Surround modulation of neuronal responses in V1 is as stable over time as responses to direct stimulation of receptive fields

In the primary visual cortex (V1) the modulation of neuronal responses by surround stimuli displays considerable variability. At present, it is not known whether this variability across neurons is due to temporal instability or to neuron-specific differences. We explored this question in the cat visual cortex by making multi-channel recordings while repeatedly presenting surround gratings of collinear and orthogonal orientation to the centre stimulus for a period of 96 h. Our results indicate that surround modulation is temporally stable to about the same degree as the responses evoked by the centre stimuli. The results support the notion that the mechanisms of surround modulation exhibit a high degree of stability and play an important role in the modulation of cortical responses.