Modified distribution patterns of responses in rat visual cortex induced by monocular enucleation.

Monocular enucleation was performed on rats at birth or on the 8th or 15th day, respectively. The animals were raised and from the age of 3 months the evoked activity was tested in the visual cortex. It was found that monocular enucleation changed the distribution of visually evoked responses. In the right hemisphere (contralateral to the preserved eye) two focuses of evoked potentials appeared with large amplitudes shifted to both sides, towards the lateral and medial borders of the primary visual area. In the left hemisphere the focus of the evoked potentials was shifted slightly laterally and posteriorly. Early enucleation caused an expansion of the somatosensory responses into the visual area. Bimodal neurons (responsive to visual and somatosensory stimuli) were observed in the anterior part of the primary and secondary visual areas contralateral to the enucleation. These changes became moderate with increasing age at which enucleation was performed and were not found in animals enucleated on the 15th day after birth.