What is Transcranial Stimulation and how does it work?

 

Non-invasive brain stimulation is a relatively novel approach to treatment of neurological and psychiatric illness. Since the 1990s there has been a growing body of evidence supporting its effectiveness for use in neurological and psychiatric disorders, as well as enhancing cognitive function in healthy individuals. Simply explained, non-invasive brain stimulation involves applying an electrical impulse or current to the scalp, thereby enhancing or diminishing excitability the cerebral cortex underneath the area of stimulation.

There are two major types of transcranial stimulation: transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS).

  • TMS involves applying a magnetic coil to a region on the scalp. An electric current is run through the coil and this generates electric pulses to the cerebral cortex just underneath the scalp (Miller, 2012).
  • TDCS involves applying a direct  electrical current to the cerebral cortex (via two electrodes that are placed on the scalp) from the positively charged anodal electrode to the negatively charged cathodal electrode (Paulus 2011; Nitsche and Paulus 2011). Anodal stimulation leads to resting membrane potential depolarization in the cortical region underneath the stimulating electrode, thus increasing the probability of neuronal firing. In contrast, cathodal stimulation leads to resting membrane potential hyperpolarization under the region of interest, thus decreasing the probability of neuronal firing ((Nitsche and Paulus 2000; Nitsche et al. 2003, Steenberg et al, 2016).

Noninvasive brain stimulation has become a promising method for treatment of certain neurological and psychiatric diseases, as well as enhancing various human cognitive abilities. Currently it is FDA approved only for the treatment of major depression, however a growing body of evidence supports that non-invasive brain stimulation is effective for migraine, chronic pain, tinnitus, dementia, dystonia, Parkinson’s Disease, and stroke. Moreover, multiple studies have shown that placing anodal and cathodal electrodes over specific regions of the brain (detailed placements are known as montages) can lead to improvement in mood, anxiety, memory and attention in healthy people.

References:

Michael Craig Miller for Harvard Health Publications. July 26, 2012 Magnetic stimulation: a new approach to treating depression?

Nitsche MA, Fricke K, Henschke U, Schlitterlau A, Liebetanz D, Lang N et al (2003a) Pharmacological modulation of cortical excitability shifts induced by transcranial direct current stimula- tion in humans. J Physiol 553:293–301

Nitsche MA, Liebetanz D, Lang N, Antal A, Tergau F, Paulus W (2003b) Safety criteria for transcranial direct current stimulation (tDCS) in humans. Clin Neurophysiol 114:2220–2222

Nitsche MA, Paulus W (2000) Excitability changes induced in the human motor cortex by weak transcranial direct current stimula- tion. J Physiol 527:633–639

Nitsche MA, Paulus W (2011) Transcranial direct current stimula- tion–update 2011. Restor. Neurol Neurosci 29:463–492

Obeso, I., Oliviero, A., & Jahanshahi, M. (2016). Editorial: Non-invasive Brain Stimulation in Neurology and Psychiatry. Front Neurosci, 10, 574. doi:10.3389/fnins.2016.00574

Steenbergen, L., Sellaro, R., Hommel, B., Lindenberger, U., Kuhn, S., & Colzato, L. S. (2016). "Unfocus" on foc.us: commercial tDCS headset impairs working memory. Exp Brain Res, 234(3), 637-643. doi:10.1007/s00221-015-4391-9