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Influence of amygdaloid lesions on self-punitive behavior in rats
Physiology & Behavior, Vol. 18, pp. 1089-1093. Pergamon Press and Brain Research Publ., 1977. Printed in the U.S.A.
Influence of Amygdaloid Lesions on Self-Punitive Behavior in Rats I D E N N I S L. R E E V E S , R. C H R I S M A R T I N A N D W I L L I A M B. G H I S E L L I
Department o f Psychology-CBA, University o f Missouri at Kansas City, Kansas City, MO 6 4 1 1 0 (Received 6 January 1977)
REEVES, D. L., MARTIN, R. C. AND GHISELLI, W. B. Influence ofamygdaloid lesions on self-punitive behavior in rats. PHYSIOL. BEHAV. 18(6) 1089-1093, 1977. - Self-punitive or masochistic behavior describes a phenomenon in which, during the extinction of escape behavior, rats will leave a start box and cross an electrified shock grid to enter a goal. Rats need only remain in the start box to avoid shock, yet they persist in running into shock. In the present study this self-punitive behavior was eliminated by bilateral lesions of the caudal amygdala: Analyses of the running speeds indicate that the lesions left the pain inducing properties of shock intact, while decrementing the fear produced by shock. Evidence was taken as support for the Mowrer - Brown explanation of self-punitive behavior as a product of conditioned fear. Amygdaloid lesions
Fear
Self-punitive behavior
S E L F - P U N I T I V E or vicious circle b e h a v i o r occurs w h e n rats, t r a i n e d to escape s h o c k in a straight alley, c o n t i n u e to r u n for h u n d r e d s of trials a f t e r s h o c k in the start b o x has b e e n d i s c o n t i n u e d b u t r e m a i n s in a small p o r t i o n of t h e i n t e r m e d i a t e alley s e c t i o n of the r u n w a y . Rats a p p e a r to be e x h i b i t i n g m a s o c h i s t i c b e h a v i o r in t h a t t h e y leave a n o n e l e c t r i f i e d start c o m p a r t m e n t to r u n t h r o u g h s h o c k i n t o a n o n e l e c t r i f i e d goal [ 14]. By c o n t r a s t , rats t h a t receive n o s h o c k in the alley e x t i n g u i s h r u n n i n g w i t h i n a few trials. T h e m a j o r t h e o r e t i c a l e x p l a n a t i o n of self-punitive behavior has b e e n t e r m e d the M o w e r - B r o w n c o n d i t i o n e d - f e a r h y p o t h e s i s [ 1 ] . Fear, c o n d i t i o n e d d u r i n g escape training, provides the m o t i v a t i o n for r u n n i n g ; f e a r - r e d u c t i o n in the goal b o x is the r e i n f o r c e r o f r u n n i n g . W i t h o u t s h o c k , fear rapidly e x t i n g u i s h e s and a n i m a l s stop r u n n i n g . W h e n s h o c k is p r e s e n t o n the r u n w a y , fear is m a i n t a i n e d and the r u n n i n g b e h a v i o r c o n t i n u e s to be m o t i v a t e d and r e i n f o r c e d [ 1 , 1 4 ] . Most investigators have e x p l o r e d e n v i r o n m e n t a l and c o n d i t i o n i n g variables in an a t t e m p t t o elucidate the basis of vicious circle b e h a v i o r . No a t t e m p t has yet b e e n m a d e to d e t e r m i n e w h a t aspect o f t h e c e n t r a l n e r v o u s s y s t e m u n d e r l i e s the p h e n o m e n o n . F e a r has b e e n integrally tied to t h e limbic s y s t e m in h i g h e r v e r t e b r a t e s . In m a n , feelings of fear are associated w i t h a c t i v a t i o n of t h a t p o r t i o n of the t e m p o r a l lobe t h a t c o n t a i n s the a m y g d a l a [ 4 ] . In r o d e n t s , it has b e e n s h o w n in a variety of behavioral c o n t e x t s t h a t large lesions of t h e a m y g d a l a result in a p r o n o u n c e d r e d u c t i o n of fear [ 6 ] . Large a m y g d a l o i d lesions have b e e n c h a r a c t e r i z e d as producing a n i m a l s t h a t are t a m e and are lacking in e v i d e n c e of
fear [ 8 ] . If t h e fear h y p o t h e s i s is c o r r e c t , a m y g d a l o i d lesions s h o u l d abolish self-punitive behavior. METHOD
Animals S e v e n t y - t w o , 120-day old rats, all h o o d e d ( L o n g - E v a n s ) males t h a t were o b t a i n e d f r o m Blue Spruce F a r m s , were used. T h e rats were individually h o u s e d u n d e r n a t u r a l lighting with free access in the h o m e cage to food a n d water.
Apparatus A straight-alley r u n w a y t h a t was m a d e of 1.25 cm pine was used for b e h a v i o r a l testing. G u i l l o t i n e - d o o r s divided t h e alley i n t o a 31 by 20 by 31 cm start b o x , a 180 b y 20 b y 31 cm alley and a 4 4 by 31 b y 33 cm goal box. T h e start box and the alley were p a i n t e d w h i t e , were f i t t e d w i t h t r a n s p a r e n t Plexiglas covers and c o n t a i n e d a f l o o r of 0.64-cm stainless stell rods t h a t were spaced at 1.90 cm. T h e goal b o x was m a d e e n t i r e l y o f w o o d and was p a i n t e d black to m a k e it o p a q u e . A s c r a m b l e d , c o n s t a n t - c u r r e n t s h o c k of 1.0 m A was delivered to the start a n d alley sections f r o m a Lehigh Valley 113-04 c o n s t a n t c u r r e n t shocker. E l e c t r o n i c timers t h a t were c o n t r o l l e d b y p h o t o b e a m s were used to r e c o r d latencies and r u n n i n g times.
Procedure A n i m a l s were divided i n t o 3 surgical g r o u p s designated
Supported by funds from the Department of Psychology and submitted by D. L. Reeves to the University in partial fulfillment of the requirements for the Master of Arts degree. Reprint requests to R. C. Martin. We thank Dr. D. R. Justeson for the critical evaluation of an earlier manuscript. 1089
1090
REEVES, M A R T I N AND G H I S E L L I
Control, Sham, and Operated (ns = 24). Ten days prior to behavioral training, bilateral amygdalar lesions were made in the Operated group while animals were under sodium pentobarbital anesthesia (35 mg/kg) and aseptic conditions. A lesion was made by passing a 2-mA d.c. current for 20 sec through the exposed (0.5 ram) tip of a m o n o p o l a r stainless steel electrode. Ten days prior to behavioral training, the Sham group u n d e r w e n t the same procedure except that no current was passed through the m o n o p o l a r electrode. The Control group u n d e r w e n t no surgical procedure prior to behavioral testing. Behavioral testing was c o n d u c t e d for each animal on a single day following 10 days of postoperative recovery. During acquisition, all groups received 35, one-way, shockescape training trials in the alley. On each acquisition trial, shock was delivered to all portions of the start and alley sections upon opening the start box door; animals escaped the shock by running to the nonelectrified goal box. Each trial was separated by a 30 sec inter-trial interval (ITI). At the end of acquisition-training, each group was randomly subdivided into punished and non-punished extinction groups (ns = 12). E x t i n c t i o n trials were c o n d u c t e d immediately upon the c o m p l e t i o n of acquisition-training (i.e., 30 sec after the last acquisition-trial) using the same 30 sec ITI. For nonpunished animals there was no shock in either the start box or the alley. F o r punished animals the first 1/3 (60 cm) of the alley was electrified on all trials. Extinction was considered complete when an animal either failed to leave the start or alley sections within 60 sec or c o m p l e t e d 100 e x t i n c t i o n trials, whichever came first. Start and alley times and the n u m b e r of trials to e x t i n c t i o n were recorded for each animal. All times were converted to speeds (reciprocals of times) for purposes of analysis. Following training, Operated and Sham animals were euthanized; their brains were perfused in 10% Formalin and removed, fixed in 10% Formalin and were e m b e d d e d in paraffin. Sections were taken every 100 um and were stained with Cresyl violet to permit assessment of extent of each lesion [ 13 ]. RESULTS Lesions were fairly u n i f o r m ; bilateral destruction occurred and was restricted to the caudal half of the amygdala. Minimally, only the ventral p o r t i o n of the caudal amygdala was damaged including some entorhinal or piriform cortex. Usually, two-thirds or more of the caudal amygdala was destroyed (Fig. 1). Using Isaacson's I8] nomenclature of the amygdala, lesions consistantly prcduced bilateral destruction of the cortical and basolateral nuclei and damage to the ventrally located piriform cortex. Sometimes the lateral, the basal portion of the medial, and the posterior nuclei were a p p r o x i m a t e l y 1/4 to 1/2 destroyed. In one nonpunished animal, lesions intruded slightly into the hippocampus. The n u m b e r of trials to reach the criterion of extinction for each group is shown in Fig. 2. Analysis of variance confirmed that nonpunished animals extinguished more quickly than punished animals, F ( 1 , 6 6 ) = 543, p< 1 0 - 6 , and amygdalectomized groups extinguished more quickly than nonlesioned groups, F(2,66) = 440, p < 1 0 6 , interaction F~2,66) = 141, p < 1 0 -6. Further, Duncan's multiple range test for post hoc comparisons [11] indicated that the Nonpunished Operated group extinguished more quickly than either the nonpunished Sham or nonpunished Control
32
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FIG. 1. Reconstructions of minimal (black) and maximal (strippled) amygdaloid destruction. Brain section numbers are from [ 131. groups (p<0.05). These data demonstrate the basic selfpunitive p h e n o m e n o n and show it to be unaffected by the general surgical procedure. All members of the punished Control and punished Sham groups were still running after 100 extinction trials, while all of their nonpunished counterparts had stopped running. All members of both a m y g d a l e c t o m i z e d groups extinguished almost immediately (< 10 trials) indicating not only that the lesion eliminated the self-punitive p h e n o m e n o n but also accelerated the course of normal extinction. To clarify this rapid extinction of lesioned animals, the speed data over the first few extinction trials were examined. Data on start-speeds for all groups on the final three acquisition trials and the first six extinction trials are given in Fig. 2. Analyses of variance on start speeds showed no detectable effects of punishment, surgery, trials or their interactions during the last three acquisition trials tall p's >0.05). Analysis of extinction start speeds indicated a marginal main effect of punishment condition, F(1,66) = 3.77, p = 0.056, and a reliable Punishment by Surgery interaction, F(2,66) - 9.83, p < 0 . 0 0 0 2 . T u k e y ' s paired comparisons were p e r f o r m e d ( [ 1 1 ] , p. 292) on the inter-
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1091
amygdalectomized Operated group were marginally faster for the nonpunished animals than for the punished animals (p~-0.06). Together these findings indicate that while start-speeds for the control groups were, in general, faster for punished animals than for nonpunished animals, the reverse was true for amygdalectomized animals, i.e., startspeeds of punished animals were slower than start-speeds of nonpunished animals. Differences in start-speed as a function of surgical condition, F(2,66) = 14.56, p< 10-S, were also clarified with Tukey's comparisons. Consistent with the rapid extinction of amygdalectomized groups (Fig. 1), the start-speeds of amygdalectomized groups were slower than both the Control (p<0.01) and Sham (p<0.01) groups. Start-speeds generally declined over the initial trials during measures of extinction, F(5,330) = 2.78, p<0.02, but the rate of decline was not a function of punishment or of surgical condition (p's > 0.05 for all interactions). In Fig. 4, data on the alley-speeds for all groups are presented for the last three acquisition trials and for the first six extinction trials. As with start-speeds, there were no detectable differences in alley-speeds (all p's > 0.05) during terminal stages of acquisition. Speeds during measures of extinction differed as a function of surgical condition, F(2,62) = 19.83, p< 10-~ . As is the case with start-speeds, the alley-speeds reflect the slower running by amygdalectomized animals as compared to Control and Sham animals (Tukey p's<0.05). However, although selfpunitive behavior was evident in extinction speeds (Punishment F(1,62) = 10.49, p<0.002), there was no Punishment by Operation interaction ( F < I ) . Tukey's comparisons showed no difference in speeds during measures of extinction for punished and Nonpunished, unoperated Controls (p>0.05). Sham operated animals that were punished ran faster than their nonpunished counterparts
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REEVES, M A R T I N AND G H I S E L L I
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TRIAL FIG. 4. Alley speeds on the final three acquisition and first six extinction trials for all groups. Labeling as in Fig. l. ( p < 0 . 0 1 ) and, in contrast to the effects seen in start speeds, punished a m y g d a l e c t o m i z e d animals ran faster than their nonpunished counterparts. Alley speeds generally slowed over trials during measures of extinction, F(5,330) = 5.14, p < 0 . 0 0 0 2 . A Punishment by Trials interaction, F(5,330) = 4.36, p < 0 . 0 0 0 8 , indicated the difference in speed between punished and nonpunished animals increased across these trials, reflecting the rapid extinction of running by nonpunished animals. Finally, the Punishment by Operation by Trials interaction, F(10,330) = 1.91, p < 0 . 0 4 , indicated that the a f o r e m e n t i o n e d extinction of nonpunished groups over the first few extinction trials p r o c e e d e d at different rates for the various surgical conditions. This is consistent with the post hoc analyses on trials which indicated a m y g d a l e c t o m y accelerated the normal (i.e., nonpunished) extinction of escape behavior. DISCUSSION Examination of Figs. 3 and 4 shows faster start and alley e x t i n c t i o n speeds for nonlesioned punished animals (i.e., self-punitive behavior). However, in lesioned animals startspeeds of punished animals were slower than start-speeds of their nonpunished counterparts while the reverse was true for the alley-speeds of lesioned animals. During punished extinction, start-speeds reflect animals running into shock, while alley-speeds reflect animals running out of shock. It appears that the amygdaloid lesions left the pain properties of shock intact in that lesioned animals whose behavior resulted in shock suppressed running (i.e., punishment Fig. 3). while lesioned animals whose behavior resulted in a termination of shock showed enhanced running (i.e., escape - Fig. 4). The lack of differences in escape behavior between lesioned and nonlesioned animals at the end of acquisition supports the conclusion of no d e c r e m e n t in pain sensitivity and confirms earlier findings which used one-way
escape with dissimilar start and goal c o m p a r t m e n t s [9]. Others have reported that amygdaloid lesions leave shock sensitivity unchanged [3] or may actually increase sensitivity to shock while c o n c o m i t a n t l y producing "a diminished fear or arousal response to the same s h o c k " ( [ 2 ] , p. 120). in consort, these data indicate the more rapid extinction of escape behavior and the absence of selfpunitive behavior shown by lesioned animals is not due to lowered shock sensitivity, that is, less pain. The fear hypothesis still remains the best behavioral explanation of self-punitive behavior (e.g., [121), and as noted earlier, the p r e d o m i n a n t characteristic of large amygdaloid lesions is a fear deficit [6,8]. The primary alternative explanation of self-punitive behavior from learning theory has been termed the "discrimination h y p o t h e s i s . " it argues that shock is a stimulus event and its removal allows the animal to discriminate acquisition from extinction conditions. Conversely, the presence of shock during extinction prevents the animal from distinguishing extinction conditions from those present during acquisition and so the animal continues to run [1]. In the c o n t e x t of the present study, the discrimination hypothesis would have to argue that amygdatoid lesions increase rats' ability to discriminate since lesioned animals extinguished more quickly and showed no self-punitive behavior relative to controls. However, collateral data indicate that, if anything, amygdaloid lesions detract from rats' ability to discriminate. F o r example, amygdaloid lesions have been shown to increase the vicarious trial and error behavior exhibited by rats at maze choice points, indicating a lowered ability to discriminate the alternatives l l 0 ] . The same study also found a m y g d a l e c t o m i z e d rats were deficient in their ability to reverse appetitive discriminations. The authors proposed that in reversing an appetitive discrimination, frustration from nonreward makes the formerly correct alternative aversive. During reversal the c o m b i n a t i o n of the now incorrect alternative being aversive
AMYGDALOID LESIONS AND SELF-PUNITIVE BEHAVIOR and the now correct alternative being rewarded would normally facilitate reversal of the discrimination. However, amygdaloid lesions reduce the aversive frustration-like responses removing a source of p u n i s h m e n t and discriminability and so retard reversal learning. F u n c t i o n a l lesions .of the amygdala are r e p o r t e d to retard learning based on fear but to have no effect on hunger-based learning [ 5 ] . These studies support the c o n t e n t i o n that lesions of the amygdala act selectively on aversive motivation and do not produce general deficits (e.g., in animals' overall ability to discriminate). Moreover, it was n o t e d [5] that reversable lesions of the amygdala only disrupted aversively based learning when they functionally occurred in the period i m m e d i a t e l y after the shock UCS. This suggests amygdaloid lesions m a y selectively disrupt
1093 negative r e i n f o r c e m e n t mechanisms. It should be n o t e d again that the original fear hypothesis argued that it was c o n t i n u e d r e i n f o r c e m e n t of fear and escape behavior which was responsible for self-punitive behavior [ 14]. Finally, concern continues to be expressed that it is n o t the amygdala per se which is critically involved in fear. It has been suggested that amygdaloid lesions only cut fibers of passage to o t h e r limbic areas which themselves are critical to the generation of fear [ 2 ] , and it has also been proposed that it m a y be the surrounding piriform cortex and n o t the amygdala itself which underlies fear [7]. While the present study does not directly bear on this question, lesions were sufficiently large t o damage b o t h fibers of passage and piriform cortex.
REFERENCES 1. Brown, J. S. Factors affecting self-punitive locomotor behavior. In: B. A. Campbell and R. M. Church. Punishment and Aversive Behavior, edited by New York: AppletonCentury-Crofts, 1969, pp. 467-514. 2. Coover, G., H. Ursin, and S. Levine. Cortiocosterone and avoidance in rats with amygdala lesions. J. comp. physiol. Psychol. 85: 111-122, 1973. 3. Eichelman, B. S. Effect of subcortical lesions on shock-induced aggression in the rat. J. comp. physiol. PsychoI. 58: 331-339, 1971. 4. Gloor, P. Temporal lobe epilepsy: Its possible contribution to the understanding of the functional significance of the amygdala and of its interaction with neocortical-temporal mechanisms. In: B. E. Eleftheriou. The Neurobiology of the Amygdala, edited by New York: Plenum, 1972 (Adv. Behav. Biol. 2:423 457, 1972). 5. Goddard, G. V. Amygdaloid stimulation and learning in the rat. J. comp. physiol. Psychol. 58: 23-30, 1964. 6. Goddard, G. V. Functions of the amygdala. Psychol. Bull. 62: 88-109, 1964. 7. Grossman, S. P. The role of the amygdala in escape-avoidance behaviors. In: B. E. Eleftheriou. The Neurobiology of the Amygdala, edited by New York: Plenum, 1972. (Adv. Behav. Biol. 2:537 551, 1972).
8. Issacson, R. L. The Limbic System. New York: Plenum, 1974. 9. Kemble, E. D. and G. J. Beckman. Escape latencies at three levels of shock in rats with amygdaloid lesions. Psychon. Sci. 14: 205-206, 1969. 10. Kemble, E. D. and G. J. Beckman. Vicarious trial and error following amygdaloid lesions in rats. Neuropsychol. 8: 161-169, 1970. 11. Kirk, R. E. Experimental Design: Procedures for the Behavioral Sciences. Belmont: Brooks/Cole, 1968, pp. 93-94. 12. Klare, W. F. Conditioned fear and post-shock emotionality in viscious circle behavior of rats. J. comp. physiol. Psychol. 87: 364-372, 1974. 13. Konig, J. F. R. and R. A. Klippel. The Rat Brain: A Stereotaxic Atlas. Baltimore: Williams and Wilkins, 1963. 14. Mowrer, O. H. On the dual nature of learning - A reinterpretation of "conditioning" and "problem-solving." HarvardEduc. Rev. 17: 102-148, 1947.
Influence of Amygdaloid Lesions on Self-Punitive Behavior in Rats I D E N N I S L. R E E V E S , R. C H R I S M A R T I N A N D W I L L I A M B. G H I S E L L I
Department o f Psychology-CBA, University o f Missouri at Kansas City, Kansas City, MO 6 4 1 1 0 (Received 6 January 1977)
REEVES, D. L., MARTIN, R. C. AND GHISELLI, W. B. Influence ofamygdaloid lesions on self-punitive behavior in rats. PHYSIOL. BEHAV. 18(6) 1089-1093, 1977. - Self-punitive or masochistic behavior describes a phenomenon in which, during the extinction of escape behavior, rats will leave a start box and cross an electrified shock grid to enter a goal. Rats need only remain in the start box to avoid shock, yet they persist in running into shock. In the present study this self-punitive behavior was eliminated by bilateral lesions of the caudal amygdala: Analyses of the running speeds indicate that the lesions left the pain inducing properties of shock intact, while decrementing the fear produced by shock. Evidence was taken as support for the Mowrer - Brown explanation of self-punitive behavior as a product of conditioned fear. Amygdaloid lesions
Fear
Self-punitive behavior
S E L F - P U N I T I V E or vicious circle b e h a v i o r occurs w h e n rats, t r a i n e d to escape s h o c k in a straight alley, c o n t i n u e to r u n for h u n d r e d s of trials a f t e r s h o c k in the start b o x has b e e n d i s c o n t i n u e d b u t r e m a i n s in a small p o r t i o n of t h e i n t e r m e d i a t e alley s e c t i o n of the r u n w a y . Rats a p p e a r to be e x h i b i t i n g m a s o c h i s t i c b e h a v i o r in t h a t t h e y leave a n o n e l e c t r i f i e d start c o m p a r t m e n t to r u n t h r o u g h s h o c k i n t o a n o n e l e c t r i f i e d goal [ 14]. By c o n t r a s t , rats t h a t receive n o s h o c k in the alley e x t i n g u i s h r u n n i n g w i t h i n a few trials. T h e m a j o r t h e o r e t i c a l e x p l a n a t i o n of self-punitive behavior has b e e n t e r m e d the M o w e r - B r o w n c o n d i t i o n e d - f e a r h y p o t h e s i s [ 1 ] . Fear, c o n d i t i o n e d d u r i n g escape training, provides the m o t i v a t i o n for r u n n i n g ; f e a r - r e d u c t i o n in the goal b o x is the r e i n f o r c e r o f r u n n i n g . W i t h o u t s h o c k , fear rapidly e x t i n g u i s h e s and a n i m a l s stop r u n n i n g . W h e n s h o c k is p r e s e n t o n the r u n w a y , fear is m a i n t a i n e d and the r u n n i n g b e h a v i o r c o n t i n u e s to be m o t i v a t e d and r e i n f o r c e d [ 1 , 1 4 ] . Most investigators have e x p l o r e d e n v i r o n m e n t a l and c o n d i t i o n i n g variables in an a t t e m p t t o elucidate the basis of vicious circle b e h a v i o r . No a t t e m p t has yet b e e n m a d e to d e t e r m i n e w h a t aspect o f t h e c e n t r a l n e r v o u s s y s t e m u n d e r l i e s the p h e n o m e n o n . F e a r has b e e n integrally tied to t h e limbic s y s t e m in h i g h e r v e r t e b r a t e s . In m a n , feelings of fear are associated w i t h a c t i v a t i o n of t h a t p o r t i o n of the t e m p o r a l lobe t h a t c o n t a i n s the a m y g d a l a [ 4 ] . In r o d e n t s , it has b e e n s h o w n in a variety of behavioral c o n t e x t s t h a t large lesions of t h e a m y g d a l a result in a p r o n o u n c e d r e d u c t i o n of fear [ 6 ] . Large a m y g d a l o i d lesions have b e e n c h a r a c t e r i z e d as producing a n i m a l s t h a t are t a m e and are lacking in e v i d e n c e of
fear [ 8 ] . If t h e fear h y p o t h e s i s is c o r r e c t , a m y g d a l o i d lesions s h o u l d abolish self-punitive behavior. METHOD
Animals S e v e n t y - t w o , 120-day old rats, all h o o d e d ( L o n g - E v a n s ) males t h a t were o b t a i n e d f r o m Blue Spruce F a r m s , were used. T h e rats were individually h o u s e d u n d e r n a t u r a l lighting with free access in the h o m e cage to food a n d water.
Apparatus A straight-alley r u n w a y t h a t was m a d e of 1.25 cm pine was used for b e h a v i o r a l testing. G u i l l o t i n e - d o o r s divided t h e alley i n t o a 31 by 20 by 31 cm start b o x , a 180 b y 20 b y 31 cm alley and a 4 4 by 31 b y 33 cm goal box. T h e start box and the alley were p a i n t e d w h i t e , were f i t t e d w i t h t r a n s p a r e n t Plexiglas covers and c o n t a i n e d a f l o o r of 0.64-cm stainless stell rods t h a t were spaced at 1.90 cm. T h e goal b o x was m a d e e n t i r e l y o f w o o d and was p a i n t e d black to m a k e it o p a q u e . A s c r a m b l e d , c o n s t a n t - c u r r e n t s h o c k of 1.0 m A was delivered to the start a n d alley sections f r o m a Lehigh Valley 113-04 c o n s t a n t c u r r e n t shocker. E l e c t r o n i c timers t h a t were c o n t r o l l e d b y p h o t o b e a m s were used to r e c o r d latencies and r u n n i n g times.
Procedure A n i m a l s were divided i n t o 3 surgical g r o u p s designated
Supported by funds from the Department of Psychology and submitted by D. L. Reeves to the University in partial fulfillment of the requirements for the Master of Arts degree. Reprint requests to R. C. Martin. We thank Dr. D. R. Justeson for the critical evaluation of an earlier manuscript. 1089
1090
REEVES, M A R T I N AND G H I S E L L I
Control, Sham, and Operated (ns = 24). Ten days prior to behavioral training, bilateral amygdalar lesions were made in the Operated group while animals were under sodium pentobarbital anesthesia (35 mg/kg) and aseptic conditions. A lesion was made by passing a 2-mA d.c. current for 20 sec through the exposed (0.5 ram) tip of a m o n o p o l a r stainless steel electrode. Ten days prior to behavioral training, the Sham group u n d e r w e n t the same procedure except that no current was passed through the m o n o p o l a r electrode. The Control group u n d e r w e n t no surgical procedure prior to behavioral testing. Behavioral testing was c o n d u c t e d for each animal on a single day following 10 days of postoperative recovery. During acquisition, all groups received 35, one-way, shockescape training trials in the alley. On each acquisition trial, shock was delivered to all portions of the start and alley sections upon opening the start box door; animals escaped the shock by running to the nonelectrified goal box. Each trial was separated by a 30 sec inter-trial interval (ITI). At the end of acquisition-training, each group was randomly subdivided into punished and non-punished extinction groups (ns = 12). E x t i n c t i o n trials were c o n d u c t e d immediately upon the c o m p l e t i o n of acquisition-training (i.e., 30 sec after the last acquisition-trial) using the same 30 sec ITI. For nonpunished animals there was no shock in either the start box or the alley. F o r punished animals the first 1/3 (60 cm) of the alley was electrified on all trials. Extinction was considered complete when an animal either failed to leave the start or alley sections within 60 sec or c o m p l e t e d 100 e x t i n c t i o n trials, whichever came first. Start and alley times and the n u m b e r of trials to e x t i n c t i o n were recorded for each animal. All times were converted to speeds (reciprocals of times) for purposes of analysis. Following training, Operated and Sham animals were euthanized; their brains were perfused in 10% Formalin and removed, fixed in 10% Formalin and were e m b e d d e d in paraffin. Sections were taken every 100 um and were stained with Cresyl violet to permit assessment of extent of each lesion [ 13 ]. RESULTS Lesions were fairly u n i f o r m ; bilateral destruction occurred and was restricted to the caudal half of the amygdala. Minimally, only the ventral p o r t i o n of the caudal amygdala was damaged including some entorhinal or piriform cortex. Usually, two-thirds or more of the caudal amygdala was destroyed (Fig. 1). Using Isaacson's I8] nomenclature of the amygdala, lesions consistantly prcduced bilateral destruction of the cortical and basolateral nuclei and damage to the ventrally located piriform cortex. Sometimes the lateral, the basal portion of the medial, and the posterior nuclei were a p p r o x i m a t e l y 1/4 to 1/2 destroyed. In one nonpunished animal, lesions intruded slightly into the hippocampus. The n u m b e r of trials to reach the criterion of extinction for each group is shown in Fig. 2. Analysis of variance confirmed that nonpunished animals extinguished more quickly than punished animals, F ( 1 , 6 6 ) = 543, p< 1 0 - 6 , and amygdalectomized groups extinguished more quickly than nonlesioned groups, F(2,66) = 440, p < 1 0 6 , interaction F~2,66) = 141, p < 1 0 -6. Further, Duncan's multiple range test for post hoc comparisons [11] indicated that the Nonpunished Operated group extinguished more quickly than either the nonpunished Sham or nonpunished Control
32
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FIG. 1. Reconstructions of minimal (black) and maximal (strippled) amygdaloid destruction. Brain section numbers are from [ 131. groups (p<0.05). These data demonstrate the basic selfpunitive p h e n o m e n o n and show it to be unaffected by the general surgical procedure. All members of the punished Control and punished Sham groups were still running after 100 extinction trials, while all of their nonpunished counterparts had stopped running. All members of both a m y g d a l e c t o m i z e d groups extinguished almost immediately (< 10 trials) indicating not only that the lesion eliminated the self-punitive p h e n o m e n o n but also accelerated the course of normal extinction. To clarify this rapid extinction of lesioned animals, the speed data over the first few extinction trials were examined. Data on start-speeds for all groups on the final three acquisition trials and the first six extinction trials are given in Fig. 2. Analyses of variance on start speeds showed no detectable effects of punishment, surgery, trials or their interactions during the last three acquisition trials tall p's >0.05). Analysis of extinction start speeds indicated a marginal main effect of punishment condition, F(1,66) = 3.77, p = 0.056, and a reliable Punishment by Surgery interaction, F(2,66) - 9.83, p < 0 . 0 0 0 2 . T u k e y ' s paired comparisons were p e r f o r m e d ( [ 1 1 ] , p. 292) on the inter-
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1091
amygdalectomized Operated group were marginally faster for the nonpunished animals than for the punished animals (p~-0.06). Together these findings indicate that while start-speeds for the control groups were, in general, faster for punished animals than for nonpunished animals, the reverse was true for amygdalectomized animals, i.e., startspeeds of punished animals were slower than start-speeds of nonpunished animals. Differences in start-speed as a function of surgical condition, F(2,66) = 14.56, p< 10-S, were also clarified with Tukey's comparisons. Consistent with the rapid extinction of amygdalectomized groups (Fig. 1), the start-speeds of amygdalectomized groups were slower than both the Control (p<0.01) and Sham (p<0.01) groups. Start-speeds generally declined over the initial trials during measures of extinction, F(5,330) = 2.78, p<0.02, but the rate of decline was not a function of punishment or of surgical condition (p's > 0.05 for all interactions). In Fig. 4, data on the alley-speeds for all groups are presented for the last three acquisition trials and for the first six extinction trials. As with start-speeds, there were no detectable differences in alley-speeds (all p's > 0.05) during terminal stages of acquisition. Speeds during measures of extinction differed as a function of surgical condition, F(2,62) = 19.83, p< 10-~ . As is the case with start-speeds, the alley-speeds reflect the slower running by amygdalectomized animals as compared to Control and Sham animals (Tukey p's<0.05). However, although selfpunitive behavior was evident in extinction speeds (Punishment F(1,62) = 10.49, p<0.002), there was no Punishment by Operation interaction ( F < I ) . Tukey's comparisons showed no difference in speeds during measures of extinction for punished and Nonpunished, unoperated Controls (p>0.05). Sham operated animals that were punished ran faster than their nonpunished counterparts
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1092
REEVES, M A R T I N AND G H I S E L L I
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TRIAL FIG. 4. Alley speeds on the final three acquisition and first six extinction trials for all groups. Labeling as in Fig. l. ( p < 0 . 0 1 ) and, in contrast to the effects seen in start speeds, punished a m y g d a l e c t o m i z e d animals ran faster than their nonpunished counterparts. Alley speeds generally slowed over trials during measures of extinction, F(5,330) = 5.14, p < 0 . 0 0 0 2 . A Punishment by Trials interaction, F(5,330) = 4.36, p < 0 . 0 0 0 8 , indicated the difference in speed between punished and nonpunished animals increased across these trials, reflecting the rapid extinction of running by nonpunished animals. Finally, the Punishment by Operation by Trials interaction, F(10,330) = 1.91, p < 0 . 0 4 , indicated that the a f o r e m e n t i o n e d extinction of nonpunished groups over the first few extinction trials p r o c e e d e d at different rates for the various surgical conditions. This is consistent with the post hoc analyses on trials which indicated a m y g d a l e c t o m y accelerated the normal (i.e., nonpunished) extinction of escape behavior. DISCUSSION Examination of Figs. 3 and 4 shows faster start and alley e x t i n c t i o n speeds for nonlesioned punished animals (i.e., self-punitive behavior). However, in lesioned animals startspeeds of punished animals were slower than start-speeds of their nonpunished counterparts while the reverse was true for the alley-speeds of lesioned animals. During punished extinction, start-speeds reflect animals running into shock, while alley-speeds reflect animals running out of shock. It appears that the amygdaloid lesions left the pain properties of shock intact in that lesioned animals whose behavior resulted in shock suppressed running (i.e., punishment Fig. 3). while lesioned animals whose behavior resulted in a termination of shock showed enhanced running (i.e., escape - Fig. 4). The lack of differences in escape behavior between lesioned and nonlesioned animals at the end of acquisition supports the conclusion of no d e c r e m e n t in pain sensitivity and confirms earlier findings which used one-way
escape with dissimilar start and goal c o m p a r t m e n t s [9]. Others have reported that amygdaloid lesions leave shock sensitivity unchanged [3] or may actually increase sensitivity to shock while c o n c o m i t a n t l y producing "a diminished fear or arousal response to the same s h o c k " ( [ 2 ] , p. 120). in consort, these data indicate the more rapid extinction of escape behavior and the absence of selfpunitive behavior shown by lesioned animals is not due to lowered shock sensitivity, that is, less pain. The fear hypothesis still remains the best behavioral explanation of self-punitive behavior (e.g., [121), and as noted earlier, the p r e d o m i n a n t characteristic of large amygdaloid lesions is a fear deficit [6,8]. The primary alternative explanation of self-punitive behavior from learning theory has been termed the "discrimination h y p o t h e s i s . " it argues that shock is a stimulus event and its removal allows the animal to discriminate acquisition from extinction conditions. Conversely, the presence of shock during extinction prevents the animal from distinguishing extinction conditions from those present during acquisition and so the animal continues to run [1]. In the c o n t e x t of the present study, the discrimination hypothesis would have to argue that amygdatoid lesions increase rats' ability to discriminate since lesioned animals extinguished more quickly and showed no self-punitive behavior relative to controls. However, collateral data indicate that, if anything, amygdaloid lesions detract from rats' ability to discriminate. F o r example, amygdaloid lesions have been shown to increase the vicarious trial and error behavior exhibited by rats at maze choice points, indicating a lowered ability to discriminate the alternatives l l 0 ] . The same study also found a m y g d a l e c t o m i z e d rats were deficient in their ability to reverse appetitive discriminations. The authors proposed that in reversing an appetitive discrimination, frustration from nonreward makes the formerly correct alternative aversive. During reversal the c o m b i n a t i o n of the now incorrect alternative being aversive
AMYGDALOID LESIONS AND SELF-PUNITIVE BEHAVIOR and the now correct alternative being rewarded would normally facilitate reversal of the discrimination. However, amygdaloid lesions reduce the aversive frustration-like responses removing a source of p u n i s h m e n t and discriminability and so retard reversal learning. F u n c t i o n a l lesions .of the amygdala are r e p o r t e d to retard learning based on fear but to have no effect on hunger-based learning [ 5 ] . These studies support the c o n t e n t i o n that lesions of the amygdala act selectively on aversive motivation and do not produce general deficits (e.g., in animals' overall ability to discriminate). Moreover, it was n o t e d [5] that reversable lesions of the amygdala only disrupted aversively based learning when they functionally occurred in the period i m m e d i a t e l y after the shock UCS. This suggests amygdaloid lesions m a y selectively disrupt
1093 negative r e i n f o r c e m e n t mechanisms. It should be n o t e d again that the original fear hypothesis argued that it was c o n t i n u e d r e i n f o r c e m e n t of fear and escape behavior which was responsible for self-punitive behavior [ 14]. Finally, concern continues to be expressed that it is n o t the amygdala per se which is critically involved in fear. It has been suggested that amygdaloid lesions only cut fibers of passage to o t h e r limbic areas which themselves are critical to the generation of fear [ 2 ] , and it has also been proposed that it m a y be the surrounding piriform cortex and n o t the amygdala itself which underlies fear [7]. While the present study does not directly bear on this question, lesions were sufficiently large t o damage b o t h fibers of passage and piriform cortex.
REFERENCES 1. Brown, J. S. Factors affecting self-punitive locomotor behavior. In: B. A. Campbell and R. M. Church. Punishment and Aversive Behavior, edited by New York: AppletonCentury-Crofts, 1969, pp. 467-514. 2. Coover, G., H. Ursin, and S. Levine. Cortiocosterone and avoidance in rats with amygdala lesions. J. comp. physiol. Psychol. 85: 111-122, 1973. 3. Eichelman, B. S. Effect of subcortical lesions on shock-induced aggression in the rat. J. comp. physiol. PsychoI. 58: 331-339, 1971. 4. Gloor, P. Temporal lobe epilepsy: Its possible contribution to the understanding of the functional significance of the amygdala and of its interaction with neocortical-temporal mechanisms. In: B. E. Eleftheriou. The Neurobiology of the Amygdala, edited by New York: Plenum, 1972 (Adv. Behav. Biol. 2:423 457, 1972). 5. Goddard, G. V. Amygdaloid stimulation and learning in the rat. J. comp. physiol. Psychol. 58: 23-30, 1964. 6. Goddard, G. V. Functions of the amygdala. Psychol. Bull. 62: 88-109, 1964. 7. Grossman, S. P. The role of the amygdala in escape-avoidance behaviors. In: B. E. Eleftheriou. The Neurobiology of the Amygdala, edited by New York: Plenum, 1972. (Adv. Behav. Biol. 2:537 551, 1972).
8. Issacson, R. L. The Limbic System. New York: Plenum, 1974. 9. Kemble, E. D. and G. J. Beckman. Escape latencies at three levels of shock in rats with amygdaloid lesions. Psychon. Sci. 14: 205-206, 1969. 10. Kemble, E. D. and G. J. Beckman. Vicarious trial and error following amygdaloid lesions in rats. Neuropsychol. 8: 161-169, 1970. 11. Kirk, R. E. Experimental Design: Procedures for the Behavioral Sciences. Belmont: Brooks/Cole, 1968, pp. 93-94. 12. Klare, W. F. Conditioned fear and post-shock emotionality in viscious circle behavior of rats. J. comp. physiol. Psychol. 87: 364-372, 1974. 13. Konig, J. F. R. and R. A. Klippel. The Rat Brain: A Stereotaxic Atlas. Baltimore: Williams and Wilkins, 1963. 14. Mowrer, O. H. On the dual nature of learning - A reinterpretation of "conditioning" and "problem-solving." HarvardEduc. Rev. 17: 102-148, 1947.