Monkeys with combined amygdalo-hippocampal lesions succeed in object discrimination learning despite 24-hour intertrial intervals.

14 rhesus monkeys, including 3 who had undergone amygdalo-hippocampal lesions before participating in a previous visual learning study, were trained on object-discrimination trials that were separated by 24 hrs to test the hypothesis that the 24-hr interval would prevent Ss with limbic lesions from learning. It is noted in previous research that monkeys with combined amygdalo-hippocampal removal show severe impairments on visual-memory tasks after delays of 1–2 min, yet they learn visual-discrimination habits nearly as quickly as normal monkeys with intertrial intervals of the same duration. Results of the present study indicate that, as long as the lesions did not encroach on the inferior temporal cortex, operated Ss could acquire concurrent sets of 20 object-discrimination habits at the same rate as unoperated Ss in an average of approximately 10 trials/set. Findings suggest that learning and retention processes are divisible into a mechanism for memory formation that is dependent on the limbic system and a mechanism for habit formation that is not. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhinal cortex ablations fail to disrupt reinforcer devaluation effects in rhesus monkeys (Macaca mulatta).

Studies have shown that excitotoxic lesions of the amygdala attenuate reinforcer devaluation effects in monkeys and rats. Because the rhinal (i.e., entorhinal and perirhinal) cortex has prominent reciprocal connections with the amygdala and has been suggested to store knowledge about objects, it is possible that it too composes part of the critical circuitry subserving learning about objects and their associated reinforcement value. To test this possibility, rhesus monkeys with rhinal cortex removals as well as unoperated controls were tested using a reinforcer devaluation procedure. Monkeys with rhinal cortex removals and controls, unlike those with amygdala lesions, tended to avoid displacing objects overlying a devalued food. These results indicate that the rhinal cortex is not a critical part of the neural circuitry mediating the effects of reinforcer devaluation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perservative errors in object discrimination learning by aged Japanese monkeys (Macaca fuscata).

To examine the nature of age-dependent cognitive decline, performance in terms of concurrent object discriminations was assessed in aged and nonaged Japanese monkeys (Macaca fuscata). Aged monkeys required more sessions and committed more errors than nonaged ones in the discriminations, even in simple object discriminations. Analyses of errors suggest that aged monkeys repeated the same errors and committed more errors when they chose a negative object at the 1st trial. A hypothesis analysis of behavior suggests that their incorrect choices were mainly due to object preference. Therefore, the impairment was probably caused by a failure to inhibit inappropriate responses. Together with previous neuropsychological findings, deficits of aged monkeys in the performance of object discriminations can be explained by dysfunction of the frontal cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monkeys (Macaca mulatta) learn category matching in a nonidentical same-different task.

Same–different judgments of familiar objects and animals were investigated in rhesus monkeys (Macaca mulatta) in a task based on category matches rather than identity matches. 18 categories of familiar animals and objects were each composed of 12 color slides and were presented as pairs of slides. Ss indicated "same" or "different" on a response lever for reinforcement. On Same trials, 2 different views of the same object were presented, typically with differences in perspective, lighting, and background. On Different trials, 2 pictures of different objects were presented. Ss acquired the category discriminations and transferred their response judgments accurately to novel pictures from the categories. Transfer was better to objects with which the monkeys had actually interacted rather than those with which they did not interact. (PsycINFO Database Record (c) 2010 APA, all rights reserved)