Layer-specific modulation of top-down spatial attention in human early visual cortex

Human visual cortex consists of six layers of neurons, with distinct roles in feedforward, feedback and lateral connections. The laminar circuits of attention in the human visual cortex remain largely unknown. Here we investigated how top-down spatial attention modulated layer-specific activities in the human visual cortex, using submillimeter-resolution fMRI at 7 Tesla (with 0.75mm 2d GE-EPI and 0.8mm 3d b-SSFP sequences). Two checkerboard patterns counterphase flickering at 7.5Hz were presented to the left and right side of fixation, at five contrast levels (2.5%, 6%, 14%, 35%, 83%). Subjects were instructed to either pay attention to the left or to the right checkerboards to detect occasional spatial frequency change of the stimulus. Results showed that compared to the middle layer activities, attention modulation was stronger in the superficial and deep layers of V1, and in the superficial layers of V2 and V3. Furthermore, contrast sensitivity was lower in the middle layer than in the superficial layer of V1, consistent with the feedforward input from the LGN. These findings suggest that top-down spatial attention mainly improves output neural signals in the superficial layers of visual cortex that project to higher cortical areas, and deep layer signals that project to the thalamus