Abstract
1. An attempt has been made to produce disuse in the lateral geniculate nucleus (LGN) of the cat, in the synapses between the optic nerve fibres and the principal cells of the nucleus. Evidence is produced that destruction of the visual receptor cells by iodoacetate or 1,5-di(p-aminophenoxy) pentane dihydrochloride effectively silences the optic nerve discharge and so achieves this result.2. Disuse of the LGN synapses does not cause any decrease in synaptic efficiency. The LGN response to a single stimulus to the optic nerve was not appreciably altered, and the depression which normally follows single or repeated stimuli was much reduced or absent. This increased responsiveness was unaffected by prolonged tetanization of the optic nerve during the experiment.3. Two possible explanations of the increased responsiveness are suggested: a post-synaptic ;decentralization'-hypersensitivity and an increased output of transmitter per impulse. The relevance of these results to theories of learning is discussed.4. The LGN response of adult cats kept in complete darkness for periods of up to 966 days was not appreciably different from that in the normal cat and there was little or no increased responsiveness. This suggests that many retinal ganglion cells continue to discharge in total darkness for long periods. There is a possibility that disuse may develop after a long time in the dark.