What is TDCS?

NON-INVASIVE BRAIN STIMULATION IS A RELATIVELY NOVEL APPROACH TO TREATMENT OF NEUROLOGICAL AND PSYCHIATRIC ILLNESS. Over the past few years, it has gained popularity among people who desire to maximize their bodies' (and brains') potential (a term also known as 'bio-hacking'). 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. But what is it exactly? How does it work? More importantly, is it safe?

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 potential 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, 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.

 

IS IT SAFE?

If the same parameters are used as those used in the studies involving transcranial stimulation, there are no serious short term side effects. The many articles published on transcranial stimulation (over 1,000 articles within the past 15 years) record no serious adverse effects. The only common side effects encountered included pain, skin redness, or tingling at the site of stimulation. Here is what we currently know about the safety of tDCS and TMS:

TDCS SAFETY

  • No formal safety guidelines.
  • The most common side effects reported are mild to moderate pain, skin redness or tingling near the site of stimulation.
  • Rare reports of mania or hypomania reported in patients with depression.
  • A single seizure reported when tdcs was performed on a pediatric patient, although it is unclear whether the tDCS actually caused the seizure (as the patient had previously been diagnosed with a seizure disorder). Thus tDCS is still considered safe (Matsumoto and Ugawa, 2016).
  • Should not be used in persons with bioelectric devices such as cochlear implants, pacemakers, surgically implanted vagal nerve stimulators, deep-brain stimulators, or responsive neurostimulation devices.
  • As there is little data on its use in the pediatric population, references have recommended against its use on children.

TMS SAFETY

  • Requires in-clinic visits and administration by a licensed physician for all sessions.
  • The most common side effect is mild to moderate pain near the site of stimulation, which typically subsides after the first week of stimulation.
  • FDA approved for treatment of depression. There is supportive evidence that it may be effective in other neurological and psychiatric disorders.
  • Can generate seizures in 0.1% of the population.
  • Should not to be used in persons with non-removable conducting metals near or within their heads or mouths.
  • Should not be used in persons with bioelectric devices such as cochlear implants, pacemakers, surgically implanted vagal nerve stimulators, deep-brain stimulators, or responsive neurostimulation devices.
  • Avoids the systemic side effects that may be seen in psychiatric medications.
  • Does not affect cognition if used in the appropriate manner by a licensed physician.
  • Patients should be monitored closely for signs of unusual behavior/suicidal behavior, although there have been no reports of this as a side effect during clinical trials.

ARE THERE ANY LONG-TERM SIDE EFFECTS?

Long Term Side Effects are unknown at this time.

Regarding both modalities, the long-term implications of use is currently unknown. Recent statements have been released by the International Federation of Clinical Neurophysiology (IFCN) and the Annals of Neurology expressing that there are scientific risks associated with the use of tES that are time and stimulation dose dependent (IFCN, 2015; Monte-Silva et al, 2013). In other words, too long of desired stimulation can lead to the opposite desired effects (IFCN, 2015; Monte-Silva et al, 2013).

Moreover, unplanned results may occur from the ‘build-up effects of multiple sessions or from influence on non-target areas’ (IFCN, 2015). In other words, placing electrodes in the wrong positions may lead to undesired/adverse structural changes over time.

 

Can I use it on my own?

There is a growing group of people who experiment with TDCS using devices that are sold on the internet or self-built. This has been controversial because of the potential for inappropriate use and thus potential for serious side effects. As stated above, health organizations have released statements that report risks associated with the use of noninvasive brain stimulation. While there are currently no regulations on self-use, many health professionals advise against self-use without supervision or guidance. If you do decide to invest in a device, this article provides a review of the best TDCS devices sold online in 2017.

 

REFERENCES

ICFN Statement on Do-It-Yourself TDCS (December, 2015)

Matsumoto, H. Yokishikazu, U. Adverse events of tDCS and tACS: A review. Clinical Neurophysiology Practice p 19-25. (2017) 

Michael Craig Miller for Harvard Health Publications. July 26, 2012

Monte-Silva, K., Kuo, M. F., Hessenthaler, S., Fresnoza, S., Liebetanz, D., Paulus, W., & Nitsche, M. A. (2013). Induction of late LTP-like plasticity in the human motor cortex by repeated non-invasive brain stimulation. Brain Stimul, 6(3), 424-432. doi:10.1016/j.brs.2012.04.01

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

Rossi, S., Hallett, M., Rossini, P. M., Pascual-Leone, A., & Safety of, T. M. S. C. G. (2009). Safety, ethical considerations, and application guidelines for the use of transcranial magnetic stimulation in clinical practice and research. Clin Neurophysiol, 120(12), 2008-2039. doi:10.1016/j.clinph.2009.08.01

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

Wexler A (2015). The practices of do-it-yourself brain stimulation: implications for ethical considerations and regulatory proposals. Journal of Medical Ethics 42, 211–215.

Wurzman, R., Hamilton, R. H., Pascual-Leone, A., & Fox, M. D. (2016). An open letter concerning do-it-yourself users of transcranial direct current stimulation. Ann Neurol, 80(1), 1-4. doi:10.1002/ana.2468