Laminar thermocoagulation of the visual cortex of the rat. I. Interlaminar connections.

Lesions were made in the visual cortex of hooded rats by laminar thermocoagulation and later examined using modifications of the Fink-Heimer method. Following lesions limited to supragranular layers a dense, descending projection to layer V was identified, as well as a probable projection to deep layer III, callosal and cortico-cortical projections, but no subcortical projections. The morphological changes in the degenerating systems were examined as a function of survival time. The anatomical basis of functional derangement related to superficial lesions of visual cortex was discussed.

Laminar thermocoagulation of the visual cortex in the rat. II. Visual pattern discrimination.

Hooded rats were trained on a series of four visual discrimination tasks in a Y-maze, and subjected to a variety of posterior cortical lesions. In 17 animals this consisted of an extensive aspiration lesion contralateral to a more superficial lesion made by laminar thermocoagulation and centered over the striate area. After operation the animals were tested on the same problem series. The behavioral deficit in this group varied with the extent and depth of the thermal lesion, and six animals with very superficial thermal lesions displayed an isolated difficulty in solving an encircled triangle problem. This deficit seemed to be referable to widespread involvement of supragranular cortex, and specifically of layer I of area striata which receives an input from the nonspecific thalamocortical afferents. The possible influence of various interlaminar projections upon underlying vertically-oriented cell columns as a mechanism for the mediation of 'selective attention' was discussed.