The role of the different layers of primary visual cortex in working memory

Abstract

Imaging studies have revealed a neuronal correlate of working memory in primary visual cortex (Harrison & Tong, Nature, 2009). However, it is unknown if working memories influence spiking activity in the primary visual cortex. To address this question, we recorded neuronal activity in the primary visual cortex of monkeys trained to perform attentional and working memory tasks with a probe that records activity in all the cortical layers. We found a consistent working memory trace in the spiking activity in the superficial and deep layers of monkey V1, and only a weak memory representation in input layer 4. This V1 memory trace could be disrupted with a visual mask, but it then quickly recovered. The advantage of the laminar probe is that is also gives insight into the current-source density, which reveals the putative synaptic sources of memory activity. The current-source density measurements revealed a characteristic signature of feedback processing with putative synaptic inputs in the superficial and deep layers for working memory. This signature resembles the signature of selective attention, supporting the view that top-down modulation of activity in primary visual cortex underlies both working memory and attention. Our results provide new insights into the role of early visual cortex in working memory.