Abstract
Previously, we reported that the receptive-field (RF) center/surround organization of V1 and V2 neurons in macaques is immature during the first postnatal 8 weeks (Zhang et al, 2005). To gain insight into such functional immaturity, we examined the development of intrinsic and corticocortical connections in some of these infant monkeys. In 2-, 4- and 16-week-old infants and adults, we placed pressure injections of the tracers CTB and WGA-HRP along the posterior bank of the lunate sulcus. Following two to four days of transport, each animal was perfused. The brain was artificially flattened, cut, and stained for cytochrome oxidase (CO) or either tracer. CO sections were used to identify the V1/V2 border, stripe types, and blobs within V1. In some respects connection patterns were relatively mature even after two weeks of postnatal development. At two weeks, thin stripe injections showed strong connections with V1 blobs, thin stripes and other stripes in V2. Thick stripe injections did not preferentially label cells associated with blob or interblob regions. The label found within stripes was patchy at two weeks of age, as in older monkeys. V1 injections in two week old monkeys resulted in patches of labeled cells near the injection site. These connectional features were also observed in older monkeys. Thus, the presence of aspects of ‘adult-like’ connections at two weeks of age suggests that the basic pattern of intrinsic connections is present in V1 and V2 near birth. However, the RF surround mechanisms of V1 and V2 neurons are very immature at this age and adult-like responses emerge much later (Zhang et al, PNAS, 2005). The RF surround mechanisms of V2 (and V1) neurons likely depend more on the developmental elaboration of long-range horizontal connections, and/or the maturation of feedback connections from higher-order visual areas.