Perirhinal cortex lesions attenuate stimulus generalization in a tactual discrimination task in rats.
Response generalization to a novel stimulus occurs when the new stimulus shares common features with the stimulus used in the original learning. Given the many recent studies suggesting that the perirhinal cortex is critical for disambiguating stimuli that share representational/perceptual elements, we hypothesize that lesions sustained to this region would attenuate response generalization. In the first part of this experiment lesioned and control rats learned a feature-ambiguous tactual discrimination task until they had all reached the same level of performance. In this task animals were asked to discriminate among 3 tactual stimuli simultaneously exposed in 3 arms of a 4-arm plus-shaped maze. In the second part of this experiment, the same rats were given a generalization test 24 h after acquisition of the tactual discrimination. In the generalization test the original tactual stimulus associated with reward during the learning of the discrimination was replaced by a novel tactual stimulus while the other two remained the same. Of the 3 stimuli used in the generalization test, the novel stimulus had the highest degree of feature overlap with respect to the original target stimulus used during the learning of the discrimination. The generalization test took place over two consecutive days, with 8 trials each day. On the first day of generalization, the results indicated that the lesioned rats generalized significantly worse than the control rats during the first 4 trials, but not during the last 4 trials. On the second day of generalization, however, both groups performed the test perfectly. These findings suggest that, in addition to the well-known mnesic function in object processing, the perirhinal cortex may also be involved in perceptual functions.
Department of Psychobiology and Mind, Brain and Behavior Research Center (CIMCYC), University of Granada, Campus de Cartuja, Granada, Spain, jmjramos@ugr.es.
Juan M J
JMJ
Ramos
D000704:Analysis of Variance; D000818:Animals; D002540:Cerebral Cortex / Q000293:injuries* / Q000502:physiology*; D004193:Discrimination Learning / Q000502:physiology*; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity; D005795:Generalization, Stimulus / Q000502:physiology*; D008297:Male; D018782:Maze Learning / Q000502:physiology; D016202:N-Methylaspartate / Q000633:toxicity; D010812:Physical Stimulation / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D012201:Reward; D013997:Time Factors; D014110:Touch / Q000502:physiology*
D018690:Excitatory Amino Acid Agonists; D016202:N-Methylaspartate