What are the Different Forms of Brain Stimulation?

Invasive and Non-Invasive Brain Stimulation (NIBS): new options in therapy

Brain stimulation techniques affect the activity of neurons. Experts refer to this emerging field of clinical neurophysiology as “interventional neurophysiology”. This field is both biomedical and technological. In contrast to drug-based therapeutic approaches, interventional neurophysiology enables doctors to act precisely on localised structures of the nervous system – even down to the individual nerve cell. Today, there are already several forms of brain stimulation used in research and clinical practice. Below we list a summary of some of the most important techniques currently being used and researched:

1. Deep Brain Stimulation (THS)

Deep Brain Stimulation (THS), also known as deep brain stimulation (DBS), is an invasive neurosurgical treatment method. It is used to relieve symptoms of movement disorders such as Parkinson’s disease, dystonia and essential tremor. In this method, electrodes are implanted in specific regions of the brain that are responsible for the respective disorder. The implanted electrodes are connected to a pulse generator that is placed under the skin in the chest or abdominal region. The pulse generator continuously sends electrical impulses to the electrodes to regulate the abnormal neuronal activity in the target regions and thus reduce the symptoms of the disorder. Deep brain stimulation is reversible and adaptable, so stimulation settings can be adjusted over time to suit individual patient needs. Although THS significantly improves quality of life for many patients, it carries risks such as infection, bleeding and possible misplacement of the electrodes. Before THS is used, extensive examinations and tests are performed to determine the patient’s suitability and the exact target point of stimulation.

2. Transcranial Magnetic Stimulation (TMS)

Transcranial Magnetic Stimulation (TMS) is a non-invasive method of stimulating regions of the brain that uses a magnetic field to generate electrical currents in the brain. A coil that generates a rapidly changing magnetic field is positioned on the scalp over the brain region of interest. TMS can be used for both diagnostic and therapeutic purposes. In diagnostics, TMS can be used to examine the function and connections of brain regions as well as the reaction speed of nerve fibres. Therapeutically, TMS is used especially to treat depression, but can also play a role in other neuropsychiatric disorders such as schizophrenia, anxiety disorders and migraines. There are two main forms of TMS: single and repetitive (rTMS). Single TMS refers to the application of a single stimulation pulse, while rTMS involves the delivery of multiple pulses in rapid succession. rTMS is particularly interesting for therapeutic purposes because it has longer-lasting effects on neuronal activity. TMS treatment is generally safe and well tolerated, although side effects such as mild headaches or unpleasant sensations at the stimulation site may occur. Severe side effects such as seizures are rare. TMS therapy is continually being researched to expand its scope and further improve its effectiveness.

3. Transcranial Pulse Stimulation (TPS)

Transcranial Pulse Stimulation (TPS) is a non-invasive brain stimulation technique that uses shock wave pulses to stimulate targeted areas of the brain. This method has shown promise in recent years as a treatment approach for various neurological and psychiatric disorders such as Alzheimer’s disease, dementia, Parkinson’s disease and depression. Unlike other brain stimulation techniques such as transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS), TPS uses focused, low-frequency shock waves to reach precise structures deep within the brain. The pulses penetrate the bones of the skull without damaging them and generate mechanical energy that is converted into neuronal activity. A handheld applicator is positioned on the patient’s scalp and sends focused pulses to the desired area of the brain. The treatment is painless and does not require sedation or anaesthesia. Typically, a session lasts about 30 minutes and patients can resume their daily activities immediately after the treatment. While the exact mechanisms of action of TPS are not fully understood, it is thought to work by modulating neural networks and improving neuroplastic processes. This may help restore disturbed brain functions and alleviate symptoms of various diseases. Studies have shown that TPS can improve cognitive function in the treatment of Alzheimer’s patients. Similarly, TPS has shown promise in treating Parkinson’s disease and other movement disorders by improving motor control. In addition, there is growing evidence that TPS may be effective for mood and anxiety disorders such as depression and generalised anxiety disorder. Transcranial pulse stimulation has great potential for the non-invasive treatment of neurological and psychiatric disorders, including for patients for whom conventional therapeutic approaches fail or cause undesirable side effects.

4. Transcranial Direct Current Stimulation (tDCS)

Transcranial Direct Current Stimulation (tDCS) is a non-invasive brain stimulation method in which weak direct currents are applied through electrodes on the scalp to affect the excitability of nerve cells in the brain. The electrodes are usually applied in the form of an anode and cathode pair, with the anode increasing the excitability of neurons and the cathode reducing it. tDCS is used to study and modulate brain function and to treat various neuropsychiatric conditions such as depression, pain, stroke rehabilitation and cognitive impairment. The method is also being researched to improve cognitive abilities such as memory, learning and attention. The tDCS treatment is generally safe and well tolerated, although mild side effects such as itching, skin redness or mild headaches may occur. The stimulation is painless and usually lasts 20 to 30 minutes per session. Because tDCS is a relatively simple and inexpensive technique, it is also being explored for home and portable applications. While tDCS has shown positive results in many studies, further research is needed to better understand long-term safety, optimal stimulation parameters and the exact mechanism of action.

5. Transcranial Alternating Current Stimulation (tACS)

Transcranial Alternating Current Stimulation (tACS) is a non-invasive brain stimulation method in which weak alternating currents are applied through electrodes on the scalp. These currents are able to influence the natural electrical oscillations of the brain. The frequency of tACS can be matched to specific brain waves, such as alpha, beta, theta or gamma waves, to specifically modulate certain brain activities. tACS is being studied in clinical research and therapy for the treatment of neuropsychiatric disorders, such as depression, schizophrenia and epilepsy, as well as for the improvement of cognitive abilities, such as learning, memory and attention. Unlike transcranial direct current stimulation (tDCS), tACS allows more precise control of neuronal activity by adjusting the frequency of stimulation. The use of tACS is usually painless and associated with few side effects, but more research is needed to better understand the long-term safety and efficacy of this method.

6. Vagus Nerve Stimulation (VNS)

Vagus Nerve Stimulation (VNS) is an invasive treatment method in which a small device, similar to a pacemaker, is implanted under the skin in the chest area. This device is connected via an electrode to the left vagus nerve, which runs from the neck to the chest and abdomen. The vagus nerve is an important nerve of the parasympathetic nervous system and influences a variety of body functions, including brain activity. The implanted device sends regular electrical impulses to the vagus nerve to modulate brain activity. VNS is mainly used to treat epilepsy, especially in patients for whom medication does not work adequately. It is also being studied for severe depression and other psychiatric disorders. VNS treatment is generally safe, but side effects such as hoarseness, cough, difficulty breathing or swallowing may occur, which are usually mild and temporary. The effectiveness of VNS can vary and not all patients respond to therapy.

7. Electroconvulsive Therapy (ECT)

Electroconvulsive Therapy (ECT) is a medical treatment in which an electric current is sent through the brain under controlled conditions to induce brief, generalised seizure activity. Electroconvulsive Therapy is mainly used to treat severe mental illness, especially treatment-resistant depression, manic episodes and acute schizophrenia. Before Electroconvulsive Therapy is used, patients are put under general anaesthesia and given a muscle relaxant to prevent possible injury due to muscle contractions during the seizure. Electrodes are then placed on the scalp and an electric current of short duration and low intensity is applied. Electroconvulsive Therapy can be performed unilaterally (on one side of the brain only) or bilaterally (on both sides of the brain). Unilateral Electroconvulsive Therapy usually causes fewer cognitive side effects, while bilateral Electroconvulsive Therapy is considered more effective. Electroconvulsive Therapy is an effective treatment for many patients who do not respond to conventional drug therapies. However, side effects such as temporary memory impairment or confusion may occur.

8. Focused Ultrasound Stimulation (FUS)

Focused Ultrasound Stimulation (FUS) is a non-invasive method of stimulating or modulating brain structures. In this process, high-frequency sound waves are precisely focused on specific regions in the brain. The ultrasound energy is converted into heat, which can influence the activity of the neurons. FUS is being researched to treat various neurological and psychiatric conditions, such as Parkinson’s disease, essential tremor, epilepsy and depression. The technology can also be used to target the opening of the blood-brain barrier to facilitate the delivery of drugs or other therapeutic substances to the brain. FUS has the advantage of working without direct contact with the brain or the need for implants. The method offers high spatial precision and can also be used to stimulate deep brain structures. Focused ultrasound stimulation is still a relatively new technique that is undergoing clinical research and development.

9. Magnetic Spasm Therapy (MST)

Magnetic Spasm Therapy (MST) is a newer, less invasive alternative to electroconvulsive therapy (ECT) for the treatment of severe psychiatric illness, particularly treatment-resistant depression. MST uses magnetic fields instead of electric current to induce controlled convulsive activity in the brain that produces therapeutic effects. In MST, a special coil that generates a rapidly changing magnetic field is positioned on the patient’s scalp. The magnetic field induces electrical currents in the brain, triggering a brief, generalised seizure that helps improve symptoms. A main advantage of MST compared to ECT is that it usually causes fewer cognitive side effects, such as memory impairment or confusion. This is because MST targets specific brain regions more precisely and the stimulation is more controlled than with ECT. MST is still a relatively new treatment option and research continues to better understand its effectiveness, safety and optimal use.

10. Focal Electrical Stimulation (FES)

Focal Electrical Stimulation (FES) is a method of using electrical currents to selectively affect the activity of nerves or muscles. FES is often used in the rehabilitation of patients with neurological diseases or injuries to improve or restore motor functions, such as movement and muscle strength. FES involves placing electrodes either on the surface of the skin (transcutaneous FES) or directly on the nerves or muscles (implanted FES). The electrodes emit controlled electrical impulses that activate nerves and muscles, triggering a desired movement or muscle contraction. FES is used in various medical settings, such as stroke rehabilitation, spinal cord injury, multiple sclerosis or cerebral palsy. The method can help increase patients’ mobility and independence, reduce muscle atrophy and prevent joint contractures. The effectiveness of focal electrical stimulation (FES) varies depending on the area of application and individual patient factors. In many cases, FES has been shown to be effective in improving motor function, reducing muscle atrophy and increasing quality of life. Studies have shown that FES can be particularly useful in the rehabilitation of stroke patients and in people with spinal cord injuries or other neurological conditions. It is important to note that the effectiveness of FES depends on a number of factors, including the type and severity of the condition, the timing of the intervention, and the adherence to and duration of the exercise programme. Further research is needed to better understand the optimal use of FES in different clinical settings and to further refine the technique.

11. Epidural Cortical Stimulation (ECS)

Epidural Cortical Stimulation (ECS) is a procedure in which electrical impulses are delivered specifically to the surface of the brain (cortex) to modulate neuronal activity. This is done by placing electrodes on the dura mater, the outer layer of the meninges surrounding the brain. ECS is mainly used in research and experimental therapeutic approaches for various neurological and psychiatric disorders, such as epilepsy, stroke, Parkinson’s disease and major depression. Because ECS is an invasive method, it is usually only considered for patients who do not respond to less invasive procedures or medications. The electrodes are implanted during neurosurgery and the stimulation device (similar to a pacemaker) is generally placed under the skin in the chest or abdomen. ECS allows targeted and customisable stimulation of specific areas of the brain, which can reduce symptoms of the condition and improve patients’ quality of life. Stimulation settings can be customised to achieve optimal therapeutic effect while minimising potential side effects. Despite promising results in some cases, epidural cortical stimulation is still a relatively new approach and requires further research and clinical trials to fully understand and optimise its long-term efficacy, safety and potential areas of use.