Monocular deprivation and the signal transmission by X- and Y-neurons of the cat lateral geniculate nucleus.

1. In adult cats deprived monocularly from the second week of life, single neurons were recorded from the optic tract (OT), the lateral geniculate body (pars dorsalis, LGN) and the optic radiation (OR). The neurons were classified according to their visual response properties (Y/X) or their latencies to OT electrical stimulation (class I/II). 2. A close positive correlation (greater than 95%) was found between the visual classification and the latency classification (Y = I, X = II). 3. The relative frequency of class I/Y-neurons was reduced in the group of pattern-deprived LGN neurons, but normal in the pattern-deprived OR neurons. 4. The ratio of the r1 and r2 wave amplitude of the OR-evoked potentials elicited by electrical stimulation of the normal or the deprived eye optic nerve was not affected by pattern deprivation. 5. The activity pattern of neurons recorded from the LGN or the OR did not differ in normal and pattern-deprived neurons belonging to the same class (on-center/off-center; Y/X). The same was true for the neuronal responses to electrical stimulation of the OT at different stimulus frequencies (1-200 stimuli/s). 6. The average maintained activity of pattern-deprived OT or OR neurons recorded while the eyelids of the deprived eye were still closed was either equal to or even somewhat higher than the average activity of the corresponding normal neurons. This was true when the patterned stimuli were presented stationary or were moved at random within the visual field simulating the effect of eye and head movements. The pattern deprivation effects found morphologically and physiologically in the visual cortex are, therefore, not induced by a diminished average activity of the input neurons from the deprived eye.