CASE 2 – A study on the effect of L-tyrosine and transcranial direct current stimulation
Transcranial direct current (DC) stimulation has been suggested to affect cognitive function in humans by inducing a polarity-dependent shift in the resting membrane potential of cortical neurons, thereby altering their likelihood of firing.
However, studies of this intervention have yielded inconsistent results or could not be replicated. Although dopamine may play a role in this effect, definitive evidence supporting this notion is lacking. Therefore, researchers designed a study to examine the putative casual role of dopamine in the effect of transcranial DC stimulation on cognition. Specifically, they propose to study the effect of the dopamine precursor L-tyrosine and transcranial DC stimulation on working memory in healthy volunteers.
After fasting, participants will consume 2.0 g of L-tyrosine (or placebo) in 400 ml orange juice at the study location, followed by transcranial DC stimulation. The stimulation will consist of a 10-second increasing current ramp to 1000 mA, followed by 15 minutes at 1000 mA, followed by a 10-second decreasing ramp to 0 mA. The effects of 15 minutes of transcranial DC stimulation typically last one hour.
After stimulation, the participants will perform the letter-based verbal N-back task to test their working memory capacity. This test takes approximately 20 minutes.
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