Enhancement of episodic memory in young and healthy adults: A paired-pulse TMS study on encoding and retrieval performance

Transcranial magnetic stimulation (TMS) is a neurophysiological tool that can transiently influence brain excitability and improve cognitive performance. Facilitation effects induced by low frequency repetitive TMS on memory functions have been shown in a few studies in young and healthy participants [29] and in older individuals with memory complaints [40]. However, regions specifically involved in encoding and retrieval were not always systematically targeted. We thus aimed to facilitate episodic memory with online TMS systematically applied over the left or right dorsolateral prefrontal cortex (DLPFC) while participants were performing a recognition task. We applied online paired-pulse TMS (ppTMS) (15 ms inter-stimulus interval) either during encoding or retrieving of verbal or non-verbal material. Participants were 11 right-handed young individuals (21.33 ± 2.27 years old). Repeated measures ANOVA showed shorter reaction time when ppTMS are applied over the left DLPFC during encoding as compared to right homologous stimulation or to Sham condition. In contrast, ppTMS over the right DLPFC during retrieval was associated with shorter reaction times compared to left homologous stimulation. Overall, our data support for the first time that online ppTMS over the DLPFCs is capable of hastening memory processes in young and healthy individuals.

Research highlights▶ Online ppTMS can facilitate episodic memory in young and healthy individuals. ▶ Left DLPFC ppTMS can facilitate episodic encoding. ▶ Right DLPFC ppTMS can facilitate episodic retrieval, compared to left-sided ppTMS.▶ Online ppTMS allows specific facilitation of encoding or retrieval processes. ▶ ppTMS usually expose participant to fewer pulses than high-frequency TMS.