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

- tDCS over left or right PFC or PPC affects differentially encoding of verbal and non-verbal material.
- tDCS over PPC enhanced recognition of non-verbal items; tDCS over left PFC decreased recognition for both materials.
- Functional hemispheric lateralization does not follow the same rules throughout the brain.

ObjectiveInformation 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.MethodsWe 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.ResultsThere 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.ConclusionsThe 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.SignificancePrefrontal and posterior parietal cortices follow different lateralization rules in recognition memory.