Changes in the circuitry of the kitten visual cortex are gated by postsynaptic activity

Abstract

MOST neurones in the visual cortex of normal adult cats are binocular and respond very selectively to elongated contours of a particular orientation¹. If a kitten is deprived of vision in one eye during a critical period in early life the afferents from this eye lose the ability to excite cortical cells². This functional deafferentation is, however, reversible if, still within the critical period, the previously open eye is closed and the other opened³. These changes in afferent connectivity are attributed to competitive interactions between the pathways from the two eyes^4,5, which have been shown to occur at the level of the striate cortex⁶. We previously demonstrated⁷ that afferents from the deprived eye remain functional when activity from the open eye is enhanced but fails to drive the common cortical target cell. This had suggested that the competitive suppression of one subset of converging afferents requires, in addition to imbalance in presynaptic activity, that the postsynaptic neurones actually respond to the more active pathways. Such postsynaptic gating was first postulated by Hebb⁸, and since then it has been assumed in most models on adaptive neuronal connections. In the study reported here more direct evidence for the participation of postsynaptic factors both in competitive suppression and in functional recovery of converging afferents was obtained. The results support Hebb's early hypotheses and demonstrate that both changes in connectivity are in fact guided by postsynaptic response properties.