Chronic asymmetry in the extraocular muscles of adult cats: stability in binocularity of cortical neurons.

During the first 2 weeks following unilateral severance of the 6 extraocular eye muscles in adult cats, the operated eye is partially immobile as shown by electrooculographic (EOG) recordings of horizontal eye movements. Although the motility of the operated eye improves with time (mainly in terms of amplitude but also with regard to direction and frequency of movements), it does not reach (up to 2 months) the level of the normal eye. Unit recording was done in visual cortex area 17 of these cats while paralyzed, either immediately (acute group, 5 cats), or 3-60 days (chronic group, 6 cats) following the operation. The number of visually inactive cells was slightly higher in the operated cats (13.8%) than in normal cats (8.3%), but the number of nonoriented cells or cells with disorganized receptive fields was similar in both groups of cats. The proportion of binocularly activated cells in the operated cats, especially in the chronic group (greater than 10 days after the operation, 71.2% of 153 cells), was similar to that of the normal control cats (72.8% of 236 cells). No ocular dominance shift was found when either the operated eye was compared to the normal one or the ipsilateral eye to the contralateral one. It was concluded that distortion of afferent proprioceptive input from the extraocular eye muscles to visual centers has no effect on binocularity of cortical neurons in adult cats.