Effect of prefrontal and parietal tDCS on learning and recognition of verbal and non-verbal material

Objective: Information learned in a spaced way is usually better recognized than information learned in a massed way. The brain mechanisms underlying this spacing effect remain unclear. Methods: We applied anodal transcranial direct current stimulation (tDCS) to the left and right prefrontal (PFC) or posterior parietal (PPC) cortices to study how stimulation influences learning and retrieval of information, as evidenced by item recognition and the spacing effect, and whether the effects are lateralized according to stimulus material and site of stimulation. We devised a continuous recognition task with verbal and non-verbal stimuli repeated either immediately or after a delay. Stimulus recognition was tested 30 min later. Results: There was a spacing effect for both materials, which, however, was not modulated by tDCS. Nonetheless, tDCS differentially impacted memory retrieval regardless of repetition mode during learning: tDCS over the PPC during learning enhanced recognition of non-verbal material regardless of side of stimulation, while tDCS over the left PFC decreased recognition regardless of material. Conclusions: The PPC seems to be involved specifically in the mnesic treatment of non-verbal material whereas the left PFC specifically influences learning irrespective of stimulus material. Significance: Prefrontal and posterior parietal cortices follow different lateralization rules in recognition memory. (C) 2016 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.