Facilitating Associative Memory Via Deep Transcranial Magnetic Stimulation to the Medial Temporal Lobe

Overview

The goal of the proposed research is to map the effects-in particular facilitation-of Transcranial Magnetic Stimulation (TMS) of the Medial Temporal Lobes (MTL) onto the processing of associative memory. TMS technology has the potential to selectively enhance functions mediated by areas in the temporal cortex, including the MTL, known to be the primary neuronal seat of episodic memory. By using this technology the investigators can further our understanding of theoretical models of human memory (specifically regarding the role of Recollection and Familiarity processes), and additionally, provide a possible route to the recovery of some of memory loss typically observed in the elderly-namely, memory for associations. Given the MTL's critical role in human memory and facilitation-inducing qualities of TMS, this research goal is to provide a nonintrusive tool to facilitate memory performance in young and elderly healthy participants.

Our theoretical motivation is to explore the mechanisms underlying recognition memory. Evidence from a variety of paradigms has converged on the notion that recognition memory comprises two processes: 1. Familiarity, entails item-specific information. 2. Recollection, entails association-specific information. Evidence suggests that recollection is associated with a network of neuronal regions, including the anterior medial prefrontal cortex, lateral parietal cortex, and the hippocampus. Familiarity, in contrast, is associated with the lateral prefrontal cortex and the peripheral cortex. Critically, for both familiarity and recollection, the vital role of the MTL is strongly implicated. To dissociate between recollection and familiarity, despite stimulating the same location in the brain, the investigators take into account the difference in processing time in which these two processes are known to operate, and use both objective and subjective cognitive tasks to accurately measure effects. In addition, this research has clinical motivation, which relates to the nature of memory decline in the elderly. If successful, the investigators will be able to set an effective TMS protocol that could be used as a tool to enhance the very types of memories-association-specific memories-that are thought to mediate poor memory performance in the elderly. To achieve both goals, the proposed experiments will target the MTL using both online stimulation (short-duration stimulation during the presentation of stimuli in recognition memory test) that will enable us to differentiate between effects of familiarity and recollection and offline stimulation mode (repetitive stimulation of several minutes separately from the recognition memory test), with the goal of achieving facilitation effects on memory performance.

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