Emergence of ocular dominance columns in cat visual cortex by 2 weeks of age

Previous anatomic studies of the geniculocortical projection showed that oc ular dominance columns emerge by 3 weeks of age in cat visual cortex, but r ecent optical imaging experiments have revealed a pattern of physiologic ey e dominance by the end of the second week of life. We used two methods to s earch for an anatomic correlate of this early functional ocular dominance p attern. First, retrograde labeling of lateral geniculate nucleus (LGN) inpu ts to areas of cortex preferentially activated by one eye showed that the g eniculocortical projection was already partially segregated by eye at postn atal day 14 (P14). Second, transneuronal label of geniculocortical afferent s in flattened sections of cortex after a tracer injection into one eye sho wed a periodic pattern at P14 but not at P7. In the classic model for the d evelopment of ocular dominance columns, initially overlapping geniculocorti cal afferents segregate by means of an activity-dependent competitive proce ss. Our data are consistent with this model but suggest that ocular dominan ce column formation begins between P7 and P14, approximately a week earlier than previously believed. The functional and anatomic data also reveal an early developmental bias toward contralateral eye afferents. This initial d evelopmental bias is not consistent with a strictly Hebbian model for genic ulocortical afferent segregation. The emergence of ocular dominance columns before the onset of the critical period for visual deprivation also sugges ts that the mechanisms for ocular dominance column formation may be partial ly distinct from those mediating plasticity later in life. J. Comp. Neurol. 430:235-249, 2001. (C) 2001 Wiley-Liss, Inc.