Abstract
Neural signatures of working memory (WM) have been reported in numerous brain areas, suggesting a distributed neural substrate for memory maintenance. In the current manuscript we provide an updated review of the literature focusing on intracranial neurophysiological recordings during WM in primates. Such signatures of WM include changes in firing rate or local oscillatory power within an area, along with measures of coordinated activity between areas based on synchronization between oscillations. In comparing the ability of various neural signatures in any brain area to predict behavioral performance, we observe that synchrony between areas is more frequently and robustly correlated with WM performance than any of the within-area neural signatures. We further review the evidence for alteration of inter-areal synchrony in brain disorders, consistent with an important role for such synchrony during behavior. Additionally, results of causal studies indicate that manipulating synchrony across areas is especially effective at influencing WM task performance. Each of these lines of research supports the critical role of inter-areal synchrony in WM. Finally, we propose a framework for interactions between prefrontal and sensory areas during WM, incorporating a range of experimental findings and offering an explanation for the observed link between intra-areal measures and WM performance.
Highlights
Working memory (WM), as a basic cognitive function, contributes to our goal-oriented behaviors such as decision-making, problem-solving, language comprehension, and learning (Gazzaniga and Ivry, 2013)
We summarize findings on changes in oscillatory and synchronized activity within and between brain areas during working memory (WM), including correlations with behavioral performance, impairments associated with mental disorders, and causal manipulations
We propose that the coherent oscillation in the receiving area allows dynamic gating of arriving spikes, such that spikes arriving at a certain phase will more effectively drive the post-synaptic neurons; such changes in the sensitivity of an area to input based on the phase of local oscillations have previously been reported, albeit in the gamma band (Cardin et al, 2009; Knoblich et al, 2010; Yonelinas, 2013; Ni et al, 2016), and are consistent with the phase coding observed within PFC during WM (Siegel et al, 2009)
Summary
Working memory (WM), as a basic cognitive function, contributes to our goal-oriented behaviors such as decision-making, problem-solving, language comprehension, and learning (Gazzaniga and Ivry, 2013). Many areas show such persistent spiking activity during the delay period of a WM task (i.e., delay activity), suggesting that memory maintenance may depend on distributed activity across multiple brain areas (Christophel et al, 2017). This hypothesis leads to the question of how these active areas interact during the task. PFC PFC PFC PFC PFC FEF FEF FEF dACC pSMA pSMA OFC LIP VIP PPC Amg HC MST IT, VMT IT MT MTL V4 V1 V1 A1 PFC PFC FEF PFC AIP IT MT MT V4 MT A1 PFC PFC LIP MT PFC
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