Impulse propagation from photically discharged neurones in the visual system

Summary

Direct pathways were shown microphysiologically in the cat from SC, a fast one to DLGN and a slow one to VLGN. Evidence for these was provided by showing antidromic unit responses in SC following stimulation of DLGN or VLGN deep layers. The pathway from SC to DLGN was studied from the point of view of the probabilities that an impulse would propagate through it when its parent neurone is discharged by light stimuli or in spontaneous discharges. These probabilities were assessed in term of the rates at which such propagation took place. The latter was determined by use of the collision technique, which provided the information when an impulse propagated and when it did not in a fiber following a neuronal discharge. Total field flashes were shown to discharge the neurones in such a way that it resulted in firm propagation through the fibers of SC neurones which projected to DLGN. In contrast, spontaneous discharges have shown failures of such propagation as well which indicated a lower probability for impulse propagation to DLGN in the latter type of neuronal discharges.