Brain Stimulation Therapy

Deep Brain Stimulation and Transcranial Direct Current Stimulation

How does it work?

Both DBS and tDCS manipulate the mechanism by which neurons transmit signals through the brain to either stimulate or inhibit that signal transmission. First, understand how neurons transmit signals. The following explanation comes from Khan Academy (Neuron Action Potentials: The Creation of a Brain Signal (Article), n.d.)

Neuron Signal Transmission

Neurons transmit signals through the body via electrical pulses. Neurons connect end to end to create communication networks where they pass signals between each other to bring information through the body.

Here is the basic anatomy of a neuron:

Dendrites Receive signals from neighbouring neurons

Axon Transmits signal over a distance

Myelin Sheath Speeds up signal transmission along the axon

Axon Terminal Transmits signal to other neuron dendrites or tissues

Electrochemical Potential

An electrochemical potential occurs when there is a difference in chemical concentration and electrical charge between two areas. Both the chemical and the charge will naturally tend towards equalizing the difference.

There is a “normal” or “resting” electrochemical potential that describes the inactive state of the neuron. A slightly negative electrochemical potential is maintained across the cell membrane at the dendrites. In the case when a lot of positively charged ions appear in the space surrounding the dendrites, the electrochemical potential will spike. This is called the action potential and it causes a signal to transmit through the axon to the terminals.

The axon terminals then release positive ions into the space surrounding the cell at the terminal end. It is these positive ions which will be recognized by the next neuron’s dendrites.

Refractory Period

Once a neuron has “fired” it cannot fire again for a duration while it works to establish its resting potential. Protein sized pumps move ions across the cell membrane against the chemical gradient to “re-charge” the neuron in preparation to receive another signal. This is called the refractory period. While this is happening, the neuron is sort of blind to further indications to transmit a signal. 

Proposed Mechanism of DBS / tDCS

Cathodal (-) Inhibition

The presence of a negatively charged cathode would attract positive ions. The resulting high concentration of positive charge would trigger frequent action potentials, eventually putting the neuron into a depressed state where it becomes less sensitive to transmitting signals. 

The leading explanation of DBS, which involves implanted negative electrodes, is that the treatment over-stimulates the region until the local region is inhibited to signal transmission. This is like ‘The Boy Who Called Wolf’ where the neuron is being constantly bombarded with a chemical signal, it will adapt and become unresponsive to the noise.

tDCS follows the same principle, but is limited to regions of the brain which are accessible from the surface as electrodes are not implanted for tDCS treatment. tDCS may also involve simultaneous anodal stimulation in another region.

Anodal (+) Stimulation

Current sent to an anode gives a positive charge and therefore repels positive ions from its immediate surroundings.  It is thought that the result of this is a shorter refractory period. Without a gradient to push against, the neuron can quickly return to a resting state, ready to transmit a new signal.

This is like after your mom mops the floor and your footprints are a blaring sign that you have passed through the house still wearing your shoes. In this way, tDCS can be used to make the region of the brain close to the anode more sensitive to signal propagation and therefore accelerate local brain activity. 

Does it work?

DBS  is being used successfully, especially for movement disorders, like Parkinson’s, where we better understand the mechanism behind the disease (Lozano et al., 2019). Mental illnesses like depression and bipolar, which doctors cannot yet point to a specific brain region to target give mixed results, though the field is not without success stories (Lozano et al., 2019).

The first ventures into tDCS treatment was to improve cognitive ability in healthy populations and there was some success (Thair et al., 2017). When the relevant brain regions were targeted, tDCS was able to enhance facial expression recognition, inhibit aggressive responses, and accelerate motor skill development. In the context of mental illness, tDCS has in some cases been able to reduce symptoms of depression, reduce hallucinations in schizophrenic patients, and reduce delays in language learning in ASD patients (Thair et al., 2017).

In a meta-analysis that looked at 10 randomized controlled trials and three other published meta-analyses, a general idea of the success rate of tDCS is given (Meron et al., 2015). In 6/10 RCT, active tDCS was not significantly different from the placebo; though, in 4/10 RCTs, it was (Meron et al., 2015).

tDCS experiments are difficult to design, due to the many factors which could influence the effects (Meron et al., 2015). Large testing populations to be able to control for these factors. Meron’s (2015) meta-analysis used statistics to extrapolate the results to tell if the outcomes would have still been significant if a sufficiently sized testing population had been used. 

Ultimately, we do not have enough information yet to tell if tDCS is a viable treatment option for mental illnesses (Meron et al., 2015).

Though preliminary results are building interest in the treatment which encourages further research in the area. 

References

Deep Brain Stimulation (DBS). (2026, March 13). National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/health-information/disorders/deep-brain-stimulation-dbs

Lozano, A. M., Lipsman, N., Bergman, H., & Brown, P. (2019, March 2). Deep brain stimulation: current challenges and future directions. Nat Rev Neurol., 15(3), 148-160.

Meron, D., Hedger, N., & Garner, M. (2015, October). Transcranial direct current stimulation (tDCS) in the treatment of depression: systematic review and meta-analysis of efficacy and tolerability. Neuroscience and Biobehavioral Reviews, 57, 46-62.

Neuron action potentials: The creation of a brain signal (article). (n.d.). Khan Academy. Retrieved April 22, 2026, from https://www.khanacademy.org/test-prep/mcat/organ-systems/neuron-membrane-potentials/a/neuron-action-potentials-the-creation-of-a-brain-signal

Thair, H., Holloway, A. L., Newport, R., & Smith, A. D. (2017, November 22). Transcranial Direct Current Stimulation (tDCS): A Beginner’s Guide for Design and Implementation. Front. Neurosci., 11(641).