Optokinetic Nystagmus and Single-cell Responses in the Nucleus Tractus Opticus After Early Monocular Deprivation in the Cat
The normal cat’s optokinetic nystagmus (OKN) can be elicited in the two horizontal directions even if one eye is stimulated alone. After early monocular deprivation OKN is only elicited by patterns moving from temporal to nasal if either the deprived or the non-deprived eye is stimulated alone. A specific class of neurons in the nucleus of the optic tract (NOT) in the pretectum of normal cats can be identified by the following criteria: (1) large area patterns rich in contour are the most effective visual stimuli; (2) all neurons in the left NOT are strongly excited by movements from right to left and all neurons in the right NOT by movements from left to right; (3) effective stimulus velocities are within a broad range of less than 0.1 deg/sec to greater than 50 deg/sec; (4) latency differences to electrical stimulation of the optic chiasma and optic tract indicate slow conducting (W-cell) retinal input to these NOT neurons; (5) all neurons could be antidromically activated from the inferior olive; (6) the neurons recorded in the NOT were either binocularly driven preferring the same direction in visual space in each eye (40%) or were activated only through the contralateral eye (60%).
After six months of early monocular deprivation the properties of NOT neurons listed above remained largely unaltered except that neurons in each NOT could only be influenced from the contralateral eye irrespective of whether it was the deprived one or not. This is considered to be the explanation for the asymmetry of OKN after early visual deprivation.
KeywordsVisual Cortex Optic Tract Optic Chiasma Inferior Olive Optokinetic Nystagmus
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