Brief periods of monocular deprivation in kittens: effects of delay prior to physiological study

1. Brief periods of selective visual exposure in 4-wk postnatal kittens can cause pronounced alterations in striate cortex. The processes underlying these changes may be similar to those of other short-term neural events such as memory or learning, and attempts have been made to link these areas. In particular, it has been reported that the effects of selective visual exposures are consolidated if a delay is interposed between rearing and physiological study. 2. We have tested this notion directly. Normally reared kittens were monocularly occluded for 8 or 24 h on postnatal day 29. Half of the 8-h and of the 24-h groups were tested physiologically immediately following monocular exposure, while the other halves were recorded after an intervening session of 8 or 48 h, respectively, during which the kittens were kept in darkness. 3. Extracellular responses of cortical neurons were analyzed, and primary attention was paid to absolute and relative interocular response strengths of each cell. Ocular dominance distributions from all kittens were significantly abnormal, but invariably, effects were less extensive for those who had experienced a period of dark rearing prior to physiological study. 4. These results are clearly at odds with the idea that the effects of monocular deprivation were consolidated by allowing a period of delay between exposure and physiological recording. On the contrary, during the time the kittens spent in darkness, it appears that some functional recovery of binocular pathways occurred. 5. To explore the minimal period of monocular occlusion that could cause cortical disruption, we studied an additional group of normally reared kittens that were occluded for only 4 h on postnatal day 29. Effects for this group were small but ocular dominance patterns were significantly abnormal. 6. An alternative procedure was used for the delay period between 24-h monocular occlusion and physiological study. Prior to recording, these kittens spent 48 h in a normally illuminated colony. Ocular dominance histograms were normal, indicating that complete recovery had occurred from the initial monocular deprivation. 7. Histological reconstructions were made to estimate effects in different cortical laminae, but conclusions must be tentative because of small samples. In the group that had been monocularly occluded for 4 h and then recorded, inactivation of binocular pathways was most apparent in layers IV and V. This results suggest that the process deprivation disconnection during monocular deprivation occurs frist in these layers. Findings from the groups in which a delay was imposed between monocular exposure and recording indicate that functional binocular recovery occurs frist in layer IV and above and last in layer VI.