The activity-dependent immediate early gene protein Krox-24, expressed in the neocortex at high basal levels, decreases rapidly upon neuronal deactivation (Chaudhuri et al. [1995] Vis. Neurosci. 12:35-50). In infant marmosets, as in most primates, the geniculo-cortical terminations segregate into eye-specific anatomical ocular dominance columns (ODCs), which disappear, however, during adolescence (Spatz [1989] Brain Res. 488:376-380), resulting in balanced inputs from the two eyes (Sengpiel et al. [1996] Vis. Neurosci. 13:145-160). Nevertheless, we found, in adult marmosets, 24 hours after monocular retinal activity blockade by tetrodotoxin, distinct alternating compartments of potentiated and depressed Krox-24-like immunoreactivity (Krox-IR) in layer IV of area 17. This pattern of Krox-IR disappeared at 10 days of retinal silencing, but was still present at this survival time in stains for cytochrome oxidase or NADPH-diaphorase. After 20 days of retinal silencing, the pattern was not demonstrable with any of the three stains. We term these compartments physiological ODCs, in contrast to the anatomical ODCs of most primates. If the anatomical ODCs of infant marmosets disappear by collateral sprouting into the inappropriate ODCs, then the collateral geniculo-cortical synapses might differ slightly in their properties from the original ones. We silenced the sets of original and collateral synapses of the one ocularity. This apparently transiently initiated, at the synapses driven by the intact eye, two different complex processes leading to molecular potentiation at the original synapses and to molecular depression at the collateral synapses.