Topography of visual and somatosensory projections to the superior colliculus of the golden hamster.

The topography of visual and somatosensory projections to the superior colliculus in the Syrian hamster was studied using electrophysiological techniques. The visual projection to the superficial layers of the colliculus is similar in general topography to that described for other rodents. The magnification of the visual field on the colliculus surface was greatest for nasal visual field. The magnification factor paralleled retinal ganglion cell density for corresponding visual field sectors. In the deep layers of the colliculus, a somatosensory projection is found in register with the visual projection such that the anterior somatosensory field and nasalmost visual field are both represented in rostral colliculus; posterior somatosensory fields and temporal visual fields are found in caudal colliculus. Likewise, upper visual and somatosensory fields are found in medial colliculus, and lower visual and somatosensory fields are found in lateral colliculus. Large receptive fields make the somatosensory topography less precise than the visual topography, but this lack of precision could serve to keep the two maps generally in register during eye and body movements.