Visual intensity and pattern discrimination after lesions of the thalamofugal visual pathway in pigeons.

Abstract

AbstractTwenty‐seven pigeons were trained to discriminate between stimuli that differed in intensity or pattern. In 16 cases, bilateral, electrolytic, stereotaxic lesions were made in the nucleus opticus principalis thalami (OPT), which is the main thalamic terminus of the optic tract. In some cases, the lesions also interrupted the efferent fibers of nucleus rotundus thalami, which receives major input from the optic tectum. In an additional 11 cases, bilateral telencephalic lesions were made by aspiration. These lesions were in the accessory hyperstriatum, which contains the nucleus intercalatus, hyperstriati accessorii (IHA), which is the telencephalic target of OPT. Extensive destruction of either IHA or OPT produced little or no impairment of discrimination performance. However, those cases in which both OPT and nucleus rotundus were involved showed serious performance losses.