Neurons have been found in V1 of mice and marmosets that exhibit a diminution of activity immediately after the start of a gaze shift (eye and head movements in mice) or saccadic eye movements (in marmosets) to signal that a command has been executed for the generation of a volitional act (Parker et al. 2023). No such inhibition was apparent for compensatory head-eye movements (i.e., during VOR) during which time the eyes remain fixated on the visual scene followed by ocular movements to center the eyes in orbit (Fig. 3D of Parker et al. 2023). The diminution of response by V1 neurons ranged between 0 and 300 ms following the onset of a gaze shift (in mice) or saccadic eye movement (in marmosets) (Fig. 3E, 4D, left panels and Fig. 6E of Parker et al. 2023; note the range was shorter for saccades by marmosets given that the duration of a saccade is typically less than 100 ms, Schiller and Tehovnik 2015). Diminution of the response occurred in both light and dark, albeit the temporal profile of the inhibition occupied the full range of latencies (0 to 300 ms) when the shift occurred in light, but during darkness the latencies were uniform averaging about 100 ms (Fig. 3C of Parker et al. 2023); this suggests that vision anchors the firing of the V1 neurons to approximate the duration of a shifts in gaze and the reacquisition of the visual scene by the retina. The latency or signal to travel between the frontal lobes and V1 (and attributed to ‘cognitive’ processing) in mammals is typically under 300 ms (Ito, Maldonado et al. 2022; Lamme 1995; Lamme and Roelfsema 2000; Leinweber et al. 2017; Schiller and Tehovnik 2015; Schnabel et al. 2018; Zhang et al. 2014; Zipser et al. 1996), which coincides with the latencies found by Parker et al. for the inhibition. At least in mice, we know that the anteromedial cortex (a frontal eye field/medial eye field homologue of primates, Tehovnik et al. 2021) sends direct projections to V1 (Froudarakis et al. 2019). We suspect that such a pathway (whether direct or indirect) must also exist in primates by which to signal to V1 that an animal’s gaze is shifting. Someone needs to work out this pathway.
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