Intensity and pattern discrimination after lesions of the pretectal complex, accessory optic nucleus and ventral geniculate in pigeons.

Abstract

Pigeons were trained to discriminate between pairs of visual stimuli that differed in intensity or pattern. After completion of training, bilateral, stereotaxic lesions were made in various cell groups in the mesencephalon and diencephalon that receive terminals of the optic tract. The target regions were nucleus ectomamillaris (accessory optic nucleus), nucleus lentiformis mesencephali and area pretectalis (prectal complex) and the nucleus geniculatus lateralis, pars ventralis (ventral geniculate). In some cases, combined lesions of nucleus lentiformis mesencephali and area pretectalis were made. Lesions of nucleus ectomamillaris, nucleus lentiformis mesencephali, area pretectalis, or ventral geniculate did not produce major impairments of discrimination performance nor did combined lesions of nucleus lentiformis mesencephali and area pretectalis. A number of cases of intended destruction of the ventral geniculate also had extensive damage of the overlying nucleus rotundus. In several of these cases of combined destruction of nucleus rotundus and ventral geniculate, the previously reported discrimination deficits following nucleus rotundus lesions did not appear. In those cases in which the nucleus rotundus deficit was observed, the lesions were found to include the nucleus subpretectalis, which, like nucleus rotundus, receives tectofugal fibers via the brachium of the superior colliculus. The data of the ventral geniculate + rotundus cases and ventral geniculate + rotundus + subpretectalis cases suggest that sensory deficits following a lesion in a particular cell group may not necessarily indicate that the sensory information is processed in that cell group, but rather that the lesion had deprived other cell groups of the appropriate input necessary for their proper functioning.