Brain Behav. Evol. 3: 295-323 (1970) Development, brain Hamster, Golden Optic system Plasticity, neuronal Retinal projections Superior colliculus Visual cortex Visual function Mechanisms of Functional Recovery Following Lesions of Visual Cortex or Superior Colliculus in Neonate and Adult Hamsters1 G. E. Schneider Department of Psychology, Massachusetts Institute of Technology, Cambridge, Mass. Brain damage inflicted early in life can have both behavioral and neu- roanatomical consequences which differ from the effects of lesions in the adult. The experimental results reported here clarify some of these differ ences, and narrow the range of tenable hypotheses concerning the roles of subcortical visual pathways in functional recovery from cortical and mid brain tectal lesions. Lesions of superior colliculus or visual cortex in the adult Syrian gold en hamster (Mesocricetus auratus) have clearly distinguishable conse quences in visually guided behavior [Schneider, 1966, 1967, 1969]. To human observers, who spend much of their time looking at the behav ior of fellow primates, the hamster is not an overwhelmingly visual ani mal, but he is more obviously visual than the laboratory rat and has a su perior colliculus more accessible to a direct surgical approach [Schnei der, 1966]. Moreover, the hamster’s colliculus is about as large in sur face area as area 17 of the neocortex; and the superficial gray layer of the colliculus, throughout which optic tract terminals are found, has a volume more than twice as great as that of the dorsal nucleus of the lateral genic ulate body (unpublished data). 1 Financial support was provided principally by US Public Health Service grant NB 06542 to W. J. H. N auta. Additional support came from grants from NASA and from the John A. Hartford Foundation to H.-L. Teuber , and from PHS grant EY 00126 to the author.