Representation of the visual field in the superior colliculus of the grey squirrel (Sciurus carolinensis) and the tree shrew (Tupaia glis)

Abstract

Microelectrodes were used to map the representation of the visual field in the superior colliculus in two arboreal diurnal mammals, the grey squirrel and the tree shrew, in which the superior colliculus is extremely well developed. For comparison, portions of lateral striate cortex of both hemispheres were mapped in the same animals. The results suggest that the projection of the visual field to the superior colliculus both in tree shrew and squirrel differs from that to striate cortex in two ways: (1) the complete visual field of each eye appears to be represented in the contralateral superior colliculus, while the most nasal 30° of the visual field of each eye is represented in ipsilateral striate cortex; and (2) neurons in the superior colliculus are activated only by stimuli to the contralateral eye, while the lateral striate cortex receives input from both the ipsilateral eye and the contralateral eye. The projection to the superior colliculus in tree shrew and squirrel resembles that to striate cortex in that the region of the visual field corresponding to the intersection of the line of decussation and the horizontal meridian of the retina is represented in a larger area of the superior colliculus than other portions of the visual field.