Corticofugal feedback improves the timing of retino-geniculate signal transmission

The temporal accuracy of visually induced spike patterns can be expected to deteriorate with increasing distance from the retina due to synaptic noise and other sources of activity unrelated to the retinal signal. Here we report the opposite effect: the interspike interval distributions of relay cells of cat lateral geniculate nucleus (LGN) are sharper than those of their retinal afferents. A biophysically realistical simulation of the retino-cortical pathway, including excitatory cortico-geniculate feedback, produced a similar effect. Without the feedback the mean firing rate in the LGN dropped and interval peaks broadened by an average of 25%. The same effect was found during reversible experimental inactivation of the visual cortex in cat. This indicates that cortico-geniculate feedback could be employed to improve the temporal accuracy of signal transmission.