Declarative memory improvement by transcranial random noise stimulation (tRNS) of the frontal cortex

Human beings devote a considerable part of their lives to learning. Before being stored in declarative (long-term) memory, knowledge is temporarily processed by working-memory. In this experiment the cortical areas supporting working-memory function were investigated by using non-invasive tRNS, to discover which one is involved in declarative memory formation. In other words, we investigated which area, frontal or parietal, is casually linked to knowledge acquisition. Participants studied a paragraph and then their memory was tested; they were required to write down anything they could remember from the paragraph. This memory task was performed five minutes and seven days after studying the paragraph. Participants received tRNS on either the frontal or the parietal cortices; a placebo group was included too. We found that frontal stimulation, but not parietal nor placebo, significantly improved declarative memory performance. This was found after five minutes and seven days. In other words, participants who were stimulated on the frontal cortex remembered more information both immediately and in the long-term. These results suggest that the frontal cortex is significantly involved in declarative memory formation. Additionally, these findings can have important practical applications, such as improving learning in healthy and pathological populations.