Neurophysiology of Perception: Non-Geniculostriate Pathways and the Neurones of Their Central Stations

The lateral geniculate body is the major processing nucleus for retinal information; however, in 1961 Altman and Carpenter drew attention to the thalamic projection from the superior colliculi; these bodies receive a powerful retinal projection, so that this collicular projection reveals an indirect access of visual information to the cerebral cortex. The target-areas of the ascending collicular projections are mainly within the pulvinar posterior system of the thalamus (PUL-PO), which, in turn, receives a strong projection from the visual cortex. Besides the colliculus, the adjacent pretectal region contains nuclei receiving retinal input; thus the circuitry for this subsidary processing system may be indicated crudely by Fig. 23.1. We shall see that the cortical influence on the colliculi is profound, so that their receptive-field characteristics become very similar to those of certain cortical cells.