Brain Research, 169 (1979) 421--431 © Elsevier/North-HollandBiomedicalPress
421
OPERANT CONDITIONING OF VERTICAL EYE MOVEMENTS WITHOUT VISUAL FEEDBACK IN THE MIDPONTINE PRETRIGEMINAL CAT
SHIRO IKEGAMI, SHINKO NISHIOKA and HIROSHI KAWAMURA*
Laboratory of Physiological Psychology and Laboratory of Neurophysiology, Mitsubishi-Kasei Institute of Life Sciences, 11 Minamiooya, Machida-shi, Tokyo 194 (Japan)
(Accepted October 19th, 1978)
SUMMARY An operant conditioning of vertical eye movements was achieved in the midpontine pretrigeminal cat in total darkness by contingent reinforcement of spontaneous eye movements with lateral hypothalamic (LHT) reward stimulation, when each movement (upward direction was chosen in this experiment) exceeded a preset amplitude. However, the response rates in the dark were lower than those in the light and the time to reach the peak response rate was much longer. Recording of evoked potentials to optic chiasma (OC) stimulation revealed enhancement of late components of the visual cortex (VC) and superior colliculus (SC) responses in relation to eye movements. Sequential records of the averaged evoked responses associated with eye movements indicated that the amplitudes of the late components of the VC and SC waves gradually increased in the course of establishment of the operant conditioning, and decreased gradually during extinction. In a yoked control test, increase in amplitudes of the late components was much less significant during non-contingent reinforcement given independently of the eye movements. These results suggest that 'corollary discharge' may play a critical role as a cue in acquisition of the operant conditioning of vertical eye movements when visual feedback is absent in total darkness.
INTRODUCTION In the midpontine pretrigeminal cat, applying as a reward stimulus a weak lateral hypothalamic electrical stimulation which by itself did not induce any marked eye movement, an operant conditioning of vertical eye movements including differentiation was obtained 1~. However, a question arises as to what sort of signal the cat utilizes * To whomcorrespondenceshould be addressed.
422 as a cue for achievement of the operant conditioning. In such a preparation, the cat is supposed to have only two external sensory inputs, namely visual and olfactory ~7. Since an olfactory signal would not be expected to have an effect on this conditioning, visual stimuli from the external environment should have a great value. Another possibility is a proprioceptive feedback from the oculomotor (III) and trochlear (IV) nerves which innervate external ocular muscles except the lateral rectus. However, there is currently no evidence of direct proprioceptive feedback from III and 1V nerves to the upper brain stem. Available data indicate that an afferent pathway from these extraocular muscles is via the trigeminal nerve roots 2-z,7. Therefore, in transection of the brain stem rostral to the entry of trigeminal nerve roots, no muscle afferents would go to the forebrain. Thus, proprioceptive feedback from extraocular muscles arising in eye movements should be, if not totally absent, very limited in this preparation. An important residual source of sensory feedback in this cat is displacement of the retinal image associated with eye movements. It is therefore important to know what signal accompanies each movement when no visual signal can be elicited in total darkness. In these conditions, the only likely cue from the eye movement could be an associated corollary discharge or, in other words, brain activity associated with generation o[ the eye movement. In this study we will present findings suggesting the possibility of participation of the corollary discharge in operant conditioning which appeared as changes in amplitude of visual evoked potentials during conditioning. A preliminary report of this investigation has been presented lz. MATERIALS AND METHODS Data were obtained from 35 experimentally naive adult cats whose brain stems were transected under ether anesthesia in front of the entry of the trigeminal roots. Experimental methods were as described in the preceding paper 12. To block extraneous visual stimuli, the cat was shielded by a black curtain with a small opening through which eye movements were monitored by a T.V. camera. A bipolar concentric electrode was located in the lateral hypothalamus (LHT). In the second group of the cats, a bipolar concentric electrode was inserted into the optic chiasma (OC) for stimulation. Two concentric recording electrodes were placed ipsilaterally in area 17 of the visual cortex (VC) and in the upper layer of the superior colliculus (SC) (A 2.0, L 2.0, V 4.0), respectively monitoring typical evoked potentials ls,26 to optic chiasma stimulation (0.05 msec pulse width) on a Tektronix dual-beam oscilloscope. When the cat was able to follow a moving visual stimulus with vertical eye movements after several hours of postoperative recovery, both eyes weCe covered by cups with black vinyl tape and its head and body were completely covered with thick black cloth inside the black curtain. Also, the experimental room was darkened. Adaptation for more than 1 h preceded the experiment. In this total darkness, a L H T stimulus intensity was determined for each cat that was below the threshold for eye movements by L H T stimulation alone. The first group of experiments included the following procedures: a control recording of the operant level of spontaneous eye movements for 20-30 min; conditioning with a continuous reinforcement schedule for
423 60-120 min; extinction for 40-60 min; reconditioning for 60 min; and final extinction for 40-60 min and a forced L H T stimulation for 20-30 min, with the L H T stimulated every 5 sec without a contingent relationship to eye movements. During the conditioning sessions, the L H T stimulus intensity was increased by 1-2 V if response rates were low. Also, a lock-out time of 1 sec was set between two successive trigger pulses for L H T stimulation. At the conclusion of these procedures in the dark, the eye cups and black covers were removed and room illumination restored. Under normal lighted condition, these procedures were repeated after more than 30 min (usually 50 min) of adaptation. In the second group of cats, evoked potentials in VC and SC to OC stimulation were observed during the same experimental procedures as in the first group. The VC and SC evoked responses were displayed by triggering the OC stimulation with a delay of 5 msec from the start of the oscilloscope sweep, whenever an upward eye movement exceeded a reinforcement level, and L H T stimulation started 495 msec later. In most cases, the OC stimulation was given 100-150 msec after the onset of each eye movement. A PDP-12 digital computer was used for averaging VC and SC potentials until N ( = 8) sweeps had been summed, and then these averaged potentials were stored on a data tape. After a short waiting period, the averaging procedure was repeated successively throughout the experimental sessions. In some cats, each evoked potential in VC and SC that was associated with an eye movement was photographed sequentially. All data were recorded on a TEAC data recorder and subsequently displayed and photographed, if necessary. Statistical evaluation of the data was made with Student's t-test. After all experimental sessions, electrode tip sites were verified histologically. RESULTS Conditioning Of eye movements in darkness In total darkness the cats acquired an operant conditioning of vertical eye movements, although they had no vision. Fig. I shows a typical process of the operant conditioning in the dark taken from a cat belonging to the first group. The average response rate per min in darkness was 3.7 with the reinforcement intensity of 2 V, which increased to 5.9 with 3 V. They were significantly higher than 0.75 (P < 0.001) which was the operant level before the conditioning. However, after conditioning the response rate during non-contingent L H T stimulation at a rate of 1/5 sec increased to 3.7, but decreased with further testing. This rate was significantly lower than that during reinforcement (P < 0.001), although the forced stimulation rate (1/5 sec) was about twice as high as L H T stimulation during contingent reinforcement with 3 V. This finding indicated that such a significant increase in response rate during conditioning was primarily dependent on the reinforcement contingency and not on mere elevation of brain excitability. In the light the response rate increased 2.4 times as much as that in the dark, even with a lower stimulus intensity of 2 V. Results obtained from 4 cats in the first group are shown in Fig. 2. In all cats the time to reach a peak response rate during conditioning and the time for return to the operant level during extinction were slower in the dark than in the lightl
424
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Fig. 1. Eye movement responses during conditioning andextinction in the dark and light. Mean response numbers per min were plotted every 2 min. Filled circles and solid line, during reinforcement periods; empty circles and broken line, without reinforcement; crosses with solid line, during forced hypothalamic stimulation at the rate of 1/5 sec.
425
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Fig. 2. Summarized results of the operant conditioning in the dark and light. Dark columns show mean responses per min during each session in total darkness and white columns, in the light. The number on top of each column indicates the percentage of responses compared with the mean response rate during the conditioning session in the light. The number under each column indicates stimulation voltage. Asterisks denote forced LHT stimulation at the rate of 1/5 sec. Data were taken from 4 cats.
VC and SC responses in the dark To investigate 'cue information' occurring in eye movements in the establishment of conditioned responses in the dark, the VC and SC responses evoked by OC stimulation in the second group of cats were analyzed in relation to eye movements. Simultaneous records of the VC and SC responses were obtained by stimulating the OC at increasing delays from the time when the upward E O G exceeded the reinforcement level. As shown in Fig. 3, the VC and SC responses associated with onset of the conditioned eye movements (B) were significantly facilitated compared to the control level (A, P < 0.001). On the other hand, at the times of L H T stimulation (C and D), facilitation was less compared to a peak at the B point (P < 0.001). This clearly shows that the enhancement of the VC and SC responses was dependent on the onset of eye movements, and not on the L H T stimulation. To clarify how amplitudes of late components in VC and SC responses associated with eye movements were modified over entire experimental sessions, these responses were successively averaged for every 8 eye movements which exceeded the preset reinforcement level. Fig. 4 illustrates a sequence of operant conditioning and extinction, showing changes in amplitudes of VC and SC responses. This cat displayed a significant increase in amplitudes of VC and SC late components over the operant level after 20 min reinforcement (P < 0.001). This increase occurred gradually during the conditioning session and reached a higher peak during reconditioning. During extinction, VC and SC responses decreased from peak values reached during conditioning and reconditioning sessions (P < 0.005 and P < 0.001), returning to the operant level after about an hour. During the period of L H T stimulation with regular
426 REINF01~MENT~""--"'~
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Fig. 3. Changes in the VC and SC responses to the OC stimulation in relation with conditioned eye movements and LHT stimulation. A : control responses to the OC stimulation at 0.2 Hz in the absence of the eye movement. B: at the time when eye movements exceeded a reinforcement level. C: during the LHT stimulation with a delay of 750 msec from the B point. D: at the end of the LHT stimulation with a delay of 1 sec from the B point. Circles with solid line show averaged amplitude of 50 late components of VC response, and triangles with broken line, of SC response. On the right side the VC (upper traces) and SC (lower traces) evoked potentials for each point were demonstrated by superposition of l0 successive records. A small dot indicates a single shock to the OC.
intervals, each increase o f VC a n d SC responses was m u c h lower t h a n the increase o b s e r v e d d u r i n g the r e c o n d i t i o n i n g session (P < 0.001). Increase in a m p l i t u d e s o f VC a n d SC responses d u r i n g c o n d i t i o n i n g occurred in 6 cats used in this type o f experiment. These cats showed a m a r k e d increase in a m p l i t u d e o f V C response, by 1 9 . 0 - 9 2 . 7 ~ over the o p e r a n t level d u r i n g r e i n f o r c e m e n t periods. Increase in SC response was f r o m 18.8 to 65.1 ~ . F a c i l i t a t i o n o f V C a n d SC responses was m o r e obvious in the light t h a n in the d a r k . E E G stages s h o w n in the b o t t o m h a l f o f Fig. 4 are illustrated in Fig. 5. E a c h a l p h a b e t i c a l sign in Fig. 5 indicates time in Fig. 4 when c o r r e s p o n d i n g records were taken. E n h a n c e m e n t o f late c o m p o n e n t s o f e v o k e d responses does n o t necessarily p a r a l l e l levels o f E E G arousal. Yoked control test To test the possibility t h a t the L H T s t i m u l a t i o n might cause a general,elevation o f excitability in the VC a n d SC systems with no r e l a t i o n to the contingent reinforcement, a y o k e d c o n t r o l e x p e r i m e n t was p e r f o r m e d in a cat in which the O C s t i m u l a t i o n p a i r e d with the L H T was delivered n o n - c o n t i n g e n t l y with respect to eye m o v e m e n t s . S t i m u l a t i o n followed a sequence o f r e i n f o r c e m e n t t a k e n f r o m a n o t h e r cat r e c o r d e d on m a g n e t i c t a p e d u r i n g the previous experiment. E a c h signal pulse
427 producing a train of L H T stimuli triggered a stimulator to the OC, eliciting VC and SC responses. Then, with a delay of 495 msec, a stimulus was triggered to the L H T of the 'test' animal. Fig. 6 demonstrates that the VC response during non-contingent reinforcement that was independent of eye movements showed no significant increase in amplitude above the operant level. The amplitude of the SC response even showed a slight decrease (P < 0.025). However, when the normal experimental procedure with contingent stimulation was introduced, a marked enhancement of VC and SC responses associated with eye movements was obtained. Amplitude increased by 24.2 % (P < 0.005) and 47.2 % (P < 0.025) respectively over the operant level. This was even greater in the reconditioning session, where amplitudes of VC and SC responses increased by 63.1% (P < 0.001) and 75.4 % (P < 0.005), respectively. These results indicate that the increased amplitudes of VC and SC responses during conditioning sessions depend primarily on the reinforcement contingency, corresponding well to the establishment of conditioned eye movements.
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428
Correlation between VC and SC responses F o r the two cats shown in Figs. 4 a n d 6, c o r r e l a t i o n coefficients between the VC a n d SC responses were 0.91 (No. 193) a n d 0.52 (No. 198) d u r i n g the conditioning. These values were higher t h a n those o f 0.71 a n d 0.22 d u r i n g the r e c o n d i t i o n i n g session. This m a y suggest that, in the course o f initial c o n d i t i o n i n g , excitability changes o f the V C a n d SC showed a closer interrelationship, whereas d u r i n g r e c o n d i t i o n i n g their c o r r e l a t i o n m a y be less significant as the increase in a m p l i t u d e reached a peak.
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421
OPERANT CONDITIONING OF VERTICAL EYE MOVEMENTS WITHOUT VISUAL FEEDBACK IN THE MIDPONTINE PRETRIGEMINAL CAT
SHIRO IKEGAMI, SHINKO NISHIOKA and HIROSHI KAWAMURA*
Laboratory of Physiological Psychology and Laboratory of Neurophysiology, Mitsubishi-Kasei Institute of Life Sciences, 11 Minamiooya, Machida-shi, Tokyo 194 (Japan)
(Accepted October 19th, 1978)
SUMMARY An operant conditioning of vertical eye movements was achieved in the midpontine pretrigeminal cat in total darkness by contingent reinforcement of spontaneous eye movements with lateral hypothalamic (LHT) reward stimulation, when each movement (upward direction was chosen in this experiment) exceeded a preset amplitude. However, the response rates in the dark were lower than those in the light and the time to reach the peak response rate was much longer. Recording of evoked potentials to optic chiasma (OC) stimulation revealed enhancement of late components of the visual cortex (VC) and superior colliculus (SC) responses in relation to eye movements. Sequential records of the averaged evoked responses associated with eye movements indicated that the amplitudes of the late components of the VC and SC waves gradually increased in the course of establishment of the operant conditioning, and decreased gradually during extinction. In a yoked control test, increase in amplitudes of the late components was much less significant during non-contingent reinforcement given independently of the eye movements. These results suggest that 'corollary discharge' may play a critical role as a cue in acquisition of the operant conditioning of vertical eye movements when visual feedback is absent in total darkness.
INTRODUCTION In the midpontine pretrigeminal cat, applying as a reward stimulus a weak lateral hypothalamic electrical stimulation which by itself did not induce any marked eye movement, an operant conditioning of vertical eye movements including differentiation was obtained 1~. However, a question arises as to what sort of signal the cat utilizes * To whomcorrespondenceshould be addressed.
422 as a cue for achievement of the operant conditioning. In such a preparation, the cat is supposed to have only two external sensory inputs, namely visual and olfactory ~7. Since an olfactory signal would not be expected to have an effect on this conditioning, visual stimuli from the external environment should have a great value. Another possibility is a proprioceptive feedback from the oculomotor (III) and trochlear (IV) nerves which innervate external ocular muscles except the lateral rectus. However, there is currently no evidence of direct proprioceptive feedback from III and 1V nerves to the upper brain stem. Available data indicate that an afferent pathway from these extraocular muscles is via the trigeminal nerve roots 2-z,7. Therefore, in transection of the brain stem rostral to the entry of trigeminal nerve roots, no muscle afferents would go to the forebrain. Thus, proprioceptive feedback from extraocular muscles arising in eye movements should be, if not totally absent, very limited in this preparation. An important residual source of sensory feedback in this cat is displacement of the retinal image associated with eye movements. It is therefore important to know what signal accompanies each movement when no visual signal can be elicited in total darkness. In these conditions, the only likely cue from the eye movement could be an associated corollary discharge or, in other words, brain activity associated with generation o[ the eye movement. In this study we will present findings suggesting the possibility of participation of the corollary discharge in operant conditioning which appeared as changes in amplitude of visual evoked potentials during conditioning. A preliminary report of this investigation has been presented lz. MATERIALS AND METHODS Data were obtained from 35 experimentally naive adult cats whose brain stems were transected under ether anesthesia in front of the entry of the trigeminal roots. Experimental methods were as described in the preceding paper 12. To block extraneous visual stimuli, the cat was shielded by a black curtain with a small opening through which eye movements were monitored by a T.V. camera. A bipolar concentric electrode was located in the lateral hypothalamus (LHT). In the second group of the cats, a bipolar concentric electrode was inserted into the optic chiasma (OC) for stimulation. Two concentric recording electrodes were placed ipsilaterally in area 17 of the visual cortex (VC) and in the upper layer of the superior colliculus (SC) (A 2.0, L 2.0, V 4.0), respectively monitoring typical evoked potentials ls,26 to optic chiasma stimulation (0.05 msec pulse width) on a Tektronix dual-beam oscilloscope. When the cat was able to follow a moving visual stimulus with vertical eye movements after several hours of postoperative recovery, both eyes weCe covered by cups with black vinyl tape and its head and body were completely covered with thick black cloth inside the black curtain. Also, the experimental room was darkened. Adaptation for more than 1 h preceded the experiment. In this total darkness, a L H T stimulus intensity was determined for each cat that was below the threshold for eye movements by L H T stimulation alone. The first group of experiments included the following procedures: a control recording of the operant level of spontaneous eye movements for 20-30 min; conditioning with a continuous reinforcement schedule for
423 60-120 min; extinction for 40-60 min; reconditioning for 60 min; and final extinction for 40-60 min and a forced L H T stimulation for 20-30 min, with the L H T stimulated every 5 sec without a contingent relationship to eye movements. During the conditioning sessions, the L H T stimulus intensity was increased by 1-2 V if response rates were low. Also, a lock-out time of 1 sec was set between two successive trigger pulses for L H T stimulation. At the conclusion of these procedures in the dark, the eye cups and black covers were removed and room illumination restored. Under normal lighted condition, these procedures were repeated after more than 30 min (usually 50 min) of adaptation. In the second group of cats, evoked potentials in VC and SC to OC stimulation were observed during the same experimental procedures as in the first group. The VC and SC evoked responses were displayed by triggering the OC stimulation with a delay of 5 msec from the start of the oscilloscope sweep, whenever an upward eye movement exceeded a reinforcement level, and L H T stimulation started 495 msec later. In most cases, the OC stimulation was given 100-150 msec after the onset of each eye movement. A PDP-12 digital computer was used for averaging VC and SC potentials until N ( = 8) sweeps had been summed, and then these averaged potentials were stored on a data tape. After a short waiting period, the averaging procedure was repeated successively throughout the experimental sessions. In some cats, each evoked potential in VC and SC that was associated with an eye movement was photographed sequentially. All data were recorded on a TEAC data recorder and subsequently displayed and photographed, if necessary. Statistical evaluation of the data was made with Student's t-test. After all experimental sessions, electrode tip sites were verified histologically. RESULTS Conditioning Of eye movements in darkness In total darkness the cats acquired an operant conditioning of vertical eye movements, although they had no vision. Fig. I shows a typical process of the operant conditioning in the dark taken from a cat belonging to the first group. The average response rate per min in darkness was 3.7 with the reinforcement intensity of 2 V, which increased to 5.9 with 3 V. They were significantly higher than 0.75 (P < 0.001) which was the operant level before the conditioning. However, after conditioning the response rate during non-contingent L H T stimulation at a rate of 1/5 sec increased to 3.7, but decreased with further testing. This rate was significantly lower than that during reinforcement (P < 0.001), although the forced stimulation rate (1/5 sec) was about twice as high as L H T stimulation during contingent reinforcement with 3 V. This finding indicated that such a significant increase in response rate during conditioning was primarily dependent on the reinforcement contingency and not on mere elevation of brain excitability. In the light the response rate increased 2.4 times as much as that in the dark, even with a lower stimulus intensity of 2 V. Results obtained from 4 cats in the first group are shown in Fig. 2. In all cats the time to reach a peak response rate during conditioning and the time for return to the operant level during extinction were slower in the dark than in the lightl
424
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Fig. 1. Eye movement responses during conditioning andextinction in the dark and light. Mean response numbers per min were plotted every 2 min. Filled circles and solid line, during reinforcement periods; empty circles and broken line, without reinforcement; crosses with solid line, during forced hypothalamic stimulation at the rate of 1/5 sec.
425
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Fig. 2. Summarized results of the operant conditioning in the dark and light. Dark columns show mean responses per min during each session in total darkness and white columns, in the light. The number on top of each column indicates the percentage of responses compared with the mean response rate during the conditioning session in the light. The number under each column indicates stimulation voltage. Asterisks denote forced LHT stimulation at the rate of 1/5 sec. Data were taken from 4 cats.
VC and SC responses in the dark To investigate 'cue information' occurring in eye movements in the establishment of conditioned responses in the dark, the VC and SC responses evoked by OC stimulation in the second group of cats were analyzed in relation to eye movements. Simultaneous records of the VC and SC responses were obtained by stimulating the OC at increasing delays from the time when the upward E O G exceeded the reinforcement level. As shown in Fig. 3, the VC and SC responses associated with onset of the conditioned eye movements (B) were significantly facilitated compared to the control level (A, P < 0.001). On the other hand, at the times of L H T stimulation (C and D), facilitation was less compared to a peak at the B point (P < 0.001). This clearly shows that the enhancement of the VC and SC responses was dependent on the onset of eye movements, and not on the L H T stimulation. To clarify how amplitudes of late components in VC and SC responses associated with eye movements were modified over entire experimental sessions, these responses were successively averaged for every 8 eye movements which exceeded the preset reinforcement level. Fig. 4 illustrates a sequence of operant conditioning and extinction, showing changes in amplitudes of VC and SC responses. This cat displayed a significant increase in amplitudes of VC and SC late components over the operant level after 20 min reinforcement (P < 0.001). This increase occurred gradually during the conditioning session and reached a higher peak during reconditioning. During extinction, VC and SC responses decreased from peak values reached during conditioning and reconditioning sessions (P < 0.005 and P < 0.001), returning to the operant level after about an hour. During the period of L H T stimulation with regular
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Fig. 3. Changes in the VC and SC responses to the OC stimulation in relation with conditioned eye movements and LHT stimulation. A : control responses to the OC stimulation at 0.2 Hz in the absence of the eye movement. B: at the time when eye movements exceeded a reinforcement level. C: during the LHT stimulation with a delay of 750 msec from the B point. D: at the end of the LHT stimulation with a delay of 1 sec from the B point. Circles with solid line show averaged amplitude of 50 late components of VC response, and triangles with broken line, of SC response. On the right side the VC (upper traces) and SC (lower traces) evoked potentials for each point were demonstrated by superposition of l0 successive records. A small dot indicates a single shock to the OC.
intervals, each increase o f VC a n d SC responses was m u c h lower t h a n the increase o b s e r v e d d u r i n g the r e c o n d i t i o n i n g session (P < 0.001). Increase in a m p l i t u d e s o f VC a n d SC responses d u r i n g c o n d i t i o n i n g occurred in 6 cats used in this type o f experiment. These cats showed a m a r k e d increase in a m p l i t u d e o f V C response, by 1 9 . 0 - 9 2 . 7 ~ over the o p e r a n t level d u r i n g r e i n f o r c e m e n t periods. Increase in SC response was f r o m 18.8 to 65.1 ~ . F a c i l i t a t i o n o f V C a n d SC responses was m o r e obvious in the light t h a n in the d a r k . E E G stages s h o w n in the b o t t o m h a l f o f Fig. 4 are illustrated in Fig. 5. E a c h a l p h a b e t i c a l sign in Fig. 5 indicates time in Fig. 4 when c o r r e s p o n d i n g records were taken. E n h a n c e m e n t o f late c o m p o n e n t s o f e v o k e d responses does n o t necessarily p a r a l l e l levels o f E E G arousal. Yoked control test To test the possibility t h a t the L H T s t i m u l a t i o n might cause a general,elevation o f excitability in the VC a n d SC systems with no r e l a t i o n to the contingent reinforcement, a y o k e d c o n t r o l e x p e r i m e n t was p e r f o r m e d in a cat in which the O C s t i m u l a t i o n p a i r e d with the L H T was delivered n o n - c o n t i n g e n t l y with respect to eye m o v e m e n t s . S t i m u l a t i o n followed a sequence o f r e i n f o r c e m e n t t a k e n f r o m a n o t h e r cat r e c o r d e d on m a g n e t i c t a p e d u r i n g the previous experiment. E a c h signal pulse
427 producing a train of L H T stimuli triggered a stimulator to the OC, eliciting VC and SC responses. Then, with a delay of 495 msec, a stimulus was triggered to the L H T of the 'test' animal. Fig. 6 demonstrates that the VC response during non-contingent reinforcement that was independent of eye movements showed no significant increase in amplitude above the operant level. The amplitude of the SC response even showed a slight decrease (P < 0.025). However, when the normal experimental procedure with contingent stimulation was introduced, a marked enhancement of VC and SC responses associated with eye movements was obtained. Amplitude increased by 24.2 % (P < 0.005) and 47.2 % (P < 0.025) respectively over the operant level. This was even greater in the reconditioning session, where amplitudes of VC and SC responses increased by 63.1% (P < 0.001) and 75.4 % (P < 0.005), respectively. These results indicate that the increased amplitudes of VC and SC responses during conditioning sessions depend primarily on the reinforcement contingency, corresponding well to the establishment of conditioned eye movements.
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Correlation between VC and SC responses F o r the two cats shown in Figs. 4 a n d 6, c o r r e l a t i o n coefficients between the VC a n d SC responses were 0.91 (No. 193) a n d 0.52 (No. 198) d u r i n g the conditioning. These values were higher t h a n those o f 0.71 a n d 0.22 d u r i n g the r e c o n d i t i o n i n g session. This m a y suggest that, in the course o f initial c o n d i t i o n i n g , excitability changes o f the V C a n d SC showed a closer interrelationship, whereas d u r i n g r e c o n d i t i o n i n g their c o r r e l a t i o n m a y be less significant as the increase in a m p l i t u d e reached a peak.
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