Perceptiral and Molor Skills, 1976,42, 616-618. @ Perceptual and Motor Skills 1976
DETECTION OF A DEFICIT I N VISUAL DISCRIMINATION OF PATTERN FOLLOWING LESIONS OF ANTERIOR CORTEX: ROLE OF TYPE OF MOTIVATION1 CHRISTINE M. RINCK, ROBERT E. SANDERS, TERRY J. HOTTMAN, AND CHARLES L. SHERIDAN University o f Misroun' and Veteran's Hospiral, Kanras City
Summa?y.-6 albino rats were trained under appetitive motivation to perform diametrically opposed visual discriminations of pattern via opposite eyes. Small lesions were subsequently placed unilaterally in anterior neocortex. Following a period of post-surgical recovery, subjects were re-trained on the diametrically opposed discriminations in alternating 10-trial blocks. Every subject made more post-surgical errors on the discrimination mediated by the eye contralateral to the lesion. Since albino rats have virtually complete decussation of the visual system, this indicates selective impairment in mediation of performance of pattern discrimination in the part of the lesioned hemispheres. Thus, findings previously obtained in srudies involving aversive motivation are general to appetitively motivated tasks.
Besley and Sheridan (1973) reported on a highly sensitive method for detecting experimentally produced cortical lesions. The method entailed using a behavioral baseline devised by Sheridan (1965a) in which albino rats were trained with diametrically opposed discriminations via opposite eyes. Since albino rats have virtually no ipsilateral optic fibers (Sheridan, 1965b; Lund, 1965; Sheridan & Shrout, 1966) and display very low levels of interocular transfer (Sheridan, 1965b; Sheridan & Shrout, 1965), their ability to perform such opposing discriminations probably has its basis in mediation by opposite hemispheres. This supposition is confirmed by the findings of Lesley and Sheridan (1973) and of Hottman, Sanders, Rinck, and Sheridan (1975) that a small lesion placed in the cerebral cortex of one hemisphere selectively impairs performance on the discrimination mediated by the eye contralateral to that hemisphere. A most important facet of the findings of Besley and Sheridan (1973) and of Hotcman, Sanders, Rinck, and Sheridan (1975) is that this method (called the "method of interocularly conflicting baselines") permits detection of behavioral effects of lesions the impact of which is not seen with the usual methods of binocular training and bilateral lesioning. In fact, Lashley (1931) reported no effect of lesions of anterior cortex on the discrimination of pattern, and his finding was confirmed more recently in an extensive study by Horel, Bettinger, Royce, and Meyer ( 1966). The massive bilateral lesions created by Lashley 'Supported in part by Veteran's Administration Research Funds.
VISUAL DISCRIMINATION OF PATTERN AFTER LESION
617
and by Hotel, Bettinger, Royce, and Meyer (1966) are in sharp contrast to the tiny, unilateral lesions detectable by the method of interocularly conflicting baselines. It is common for a great deal of research to be requited before a detected effect of lesioning is well understood. A great deal of work will no doubt have to be done before we delineate the functional deficit underlying reduction in performance following small lesions of anterior cortex superimposed on interocularly conflicting baselines. The present experiment was done to take an initial step in that direction. It was designed to answer the question whether aversively motivated behavior is an essential component underlying the impairment. In particular, since many of rhe lesions studied with this method in the past have impinged on cingulate cortex, an impairment in motivation to avoid electric shock might play a central role in the deficits. The present experiment is essentially a replication of the previous experiment using the method of interocularly conflicting baselines, except that subjects were deprived of and rewarded with food.
METHOD Six male albino rats of the Sprague-Dawley strain, averaging 90 days of age and reduced to 80% of their free-feeding weight were tested in an apparatus similar to that described by Thompson and Bryant (1955). It consisted of a startbox, runway, two alternative entryways and a goal box. Stimulus materials were incorporated into the surfaces of doors which obstructed the entryways. Discriminanda were %-in. stripes oriented either horizontally or vertically. Vision was restricted to one eye by covering the opposite eye with black contact occluder which fit all the way to the base of the eye. The effectiveness of the occluders has been verified repeatedly in a series of experiments done in our laboratory. Reinforcers were Gaines dog pellets soaked in a dextrose solution. Animals were reduced to 80% of their ad lib. weight, then pretrained to eat the pellets in the goal box within 20 sec. after being placed there. They were then shaped to run promptly into the goal box, knocking down obstructing doors which were grey. They were then trained by the method of interocularly conflicting baselines with the patterned stimuli until performances were consistently 90% correct with the horizontal stripes correct with one eye open and 90% correct with the vertical stripes correct with the opposite eye open. Next, they were retired from training for 3 wk., then retrained to the original criterion. After reaching criterion a second time, each subject was given a lesion of anterior cortex just lateral to neocortex. Postoperative examination of the brains showed that lesions were highly uniform, and of approximately 3 mms in surface extent, and of a depth approximating that of cortex. After 10 to 12 days of post-surgical recovery, animals were again trained to criterion in 10-trial blocks with alternating eyes.
C. M. RINCK, ET AL.
RESULTSAND DISCUSSION As in previous studies using the method of interocularly conflicting baselines, the basic dependent measure used for evaluation was the number of errors in post-operative reacquisition for lesioned versus unlesioned hemispheres corrected by subtracting the number of errors for the same hemisphere during preoperative reacquisition. The use of scores thus corrected reduces the influence of individual differences in over-all stability of performance. In every subject, performance on the unlesioned hemisphere was superior to performance on the lesioned hemisphere. The mean number of errors for the lesioned hemisphere was 7.7, whereas the mean number of errors for the unlesioned hemisphere was 0.7. Performances associated with lesioned hemispheres were reliably worse than performances associated with unlesioned hemispheres ( t = 2.86, d f = 5 , p < .05). It appears, then, that the deficit observed with the method of interocularly conflicting baselines and lesions of anterior cortex does not depend on aversive motivation of the subject. The performances of the appetitively motivated subjects of the present experiment were indistinguishable from performances of aversively motivated subjects in the previous series of experiments. It is clear that the method of interocularly conflicting baselines permits detection of a deficit in performance of visual discrimination of pattern after damage to anterior cortex. This is a deficit which is undetectable by the traditional method of bilateral lesioning and binocular discrimination. The finding is highly reliable, now having been replicated several times. The present study confirms its reliability and establishes its generality. REFERENCES SHERIDAN,C. L. Sensitive method for the detection of experimental brain lesions. Perceptual and Motor Skills, 1973, 36, 584-586. HOREL,J. A., B E ~ I N G E R L., A., ROYCE,G . J., & MEYER,D. R. Role of neocortex in the learning and relearning of two visual habits by the rat. Journal o f Comparative and Physiological Psychology, 1966, 61, 66-78. H O ~ T M AT. N J., , SANDERS,R. E., RINCK, C. M., & SHERIDAN,C. L. Further evaluation of a sensitive method for detecting experimental brain lesions. Perceptucrl and Motor Skills, 1975, 41, 407-410. LASHLEY.K. S. The mechanism of vision: IV. The cerebral areas necessary for pattern vision in the rat. Journal of Comparative Neurology, 1931, 5 3 , 419-478. LUND, R. D. Uncrossed visual pathways of hooded and albino rats. Science, 1965, 149, 1506-1507. SHERIDAN,C. L. Interocular interaction of conflicting discrimination habits in the albino rat: a preliminary report. Psychonomic Science, 1965, 3, 303-304. ( a ) SHWIDAN,C. L. Inrerocular transfer of brightness and pattern discriminations in normal and corpus callosum-sectioned rats. Journal of Comparative and ~hyriological Psychology, 1965, 59, 292-294. ( b ) SHERTDAN, C. L., & SHROUT,L. L. Interocular transfer in the rat: the role of the occlusion process. Psychonomic Science, 1965, 2, 173-174. SHBRIDAN.C. L., & SHROUT. L. L. Difference in the effectiveness of optic uncrossed fiber systems in albino and hooded rars. Psychonomic Science, 1966, 4, 177-178. THOMPSON, R. M., & BRYANT,H. Memory as affected by activity of the relevant receptors. Psychological Reports, 1955, 1, 383-490. Accepced J a n w t y 16,1976.
BESLEY, S. S.,
&
DETECTION OF A DEFICIT I N VISUAL DISCRIMINATION OF PATTERN FOLLOWING LESIONS OF ANTERIOR CORTEX: ROLE OF TYPE OF MOTIVATION1 CHRISTINE M. RINCK, ROBERT E. SANDERS, TERRY J. HOTTMAN, AND CHARLES L. SHERIDAN University o f Misroun' and Veteran's Hospiral, Kanras City
Summa?y.-6 albino rats were trained under appetitive motivation to perform diametrically opposed visual discriminations of pattern via opposite eyes. Small lesions were subsequently placed unilaterally in anterior neocortex. Following a period of post-surgical recovery, subjects were re-trained on the diametrically opposed discriminations in alternating 10-trial blocks. Every subject made more post-surgical errors on the discrimination mediated by the eye contralateral to the lesion. Since albino rats have virtually complete decussation of the visual system, this indicates selective impairment in mediation of performance of pattern discrimination in the part of the lesioned hemispheres. Thus, findings previously obtained in srudies involving aversive motivation are general to appetitively motivated tasks.
Besley and Sheridan (1973) reported on a highly sensitive method for detecting experimentally produced cortical lesions. The method entailed using a behavioral baseline devised by Sheridan (1965a) in which albino rats were trained with diametrically opposed discriminations via opposite eyes. Since albino rats have virtually no ipsilateral optic fibers (Sheridan, 1965b; Lund, 1965; Sheridan & Shrout, 1966) and display very low levels of interocular transfer (Sheridan, 1965b; Sheridan & Shrout, 1965), their ability to perform such opposing discriminations probably has its basis in mediation by opposite hemispheres. This supposition is confirmed by the findings of Lesley and Sheridan (1973) and of Hottman, Sanders, Rinck, and Sheridan (1975) that a small lesion placed in the cerebral cortex of one hemisphere selectively impairs performance on the discrimination mediated by the eye contralateral to that hemisphere. A most important facet of the findings of Besley and Sheridan (1973) and of Hotcman, Sanders, Rinck, and Sheridan (1975) is that this method (called the "method of interocularly conflicting baselines") permits detection of behavioral effects of lesions the impact of which is not seen with the usual methods of binocular training and bilateral lesioning. In fact, Lashley (1931) reported no effect of lesions of anterior cortex on the discrimination of pattern, and his finding was confirmed more recently in an extensive study by Horel, Bettinger, Royce, and Meyer ( 1966). The massive bilateral lesions created by Lashley 'Supported in part by Veteran's Administration Research Funds.
VISUAL DISCRIMINATION OF PATTERN AFTER LESION
617
and by Hotel, Bettinger, Royce, and Meyer (1966) are in sharp contrast to the tiny, unilateral lesions detectable by the method of interocularly conflicting baselines. It is common for a great deal of research to be requited before a detected effect of lesioning is well understood. A great deal of work will no doubt have to be done before we delineate the functional deficit underlying reduction in performance following small lesions of anterior cortex superimposed on interocularly conflicting baselines. The present experiment was done to take an initial step in that direction. It was designed to answer the question whether aversively motivated behavior is an essential component underlying the impairment. In particular, since many of rhe lesions studied with this method in the past have impinged on cingulate cortex, an impairment in motivation to avoid electric shock might play a central role in the deficits. The present experiment is essentially a replication of the previous experiment using the method of interocularly conflicting baselines, except that subjects were deprived of and rewarded with food.
METHOD Six male albino rats of the Sprague-Dawley strain, averaging 90 days of age and reduced to 80% of their free-feeding weight were tested in an apparatus similar to that described by Thompson and Bryant (1955). It consisted of a startbox, runway, two alternative entryways and a goal box. Stimulus materials were incorporated into the surfaces of doors which obstructed the entryways. Discriminanda were %-in. stripes oriented either horizontally or vertically. Vision was restricted to one eye by covering the opposite eye with black contact occluder which fit all the way to the base of the eye. The effectiveness of the occluders has been verified repeatedly in a series of experiments done in our laboratory. Reinforcers were Gaines dog pellets soaked in a dextrose solution. Animals were reduced to 80% of their ad lib. weight, then pretrained to eat the pellets in the goal box within 20 sec. after being placed there. They were then shaped to run promptly into the goal box, knocking down obstructing doors which were grey. They were then trained by the method of interocularly conflicting baselines with the patterned stimuli until performances were consistently 90% correct with the horizontal stripes correct with one eye open and 90% correct with the vertical stripes correct with the opposite eye open. Next, they were retired from training for 3 wk., then retrained to the original criterion. After reaching criterion a second time, each subject was given a lesion of anterior cortex just lateral to neocortex. Postoperative examination of the brains showed that lesions were highly uniform, and of approximately 3 mms in surface extent, and of a depth approximating that of cortex. After 10 to 12 days of post-surgical recovery, animals were again trained to criterion in 10-trial blocks with alternating eyes.
C. M. RINCK, ET AL.
RESULTSAND DISCUSSION As in previous studies using the method of interocularly conflicting baselines, the basic dependent measure used for evaluation was the number of errors in post-operative reacquisition for lesioned versus unlesioned hemispheres corrected by subtracting the number of errors for the same hemisphere during preoperative reacquisition. The use of scores thus corrected reduces the influence of individual differences in over-all stability of performance. In every subject, performance on the unlesioned hemisphere was superior to performance on the lesioned hemisphere. The mean number of errors for the lesioned hemisphere was 7.7, whereas the mean number of errors for the unlesioned hemisphere was 0.7. Performances associated with lesioned hemispheres were reliably worse than performances associated with unlesioned hemispheres ( t = 2.86, d f = 5 , p < .05). It appears, then, that the deficit observed with the method of interocularly conflicting baselines and lesions of anterior cortex does not depend on aversive motivation of the subject. The performances of the appetitively motivated subjects of the present experiment were indistinguishable from performances of aversively motivated subjects in the previous series of experiments. It is clear that the method of interocularly conflicting baselines permits detection of a deficit in performance of visual discrimination of pattern after damage to anterior cortex. This is a deficit which is undetectable by the traditional method of bilateral lesioning and binocular discrimination. The finding is highly reliable, now having been replicated several times. The present study confirms its reliability and establishes its generality. REFERENCES SHERIDAN,C. L. Sensitive method for the detection of experimental brain lesions. Perceptual and Motor Skills, 1973, 36, 584-586. HOREL,J. A., B E ~ I N G E R L., A., ROYCE,G . J., & MEYER,D. R. Role of neocortex in the learning and relearning of two visual habits by the rat. Journal o f Comparative and Physiological Psychology, 1966, 61, 66-78. H O ~ T M AT. N J., , SANDERS,R. E., RINCK, C. M., & SHERIDAN,C. L. Further evaluation of a sensitive method for detecting experimental brain lesions. Perceptucrl and Motor Skills, 1975, 41, 407-410. LASHLEY.K. S. The mechanism of vision: IV. The cerebral areas necessary for pattern vision in the rat. Journal of Comparative Neurology, 1931, 5 3 , 419-478. LUND, R. D. Uncrossed visual pathways of hooded and albino rats. Science, 1965, 149, 1506-1507. SHERIDAN,C. L. Interocular interaction of conflicting discrimination habits in the albino rat: a preliminary report. Psychonomic Science, 1965, 3, 303-304. ( a ) SHWIDAN,C. L. Inrerocular transfer of brightness and pattern discriminations in normal and corpus callosum-sectioned rats. Journal of Comparative and ~hyriological Psychology, 1965, 59, 292-294. ( b ) SHERTDAN, C. L., & SHROUT,L. L. Interocular transfer in the rat: the role of the occlusion process. Psychonomic Science, 1965, 2, 173-174. SHBRIDAN.C. L., & SHROUT. L. L. Difference in the effectiveness of optic uncrossed fiber systems in albino and hooded rars. Psychonomic Science, 1966, 4, 177-178. THOMPSON, R. M., & BRYANT,H. Memory as affected by activity of the relevant receptors. Psychological Reports, 1955, 1, 383-490. Accepced J a n w t y 16,1976.
BESLEY, S. S.,
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