Abstract
Previous studies have reported conflicting results regarding the effect of direct electrical stimulation of the human hippocampus on memory performance. A major function of the hippocampus is to form associations between individual elements of experience. However, the effect of direct hippocampal stimulation on associative memory remains largely inconclusive, with most evidence coming from studies employing non-invasive stimulation. Here, we therefore tested the hypothesis that direct electrical stimulation of the hippocampus specifically enhances hippocampal-dependent associative memory. To test this hypothesis, we recruited surgical patients with implanted subdural electrodes to perform a word pair memory task during which the hippocampus was stimulated. Our results indicate that stimulation of the hippocampus during encoding helped to build strong associative memories and enhanced recollection in subsequent trials. Moreover, stimulation significantly increased theta power in the lateral middle temporal cortex during successful memory encoding. Overall, our findings indicate that hippocampal stimulation positively impacts performance during a word pair memory task, suggesting that successful memory encoding involves the temporal cortex, which may act together with the hippocampus.
Highlights
The hippocampus plays a pivotal role in associative memory (Olsen et al, 2012; Yonelinas, 2013), serving as a hub that supports the binding of information (Battaglia et al, 2011); it is regarded as a core region for stimulation in attempts to manipulate the memory circuit (Eichenbaum et al, 2007)
We quantified the effect of stimulation on memory performance in two ways: first, we determined the hit rate of associative memory; second, we examined whether stimulation affected the ability to remember a learning episode or the capacity to judge items as familiar
We examined the effect of hippocampal stimulation on a word pair memory task
Summary
The hippocampus plays a pivotal role in associative memory (Olsen et al, 2012; Yonelinas, 2013), serving as a hub that supports the binding of information (Battaglia et al, 2011); it is regarded as a core region for stimulation in attempts to manipulate the memory circuit (Eichenbaum et al, 2007). Several non-invasive stimulation studies have reported that hippocampal stimulation enhances paired associative memory (Wang et al, 2014; Wang and Voss, 2015). Item memory was unaffected, demonstrating a selective influence on associative memory vs item memory (Tambini et al, 2018).
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