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Instrumental learning on fixed ratio and GO-NOGO schedules in neodecorticate rats
356
Braht Research, 161 (1979) 356 360 © Elsevier/North-Holland Biomedical Press
Instrumental learning on Fixed Ratio and G O - N O G O decorticate rats
schedules in neo-
DAVID A. OAKLEY* and I. STEELE RUSSELL M R C Unit on Neural Mechanisms of Behaviour, 3, Malet Place, London, WC1E 7JG (U.K.)
(Accepted October 12th, 1978)
Totally neocorticated rabbits have been shown to acquire a treadle pressing response for food reinforcementa,7, 8 but were unable, without specific pretraining, to progress on Fixed Ratio schedules beyond FR8. They also persisted in opening the food tray door throughout the interval between consecutive reinforcements whereas normal animals restricted their food tray activity to the postreinforcement pause. Both of these limitations to FR performance in the neodecorticates could, however, be overcome by remedial pretraining aimed at enhancing manipulandum identification 4. The present experiments investigate the performance of neodecorticate rats to establish the across-species generality of the earlier results and to investigate further the types of pretraining which are effective in improving FR performance in the absence of neocortex. The first experiment involves 5 neodecorticated and 5 normal rats (male, Hooded Lister) on FR schedules using a bar-press response for food reward. These animals had no specific pretraining but all had received postoperative experience in other instrumental learning situations involving food reward : chain pulling (2 animals in each group), horizontal/vertical pattern discrimination in a two-choice box (2 from each group) and alleyway running (1 from each group). Neodecortication (99.6 SD :~ 0.29 ~ of total neocortex removed) was achieved by removing pia from the surface of the hemisphere2, ~& The normal animals were sham operated and received two 5 mm diameter trephine holes over parietal cortex. Surgical procedures were under pentobarbitone sodium (Sagatal) anesthesia and were performed in two stages (5-9 weeks between operations) in 4 animals in each group and in one stage in the fifth animal. All animals had 49-52 weeks of postoperative recovery prior to this experiment. Histological investigation of the neodecorticate brains revealed small amounts of anterior neocortical sparing adjacent to the rhinal fissure. Transitional neocortex was invaded in all brains along the rhinal fissure, particularly caudally, and in midline regions. Postoperative degenerative changes had removed all cortical tissue below the de* Present address. Department of Psychology, University College London, Gower Street, London, WC1E 6BT, England.
357 vascularized surface of the hemisphere and in the majority of cases associated white matter, including corpus callosum, had also disappeared. Ventricular expansion was evident in all lesioned brains and resulted in lateral displacement of caudate-putamen. No neocortical or other neural changes were found in the sham operated animals. The apparatus was a standard rodent operant box with a 6 mm diameter aluminium bar manipulandum situated in one end wall 3.5 cm to the left of a centrally placed food tray opening (5 cm × 5 cm). This aperature was fitted with a top-hung transparent door which closed it except for a 4 mm gap at the bottom. Both bar pressing, requiring a force of approximately 10 gms, and tray door operation caused distinct clicks from nearby relays. Reinforcement consisted of Noyes pellets (45 mg) and was signalled by the sound of the pellet dispenser operating. The box was continuously illuminated by a 24 V, 2.8 W houselight. All animals were removed from ad lib feeding 1 month before the study commenced and were fed 25 g of standard laboratory diet (41B) daily as a single amount at a fixed time. Once training commenced all animals received sufficient food after each session to maintain their body weights at a constant level. Following 12 sessions of magazine training in the operant box, during which a reinforcement pellet was delivered to the food tray every 30 sec, the response bar was introduced for 16 sessions on a continuous reinforcement (FR1) schedule. For the first 3 FRI sessions the bar was 3 in. long, for the next three sessions it was 2 in. long and for the final 10 sessions it was 1.5 in. long. Reinforcement ratios were then increased using the 1.5 in. bar from FR1 to FR12 in single response steps. Four sessions were given on FR2 and FR3 and two sessions at each of the remaining FR values. All sessions were daily and lasted for 30 min. Unless noted otherwise, between group statistical analysis was based on one-tailed Mann-Whitney U tests 1° and within-group trends were evaluated using Page's L-test 9. Bar pressing response rates in responses per minute and tray/reinforcement ratios are shown for both groups of animals in Fig. 1. The tray/reinforcement ratio gives the number of tray door entries per reinforcement and has an ideal value of 1.0. Higher tray/reinforcement scores indicate less efficient performance. All animals successfully completed tray feeding, magazine training and FR1 stages of the experiment to produce levels of bar pressing at the end of FR1 training which were very similar in both groups ( N l = N 2 = 5 , U = 7 , P > 0.05) but the number of tray entries per reinforcement was significantly higher in the neodecorticates (N 1--N z-- 5, U = 0 , P=0.004). With increasing FR values response rates on the bar increased rapidly in the normal animals, becoming significantly higher than those of the neodecorticates from FR3 onwards (FR3: N I = N Z = 5 , U----2, P=0.016). After an initial significant increase in bar press response rate (FR1-3, k = 3 , N - - 5 , L = 6 9 , P < 0.01), performance became asymptotic in the neodecorticates between FR4 and FR10 and declined sharply on FR11 and FR12. Tray/reinforcement ratios remained stable in the neodecorticates until FR4 and then increased steadily to FR10 becoming enormous as the bar press response deteriorated at F R l l - 1 2 . Tray/reinforcement ratios in the normal animals remained near the optimal value of 1.0. The mean tray/reinforcement ratio for the normal animals over the entire 42 sessions of FR
358 40-
tt?
~ ~20 o
wt, L
o ~z
_f -- NORMAL
40
W m cr
_z<20 W C[:
cr I--
O.
a:
10
L
o
0
10 20 30 SESSIONS
40
Fig. 1. Bar-press response rate, tray/reinforcement ratios and sequence o f F R values during training for 5 normal and 5 neodecorticate rats.
training was 1.4 (SD ~: 0.14). The neodecorticated rats in this experiment thus performed in an almost identical fashion to naive neodecorticated rabbits in our previous studiesmT,8. Both neodecorticate rabbits 4 and partially neodecorticate rats 1 show impaired performance in operant G O - N O G O situations. The second experiment used three neodecorticate and four normal rats from Experiment 1 on a G O - N O G O schedule using houselight cues. Apart from an interest in the effects of neodecortication on GON O G O performance this experiment sought to evaluate G O - N O G O experience as a remedial pretraining procedure for subsequent FR performance. Using the same apparatus as in the previous experiment a multiple (FR5, Extinction) schedule was introduced on the 1.5 in. bar for 8 daily, 36 min sessions during which GO (houselight on) and N O G O (houselight off) periods alternated at 2 min intervals. A multiple (FR1, Extinction) schedule was subsequently introduced for a further 30 sessions in order to increase the difference between response consequences in the two phases. The normal animals acquired a significant differentiation in bar pressing rate between the GO and N O G O phases under both the FR5 and the FR 1 based multiple schedules. The neodecorticates, on the other hand, showed no significant improvement under either G O - N O G O schedule and persisted in fact in responding to the bar more rapidly under N O G O conditions throughout the 38 days of training. An analysis of food tray responses during GO and N O G O phases, however, revealed a significant trend in the neodecorticates towards concentrating their tray responses into the GO phase (blocks of 10 sessions, k = 3 , N = 3 , L = 4 2 , P < 0.01) to produce final
359 G O - N O G O scores on this measure which were not significantly different from those of normal animals. In order to assess the effect of experience gained during G O - N O G O training on subsequent F R performance the 3 neodecorticates and four normal rats were returned to a simple FR1 schedule for three 30-min sessions in the same operant box with the houselight continuously on as in the first experiment. The reinforcement ratio was then increased in single response steps until FR10 was reached. Three daily sessions were given at each F R value and each session lasted for 30 min. The result was a virtual replication of the data from Experiment 1 (see Fig. 1). Bar press rates in normals increased as the F R value was raised whereas the neodecorticates showed a significant increase in response rate from FR1 to FR4 ( k = 4 , N = 3 , L = 8 6 , P < 0.05) followed by a steady decline to reach minimal levels from FR7 onwards. Tray/reinforcement ratios remained stable in the neodecorticates around a mean of 4.2 (SD -+- 1.1) up to FR4, becoming steadily higher (less efficient) thereafter to reach a mean value of 32.7 (zk 1.6) tray responses per reinforcement at F R I 0 . The mean tray/reinforcement ratio for the normal animals was stable over the entire 30 sessions of F R training in this experiment at 1.9 (-4- 0.44). These experiments have confirmed that earlier reports of F R performance in free-operant situations in neodecorticated rabbits were not describing species-specific effects. FR performance in the neodecorticated rats had an apparent ceiling in the region of F R 4 - F R l 0 beyond which bar pressing ceased, tray/reinforcement ratios were higher at all stages of F R training in the lesioned animals, and their tray door responding persisted at high intensities even when bar pressing had ceased at the higher FR ratios. Also in confirmation of earlier rabbit studies the neodecorticated rats were severely impaired in performing a G O - N O G O discrimination based on the free-operant response. Neither prior experience of other instrumental procedures nor of a G O - N O G O schedule, in the same apparatus, despite its clear effect on tray response distributions, was a sufficient pretraining condition for improving subsequent F R performance. This is consistent with our earlier suggestion that to be effective the pretraining should be specifically designed to direct the animal's attention to the relevant manipulandum4, s. The authors are grateful to Sandra Pereira for running most of the animals and for helping in the data analyses, to Alison Hogg for preparing the histological material and to Marita McLaughlin for typing the manuscript.
1 Bloch, S. and Bello, M., Differential instrumental learning with food reward after extensive neocortical lesions in rats, Acta Neurobiol. Exp., 34 (1974) 603-613. 2 Meyer, P. M. and Meyer, D. R., Neurosurgical procedures with special reference to aspiration lesions. In R. D. Myers (Ed.), Methods in Psychobiology, Vol. 1, Academic Press, London, 1971, pp. 91-130. 3 Oakley, D. A., Instrumental learning in neodecorticate rabbits, Nature (New BioL), 233 (1971) 185-187. 40akley, D. A., Instrumental reversal learning and subsequent Fixed Ratio performance on simple and GO-NOGO schedules in neodecorticate rabbits, Physiol. PsychoL, in press.
360 5 0 a k l e y , D. A. and Russell, I. S., Neocortical lesions and Pavlovian conditioning, Physiol. Behav., 8 (1972) 915-926. 6 0 a k l e y , D. A. and Russell, I. S., Role of cortex in Pavlovian discrimination learning, PhysioL Behav., 15 (1975) 315-321. 7 0 a k l e y , D. A. and Russell, I. S., Performance ofneodecorticated rabbitsin a Free-operant situation, Physiol. Behav., 20 (1978) 157-170. 8 0 a k l e y , D. A. and Russell, I. S., Manipulandum identification in o!0erant behaviour in neodecorticate rabbits, Physiol. Behav., in press. 9 Page, E. B., Ordered hypotheses for multiple treatments: A significance test for linear ranks, J. Amer. Statist. Ass., 58 (1963) 216-230. 10 Siegel, S., Non-parametric Statistics for the Behavioural Sciences, New York, McGraw-Hill, 1956, ll6pp.
Braht Research, 161 (1979) 356 360 © Elsevier/North-Holland Biomedical Press
Instrumental learning on Fixed Ratio and G O - N O G O decorticate rats
schedules in neo-
DAVID A. OAKLEY* and I. STEELE RUSSELL M R C Unit on Neural Mechanisms of Behaviour, 3, Malet Place, London, WC1E 7JG (U.K.)
(Accepted October 12th, 1978)
Totally neocorticated rabbits have been shown to acquire a treadle pressing response for food reinforcementa,7, 8 but were unable, without specific pretraining, to progress on Fixed Ratio schedules beyond FR8. They also persisted in opening the food tray door throughout the interval between consecutive reinforcements whereas normal animals restricted their food tray activity to the postreinforcement pause. Both of these limitations to FR performance in the neodecorticates could, however, be overcome by remedial pretraining aimed at enhancing manipulandum identification 4. The present experiments investigate the performance of neodecorticate rats to establish the across-species generality of the earlier results and to investigate further the types of pretraining which are effective in improving FR performance in the absence of neocortex. The first experiment involves 5 neodecorticated and 5 normal rats (male, Hooded Lister) on FR schedules using a bar-press response for food reward. These animals had no specific pretraining but all had received postoperative experience in other instrumental learning situations involving food reward : chain pulling (2 animals in each group), horizontal/vertical pattern discrimination in a two-choice box (2 from each group) and alleyway running (1 from each group). Neodecortication (99.6 SD :~ 0.29 ~ of total neocortex removed) was achieved by removing pia from the surface of the hemisphere2, ~& The normal animals were sham operated and received two 5 mm diameter trephine holes over parietal cortex. Surgical procedures were under pentobarbitone sodium (Sagatal) anesthesia and were performed in two stages (5-9 weeks between operations) in 4 animals in each group and in one stage in the fifth animal. All animals had 49-52 weeks of postoperative recovery prior to this experiment. Histological investigation of the neodecorticate brains revealed small amounts of anterior neocortical sparing adjacent to the rhinal fissure. Transitional neocortex was invaded in all brains along the rhinal fissure, particularly caudally, and in midline regions. Postoperative degenerative changes had removed all cortical tissue below the de* Present address. Department of Psychology, University College London, Gower Street, London, WC1E 6BT, England.
357 vascularized surface of the hemisphere and in the majority of cases associated white matter, including corpus callosum, had also disappeared. Ventricular expansion was evident in all lesioned brains and resulted in lateral displacement of caudate-putamen. No neocortical or other neural changes were found in the sham operated animals. The apparatus was a standard rodent operant box with a 6 mm diameter aluminium bar manipulandum situated in one end wall 3.5 cm to the left of a centrally placed food tray opening (5 cm × 5 cm). This aperature was fitted with a top-hung transparent door which closed it except for a 4 mm gap at the bottom. Both bar pressing, requiring a force of approximately 10 gms, and tray door operation caused distinct clicks from nearby relays. Reinforcement consisted of Noyes pellets (45 mg) and was signalled by the sound of the pellet dispenser operating. The box was continuously illuminated by a 24 V, 2.8 W houselight. All animals were removed from ad lib feeding 1 month before the study commenced and were fed 25 g of standard laboratory diet (41B) daily as a single amount at a fixed time. Once training commenced all animals received sufficient food after each session to maintain their body weights at a constant level. Following 12 sessions of magazine training in the operant box, during which a reinforcement pellet was delivered to the food tray every 30 sec, the response bar was introduced for 16 sessions on a continuous reinforcement (FR1) schedule. For the first 3 FRI sessions the bar was 3 in. long, for the next three sessions it was 2 in. long and for the final 10 sessions it was 1.5 in. long. Reinforcement ratios were then increased using the 1.5 in. bar from FR1 to FR12 in single response steps. Four sessions were given on FR2 and FR3 and two sessions at each of the remaining FR values. All sessions were daily and lasted for 30 min. Unless noted otherwise, between group statistical analysis was based on one-tailed Mann-Whitney U tests 1° and within-group trends were evaluated using Page's L-test 9. Bar pressing response rates in responses per minute and tray/reinforcement ratios are shown for both groups of animals in Fig. 1. The tray/reinforcement ratio gives the number of tray door entries per reinforcement and has an ideal value of 1.0. Higher tray/reinforcement scores indicate less efficient performance. All animals successfully completed tray feeding, magazine training and FR1 stages of the experiment to produce levels of bar pressing at the end of FR1 training which were very similar in both groups ( N l = N 2 = 5 , U = 7 , P > 0.05) but the number of tray entries per reinforcement was significantly higher in the neodecorticates (N 1--N z-- 5, U = 0 , P=0.004). With increasing FR values response rates on the bar increased rapidly in the normal animals, becoming significantly higher than those of the neodecorticates from FR3 onwards (FR3: N I = N Z = 5 , U----2, P=0.016). After an initial significant increase in bar press response rate (FR1-3, k = 3 , N - - 5 , L = 6 9 , P < 0.01), performance became asymptotic in the neodecorticates between FR4 and FR10 and declined sharply on FR11 and FR12. Tray/reinforcement ratios remained stable in the neodecorticates until FR4 and then increased steadily to FR10 becoming enormous as the bar press response deteriorated at F R l l - 1 2 . Tray/reinforcement ratios in the normal animals remained near the optimal value of 1.0. The mean tray/reinforcement ratio for the normal animals over the entire 42 sessions of FR
358 40-
tt?
~ ~20 o
wt, L
o ~z
_f -- NORMAL
40
W m cr
_z<20 W C[:
cr I--
O.
a:
10
L
o
0
10 20 30 SESSIONS
40
Fig. 1. Bar-press response rate, tray/reinforcement ratios and sequence o f F R values during training for 5 normal and 5 neodecorticate rats.
training was 1.4 (SD ~: 0.14). The neodecorticated rats in this experiment thus performed in an almost identical fashion to naive neodecorticated rabbits in our previous studiesmT,8. Both neodecorticate rabbits 4 and partially neodecorticate rats 1 show impaired performance in operant G O - N O G O situations. The second experiment used three neodecorticate and four normal rats from Experiment 1 on a G O - N O G O schedule using houselight cues. Apart from an interest in the effects of neodecortication on GON O G O performance this experiment sought to evaluate G O - N O G O experience as a remedial pretraining procedure for subsequent FR performance. Using the same apparatus as in the previous experiment a multiple (FR5, Extinction) schedule was introduced on the 1.5 in. bar for 8 daily, 36 min sessions during which GO (houselight on) and N O G O (houselight off) periods alternated at 2 min intervals. A multiple (FR1, Extinction) schedule was subsequently introduced for a further 30 sessions in order to increase the difference between response consequences in the two phases. The normal animals acquired a significant differentiation in bar pressing rate between the GO and N O G O phases under both the FR5 and the FR 1 based multiple schedules. The neodecorticates, on the other hand, showed no significant improvement under either G O - N O G O schedule and persisted in fact in responding to the bar more rapidly under N O G O conditions throughout the 38 days of training. An analysis of food tray responses during GO and N O G O phases, however, revealed a significant trend in the neodecorticates towards concentrating their tray responses into the GO phase (blocks of 10 sessions, k = 3 , N = 3 , L = 4 2 , P < 0.01) to produce final
359 G O - N O G O scores on this measure which were not significantly different from those of normal animals. In order to assess the effect of experience gained during G O - N O G O training on subsequent F R performance the 3 neodecorticates and four normal rats were returned to a simple FR1 schedule for three 30-min sessions in the same operant box with the houselight continuously on as in the first experiment. The reinforcement ratio was then increased in single response steps until FR10 was reached. Three daily sessions were given at each F R value and each session lasted for 30 min. The result was a virtual replication of the data from Experiment 1 (see Fig. 1). Bar press rates in normals increased as the F R value was raised whereas the neodecorticates showed a significant increase in response rate from FR1 to FR4 ( k = 4 , N = 3 , L = 8 6 , P < 0.05) followed by a steady decline to reach minimal levels from FR7 onwards. Tray/reinforcement ratios remained stable in the neodecorticates around a mean of 4.2 (SD -+- 1.1) up to FR4, becoming steadily higher (less efficient) thereafter to reach a mean value of 32.7 (zk 1.6) tray responses per reinforcement at F R I 0 . The mean tray/reinforcement ratio for the normal animals was stable over the entire 30 sessions of F R training in this experiment at 1.9 (-4- 0.44). These experiments have confirmed that earlier reports of F R performance in free-operant situations in neodecorticated rabbits were not describing species-specific effects. FR performance in the neodecorticated rats had an apparent ceiling in the region of F R 4 - F R l 0 beyond which bar pressing ceased, tray/reinforcement ratios were higher at all stages of F R training in the lesioned animals, and their tray door responding persisted at high intensities even when bar pressing had ceased at the higher FR ratios. Also in confirmation of earlier rabbit studies the neodecorticated rats were severely impaired in performing a G O - N O G O discrimination based on the free-operant response. Neither prior experience of other instrumental procedures nor of a G O - N O G O schedule, in the same apparatus, despite its clear effect on tray response distributions, was a sufficient pretraining condition for improving subsequent F R performance. This is consistent with our earlier suggestion that to be effective the pretraining should be specifically designed to direct the animal's attention to the relevant manipulandum4, s. The authors are grateful to Sandra Pereira for running most of the animals and for helping in the data analyses, to Alison Hogg for preparing the histological material and to Marita McLaughlin for typing the manuscript.
1 Bloch, S. and Bello, M., Differential instrumental learning with food reward after extensive neocortical lesions in rats, Acta Neurobiol. Exp., 34 (1974) 603-613. 2 Meyer, P. M. and Meyer, D. R., Neurosurgical procedures with special reference to aspiration lesions. In R. D. Myers (Ed.), Methods in Psychobiology, Vol. 1, Academic Press, London, 1971, pp. 91-130. 3 Oakley, D. A., Instrumental learning in neodecorticate rabbits, Nature (New BioL), 233 (1971) 185-187. 40akley, D. A., Instrumental reversal learning and subsequent Fixed Ratio performance on simple and GO-NOGO schedules in neodecorticate rabbits, Physiol. PsychoL, in press.
360 5 0 a k l e y , D. A. and Russell, I. S., Neocortical lesions and Pavlovian conditioning, Physiol. Behav., 8 (1972) 915-926. 6 0 a k l e y , D. A. and Russell, I. S., Role of cortex in Pavlovian discrimination learning, PhysioL Behav., 15 (1975) 315-321. 7 0 a k l e y , D. A. and Russell, I. S., Performance ofneodecorticated rabbitsin a Free-operant situation, Physiol. Behav., 20 (1978) 157-170. 8 0 a k l e y , D. A. and Russell, I. S., Manipulandum identification in o!0erant behaviour in neodecorticate rabbits, Physiol. Behav., in press. 9 Page, E. B., Ordered hypotheses for multiple treatments: A significance test for linear ranks, J. Amer. Statist. Ass., 58 (1963) 216-230. 10 Siegel, S., Non-parametric Statistics for the Behavioural Sciences, New York, McGraw-Hill, 1956, ll6pp.