Absolute threshold of vision in the rat after removal of striate cortex.

Abstract

Rats without visual cortex and control rats were trained to make a lightdark discrimination in a Skinner box. In agreement with previous investigations with eats, the rats without striate cortex exhibited an impairment at low light intensities. In contrast to the previous experiments with cats, however, it could not be concluded that the absolute threshold to light is directly affected by removal of visual cortex. The consequences of visual cortex removal on retention of the light-dark discrimination habit were also investigated and were found to have little or no effect.

The gustatory neocortex of the rat

“…Rats lacking VN readily learn brightness discrimination habits , but with reduced efficiency (Horel et al, 1966), which can be modulated somewhat by varying the brightness intensity differences between the discriminative stimuli (Spear & Braun, 1969). This suggests reduced associative salience of brightness stimuli for rats lacking VN, although detection thresholds for a brightness cue ultimately appear to be the same in normal and VN-ablated rats (Cooper et at, 1967;LeVere & Mills, 1977).…”

“…Because of this, potentially separable reflexive, perceptual, and associative capacities tended to be confounded in those studies. Thus, while Lashley's (1930) early data indicated that rats lacking visual neocortex suffered basic sensory deficits in perceiving brightness, the deficits appear to have been related to associative or performance dimensions of the learning task that was used by Lashley to assess brightness discrimination (Cooper, Freeman, & Pinel, 1967;LeVere & Mills, 1977). There were, however, exceptions in the literature to this kind of methodological confounding.…”

Recovery of function after brain damage: A theory of the behavioral deficit

“…On the other hand, there are disruptions that are not necessarily permanent and may be recovered. For example, there is a general performance deficit associated with striate ablations in rats (Cooper, Freeman, & Pinel, 1967;Lashley, 1930;LeVere & Mills, 1977) that is permanent and persists even though postoperative training will normalize the absolute (Cooper et aI., 1967) and relative (LeVere & Mills, 1977) brightness thresholds. Or, as another example, consider the destriate rat's ability to recover both a preoperatively learned brightness discrimination and a horizontal-vertical line discrimination.…”

The effect of occipital ablation on visual sensitivity in young and old rats

“…Further, the findings of Bridgmen and Smith (1942) demonstrate that the deficits seen are not a consequence of cortical insult, but are the consequence of total ablation of the visual projection cortex. Recently, Kenshalo (1976) found an increase in the absolute visual threshold of rats following bilateral occipital ablation.After finding that the performance of occipitally ablated rats on a light-dark discrimination task was inferior at intensities well above visual threshold as well as at lower intensities, Cooper, Freeman, and Pinel (1967) suggested that performance deficits were due to postoperative changes in the sensory criterion (the sensory level set by the subject for deciding whether a visual signal was administered or not) rather than to a deficit in visual sensitivity. Lashley (1935) also suggested that deficits on a light-dark discrimination task following occipital ablation were due to a decrease in the subjects' attention.…”

“…After finding that the performance of occipitally ablated rats on a light-dark discrimination task was inferior at intensities well above visual threshold as well as at lower intensities, Cooper, Freeman, and Pinel (1967) suggested that performance deficits were due to postoperative changes in the sensory criterion (the sensory level set by the subject for deciding whether a visual signal was administered or not) rather than to a deficit in visual sensitivity. Lashley (1935) also suggested that deficits on a light-dark discrimination task following occipital ablation were due to a decrease in the subjects' attention.…”