Centre and surround responses of marmoset lateral geniculate neurones at different temporal frequencies

The responses of marmoset lateral geniculate neurones to stimuli that were composed of a sinusoidally modulating centre stimulus and a surround that was modulated in counterphase were measured. The size of the stimulus centre was varied. These measurements were repeated at different temporal frequencies between 1 and 30 Hz. The response amplitudes and phases depended in a characteristic manner on the stimulus centre size. The response behaviour could be modelled by assuming Gaussian responsivity profiles of the cells' receptive field (RF) centres and surrounds and a phase delay in the RF surround responses, relative to the centre, enabling the description of RF centre and surround response characteristics. We found that the RF centre-to-surround phase difference increased linearly with increasing temporal frequency, indicating a constant delay difference of about 4.5 to 6 ms. A linear model, including low-pass filters, a lead lag stage and a delay, was used to describe the mean RF centre and surround responses. The separate RF centre and surround responses were less band pass than the full receptive field responses of the cells. The linear model provided less satisfactory fits to M-cell responses than to those of P-cells, indicating additional nonlinearities.