Failure to Improve Verbal Fluency with Transcranial Direct Current Stimulation.

Area of Science:

• Cognitive Neuroscience
• Neurostimulation

Background:

• Evidence is mixed on whether anodal transcranial direct current stimulation (tDCS) over the left prefrontal cortex (PFC) improves verbal fluency in healthy individuals.
• Previous studies yielding positive results may be subject to false positives.

Purpose of the Study:

• To investigate the efficacy of anodal tDCS over the left PFC in enhancing verbal fluency performance compared to sham tDCS.
• To examine the impact of tDCS on task initiation time and picture naming latencies.

Main Methods:

• A double-blind, randomized, within-participant design was employed.
• Forty-eight healthy native German speakers received 20 minutes of anodal or sham tDCS over the left PFC.
• Participants completed verbal fluency tasks and a picture naming task during stimulation.

Main Results:

• No significant difference in overall verbal fluency scores was observed between anodal and sham tDCS conditions.
• tDCS did not affect the time to initiate verbal responses.
• Picture naming latencies were unexpectedly longer during anodal tDCS compared to sham stimulation.

Conclusions:

• Excitatory stimulation of the left PFC via anodal tDCS does not improve verbal fluency in healthy individuals.
• The findings cast doubt on the utility of tDCS for cognitive enhancement in the healthy brain.
• Previously reported positive effects of tDCS on verbal fluency warrant cautious interpretation.