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Medial septal lesions and the frustration effect
Physiology and Behavior, Vol. 14, pp. 387--389. Brain Research Publications Inc., 1975. Printed in the U.S.A.
BRIEF COMMUNICATION Medial Septal Lesions and the Frustration
Effect 1
ROBERT GOLDSTEIN, J. MICHAEL WYSS AND F R A N K E. GOMER z
. Washington University Behavior Research Laboratory, 1420 Grattan Street St. Louis, MO 63104
(Received 2 July 1974) GOLDSTEIN, R., J. M. WYSS AND F. E. GOMER. Medial septal lesions and the frustration effect. PHYSIOL. BEHAV. 14(3) 387-389, 1975. - Rats with medial septal lesions and sham operates were run in a straight runway. After running stabilized, food was omitted on selected trials and the running speed on the following trial was observed for a frustration effect (FE). The septals exhibited a significantly greater increase in speed on this trial than controls. This enhanced FE in septals is at variance with predictions from frustration theory considering the greater resistance to extinction in septals and suggests a dissociation between the immediate and conditionable effects of frustration in such animals. Septal lesion
Frustration
Brain
IN a study by Caplan [2], pressing rates of septal rats increased significantly over controls following nonreinforced presses on a DRL schedule. A similar response to nonreward has been reported by Dickinson [4]. His septals, more readily than controls, acquired a response which reinstated an $ 9 , following the introduction of S a. Another indicatlon of an amplified effect of reward omission in septals is contained in a study by Schnelle, Walker and Hurwitz [12]. There, the normal extinction of one response was accompanied by an increase in the rate of a previously learned alternative response. However, in a study designed to explore this variable, Mabry and Peeler [9] found no differential frustration effect (FE). The possibility exists that the double runway which they used is not the apparatus of choice for this purpose. The tendency of septals to perseverate in their attention to food cues in the first goal box might well introduce an artifact (cf. Skull, [14] ). It was felt, therefore, that a single runway would be more useful in this regard. In addition, the differential goal box time following reward and nonreward trials and the 50% partial reinforcement schedule utilized in Mabry's study might have masked any enhanced FE that may have been evinced otherwise. METHOD
Surgery Animals were assigned randomly to either the sham control or septal group and underwent surgery while under ether anesthesia. Target coordinates, determined from Pellegrino and Cushman [ 11 ] were: 1.7 mm anterior to bregma, bilaterally 0.5 mm from the midline, and 5.6 mm dorsal to the interaural line. The lesions were made by discharging a capacitor through a stainless steel electrode (0.25 mm dia., insulated except for 1.0 mm at the tip) until the condensor voltage declined to 10% of the initial 200 V level. Sham operations were carried out by drilling a hole through the skull and puncturing the dura; the electrode was not lowered. Animals were allowed 8 days recovery prior to deprivation.
Histology Following testing, the animals were perfused with 0.9% saline and 10% formal saline. Frozen coronal sections ( I 0 0 u) were cut through the full extent of the lesion and stained with cresyl violet.
Apparatus The sides and floor of the alley were constructed of plywood and painted gray. It consisted of 3 Plexiglas covered sections: start box, runway and goal box, which were 30, 122 and 40 cm in length, respectively. The depth was 24 cm, and the width, 10 cm. Masonite guillotine doors
Animals Thirteen male albino rats (Holtzman), 9 5 - 1 0 0 days old at surgery were used. The animals were housed singly.
Supported in part by USPHS Biological Sciences Training Grant MH7081. 2Now at Wright-Patterson AFB, Dayton, Ohio. 387
388
G O L D S T E I N , WYSS AND G O M E R
separated the sections and were operable via overhead pulleys. A food cup, 8 cm dia. by 4 cm was placed against the rear wall of the goal box. It was filled with a wet mash (35% by weight of Purina p o w d e r in water). T w o photocells were located 2 cm above the floor of the runway section and 2 cm from either end. These were c o n n e c t e d via Hunter amplifiers to a relay which powered an electric clock when the first beam was broken, and stopped the clock when the second beam was interrupted. The beams passed through red filters attached to the outside of the runway.
TABLE 1 MEANS OF MEDIAN RUNNING SPEEDS (I/LA'I.) ON PREFRUSTRATION (PF) AND FRUSTRATION (El 'TRIALS 1N LESIONED AND CONTROL ANIMALS Trial Condition PF
F
Lesion Status
Procedure
Septal
0.974
1.068
A f t e r adaptation to a 23 hour deprivation schedule, runway training began. Animals were run in the same order on all days. The first 130 trials (10 trials/day) were devoted to training: The animal was placed in the start box, the d o o r was opened i m m e d i a t e l y and closed after the animal had exited. When the end of the tail crossed the goal b o x threshold, the d o o r was closed and 3 sec were allowed for feeding during which running time was recorded. A f t e r the 3 sec, the animal was returned to the start b o x for the next trial. The wet mash was changed b e t w e e n animals and the a p p a r a t u s was cleaned and dried after each animal. T h r o u g h o u t the experiment, a white noise (60 dB) was delivered through an overhead speaker. The light level (at the center of the runway) was held constant at 2 ft-c. On each of the 9 test days (Days 1 4 - 2 2 ) , r e i n f o r c e m e n t was omitted on one trial. This trial was either the 4th, 5th or 6th for all animals on a given day, but rotated over days in an ACB pattern. On nonreinforced trials the food cup was replaced by an e m p t y cup. Goal b o x time for nonreward trials was the same as for reward trials (3 sec).
Control
0.935
0.959
RESULTS
Behavioral A f t e r adaptation to deprivation no significant difference existed in the weights of the two groups (Septal: 398 g, Control: 410 g). No septal animal d e m o n s t r a t e d hyperirritability. On the contrary they appeared on casual observation to be easier to handle than control animals, a finding which agrees with the report of Clody and Carlton [3]. F o r statistical t r e a t m e n t of the running data, latencies were converted to speed scores (1/latency). Each animal contributed two measures: the median speed of the 9 prefrustration (PF) runs terminating in nonreward, and of the 9 frustration (F) runs following nonreward. The g r o u p ' means of these are presented in Table 1. These measures were subjected to a 2 × 2 unweighted means analysis of variance (lesion groups X PF-F) with repeated measures on the latter dimension. The frustration main effect (PF-F) was significant (F = 50.22, 1/11, p < 0 . 0 1 ) as was the interaction (F=17.33, 1/11, p < 0 . 0 1 ) ; the lesion effect was not significant (F=1.47, 1/11, p > 0 . 0 5 ) . These results can be elucidated if one considers the high degree of overlap b e t w e e n lesion and control groups in PF speeds and, t h o u g h obviously less so, in F speeds as well. This was coupled, however, with very high intrasubject (PF-F) correlations: Spearman rho's were 0.99 for septals, and 0.94 for controls.
Histological Sections at the plane of maximal damage are presented in Fig. 1. Microscopic e x a m i n a t i o n revealed, in all instances,
FIG. 1. Sections at plane of maximal damage for lesioned animals reconstructed on plates from Pellegrino and Cushman [ 11 ]. Animals are ordered from top to bottom, left to right according to total volume of lesion. Numbers in caudate area are median PF speeds and PF to F increase, respectively. complete destruction of the medial septal nucleus. In 3 cases (Fig. 1, right column), the damage extended bilaterally into the lateral septal nucleus destroying from about 4 0 - 8 0 % of that structure in its A-P extent. Destruction also e x t e n d e d in these 3 septals, into the dorsal nucleus and tract of the diagonal band of Broca. In no case did the lesion invade the corpus callosum, the anterior commissure or the caudate nuclei although damage to the triangularis septal nucleus as well as the pre and postcommissural fornix was noted in most cases. There were no apparent variations in PF speeds or PF to F increases that could be ascribed to extramedial damage. DISCUSSION The results of the present study indicate that medial
SEPTAL LESIONS AND F R U S T R A T I O N
389
septal lesions render a rat more responsive to nonreward. This aberrant reactivity was manifested as a significantly greater increase in running speed in lesioned animals on trials immediately following withdrawal of reinforcement. A potential source of confounding in this effect could exist if the septals exhibited a more rapid within-day increase in running speed over trials than did the controls, an effect which would not be inconsistent necessarily with the essential equivalence in mean PF speeds. The evidence does not support this supposition; first, there was no systematic relationship between PF speed and PF trial number (4th, 5th or 6th) and second, the PF speeds of the controls and septals covaried over the 9 test days. While a response perseveration hypothesis might apply if PF speed was maintained on F trials by septals in conjunction with a slowing from PF to F trials in controls, it is not applicable in the present case where the effect was a differential increase from PF to F trials. Nor does it seem that these data can be subsumed under an enhanced incentive explanation [1]. According to an incentive hypothesis, septal lesions would result in a magnification of incentive motivation which in turn would be associated with a more intense FE [8, 10, 12]. However, near equivalence in PF speeds of the 2 groups does not lend support to this interpretation. An appealing alternative to these hypotheses is the proposition that the stimulus change represented by reward omission is, as other stimuli, overreacted to by medial septal animals. This position, however, is not entirely secure; while the absence of evidence for an incentive difference seems to eliminate this most compelling alternative hypothesis, an incentive difference might itself be viewed as predicted by the present hypothesis. Why this
differential was not observed in the present study is not evident, but since the FE was manifested as an increase in speed, it is apparently not due to the limiting effect of a ceiling on baseline. Perhaps the present position may be refined to incorporate the attentional restriction deficit postulated earlier [5]. Accordingly, the perceptual field of septal animals is relatively restricted to those aspects relevant to the current task. Alteration of any of these salient stimuli (absence of food here) represents a more significant change in conditions for septals than for controls and hence the greater likelihood in septals of the characteristic (frustrative) response. The present results suggest that this mechanism is independent of an incentive enhancement in septal animals. Viewing this phenomenon from another perspective, it is interesting to note that in the development of the rationale for their study, Mabry and Peeler suggested the possibility of an attenuated frustrative response in septal animals rather than the amplification predicted here. Alluding to the increased resistance to extinction reported for septal animals [13], they argued that if reduced conditioned anticipatory frustration (sf) was the underlying cause, it would be reflected as well in a weaker FE (rf) measured in the double runway. Indirect data supporting deductions from this position are available [6,7] all of which, however, dealt with extinction. In the present study, involving a direct assessment of the facilitative response to frustration, the opposite appears to be the case. Thus, within the framework of frustration theory, there seems to be a dissociation in septal animals, between the short-term response to nonreward and the longer term (conditioned) consequences of this enhancement.
REFERENCES 1. Beatty, W. W. and J. S. Schwartzbaum. Consummatory behavior for sucrose following septal lesions in the rat. J. cornp. physiol. Psychol. 65: 93-102, 1968. 2. Caplan, M. Effects of withheld reinforcement on timing behavior of rats with limbic lesions. J. cornp, physiol. Psychol. 71: 119-135, 1970. 3. Clody, D. E. and P. L. Carlton. Behavioral effects of lesions of the medial septum of rats. J. comp. physiol. Psychol. 67: 344-351, 1969. 4. Dickinson, A. Septal lesions in rats and the acquisition of freeoperant successive discriminations. Physiol. Behav. 10: 305-314, 1973. 5. Gomer, F. E. and R. Goldstein. Attentional rigidity during exploratory and simultaneous discrimination behavior in septal lesioned rats. Physiol. Behav. 12: 19-28, 1974. 6. Gray, J. A., L. Quint~io and M. T. Araujo-Silva. The partial reinforcement extinction effect in rats with septal lesions. Physiol. Behav. 8: 491-496, 1972. 7. Henke, P. G. Persistance of runway performance after septal lesions in rats. J. comp. physiol. Psychol. 86: 760-767, 1974.
8. Krippner, R. A., R. C. Endsley and R. S. Tucker. Magnitude of G 1 reward and frustration effect in a between subjects design. Psychon. ScL 9: 385-386, 1967. 9. Mabry, P. D. and D. F. Peeler. Effect of septal lesions on response to frustrative nonreward. Physiol. Behav. 8: 909-913, 1972. 10. Peckham, R. N. and A. Amsel. Within-subject demonstration of a relationship between frustration and magnitude of reward in a differential magnitude of reward discrimination. J. exp. Psychol. 73: 187-195, 1967. 11. Pellegrino, L. J. and A. J. Cushman. A Stereotaxic Atlas of the Rat Brain. New York: Appleton-Century-Crofts, 1967. 12. Schnelle, J. F., S. F. Walker and H. M. B. Hurwitz. Concurrent performance in septally operated rats: One and two response extinction.Physiol. Behav. 6: 649-654, 1971. 13. Schwartzbaum, J. S., M. H. Kellicutt, T. M. Spieth and J. B. Thompson. Effects of septal lesions in rats on response inhibition associated with food reinforced behavior. J. comp. physiol. Psychol. 58: 217-224, 1964. 14. Skull, J. W. The Amsel frustration effect: interpretations and research. Psychol. Bull. 79: 352-361, 1973.
BRIEF COMMUNICATION Medial Septal Lesions and the Frustration
Effect 1
ROBERT GOLDSTEIN, J. MICHAEL WYSS AND F R A N K E. GOMER z
. Washington University Behavior Research Laboratory, 1420 Grattan Street St. Louis, MO 63104
(Received 2 July 1974) GOLDSTEIN, R., J. M. WYSS AND F. E. GOMER. Medial septal lesions and the frustration effect. PHYSIOL. BEHAV. 14(3) 387-389, 1975. - Rats with medial septal lesions and sham operates were run in a straight runway. After running stabilized, food was omitted on selected trials and the running speed on the following trial was observed for a frustration effect (FE). The septals exhibited a significantly greater increase in speed on this trial than controls. This enhanced FE in septals is at variance with predictions from frustration theory considering the greater resistance to extinction in septals and suggests a dissociation between the immediate and conditionable effects of frustration in such animals. Septal lesion
Frustration
Brain
IN a study by Caplan [2], pressing rates of septal rats increased significantly over controls following nonreinforced presses on a DRL schedule. A similar response to nonreward has been reported by Dickinson [4]. His septals, more readily than controls, acquired a response which reinstated an $ 9 , following the introduction of S a. Another indicatlon of an amplified effect of reward omission in septals is contained in a study by Schnelle, Walker and Hurwitz [12]. There, the normal extinction of one response was accompanied by an increase in the rate of a previously learned alternative response. However, in a study designed to explore this variable, Mabry and Peeler [9] found no differential frustration effect (FE). The possibility exists that the double runway which they used is not the apparatus of choice for this purpose. The tendency of septals to perseverate in their attention to food cues in the first goal box might well introduce an artifact (cf. Skull, [14] ). It was felt, therefore, that a single runway would be more useful in this regard. In addition, the differential goal box time following reward and nonreward trials and the 50% partial reinforcement schedule utilized in Mabry's study might have masked any enhanced FE that may have been evinced otherwise. METHOD
Surgery Animals were assigned randomly to either the sham control or septal group and underwent surgery while under ether anesthesia. Target coordinates, determined from Pellegrino and Cushman [ 11 ] were: 1.7 mm anterior to bregma, bilaterally 0.5 mm from the midline, and 5.6 mm dorsal to the interaural line. The lesions were made by discharging a capacitor through a stainless steel electrode (0.25 mm dia., insulated except for 1.0 mm at the tip) until the condensor voltage declined to 10% of the initial 200 V level. Sham operations were carried out by drilling a hole through the skull and puncturing the dura; the electrode was not lowered. Animals were allowed 8 days recovery prior to deprivation.
Histology Following testing, the animals were perfused with 0.9% saline and 10% formal saline. Frozen coronal sections ( I 0 0 u) were cut through the full extent of the lesion and stained with cresyl violet.
Apparatus The sides and floor of the alley were constructed of plywood and painted gray. It consisted of 3 Plexiglas covered sections: start box, runway and goal box, which were 30, 122 and 40 cm in length, respectively. The depth was 24 cm, and the width, 10 cm. Masonite guillotine doors
Animals Thirteen male albino rats (Holtzman), 9 5 - 1 0 0 days old at surgery were used. The animals were housed singly.
Supported in part by USPHS Biological Sciences Training Grant MH7081. 2Now at Wright-Patterson AFB, Dayton, Ohio. 387
388
G O L D S T E I N , WYSS AND G O M E R
separated the sections and were operable via overhead pulleys. A food cup, 8 cm dia. by 4 cm was placed against the rear wall of the goal box. It was filled with a wet mash (35% by weight of Purina p o w d e r in water). T w o photocells were located 2 cm above the floor of the runway section and 2 cm from either end. These were c o n n e c t e d via Hunter amplifiers to a relay which powered an electric clock when the first beam was broken, and stopped the clock when the second beam was interrupted. The beams passed through red filters attached to the outside of the runway.
TABLE 1 MEANS OF MEDIAN RUNNING SPEEDS (I/LA'I.) ON PREFRUSTRATION (PF) AND FRUSTRATION (El 'TRIALS 1N LESIONED AND CONTROL ANIMALS Trial Condition PF
F
Lesion Status
Procedure
Septal
0.974
1.068
A f t e r adaptation to a 23 hour deprivation schedule, runway training began. Animals were run in the same order on all days. The first 130 trials (10 trials/day) were devoted to training: The animal was placed in the start box, the d o o r was opened i m m e d i a t e l y and closed after the animal had exited. When the end of the tail crossed the goal b o x threshold, the d o o r was closed and 3 sec were allowed for feeding during which running time was recorded. A f t e r the 3 sec, the animal was returned to the start b o x for the next trial. The wet mash was changed b e t w e e n animals and the a p p a r a t u s was cleaned and dried after each animal. T h r o u g h o u t the experiment, a white noise (60 dB) was delivered through an overhead speaker. The light level (at the center of the runway) was held constant at 2 ft-c. On each of the 9 test days (Days 1 4 - 2 2 ) , r e i n f o r c e m e n t was omitted on one trial. This trial was either the 4th, 5th or 6th for all animals on a given day, but rotated over days in an ACB pattern. On nonreinforced trials the food cup was replaced by an e m p t y cup. Goal b o x time for nonreward trials was the same as for reward trials (3 sec).
Control
0.935
0.959
RESULTS
Behavioral A f t e r adaptation to deprivation no significant difference existed in the weights of the two groups (Septal: 398 g, Control: 410 g). No septal animal d e m o n s t r a t e d hyperirritability. On the contrary they appeared on casual observation to be easier to handle than control animals, a finding which agrees with the report of Clody and Carlton [3]. F o r statistical t r e a t m e n t of the running data, latencies were converted to speed scores (1/latency). Each animal contributed two measures: the median speed of the 9 prefrustration (PF) runs terminating in nonreward, and of the 9 frustration (F) runs following nonreward. The g r o u p ' means of these are presented in Table 1. These measures were subjected to a 2 × 2 unweighted means analysis of variance (lesion groups X PF-F) with repeated measures on the latter dimension. The frustration main effect (PF-F) was significant (F = 50.22, 1/11, p < 0 . 0 1 ) as was the interaction (F=17.33, 1/11, p < 0 . 0 1 ) ; the lesion effect was not significant (F=1.47, 1/11, p > 0 . 0 5 ) . These results can be elucidated if one considers the high degree of overlap b e t w e e n lesion and control groups in PF speeds and, t h o u g h obviously less so, in F speeds as well. This was coupled, however, with very high intrasubject (PF-F) correlations: Spearman rho's were 0.99 for septals, and 0.94 for controls.
Histological Sections at the plane of maximal damage are presented in Fig. 1. Microscopic e x a m i n a t i o n revealed, in all instances,
FIG. 1. Sections at plane of maximal damage for lesioned animals reconstructed on plates from Pellegrino and Cushman [ 11 ]. Animals are ordered from top to bottom, left to right according to total volume of lesion. Numbers in caudate area are median PF speeds and PF to F increase, respectively. complete destruction of the medial septal nucleus. In 3 cases (Fig. 1, right column), the damage extended bilaterally into the lateral septal nucleus destroying from about 4 0 - 8 0 % of that structure in its A-P extent. Destruction also e x t e n d e d in these 3 septals, into the dorsal nucleus and tract of the diagonal band of Broca. In no case did the lesion invade the corpus callosum, the anterior commissure or the caudate nuclei although damage to the triangularis septal nucleus as well as the pre and postcommissural fornix was noted in most cases. There were no apparent variations in PF speeds or PF to F increases that could be ascribed to extramedial damage. DISCUSSION The results of the present study indicate that medial
SEPTAL LESIONS AND F R U S T R A T I O N
389
septal lesions render a rat more responsive to nonreward. This aberrant reactivity was manifested as a significantly greater increase in running speed in lesioned animals on trials immediately following withdrawal of reinforcement. A potential source of confounding in this effect could exist if the septals exhibited a more rapid within-day increase in running speed over trials than did the controls, an effect which would not be inconsistent necessarily with the essential equivalence in mean PF speeds. The evidence does not support this supposition; first, there was no systematic relationship between PF speed and PF trial number (4th, 5th or 6th) and second, the PF speeds of the controls and septals covaried over the 9 test days. While a response perseveration hypothesis might apply if PF speed was maintained on F trials by septals in conjunction with a slowing from PF to F trials in controls, it is not applicable in the present case where the effect was a differential increase from PF to F trials. Nor does it seem that these data can be subsumed under an enhanced incentive explanation [1]. According to an incentive hypothesis, septal lesions would result in a magnification of incentive motivation which in turn would be associated with a more intense FE [8, 10, 12]. However, near equivalence in PF speeds of the 2 groups does not lend support to this interpretation. An appealing alternative to these hypotheses is the proposition that the stimulus change represented by reward omission is, as other stimuli, overreacted to by medial septal animals. This position, however, is not entirely secure; while the absence of evidence for an incentive difference seems to eliminate this most compelling alternative hypothesis, an incentive difference might itself be viewed as predicted by the present hypothesis. Why this
differential was not observed in the present study is not evident, but since the FE was manifested as an increase in speed, it is apparently not due to the limiting effect of a ceiling on baseline. Perhaps the present position may be refined to incorporate the attentional restriction deficit postulated earlier [5]. Accordingly, the perceptual field of septal animals is relatively restricted to those aspects relevant to the current task. Alteration of any of these salient stimuli (absence of food here) represents a more significant change in conditions for septals than for controls and hence the greater likelihood in septals of the characteristic (frustrative) response. The present results suggest that this mechanism is independent of an incentive enhancement in septal animals. Viewing this phenomenon from another perspective, it is interesting to note that in the development of the rationale for their study, Mabry and Peeler suggested the possibility of an attenuated frustrative response in septal animals rather than the amplification predicted here. Alluding to the increased resistance to extinction reported for septal animals [13], they argued that if reduced conditioned anticipatory frustration (sf) was the underlying cause, it would be reflected as well in a weaker FE (rf) measured in the double runway. Indirect data supporting deductions from this position are available [6,7] all of which, however, dealt with extinction. In the present study, involving a direct assessment of the facilitative response to frustration, the opposite appears to be the case. Thus, within the framework of frustration theory, there seems to be a dissociation in septal animals, between the short-term response to nonreward and the longer term (conditioned) consequences of this enhancement.
REFERENCES 1. Beatty, W. W. and J. S. Schwartzbaum. Consummatory behavior for sucrose following septal lesions in the rat. J. cornp. physiol. Psychol. 65: 93-102, 1968. 2. Caplan, M. Effects of withheld reinforcement on timing behavior of rats with limbic lesions. J. cornp, physiol. Psychol. 71: 119-135, 1970. 3. Clody, D. E. and P. L. Carlton. Behavioral effects of lesions of the medial septum of rats. J. comp. physiol. Psychol. 67: 344-351, 1969. 4. Dickinson, A. Septal lesions in rats and the acquisition of freeoperant successive discriminations. Physiol. Behav. 10: 305-314, 1973. 5. Gomer, F. E. and R. Goldstein. Attentional rigidity during exploratory and simultaneous discrimination behavior in septal lesioned rats. Physiol. Behav. 12: 19-28, 1974. 6. Gray, J. A., L. Quint~io and M. T. Araujo-Silva. The partial reinforcement extinction effect in rats with septal lesions. Physiol. Behav. 8: 491-496, 1972. 7. Henke, P. G. Persistance of runway performance after septal lesions in rats. J. comp. physiol. Psychol. 86: 760-767, 1974.
8. Krippner, R. A., R. C. Endsley and R. S. Tucker. Magnitude of G 1 reward and frustration effect in a between subjects design. Psychon. ScL 9: 385-386, 1967. 9. Mabry, P. D. and D. F. Peeler. Effect of septal lesions on response to frustrative nonreward. Physiol. Behav. 8: 909-913, 1972. 10. Peckham, R. N. and A. Amsel. Within-subject demonstration of a relationship between frustration and magnitude of reward in a differential magnitude of reward discrimination. J. exp. Psychol. 73: 187-195, 1967. 11. Pellegrino, L. J. and A. J. Cushman. A Stereotaxic Atlas of the Rat Brain. New York: Appleton-Century-Crofts, 1967. 12. Schnelle, J. F., S. F. Walker and H. M. B. Hurwitz. Concurrent performance in septally operated rats: One and two response extinction.Physiol. Behav. 6: 649-654, 1971. 13. Schwartzbaum, J. S., M. H. Kellicutt, T. M. Spieth and J. B. Thompson. Effects of septal lesions in rats on response inhibition associated with food reinforced behavior. J. comp. physiol. Psychol. 58: 217-224, 1964. 14. Skull, J. W. The Amsel frustration effect: interpretations and research. Psychol. Bull. 79: 352-361, 1973.