Low frequency rTMS over the right parietal cortex at retrieval increases recognition memory in healthy subjects

Neuroimaging and lesion studies have led to contrasting findings regarding the potential role of the parietal lobe in episodic memory. Imaging studies strongly suggest an important participation of the posterior parietal cortex (PPC) in episodic memory, whereas lesion studies are not conclusive at this regard. Using off-line 1 Hz rTMS paradigm, we conducted 2 experiments to investigate the role of PPCs in recognition memory. Real or sham rTMS were applied over the left or the right PPC (P3 and P4 of the 10–20 EEG system) of healthy subjects before encoding (Experiment 1) and just before retrieval (Experiment 2) of forced-choice non verbal recognition memory tasks. rTMS over the left and the right PPC at encoding did not modulate memory performance . Conversely, rTMS over the right (p < 0.02) but not left (p < 0.3) PPC at retrieval significantly improved recognition memory performance. These findings suggest that PPC is involved at retrieval but not at encoding of recognition memory. Inhibition of the right PPC at retrieval enhances memory function in healthy subjects. These findings are in line with our recent work showing that rTMS inhibition of the right dorsolateral prefrontal cortex (DLPFC) enhanced recognition memory in healthy subjects as well as in patients with mild cognitive impairment. We propose that the right DLPFC and the right PPC may be part of a neural network recruited during recognition memory retrieval. Temporary inhibition of these regions enhances memory performance suggesting a cognitive benefit when there is a reduced activity in these regions during recognition memory tasks. Our findings may give support to an inhibitory control account of the interactions between the DLPFC - PPC and the medial temporal lobe during retrieval of memory information.