Fell, J. | bioRxiv Science

bioRxiv2017

Alpha activity in the ventral and dorsal visual stream controls information flow during working memory

The electrophysiological mechanisms underlying working memory maintenance of information in the ventral and dorsal visual stream (VVS, DVS) remain elusive. Here we used electrocorticography recordings covering VVS, DVS and prefrontal cortex (PFC) in epilepsy patients while they were performing a delayed match-to-sample task. The experimental conditions (face identity, orientation) were designed to engage either the VVS or DVS. Alpha power was reduced in the VVS during maintenance of face identity and in the DVS during maintenance of spatial orientation of the very same stimuli. The phase of alpha oscillations modulated broadband high-frequency activity (BHA) in both regions. Interestingly, BHA occurred across broader alpha phase ranges when task-relevant information was maintained, putatively reflecting longer excitable \"duty cycles\". Our findings support a model in which the VVS and DVS are recruited by the PFC via selective reduction of alpha power. As a result, excitable duty cycles in the relevant area are extended.

neuroscience↗

bioRxiv2017

Theta Phase Synchronization Between The Human Hippocampus And The Prefrontal Cortex Supports Learning Of Unexpected Information

Events that violate predictions are thought to not only modulate activity within the hippocampus and prefrontal cortex, but also to enhance communication between the two regions. Several studies in rodents have shown that synchronized theta oscillations facilitate communication between the prefrontal cortex and hippocampus during salient events, but it remains unclear whether similar oscillatory mechanisms support interactions between the two regions in humans. Here, we had the rare opportunity to conduct simultaneous electrophysiological recordings from the human hippocampus and prefrontal cortex from two patients undergoing presurgical evaluation for pharmaco-resistant epilepsy. Recordings were conducted during a task that involved encoding of contextually expected and unexpected visual stimuli. Across both patients, hippocampal-prefrontal theta phase synchronization was significantly higher during encoding of unexpected study items, compared to contextually expected study items. In contrast, we did not find increased theta synchronization between the prefrontal cortex and rhinal cortex. Our findings are consistent with the idea that theta oscillations orchestrate communication between the hippocampus and prefrontal cortex during the processing of contextually salient information.

neuroscience↗