Spatial contrast and flicker sensitivity following medial thalamic or visual cortex lesions in hooded rats

In rats, lesions of the medial thalamus that involve the intralaminar nuclei produce a number of visual impairments similar to those obtained with visual cortex ablation, suggesting that the former functionally disrupt visual cortex. This was tested by a direct comparison between the two lesions on spatial contrast and flicker sensitivity, using behavioural techniques. Both lesions depressed spatial contrast sensitivity, visual cortex damage more than thalamic lesions. Only medial thalamic lesions produced statistically significant changes in flicker sensitivity. This dissociation suggests that medial thalamic and visual cortex lesions are disrupting different mechanisms. Alternative explanations of the thalamic deficit are discussed.