Electroencephalography and Clinical Neurophysiology, 1977, 4 2 : 3 5 5 - - 3 6 3
355
© Elsevier/North-Holland Scientific Publishers Ltd.
A CORTICAL EVOKED P O T E N T I A L T H A T R E F L E C T S T H E CONDITIONED, POSITIVE INCENTIVE VALUE OF THE STIMULUS. II. DRIVE MOTIVATION (H U N G E R) * E.S. BOYD, E.H. BOYD and L.E. BROWN
Department of Pharmacology and Toxicology, University of Rochester School of Medicine and Dentistry, Rochester, N.Y. 14642 (U.S.A.) (Accepted for publication: June 14, 1976)
In a preceding paper (Boyd et al. 1977a) we described a cortical, surface negative, wave in the squirrel m o n k e y evoked by t one cues t h a t signalled the availability o f a f ood reward. We concluded t ha t this wave, which for ease of reference we have called an M-wave, reflected cortical activity somewhere in the stimulus--response sequence between the recognition of the meaning of the cue and the decision to act. We first became seriously interested in this evoked wave when we noticed t hat it was smaller if the animal did n o t respond to the cue than if he did, and t hat it decreased in amplitude as any given session progressed. The influence of drive motivation (hunger) on the M-wave will be presented in this paper, and that o f manipulative motivation and the value o f the reward, in the following paper (Boyd et al. 1977b).
Methods The methods were similar to those described previously (Boyd et al. 1977a). In brief, bipolar, transcortical recording electrodes were implanted in male squirrel m o n k e y s (Saimiri sciureus) unde r pentobarbital anesthesia. The animals t he n learned t h a t t h e y * This investigation was supported in part by U.S. Public Health Service General Research Support Grant to the University of Rochester.
would be rewarded with a 75 mg banana flavored pellet if they pressed a bar within 2 sec after a 10 msec tone cue. On the standard schedule, 150 t o n e cues were presented at varying intervals (mean, 22 sec) and the animal was allowed 1 1/8 min of continuous rei n f o r c e m e n t (CRF) after every 50 cues. In part of the work reported here, the average rate of cue presentation was increased, as needed, to approximately double the reinf o r c e m e n t rate. Some testing sessions were also prolonged, as needed, to obtain evoked activity after the animal had ceased to respond behaviorally to the cues. Animals were also tested, alternately, with and w i t h o u t the usual 24 h fast period before a test session.
Results
Changes within a test session Once an animal was well trained, failures to respond to the tone cue could be divided roughly into two categories. In the first category were single, or occasionally double, misses, spaced r a n d o m l y t h r o u g h o u t the session. These ranged from as low as 0 out of 150 cues to as high as 50--60 out of 150 cues. These have been called " n o t responded t o " . In all animals studied, M-waves evoked by cues " n o t responded t o " tended to be significantly smaller than those evoked by cues responded to. In the second category were longer runs of misses, usually toward, or at, the
356
E.S. BOYD ET A L
end of a session. Such runs ranged in d u r a t i o n f r o m 2--3 m i n up to as m u c h as the last third o f the session ( a b o u t 15 min). T h e s e failures have b e e n called " n o r e s p o n d i n g " . " N o res p o n d i n g " o c c u r r e d r a t h e r i n f r e q u e n t l y and, in o r d e r to m a k e m e a s u r e m e n t s during it, s o m e sessions w i t h s o m e animals were e x t e n d ed until the animal did cease to r e s p o n d . An e x a m p l e is s h o w n in Fig. 1. T h e M-waves e v o k e d b y cues during periods o f " n o res p o n d i n g " were even smaller t h a n t h o s e evoked b y r a n d o m cues n o t r e s p o n d e d to, s o m e t i m e s being u n d e t e c t a b l e . Average results are given in T a b l e I. In general, the n u m b e r s in T a b l e I for " n o r e s p o n d i n g " are m a x i m a l
since it was o f t e n q u e s t i o n a b l e w h e t h e r the small, r e m a i n i n g e v o k e d activity t h a t was m e a s u r e d was real a n d / o r still r e p r e s e n t e d Mwave activity. As each session p r o g r e s s e d t h e r e was a definite t e n d e n c y for the a m p l i t u d e o f the e v o k e d M-wave to decrease. This was a n a l y z e d , in f o u r animals, b y dividing each o f 5 t o 7 sessions into four sequential periods. O n l y activity e v o k e d b y cues to w h i c h the a n i m a l res p o n d e d b e h a v i o r a l l y was averaged a n d an att e m p t was m a d e to divide the n u m b e r o f e v o k e d responses as evenly as possible a m o n g the f o u r sequential parts o f the session. In all cases, the a m p l i t u d e o f t h e M-wave d e c r e a s e d
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i:/ Fig. 1. A session w i t h Phil, e x t e n d e d u n t i l he s t o p p e d r e s p o n d i n g t o t h e t o n e cues. A t t h e t o p is t h e behavioral record. T h e u p p e r line traveled u p w a r d as t h e a n i m a l bar-pressed, a n d m a d e d o w n w a r d m a r k s at each reinforcem e n t . T h e l o w e r line s h o w s t h e s e q u e n c e o f the schedule, consisting o f 50 t o n e cues at varying intervals ( m e a n , 22 sec), a n d 1 1/8 rain o f C R F , i n d i c a t e d b y t h e d o w n w a r d p a r t s o f t h e line. Below is t h e activity e v o k e d b y t h e cues in r i g h t a n d left p o s t - a r c u a t e c o r t e x , s e p a r a t e d i n t o averages for: (a) cues t h a t were r e s p o n d e d t o ; (b) cues t h a t were n o t r e s p o n d e d t o ; and (c) t h e last 10 cues, after t h e a n i m a l ceased r e s p o n d i n g . The bars s h o w t h e time o f cue p r e s e n t a t i o n . T h e c a l i b r a t i o n s o n t h e left, for t h e behavioral record, r e p r e s e n t 10 rain and 100 responses; t h o s e on the right, for t h e e v o k e d activity, r e p r e s e n t 100 msec and 50 p V . Time c o n s t a n t , 600 msec. In this, a n d s u b s e q u e n t figures, n u m b e r s at the e n d s o f average e v o k e d responses are the n u m b e r o f responses in t h e average, a n d n e g a t i v i t y at the cortical surface is p l o t t e d upward•
E V O K E D P O T E N T I A L A N D I N C E N T I V E . II.
357
TABLE I Changes in t h e a m p l i t u d e o f e v o k e d M-waves in p o s t - a r c u a t e c o r t e x : (1) w h e n t h e a n i m a l i n t e r m i t t e n t l y failed to r e s p o n d b e h a v i o r a l l y to t h e cue ( n o t r e s p o n d e d t o ) ; a n d (2) w h e n t h e a n i m a l ceased r e s p o n d i n g for periods of 2--15 min (no responding). Animal and hemisphere
N o t r e s p o n d e d to X 1 0 0 * R e s p o n d e d to
P ~
355
© Elsevier/North-Holland Scientific Publishers Ltd.
A CORTICAL EVOKED P O T E N T I A L T H A T R E F L E C T S T H E CONDITIONED, POSITIVE INCENTIVE VALUE OF THE STIMULUS. II. DRIVE MOTIVATION (H U N G E R) * E.S. BOYD, E.H. BOYD and L.E. BROWN
Department of Pharmacology and Toxicology, University of Rochester School of Medicine and Dentistry, Rochester, N.Y. 14642 (U.S.A.) (Accepted for publication: June 14, 1976)
In a preceding paper (Boyd et al. 1977a) we described a cortical, surface negative, wave in the squirrel m o n k e y evoked by t one cues t h a t signalled the availability o f a f ood reward. We concluded t ha t this wave, which for ease of reference we have called an M-wave, reflected cortical activity somewhere in the stimulus--response sequence between the recognition of the meaning of the cue and the decision to act. We first became seriously interested in this evoked wave when we noticed t hat it was smaller if the animal did n o t respond to the cue than if he did, and t hat it decreased in amplitude as any given session progressed. The influence of drive motivation (hunger) on the M-wave will be presented in this paper, and that o f manipulative motivation and the value o f the reward, in the following paper (Boyd et al. 1977b).
Methods The methods were similar to those described previously (Boyd et al. 1977a). In brief, bipolar, transcortical recording electrodes were implanted in male squirrel m o n k e y s (Saimiri sciureus) unde r pentobarbital anesthesia. The animals t he n learned t h a t t h e y * This investigation was supported in part by U.S. Public Health Service General Research Support Grant to the University of Rochester.
would be rewarded with a 75 mg banana flavored pellet if they pressed a bar within 2 sec after a 10 msec tone cue. On the standard schedule, 150 t o n e cues were presented at varying intervals (mean, 22 sec) and the animal was allowed 1 1/8 min of continuous rei n f o r c e m e n t (CRF) after every 50 cues. In part of the work reported here, the average rate of cue presentation was increased, as needed, to approximately double the reinf o r c e m e n t rate. Some testing sessions were also prolonged, as needed, to obtain evoked activity after the animal had ceased to respond behaviorally to the cues. Animals were also tested, alternately, with and w i t h o u t the usual 24 h fast period before a test session.
Results
Changes within a test session Once an animal was well trained, failures to respond to the tone cue could be divided roughly into two categories. In the first category were single, or occasionally double, misses, spaced r a n d o m l y t h r o u g h o u t the session. These ranged from as low as 0 out of 150 cues to as high as 50--60 out of 150 cues. These have been called " n o t responded t o " . In all animals studied, M-waves evoked by cues " n o t responded t o " tended to be significantly smaller than those evoked by cues responded to. In the second category were longer runs of misses, usually toward, or at, the
356
E.S. BOYD ET A L
end of a session. Such runs ranged in d u r a t i o n f r o m 2--3 m i n up to as m u c h as the last third o f the session ( a b o u t 15 min). T h e s e failures have b e e n called " n o r e s p o n d i n g " . " N o res p o n d i n g " o c c u r r e d r a t h e r i n f r e q u e n t l y and, in o r d e r to m a k e m e a s u r e m e n t s during it, s o m e sessions w i t h s o m e animals were e x t e n d ed until the animal did cease to r e s p o n d . An e x a m p l e is s h o w n in Fig. 1. T h e M-waves e v o k e d b y cues during periods o f " n o res p o n d i n g " were even smaller t h a n t h o s e evoked b y r a n d o m cues n o t r e s p o n d e d to, s o m e t i m e s being u n d e t e c t a b l e . Average results are given in T a b l e I. In general, the n u m b e r s in T a b l e I for " n o r e s p o n d i n g " are m a x i m a l
since it was o f t e n q u e s t i o n a b l e w h e t h e r the small, r e m a i n i n g e v o k e d activity t h a t was m e a s u r e d was real a n d / o r still r e p r e s e n t e d Mwave activity. As each session p r o g r e s s e d t h e r e was a definite t e n d e n c y for the a m p l i t u d e o f the e v o k e d M-wave to decrease. This was a n a l y z e d , in f o u r animals, b y dividing each o f 5 t o 7 sessions into four sequential periods. O n l y activity e v o k e d b y cues to w h i c h the a n i m a l res p o n d e d b e h a v i o r a l l y was averaged a n d an att e m p t was m a d e to divide the n u m b e r o f e v o k e d responses as evenly as possible a m o n g the f o u r sequential parts o f the session. In all cases, the a m p l i t u d e o f t h e M-wave d e c r e a s e d
z/n/7.1
RESPONDED
DID NOT RESPOND, AT END
DID NOT RESPOND TO TONE
TO TONE
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.
.
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.
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i:/ Fig. 1. A session w i t h Phil, e x t e n d e d u n t i l he s t o p p e d r e s p o n d i n g t o t h e t o n e cues. A t t h e t o p is t h e behavioral record. T h e u p p e r line traveled u p w a r d as t h e a n i m a l bar-pressed, a n d m a d e d o w n w a r d m a r k s at each reinforcem e n t . T h e l o w e r line s h o w s t h e s e q u e n c e o f the schedule, consisting o f 50 t o n e cues at varying intervals ( m e a n , 22 sec), a n d 1 1/8 rain o f C R F , i n d i c a t e d b y t h e d o w n w a r d p a r t s o f t h e line. Below is t h e activity e v o k e d b y t h e cues in r i g h t a n d left p o s t - a r c u a t e c o r t e x , s e p a r a t e d i n t o averages for: (a) cues t h a t were r e s p o n d e d t o ; (b) cues t h a t were n o t r e s p o n d e d t o ; and (c) t h e last 10 cues, after t h e a n i m a l ceased r e s p o n d i n g . The bars s h o w t h e time o f cue p r e s e n t a t i o n . T h e c a l i b r a t i o n s o n t h e left, for t h e behavioral record, r e p r e s e n t 10 rain and 100 responses; t h o s e on the right, for t h e e v o k e d activity, r e p r e s e n t 100 msec and 50 p V . Time c o n s t a n t , 600 msec. In this, a n d s u b s e q u e n t figures, n u m b e r s at the e n d s o f average e v o k e d responses are the n u m b e r o f responses in t h e average, a n d n e g a t i v i t y at the cortical surface is p l o t t e d upward•
E V O K E D P O T E N T I A L A N D I N C E N T I V E . II.
357
TABLE I Changes in t h e a m p l i t u d e o f e v o k e d M-waves in p o s t - a r c u a t e c o r t e x : (1) w h e n t h e a n i m a l i n t e r m i t t e n t l y failed to r e s p o n d b e h a v i o r a l l y to t h e cue ( n o t r e s p o n d e d t o ) ; a n d (2) w h e n t h e a n i m a l ceased r e s p o n d i n g for periods of 2--15 min (no responding). Animal and hemisphere
N o t r e s p o n d e d to X 1 0 0 * R e s p o n d e d to
P ~
