Effects of repetitive transcranial magnetic stimulation on memory subtypes: a controlled study

Repetitive transcranial magnetic stimulation (rTMS) of human cortex may disrupt or facilitate cortical activity. The aim of the present study was to investigate the consequences of rTMS applied over different cortical areas during various memory tasks, measuring immediate, working and episodic verbal memory. The study was performed in 16 right-handed healthy men. A double-blind, cross-over, within-subject repeated measures design was used. There were five rTMS conditions: baseline without stimulation, high frequency (HF) rTMS over right and left dorsolateral prefrontal cortex (DLPFC) and over right cerebellum, and low frequency (LF) parameters over left DLPFC. Digits forwards and backwards and letter-number sequencing of the Wechsler Adults Intelligence Scale (WAIS) were used to assess immediate and working verbal memory, and logical memory of the Rivermead Behavioural Memory Test was used to assess episodic memory encoding. An analysis of variance (ANOVA) for repeated measures in the scores of each memory task according to rTMS conditions was used. Significantly lower scores in the number of memory units of the episodic memory task were observed when rTMS high frequency parameters were applied over left DLPFC (P=0.009). No significant differences were found in the other memory subtype tasks analysed during the different rTMS conditions. These findings provide evidence for the significant role of the left DLPFC in episodic verbal memory processes.