Intensity and pattern discrimination in turtles after lesions of nucleus rotundus

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In turtles, the nucleus rotundus, a dorsal thalamic cell group, is known to receive a massive input from the optic tectum. Electrophysiological and anatomical data indicate that nucleus rotundus has a role in visual functions. To study role, 21 eastern painted turtles (Chrysemys picta picta) were trained in an appetitive situation on a simultaneous intensity discrimination or a simultaneous pattern discrimination. After reaching criterion, most Ss received lesions aimed at nucleus rotundus. Two Ss in the intensity-discrimination group received sham lesions. Following surgery, Ss were retrained and then sacrificed, and the lesion damage in each S was reconstructed. Ss with severe damage to nucleus rotundus were unable to relearn the discriminative task, and those with moderate amounts of damage required more sessions to relearn than they had required preoperatively. Ss with slight damage to nucleus rotundus were unimpaired. For both the intensity- and the pattern-discrimination groups, there was a significant correlation between postoperative performance and amount of damage to nucleus rotundus. Results suggest that nucleus rotundus plays a critical role in visual discriminative functions in the turtle. (57 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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