P 138. Right cathodal transcranial direct current stimulation over the prefrontal cortex improves implicit learning in healthy individuals

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The fronto-striatal network is a key region in implicit sequence learning in the human brain. Previous studies suggested the functional involvement of the right prefrontal cortex, however, the exact contribution of this region in implicit learning and consolidation is still under debate. In the present study, we aimed at further exploring the putative role of the right dorsolateral prefrontal cortex (rDLPFC) by using transcranial direct current stimulation (tDCS) technique. In a sham-controlled, single-blinded, parallel group design, 20 participants received verum tDCS (1.0 mA for 10 min) and additional 20 participants (matched on age, gender and years of education) received sham stimulation (1.0 mA for 30 s) while performing the Alternating Serial Reaction Time (ASRT) task. Using this task we can measure sequence-specific and general skill improvement separately. In both groups, the cathodal electrode was placed over the rDLPFC with the anodal return electrode over Cz. (electrode size 35 cm2 each). Accuracy and reaction time were measured in three consecutive ASRT sessions. Consolidation (second and third session) was examined 2 and 24 h following the learning phase (first session). Results comparing sham (n = 20) and cathodal (n = 10) stimulation groups show a significant general improvement in task performance as well as sequence-specific learning for both groups. Additionally, cathodal stimulation caused a better general performance in the second and third sessions regarding both accuracy and reaction times, but not in the first session. These results suggest that cathodal stimulation of the rDLPFC causes greater general improvement in task performance only after consolidation but no alterations in sequence-specific learning. Further experiments are required to understand the specificity of the results regarding polarity and region used for stimulation.

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