Sensitivity of the mature lateral geniculate nucleus to components of monocular paralysis.

Immobilization of the globe by tenotomization of the extrinsic muscles of one eye reduces the encounter rate for X-latency cells in the contralateral dorsal lateral geniculate nucleus (LGN) of adult cats. The reduction in the relative encounter rate for X-latency cells after tenotomy was comparable to that previously observed in the adult cat following concurrent paralysis of the extrinsic and intrinsic muscles of one eye by transection of cranial nerves III, IV, and VI. Paralysis of the intrinsic muscles alone by atropinization, on the other hand, had no detectable effect upon this aspect of LGN physiology. It appears, therefore, that monocular paralysis by cranial nerve section has its effects on LGN X-latency cells through its paralysis of the extrinsic eye muscles. Furthermore, the reduction in the relative encounter rate for X-latency cells produced by tenotomy occurred in spite of early, incomplete return of mobility of the globe. Thus, unilaterally diminished mobility of the globe, in contrast to the complete, sustained immobility characteristic of monocular praralysis, appears sufficient to alter this aspect of LGN physiology in adult cats. The general observation that sensory modifications, in the adult cat, are capable of inducing shifts in the relative recording probabilities for X- and Y-latency cells in the LGN has been repeatedly made. Further, recent, independent observations have provided confirmation for the phenomenon of X/Y ratio shifts in the LGN following adult-onset stimulus modification.