Prefrontal and parietal cortex in human episodic memory: an interference study by repetitive transcranial magnetic stimulation

Abstract

Neuroimaging findings, including repetitive transcranial magnetic stimulation (rTMS) interference, point to an engagement of prefrontal cortex (PFC) in learning and memory. Whether parietal cortex (PC) activity is causally linked to successful episodic encoding and retrieval is still uncertain. We compared the effects of event-related active or sham rTMS (a rapid-rate train coincident to the very first phases of memoranda presentation) to the left or right intraparietal sulcus, during a standardized episodic memory task of visual scenes, with those obtained in a fully matched sample of subjects who received rTMS on left or right dorsolateral PFC during the same task. In these subjects, specific hemispheric effects of rTMS included interference with encoding after left stimulation and disruption of retrieval after right stimulation. The interference of PC-rTMS on encoding/retrieval performance was negligible, lacking specificity even when higher intensities of stimulation were applied. However, right PC-rTMS of the same intensity lengthened reaction times in the context of a purely attentive visuospatial task. These results suggest that the activity of intraparietal sulci shown in several functional magnetic resonance studies on memory, unlike that of the dorsolateral PFC, is not causally engaged to a useful degree in memory encoding and retrieval of visual scenes. The parietal activations accompanying the memorization processes could reflect the engagement of a widespread brain attentional network, in which interference on a single 'node' is insufficient for an overt disruption of memory performance.

Does lateral parietal cortex support episodic memory?

“…Thus, a particularly fruitful technique may be to combine functional neuroimaging and lesion approaches where patients' lesions are well-defined, and memory performance is studied in depth (Price & Friston, 2002). Another potentially useful strategy is to induce temporary functional lesions using transcranial magnetic stimulation, although the behavioral effects of this method tend to be quite small (for an initial study, see Rossi et al, 2006). Because every method in cognitive neuroscience has its own strengths and weaknesses, using a combination of them is crucial to developing a more sophisticated picture of how episodic memory is supported by the brain.…”

Memory Retrieval in Mice and Men

“…Conversely, most lesion studies find limited, if any, impairment in episodic retrieval (Berryhill et al 2007(Berryhill et al , 2010Haramati et al 2008), supported by an repetitive transcranial magnetic stimulation (rTMS) study that found disruption of the posterior parietal cortex does not significantly impair memory (Rossi et al 2006). A study directly comparing patients lesioned in this cortex with fMRI of healthy individuals found an anatomical overlap between the parietal recollection-related activations and the locus of the damage in patients that showed normal performance on the same task (Simons et al 2008).…”

Primary motor cortex functionally contributes to language comprehension: An online rTMS study

“…4 pulses were sent for every word, with 50-ms gaps between consecutive pulses), based on previous studies which on the one hand demonstrated local interference effects following this protocol and on the other hand excluded any inter-hemispheric effect (Hamada and Ugawa 2010;Tsutsumi et al 2014;Gerloff et al 1997;Rossi et al 2002Rossi et al , 2006Rossi et al , 2011Berent et al 2015).…”