What is brain stimulation?

Brain stimulation represents a modern, scientifically grounded approach to influencing brain activity through targeted physical stimuli such as electromagnetic pulses, electric current, acoustic waves, including ultrasound or laser radiation. Brain stimulation methods are used both in research aimed at understanding brain function and as therapeutic interventions. Some of these methods remain in the experimental development phase, while others are already well established in clinical practice and are used in the treatment of neurological and psychiatric disorders, as well as in rehabilitation. 

Non-invasive brain stimulation (NIBS)

Transcranial Magnetic Stimulation (TMS)

Transcranial magnetic stimulation (TMS) uses a strong magnetic field to non-invasively stimulate the brain. The magnetic field induces an electric current in the brain tissue, which can increase or decrease cortical excitability. Unlike transcranial electrical stimulation, TMS can directly evoke or suppress action potentials when delivered at sufficient intensity, which also makes it possible to produce a silent period. TMS is used diagnostically to examine the motor cortex using motor-evoked potentials (MEPs), which indicate the functional state of the brain and spinal cord, for example in multiple sclerosis.

Repetitive TMS (rTMS) serves as a therapeutic tool to induce long-term changes in brain activity, enabling the treatment of various conditions such as depression, chronic pain, obsessive–compulsive disorder, or certain symptoms of schizophrenia. This method is the main representative of NIBS techniques. 

Transcranial Direct-Current Stimulation (tDCS)

tDCS is a safe and non-invasive brain stimulation method that uses a low-intensity electric current (up to 2 mA) to modulate the activity of selected brain regions. Depending on the polarity of the current, stimulation can increase (anodal) or decrease (cathodal) cortical excitability. A short stimulation session (about 10 minutes) can induce changes in neuronal activity that, with repeated applications, may lead to long-term beneficial effects such as reduction of chronic pain or improvement of cognitive functions. Anodal tDCS applied to the dorsolateral prefrontal cortex is considered an evidence-based treatment for unipolar depression.

Transcranial Alternating-Current Stimulation(tACS)

tACS differs from transcranial direct current stimulation (tDCS) in that it applies a low-energy sinusoidal electric current to the brain at a selectable frequency, allowing interaction with cortical brain oscillations. By modulating brain activity through the synchronization of oscillations and the induction of long-term synaptic plasticity, this method can influence cognitive processes. tACS is used in cognitive neuroscience and is currently being investigated in psychiatric clinical studies as a potential therapeutic tool. The stimulation parameters (frequency, amplitude, and duration) can be adjusted to target specific brain regions. By modulating brain oscillations and connectivity, tACS alters neuronal activity without directly affecting the frequency of action potentials, thereby changing the excitability of selected brain structures.

Transcranial Random Noise Stimulation (tRNS)

Transcranial random noise stimulation (tRNS) uses low-energy alternating currents with randomly varying frequencies and amplitudes. This "noise" increases neuronal excitability and enhances the sensitivity of neurons to weak stimuli. The mechanisms of action are not yet fully understood. tRNS has shown beneficial effects on cortical circuits, modulating neuronal processing in sensory and motor areas and improving cognitive and motor functions. The effectiveness of this method is attributed to its influence on cortical rhythms, enhancement of plasticity, and improvement of the signal-to-noise ratio.

Electroconvulsive Therapy (ECT)

Electroconvulsive therapy is a medical procedure in which short electrical pulses are delivered to the brain under general anesthesia to induce a brief seizure. ECT is used primarily for severe psychiatric conditions, such as treatment-resistant depression. It provides rapid and significant symptom improvement, especially when other treatments have failed. Modern ECT techniques are safer than earlier approaches due to precise control of stimulation parameters and the use of a fully monitored clinical environment. Treatment is typically administered as a series of sessions over several weeks, with improvement often noticeable after just a few sessions. ECT is a well-established and effective method widely recommended by professional societies and is suitable for patients of various age groups with severe mental disorders.

Transcranial Ultrasound Stimulation (TUS)

Transcranial ultrasound stimulation is an innovative, non-invasive brain stimulation method that uses pulsed ultrasonic waves to modulate targeted brain regions and influence neuronal circuits. The method allows excitation or inhibition of neuronal activity with high spatial resolution and deep penetration. TUS is a promising tool for both basic and clinical research, with potential applications in the treatment of neurological disorders such as Alzheimer's disease, epilepsy, and stroke. Ultrasonic waves are generated through the piezoelectric effect, in which an electric current induces mechanical vibrations in a crystal, which are then transmitted by an ultrasound transducer.

Vagus Nerve Stimulation (VNS)

Vagus nerve stimulation (VNS) is a neuromodulation method in which brain activity is influenced peripherally through electrical impulses delivered to the vagus nerve (n. vagus), which then transmits the signals to the brain. This type of stimulation can modulate brain activity and is used in the treatment of epilepsy and depressive disorder, and more recently as a support for neurorehabilitation, for example after a stroke. The device may be non-invasive, with stimulation applied through the skin in the area of the ear or neck, or it may take the traditional form of an implanted device placed under the skin in the chest and connected to the vagus nerve in the neck via a lead. VNS represents a promising approach to influencing the nervous system without the need for a transcranial intervention into brain tissue.

Invasive brain stimulation 

Deep Brain Stimulation (DBS)

Deep brain stimulation (DBS) is a neurosurgical procedure in which electrodes are implanted into precisely defined areas of the brain. These electrodes deliver electrical impulses that modulate brain activity and thereby help treat various neurological and psychiatric disorders. DBS is commonly used for Parkinson's disease, essential tremor, dystonia, epilepsy, Tourette syndrome, and obsessive–compulsive disorder. The stimulation influences the activity of nerve cells and the chemical processes in the brain associated with the specific condition. The entire system is controlled by a neurostimulator placed under the skin, which is connected to the brain electrodes via leads. Research is further exploring the potential use of DBS in Huntington's disease, chronic pain, cluster headaches, dementia, depression, addictions, and obesity.