Abstract
Neuronal activity in early visual cortex depends on attention shifts but the contribution to working memory has remained unclear. Here, we examine neuronal activity in the different layers of the primary visual cortex (V1) in an attention-demanding and a working memory task. A current-source density analysis reveales top-down inputs in the superficial layers and layer 5, and an increase in neuronal firing rates most pronounced in the superficial and deep layers and weaker in input layer 4. This increased activity is strongest in the attention task but it is also highly reliable during working memory delays. A visual mask erases the V1 memory activity, but it reappeares at a later point in time. These results provide new insights in the laminar circuits involved in the top-down modulation of activity in early visual cortex in the presence and absence of visual stimuli.
Highlights
Neuronal activity in early visual cortex depends on attention shifts but the contribution to working memory has remained unclear
A recent study[13] demonstrated that persistent firing during working memory for the movement direction of a briefly presented stimulus is virtually absent from the middle temporal (MT) area, a lower-level motion-sensitive area, but that it is strong in the higher medial superior temporal (MST) area and in the frontal cortex
Studies in human observers demonstrated that memory traces of low-level stimulus attributes may persist for seconds[14], and fMRI studies revealed that is it possible to decode the orientation or colour of a stimulus in working memory from activity in primary visual cortex (V1), in accordance with ‘sensory recruitment’ theories postulating that vivid memories require feedback from higher cortical areas to reinstate activity patterns in sensory cortices[15,16,17,18]
Summary
Neuronal activity in early visual cortex depends on attention shifts but the contribution to working memory has remained unclear. Previous studies used a version of this task where the stimulus remained in view and demonstrated that the feedforward response is followed by a phase where horizontal connections and feedback connections modulate V1 activity[24,25,26] In this later phase, enhanced neuronal activity spreads gradually along the V1 representation of the target curve, starting at the fixation point until the entire curve has been labelled with enhanced neuronal activity[24,27], a process that corresponds to the spread of object-based attention at a psychological level of description[28,29]. A current-source density analysis indicates that both cognitive functions increase the magnitude of synaptic input into the superficial layers and layer 5, providing a canonical signature of top-down influences from higher visual cortical areas back to V1
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