Reaction time improvement by transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) has been developed as a safe and effective method to modulate cortical activity by weak currents of 1 mA without side effects. The mechanism of action is a brief shift of the resting membrane potential influencing the excitability of the central nervous system. Depending on the time of this painless stimulation, after-effects can be measured up to 10–20 minutes after the stimulation.

Applying tDCS to children with pharmacoresistant epilepsy, parents reported an improved alertness for a few days. So, we decided to evaluate this effect in healthy volunteers by using a reaction time test.

20 healthy right-handed adults participated in this study. Before and after tDCS a simple reaction time test from the digital TAP (Testbatterie zur Aufmerksamkeitsprüfung) was accomplished over 8 minutes. tDCS was applied by two large spongue wrapped electrodes on both temporal brain regions using a CE certified stimulation unit (Neuroconn, Germany). with 1mA, continuously for 15min. All probands were examined three times, with one week interval after every tDCS session. Randomly a cathodal, anodal or placebo stimulation was performed. The results have shown that tDCS resulted in significant changes for cathodal left temporal tDCS after left versus right (p=0.030), and left versus placebo (p=0.017) simulation, and did not change after right versus placebo (p=0.803).

These results show that cathodal tDCS improves reaction time, which was not confirmed by anodal tDCS. The neurophysiological basis of an increased alertness caused by hyperpolarization of the temporal region, including the Hippocampus and Amygdale is not established, however confirmed by the clinical observation of an improved alertness after performing tDCS. Further investigations should be done to elucidate whether the tDCS of other brain regions can produce similar effects.