Offset-related brain activity in the left ventrolateral prefrontal cortex promotes long-term memory formation of verbal events

Abstract

Background: Recent evidence suggests that brain activity following the offset of a stimulus during encoding contributes to long-term memory formation, however the exact mechanisms underlying offset-related encoding are still unclear. Objectives: Here, in three repetitive transcranial magnetic stimulation studies (rTMS) we investigated offset-related activity in the left ventrolateral prefrontal cortex (VLPFC). rTMS was administered at different points in time around stimulus offset while participants encoded visually-presented words or pairs of words. The analyses focused on the effects of the stimulation on subsequent memory performance. Results: rTMS administered at the offset of the stimuli, but not during online encoding, disrupted subsequent memory performance. In Experiment 1 we found that rTMS specifically disrupted encoding mechanisms initiated by the offset of the stimuli rather than general, post-stimulus processes. Experiment 2 showed that this effect was not dependent upon rTMS-induced somatosensory effects. In a third rTMS experiment we further demonstrated a robust decline in associative memory performance when the stimulation was delivered at the offset of the word pairs, suggesting that offset-related encoding may contribute to the binding of information into an episodic memory trace. Conclusions: The offset of the stimulus may represent an event boundary that promotes the reinstatement of the previously experienced event and episodic binding.

Keywords

• Ventrolateral prefrontal cortex
• Long-term memory
• rTMS
• Episodic memory formation
• Verbal memory