurons. It passes a weak electric current of 1-2mA continuously through the scalp. There might be some resistance faced due to the tissues but the effect of There can be mild pain experienced by the users because of the penetration of the current.

MECHANISM OF ACTION OF TRANSCRANIAL DIRECT CURRENT STIMULATION:

Stimulation of the anode leads to the shift in the membrane potential (difference between electric charge inside and outside the neuron) causing a rapid rise in the potential (depolarization).

This is how the neuronal cells are activated and swiftly pass on the information. Once the anodal stimulation is completed, cathodal stimulation then repolarizes the neuron, thus bringing it to a normal state.

The activation of neurons leads to the activation of a particular part of the cortical region that was targeted for treating depression. Using tDCS, the penetration and overall results are better as compared to TMS.

The upside of using tDCS is its portability. At Mave Health, people suffering from depression are treated with the help of tDCS. It is India’s first wearable and portable device that can improve brain health efficiently. The wearable - “ARC” uses tDCS as its base to treat depression and anxiety.

TRANSCRANIAL ALTERNATE CURRENT STIMULATION:

Transcranial alternating current stimulation (tACS) is a unique form of non-invasive brain stimulation. Alternating electric currents are delivered to the scalp to affect mostly cortical neurons. They can modulate the brain function and in turn cognitive processes as well.

The primary feature of this technique is the sinusoidal alternate current that is directly applied to the brain. tACS involves the direct delivery of alternating electric currents to the scalp.

The current travels through the skull to affect mostly cortical neurons. With such alternating current the voltage changes gradually from positive to negative every half-cycle. Therefore, the current flows from an anodal electrode to a cathodal electrode in one half-cycle and in the reverse direction in the second half-cycle.

MECHANISM OF ACTION OF TRANSCRANIAL ALTERNATE CURRENT STIMULATION:

Our brain has a naturally occurring rhythmic patterns that oscillate at a certain frequency. These oscillations are connected to the brain functions. Even if the cortical regions are far away, they are in sync due to these brain oscillations. tACS helps to couple or decouple these oscillations thus helping to modulate the brain functions. Modulations can be done over a large area of the brain. tACS’s ability to determine the connectivity issues can be used to diagnose psychiatric disorders.

TRANSCRANIAL FOCUSED ULTRASOUND STIMULATION:

The ultrasound waves have a higher range than the human hearing. Due to its frequency, it can travel long distances and also penetrate soft tissues effectively. There are three types of ultrasounds currently used in medicine. High, medium, and low frequency. Out of these, low-frequency ultrasound is used for neuromodulation.

MECHANISM OF ACTION OF TRANSCRANIAL FOCUSED ULTRASOUND STIMULATION:

The basis of this technique lies in the piezoelectric effect. The piezoelectric effect refers to the process where electricity is converted into pressure. The change in intensity of the current leads to changes in pressure which in turn produces vibrations. These vibrations are the acoustic energy that directly affects the neural circuits in our brain and help with the clinical application of neuromodulation. The electrical energy is converted to acoustic energy by an ultrasound transducer.

APPLICATIONS OF NON-INVASIVE BRAIN STIMULATION:

1.COGNITIVE ENHANCEMENT:

MEMORY IMPROVEMENT:

Even a single session of rTMS and tDCS has shown results that enhance the functionality of the brain. It has positive results on memory enhancement when tried on adults and adolescents. tDCS enhanced the working memory of the patients. Enhanced working memory of the patients persisted even after a week of stimulation indicating the lasting effect of the brain stimulation post the session.

ATTENTION AND FOCUS ENHANCEMENT:

The ability to concentrate on a locus towards a specific stimulus is known as focused attention. Past studies demonstrate that NIBS leads to improved focus attention. Attention and focus is regulated by the posterior part of the parietal cortex (crown of the head). When low-frequency rTMS is applied, attention to the visual stimuli is enhanced. When electrodes of tDCS are attached to the parietal cortex and others on the frontal lobe, attention to the auditory stimuli is increased.

LEARNING ACCELERATION:

Anodal tDCS, when attached to the side of the forehead opposite to that of the working hand, improves the ability of a person to learn a particular sequence or event. The ability to learn a complex motor task is also enhanced. Low and high-frequency rTMS is also used frequently to enhance the learning capabilities of an individual.

2. CLINICAL INTERVENTION:

DEPRESSION AND ANXIETY TREATMENT:

NIBS can induce neuroplastic changes in an individual. It activates the cortical activity of the dorsolateral prefrontal cortex of an individual and hence is used for neurostimulation regularly. Usually, lesions in the brain are responsible for mood disorders in 80% of the cases. Using this technique has a deep impact on the synaptic transmission of the neurons thus increasing its activity. This in turn has a positive impact on the cognitive function of the brain.

CHRONIC PAIN MANAGEMENT:

NIBS is being successfully implemented in chronic pain management. It enhances neural activity establishes specific neural activity that deals with pain management. Research has shown that using non-invasive brain stimulation has reduced the effects of pain effectively. rTMS has been used on the primary motor cortex to treat neuropathic pain.

REHABILITATION AFTER STROKE OR CHRONIC BRAIN INJURY:

Non-invasive brain stimulation (NIBS) has been seen as more common in rehabilitation settings. It can be used for the treatment of stroke, spinal cord injury, traumatic brain injury, and multiple sclerosis, as well as for some diagnostic neurophysiological measurements. TMS and tDCS are used extensively. NIBS application improves motor function in stroke patients by using their physiological peculiarity. It increases the activity of the affected hemisphere of the brain post-trauma and simultaneously decreases the activity of the unaffected hemisphere. This leads to the rectification of the motor dysfunction.

3.NEUROLOGICAL DISORDERS:

1.PARKINSON’S DISEASE:

1.5% of the population above the age of 65 years suffers from Parkinson’s disease. It is a neurodegenerative disease. Patients may show deficits of memory retrieval, fluctuations in attention, impaired executive functions, etc. It affects the dopamine networks of the brain. tDCS worked wonders by showing improvements in motor functions. It reduced tremors and rigidity of muscles and helped patients to walk again.

2.ALZHEIMER'S DISEASE:

3.9% of people above the age of 60 suffer from Alzheimer’s disease. It is the most common neurodegenerative disease. There are behavioral changes along with memory loss and decline in motor function. Alzheimer’s disease affects the neurons in the hippocampus region of the brain.

When NIBS was applied to the patients suffering from the disease, promising results were observed. NIBS helped in the memory enhancement of the patients by neural plasticity.

3.EPILEPSY:

Epilepsy occurs because of the synchronous activity of neurons leading to excessive excitation. Currently, 2.5 million adolescents suffer from epilepsy. Low-frequency NIBS can help to manage the excitation of neurons thus decreasing the epileptic symptoms. tDCS uses low electric current to depolarize the neurons and thus acts effectively to control epilepsy.

ADVANCEMENTS AND FUTURE DIRECTIONS:

1.EMERGING TECHNOLOGIES IN NIBS:

Using neuromodulation for treating psychiatric disorders is growing tremendously.

Continuous efforts are being made to develop the existing NIBS technologies to increase their efficacy. tDCS is now a portable and home-friendly device with the help of a doctor’s consultation. Besides these, there are also new techniques that have been developed recently.

A. TI electrical stimulation:

A new technology called TI (temporarily interfering) electrical stimulation has the ability to stimulate deep brain targets. It treats the conduction block (non-responsiveness of a neuron).

B. Patterned Low-Intensity Low-Frequency Ultrasound:

Another technique developed called Patterned Low-Intensity Low-Frequency Ultrasound (LILFUS), holds tremendous potential for inducing long-lasting changes in brain function. The ultrasound waves are similar to the brain wave patterns observed during the learning and retention process.

2.INDIVIDUALIZED STIMULATION APPROACHES:

NIBS has made abundant progress with tDCS being used extensively in the past two decades. NIBS encounters a unique case for every individual. Every person has a different neural network and personalized approaches to tackle their problems are required. However, individualized stimulation approaches can be used to set treatment-related trajectories. This is called precision medicine. Precision interventions can be introduced on three levels:

1) The NIBS intervention

2) The constitutional factors of a single patient

3) The phenotypes and pathophysiology of illness.

3.INTEGRATION WITH NEUROIMAGING TECHNIQUES:

Neuroimaging has revolutionized our understanding of brain function and has become an essential tool for researchers studying neurological disorders. Functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) are two widely used neuroimaging techniques to review changes in brain activity. fMRI is a non-invasive technique that uses magnetic fields and radio waves to produce detailed brain images. EEG is a noninvasive technique that records the brain’s electrical activity through electrodes placed on the scalp. ALONG WITH THESE, Diffusion tensor imaging (DTI) and Transcranial Electrical Stimulation (TES) are also used.

4.POTENTIAL CHALLENGES AND LIMITATIONS:

Using NIBS might have some limitations. These include:

Inter-individual variation (Variation in skull and cortex thickness)
Varied results for each patient
Orientation of neurons being stimulated
Circadian rhythms
Genetic pre-dispositions
Age
Menstrual cycle

CONCLUSION:

Non-invasive brain stimulation has proven to emerge as one of the most effective techniques to treat neurological disorders. The use of these techniques to treat mental health-related disorders is slowly gaining momentum. It is a saviour for people suffering from depression and anxiety. NIBS helps to enhance an individual’s memory, focus, and attention, and reverse the effects of psychological disorders.

With the help of neuroimaging and studying neurophysiological aspects of an individual's brain, NIBS will rise to its full potential.

NIBS techniques are continuously evolving and providing simple treatments for people suffering through depression or any other mental health disorders.

FAQs of NIBS:

Is non-invasive brain stimulation safe?

The overall safety profile of NIBS is excellent when the safety guidelines are adhered to closely. The safety profile differs for different populations. When it comes to tDCS, the patient might experience slight scalp discomfort. TMS might lead to a headache.

It is mandatory to obtain medical opinion before using NIBS to avoid any kind of misuse of the technique. The “ARC-tDCS” technology produced by Mave Health is painless and produces no side effects. All in all, NIBS has an excellent safety record to date.

What is non-invasive brain stimulation in Neurorehabilitation?

Since NIBS promotes neural plasticity, NIBS may enhance motor recovery after a neurological injury through the induction of the plasticity process. TMS and tDCS, along with other neurohabilitative treatments help to regain motor functions in brain injury survivors and victims of stroke.

REFERENCES:

Non-Invasive Brain Stimulation[NIBS] in 2024: How It works | Applications & Types