Late effects of early binocular visual deprivation on the function of Brodmann's area 7 of monkeys (Macaca arctoides)

It has been shown earlier that binocular visual deprivation during the early sensitive period of life reduces the representation of visual functions in the posterior parietal association cortex of monkeys, in Brodmann's area 7 (Exp. Brain Res., 42 (1981) 1–8). Moreover, the representation of somatic functions increases suggesting that competitive mechanisms between the inputs from different modalities function during the early sensitive period of life in area 7. The aim of the present study was to find out whether further reorganization of functions takes place in the posterior parietal association cortex if monkeys that have experienced binocular visual deprivation through the first year of their life, are allowed to recover from the deprivation for a longer period of time. Four monkeys were deprived of binocular vision after the birth by lid closure for 12 months. Transdural extracellular multiunit recordings were performed in Brodmann's area 7 at the end of the deprivation period after the opening of the eyes. A second set of recordings was conducted in area 7 after a recovery period of 12 months from the deprivation. The results of the recordings at the end of the deprivation period confirmed the already known deprivation effect: there was a reduction in visually responsive neurons, an increase in the representation of somatosensory and somatomotor functions as well as an increase in the amount of cell groups that were ‘only spontaneously active’. The recordings performed after the recovery period showed that the representation of visual functions had remained low. However, the amount of ‘only spontaneously active’ neurons had decreased and the amount of cell groups responding to the monkey's own explorative movements of the hand had further increased. The results indicate that visual deprivation during the early critical period of life results in a profound and persistent reduction of visual functions in area 7. However, activity-dependent competition between inputs from different modalities continue, resulting in the domination of somatosensory and somatomotor functions over visual functions in area 7. The results also suggest that neurons which during the visual deprivation are left without active input from the visual system, gradually become integrated into other functionally active neuronal networks increasing the representation of somatic functions in this cortical area.