Changes in ocular dominance induced in monocularly deprived lambs by stimulation with rotating gratings

Abstract

AMBLYOPIA in children aged about 6 yr can be rapidly diminished by stimulating the amblyopic eye alone with rotating disks of square-wave gratings¹. Such exposure for four periods each of 7 min has brought many of the patients up to 6/6 acuity, in some cases, after ‘patching’ of the good eye had been largely ineffective. However, in children of this age, the ‘critical period’ has probably passed. We decided to study the effects of presenting rotating gratings during the critical period, when the visual system is known to be acutely sensitive to visual deprivation. Could changes in the ocular dominance of cortical neurones be induced even in the relatively unfavourable conditions of moderate to light anaesthesia? We report here that monocular deprivation of 2–3 d in young lambs results in a marked decrease in the number of cells in the primary visual cortex which can be stimulated through the deprived eye, but that this can be rapidly increased by subsequent brief exposure of the deprived eye to a rotating square-wave grating. We chose to work on lambs and a pygmy goat in which one eye had been closed for a few days shortly after birth because we thought that such treatment would leave few cells driven initially by the deprived eye. As the visual cortex at that time is showing its greatest plasticity, it seemed likely that short exposures to the gratings would then have their greatest effect on the ocular dominance. Others had used repeated stimulation by moving bars on single cells of normal animals, but had obtained rather slight and transient effects². We hoped to obtain reasonable changes in eye dominance during the limits of single acute experiments. Seven animals were used. They had normal binocular visual experience until the 4th day of life and were then monocularly deprived for either 2 (nos 1–4) or 3 (no. 5) d, after which they were anaesthetised and used for the experiment.