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Classical conditioning of the corneal reflex in the chronic decerebrate rat
Brain Research, 89 (1975) 337-340
337
'.CJ Elsewer Scientific Pubhshmg Company, Amsterdam - Printed m The Netherlands
Classical conditioning of the corneal reflex in the chronic decerebrate rat
THELMA A. LOVICK ANDANDRZEJ W ZBROZYNA Department ot Phy~tology, The Medtcal School, Untvers~ty of Birmingham, Birmingham B15 2TJ (Great Brttam)
(Accepted February 18th, 1975)
The rodent brain stem is able to integrate behavloural activities to such a great extent that after chronic decerebratlon, when the forebrain structures rostral to the superior colhcuh have been removed, the rat can exhibit a wide range of well coordinated behavloural patterns 4. It seemed worthwhile, therefore, to determine whether this type of preparation would be capable of a simple form of learning. Adult female rats (250-350 g) o f a Wlstar strain were decerebrated under Avertin anaesthesia (tribromoethanol, 0.65 ml/100 g of a 2.5~o solution l.p.) All neural tissue rostral to the superior colhculi was removed by aspiration (Fig. 1). The preparatlons were maintained by intragastric admimstratlon of an egg-milk-glucose mixture 3 times daily. Conditioning was started 5-7 days postoperatively. A puff of air to the cornea (unconditioned stimulus, UCS) was applied at the end of an 800 msec, 1000 Hz tone (conditioned stimulus, CS). A conditioned response (CR) was defined as a blink which occurred during the presentation of the CS but before the apphcation of the UCS. Spontaneous, conditioned and unconditioned blinks were noted by visual inspection. A control series of experiments in which 4 normal, unoperated rats were used was carried out to determine the characteristic pattern for conditioning of eyelid movements in the species. Each rat received 20 C S - U C S presentations in the course of each training session During the early training sessions there was a rapid increase in the number of conditioned blinks and a peak value was reached on the 3rd or 4th training session, i.e., after 60-80 C S - U C S presentations. Thereafter performance declined and stablhsed at a value which was 1 0 - 3 0 ~ below the peak value (Fig. 2, open circles). These results compare favourably with those of previous studies 1,3. The training schedule which produced learning in the intact rat - - 20 C S - U C S presentations per training session - - was ineffective when applied to the chronic decerebrate animal (Fig. 2, closed circles). However, a training schedule in which 40 CS UCS pairings were presented during each training session was effective In the 4 decerebrate rats which were tested using this schedule, the incidence of conditioned blinks gradually increased to a level ( 15-38 °/oocorrect responses) which was significantly higher (P < 0.05) than would have been expected from the spontaneous blink rate. With continued presentation of this pairing, up to 500 C S - U C S presentations, the
338
F~g 1 Pa~asag~ttal sectmn taken t r o m the lemnants ol the brain o f a c h m m c deccrchralc tat The graph of acqtlls]tlon of the conditioned corneal telte\ m th~s animal I~ s h o ~ n H~ I ig ~(
number of CRs gradually declined to non-s~gnlficant values. The results from one of the ammals m this group are Illustrated in F~g. 3A. A second group of" 4 decerebrate rats received 50 CS +UCS presentations during each training session. Once again each ammal attained significant conditioned response scores before its performance declined to a non-sigmficant ~alue. In 2 animals within this group, training was pursued
339 80 (b
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Fig. 2 O p e n c~rcles g r a p h o f a c q m s i t l o n of the c o n d i t i o n e d corneal reflex m a n intact rat w h m h recewed 20 C S - U C S p m r m g s d u n n g each training session. Filled circles: the results f r o m a c h r o m c decerebrate rat w h m h u n d e r w e n t a s]mdar training schedule a n d s h o w e d no s~gn o f c o n d m o n m g .
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10 12 14 16 18 20 22 24 26 28 30 32 34 36 3g Session Number
Ftg 3. A : s o h d line. g r a p h o f acqumltlon o f the c o n d i t i o n e d corneal reflex in a c h r o m c decerebrate rat w h m h received 40 C S - U C S pairings d u r i n g each t r a l m n g session. Broken hne" the results from a decerebrate rat w h m h received 40 u n p a i r e d p r e s e n t a t i o n s o f the CS a n d U C S d u r m g each training session. B a n d C: g r a p h s o f a c q m s m o n o f the c o n d m o n e d reflex m 2 decerebrate rats w h m h received 50 C S - U C S p m r m g s during each training session. O p e n trmngles indicate the training sessions m V,hlch the n u m b e r of b h n k s m a d e during the presentation of the tone was slgmficantly greater (P < 0.05) t h a n the n u m b e r expected f r o m the s p o n t a n e o u s b h n k rate
340 l'urther and led to ,t ,e~ond increase m the n u m b e r of CRs made I Flg 3B and ~ j However, the ne~. performance was not m a i n t a i n e d and the n u m b e r o f ( Rs dJ tarnished once moJe One a m m a l recm,,ed more prolonged t r a i n i n g (F~g. 3( t and a third peak appeared in the graph o f a c q m s m o n of the c o n d i t m n e d response As a control for p h e n o m e n a such as " p s e u d o c o n d l t m n m g "e a further 4 dccercbrate rats received 40 u n p a i r e d p r e s e n t a t m n s of both the tone and air puff d u r i n g each t r a i n i n g session Fig 3A (broken hne) illustrates the results from a typical a m m a l in this serms. The n u m b e r of b h n k s made d u r i n g the p r e s e n t a t m n of the tone ncxer exceeded the n u m b e r expected from the s p o n t a n e o u s b h n k rate C o n d l t m n e d blinks therefore appeared only ab a result of CS UCS p a m n g s . C o m p a r e d to the intact a m m a l the rate of acquisition of the c o n d m o n e d bhnk reflex m the chrome decerebrate rat was slow a n d the m a x i m u m scores that ~.ere attained were low. F u r t h e r m o r e , c o n d m o n i n g m the decerebrate rat occurred only as a result of prolonged training. This could explam the failure of prevmus workerv' to d e m o n s t r a t e classlcal c o n d m o n l n g m a similar p r e p a r a t m n . Although, m the present study, there was some ewdence for r e t e n t m n of the CR between t r a i n i n g sessions. ~t was very small when compared w~th that m the intact rat The rat brain stem would appear to c o n t a i n a neural substrate e n a b h n g the e s t a b h s h m e n t of the new ' c o n d m o n ed l i n k ' between the CS and the U C S but the fact that the C R scores were not maret a m e d at a sJgmficant level would mlpl~ that the n o r m a l process ol c o n s o l i d a t m n o[ the newly acquired reformation Is rather absent or ~e~erelv impaired This work was supported by The Mental Health Trust and Research F u n d
1 BIEL, W C, AND WICKENS,D D, The effects of vitamin B1 deficmncy on the condmonmg of eyehd responses in the rat, J comp. Neutol, 32 (1941) 329-340 2 GRANT, D A., The pseudo-condmoned eyehd response, J exp Psychol. 32 (1943) 139 149. 3 HUGHES,B, AND SCHLOS,UERG,H, Condltmmng m the v,hlte rat. lV The conditioned hd reflex, J exp. Psychol, 23 (1938) 641-650 4 LOVlCK,T A, The beha'~loural repertowe of precolhcular decerebrate Jars, J Ph~atol i L o n d ) , 226 (1972) 4-6P. 5 MARKEL, E , AND ADAM, G , Learmng phenomena m meseneephallc rats, At tu physto[. A c a d S t t hung., 36 (1969) 265--270.
337
'.CJ Elsewer Scientific Pubhshmg Company, Amsterdam - Printed m The Netherlands
Classical conditioning of the corneal reflex in the chronic decerebrate rat
THELMA A. LOVICK ANDANDRZEJ W ZBROZYNA Department ot Phy~tology, The Medtcal School, Untvers~ty of Birmingham, Birmingham B15 2TJ (Great Brttam)
(Accepted February 18th, 1975)
The rodent brain stem is able to integrate behavloural activities to such a great extent that after chronic decerebratlon, when the forebrain structures rostral to the superior colhcuh have been removed, the rat can exhibit a wide range of well coordinated behavloural patterns 4. It seemed worthwhile, therefore, to determine whether this type of preparation would be capable of a simple form of learning. Adult female rats (250-350 g) o f a Wlstar strain were decerebrated under Avertin anaesthesia (tribromoethanol, 0.65 ml/100 g of a 2.5~o solution l.p.) All neural tissue rostral to the superior colhculi was removed by aspiration (Fig. 1). The preparatlons were maintained by intragastric admimstratlon of an egg-milk-glucose mixture 3 times daily. Conditioning was started 5-7 days postoperatively. A puff of air to the cornea (unconditioned stimulus, UCS) was applied at the end of an 800 msec, 1000 Hz tone (conditioned stimulus, CS). A conditioned response (CR) was defined as a blink which occurred during the presentation of the CS but before the apphcation of the UCS. Spontaneous, conditioned and unconditioned blinks were noted by visual inspection. A control series of experiments in which 4 normal, unoperated rats were used was carried out to determine the characteristic pattern for conditioning of eyelid movements in the species. Each rat received 20 C S - U C S presentations in the course of each training session During the early training sessions there was a rapid increase in the number of conditioned blinks and a peak value was reached on the 3rd or 4th training session, i.e., after 60-80 C S - U C S presentations. Thereafter performance declined and stablhsed at a value which was 1 0 - 3 0 ~ below the peak value (Fig. 2, open circles). These results compare favourably with those of previous studies 1,3. The training schedule which produced learning in the intact rat - - 20 C S - U C S presentations per training session - - was ineffective when applied to the chronic decerebrate animal (Fig. 2, closed circles). However, a training schedule in which 40 CS UCS pairings were presented during each training session was effective In the 4 decerebrate rats which were tested using this schedule, the incidence of conditioned blinks gradually increased to a level ( 15-38 °/oocorrect responses) which was significantly higher (P < 0.05) than would have been expected from the spontaneous blink rate. With continued presentation of this pairing, up to 500 C S - U C S presentations, the
338
F~g 1 Pa~asag~ttal sectmn taken t r o m the lemnants ol the brain o f a c h m m c deccrchralc tat The graph of acqtlls]tlon of the conditioned corneal telte\ m th~s animal I~ s h o ~ n H~ I ig ~(
number of CRs gradually declined to non-s~gnlficant values. The results from one of the ammals m this group are Illustrated in F~g. 3A. A second group of" 4 decerebrate rats received 50 CS +UCS presentations during each training session. Once again each ammal attained significant conditioned response scores before its performance declined to a non-sigmficant ~alue. In 2 animals within this group, training was pursued
339 80 (b
u~ 6 0
~5 er.
-
40
o
g o
20
®
2
3 4 5 6 7 Session Number
B 9
Fig. 2 O p e n c~rcles g r a p h o f a c q m s i t l o n of the c o n d i t i o n e d corneal reflex m a n intact rat w h m h recewed 20 C S - U C S p m r m g s d u n n g each training session. Filled circles: the results f r o m a c h r o m c decerebrate rat w h m h u n d e r w e n t a s]mdar training schedule a n d s h o w e d no s~gn o f c o n d m o n m g .
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40
40
,
A 30 2O
++ U3
10
10 @
i
2
4
6
B 10 12
?
VV
2 v
i
4
v
6
i
8
10 12 14 16 18 20 22 q
V
VV
vv
v
~, 3(? E 2O 10
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32 34 36 3g Session Number
Ftg 3. A : s o h d line. g r a p h o f acqumltlon o f the c o n d i t i o n e d corneal reflex in a c h r o m c decerebrate rat w h m h received 40 C S - U C S pairings d u r i n g each t r a l m n g session. Broken hne" the results from a decerebrate rat w h m h received 40 u n p a i r e d p r e s e n t a t i o n s o f the CS a n d U C S d u r m g each training session. B a n d C: g r a p h s o f a c q m s m o n o f the c o n d m o n e d reflex m 2 decerebrate rats w h m h received 50 C S - U C S p m r m g s during each training session. O p e n trmngles indicate the training sessions m V,hlch the n u m b e r of b h n k s m a d e during the presentation of the tone was slgmficantly greater (P < 0.05) t h a n the n u m b e r expected f r o m the s p o n t a n e o u s b h n k rate
340 l'urther and led to ,t ,e~ond increase m the n u m b e r of CRs made I Flg 3B and ~ j However, the ne~. performance was not m a i n t a i n e d and the n u m b e r o f ( Rs dJ tarnished once moJe One a m m a l recm,,ed more prolonged t r a i n i n g (F~g. 3( t and a third peak appeared in the graph o f a c q m s m o n of the c o n d i t m n e d response As a control for p h e n o m e n a such as " p s e u d o c o n d l t m n m g "e a further 4 dccercbrate rats received 40 u n p a i r e d p r e s e n t a t m n s of both the tone and air puff d u r i n g each t r a i n i n g session Fig 3A (broken hne) illustrates the results from a typical a m m a l in this serms. The n u m b e r of b h n k s made d u r i n g the p r e s e n t a t m n of the tone ncxer exceeded the n u m b e r expected from the s p o n t a n e o u s b h n k rate C o n d l t m n e d blinks therefore appeared only ab a result of CS UCS p a m n g s . C o m p a r e d to the intact a m m a l the rate of acquisition of the c o n d m o n e d bhnk reflex m the chrome decerebrate rat was slow a n d the m a x i m u m scores that ~.ere attained were low. F u r t h e r m o r e , c o n d m o n i n g m the decerebrate rat occurred only as a result of prolonged training. This could explam the failure of prevmus workerv' to d e m o n s t r a t e classlcal c o n d m o n l n g m a similar p r e p a r a t m n . Although, m the present study, there was some ewdence for r e t e n t m n of the CR between t r a i n i n g sessions. ~t was very small when compared w~th that m the intact rat The rat brain stem would appear to c o n t a i n a neural substrate e n a b h n g the e s t a b h s h m e n t of the new ' c o n d m o n ed l i n k ' between the CS and the U C S but the fact that the C R scores were not maret a m e d at a sJgmficant level would mlpl~ that the n o r m a l process ol c o n s o l i d a t m n o[ the newly acquired reformation Is rather absent or ~e~erelv impaired This work was supported by The Mental Health Trust and Research F u n d
1 BIEL, W C, AND WICKENS,D D, The effects of vitamin B1 deficmncy on the condmonmg of eyehd responses in the rat, J comp. Neutol, 32 (1941) 329-340 2 GRANT, D A., The pseudo-condmoned eyehd response, J exp Psychol. 32 (1943) 139 149. 3 HUGHES,B, AND SCHLOS,UERG,H, Condltmmng m the v,hlte rat. lV The conditioned hd reflex, J exp. Psychol, 23 (1938) 641-650 4 LOVlCK,T A, The beha'~loural repertowe of precolhcular decerebrate Jars, J Ph~atol i L o n d ) , 226 (1972) 4-6P. 5 MARKEL, E , AND ADAM, G , Learmng phenomena m meseneephallc rats, At tu physto[. A c a d S t t hung., 36 (1969) 265--270.