Transcranial Direct Current Stimulation

What is transcranial direct current stimulation?
With tDCS a weak electrical current of 1 or 2 m Ampere is applied to the head with an electrode. The electrode is a non-metalic conductive rubber electrode, covered completely by saline soaked sponges.It is a noninvasive brain stimulation technique that utilizes low amplitude direct currents applied via scalp electrodes to inject currents in the brain and thus modulates the level of excitability. It doesn’t elicit seizures and it doesn’t require anesthesia. For comparison in ECT current of 9 m Ampere is used to elicit seizures during narcosis.

Advantages for tDCS above rTMS?
In comparison with rTMS, tDCS has some advantages
and disadvantages. The main advantages are that this is

• a simple, nonexpensive procedure, which is painless and allows inducing effects of opposite directions (facilitation or inhibition) on different parts of the brain
• It has a reliable sham condition, therefore providing more robust double blind clinical trials than TMS.
• tDCS is a good tool to be used simultaneously with cognitive training as it induces much less scalp sensation than rTMS and therefore is not prey to aspecific effects on attention

Limitations of tDCS compared to rTMS.

• tDCS is less focal than TMS, it is not focal enough to target localized areas and to map cognitive functions accurately

Efficacy in cognitive neurorehabilitation
Overall the use of tDCS in cognitive neurorehabilitation is limited. The data to date are insufficient to assess the therapeutic use of tDCS in cognitive rehabilitation.
tDCS has been used to modulate cognitive performance in healthy subjects. tDCS improved long-term memory consolidation for word pairs, enhanced working memory and language learning It also improved other language related tasks such as verbal fluency or picture naming. All these results were found in healthy subjects.

tDCS applied to the left frontotemporal cortex of nonfluent aphasic patients, resulted in a 34% improvement in the ability to name object pictures correctly. The effects of tDCS in patients with Alzheimer’s Disease. Results showed that after anodal tDCS in temporoparietal areas, accuracy on a word recognition memory task increased.

Limitations
There is still a large field to explore with tDCS. The site of application, the excitability status of the underlying cortical tissue, and the timing, frequency, and duration of stimulation are still to be determined. Changes induced in cortical response induced by tDCS are dependent on a number of technical variables. Some are still subject of much debate because tDCS is marginally researched in the literature of neurostimulation. Depression trial discussed in a post on this blog suggest that
at least 4 weeks of treatment are necessary to achieve clinically meaningful benefits. Therefore, the duration of treatment remain a key point in further studies. Follow-up on efficacy is needed, the effects could be temporarily.

C MINIUSSI, S CAPPA, L COHEN, A FLOEL, F FREGNI, M NITSCHE, M OLIVERI, A PASCUALLEONE, W PAULUS, A PRIORI (2008). Efficacy of repetitive transcranial magnetic stimulation/transcranial direct current stimulation in cognitive neurorehabilitation Brain Stimulation DOI: 10.1016/j.brs.2008.07.002

Thanks Brain Stimulant for the video

 

Transcranial direct current stimulation (TDCS) could improve memory in participants asked to learn and then recall a list of 12 words. The effect was significant in the early learning stages: in the first few trials, in which participants were given the same list over and over again, people in the treatment group could remember more words. But the learning curve for those working without the device quickly caught up to the zapped learners.

This conclusion of a recent research on TDCS published on Technology Review: Want to Enhance Your Brain Power?

At first the encoding of of the words is better in subjects treated with TDCS. Improving the encoding by training this test catches up after a while. The treatment with TDCS was done prior to the learning task, what if it was done during the test?

What is TDCS?

The device is simple: a nine-volt battery that’s been approved by the Food and Drug Administration for delivering drugs across the skin is connected to large flat sponges that are moistened and then applied to the head. It delivers a gentle 2 to 2.5 milliamps of current spread over a 20 to 50 square millimeter area of the scalp for up to 15 minutes. Little of that current actually reaches the brain–about half is shunted away from the target area, and the other half quickly dissipates as it gets farther from the scalp. The target in this research was the part of the brain known as the dorsolateral prefrontal cortex, a brain area involved in higher-level organization and planning, as well as in working memory. Because activity in this region has been shown in previous imaging studies to predict an individual’s ability to recall information, the idea is that giving it an electrical boost will enhance memory function.

TDCS is something completely different than ECT. It is not used to elicit a general seizure, it doesn’t require anesthesia and it is not tested properly for the treatment of depression.

Side-effects of TDCS
In the afore mentioned article only a slight dizziness was reported as side effect. In a upcoming publication in Brain Stimulation other side-effects are reported with TDCS. In 4 out of 4 patients treated with a higher dose (2mAmpere) during each active TDCS session with over 20 minutes (15-second ramp in and ramp out each) of stimulation on 5 days per week during a 2-week period, skin lesions were present. Generally, these lesions occurred after the fourth or fifth DC-stimulation, showed stable superficial extensions during further tDCS, and healed without scars about 1-3 weeks after the end of tDCS treatment.

The occurrence of lesions may depend on the intensity and duration of TDCS as well as on the impedance between electrode and skin.

Thanks Neuromod Blog

Related post on this blog: tDCS electrifying?

PALM, U., KEESER, D., SCHILLER, C., FINTESCU, Z., REISINGER, E., PADBERG, F., NITSCHE, M. (2008). Skin lesions after treatment with transcranial direct current stimulation (tDCS). Brain Stimulation DOI: 10.1016/j.brs.2008.04.003