Neural responses in cat visual cortex reflect state changes in correlated activity

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Abstract
Cortical state is characterized by ongoing rhythmic neural activity. Changes in rhythmic activity and thus in cortical state are shown to occur spontaneously in the anesthetized cat. We were interested in whether these state changes have an affect on the cortical processing of sensory stimuli. This was investigated by recording spontaneous and stimulus-evoked local field potentials and multi-unit neuronal activity (MUA) from trans-cortical electrode arrays in the visual cortex of the anesthetized cat. Changes in cortical state were identified by calculating the cross-correlation strength and cross-coherency, between MUA channels at different layers and on separate electrode arrays. Spontaneous changes in rhythmic activity were associated with changes in the strength of stimulus-evoked multiple unit responses of cortical neurons. The highest multi-unit responses were found in periods when low-frequency rhythms of the electroencephalogram increase in magnitude and high-frequency rhythms decrease. Such changes in evoked responses were maximal at layer IV, the input layer of the visual cortex. Our findings suggest that stimulus response magnitude depends on rhythmic state and reflects changes in functional connectivity within the visual cortex.