Is there a ‘consolidation’ effect for monocular deprivation?

Abstract

During a time of high vulnerability early in a kitten's postnatal life, a few days of monocular vision can result in the control of most striate cortical neurones exclusively by the open eye^1–5. Although the general consequences of this procedure have been known for some time⁶, the mechanisms remain unknown. Because they develop rapidly^3,4, it has been suggested that the processes involved are similar to those of memory and learning. One aspect of this analogy is that memory is thought to be ‘consolidated’ from a weak to a stable form and that the process can be disrupted by the administration of drugs, electroconvulsive shock or physical trauma⁷. The connection with plasticity in the visual cortex has been suggested by studies in which kittens were first bilaterally deprived and then briefly exposed either monocularly or binocularly^3,4,8. The effects of exposure were reported to be greatest if there was a delay between exposure and Physiological study. Although this has been referred to as a ‘consolidation’ effect^3,4,5,8, it was a delay process rather than a process of stabilisation that was investigated. Furthermore, even though the evidence for this effect is not compelling, it has been assumed that the consequences of monocular deprivation in kittens with prior normal rearing also are consolidated, that is, they become accentuated if the unilateral occlusion is followed by a period without vision⁵. We tested directly the notion that short-term monocular deprivation effects are more extensive if, after unilateral exposure, a period is imposed before Physiological study during which kittens are kept in darkness. We report here that the consolidation idea is not supported by our results. On the contrary, the post-monocular period spent in darkness actually diminished the consequences of the deprivation, allowing some functional recovery of binocular connections.