Tone cessation as a conditioned stimulus II. Inhibition

Electroencephalography and Clinical Neurophysiology Elsevier Publishing Company, Amsterdam - Printed in The Netherlands

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T O N E C E S S A T I O N AS A C O N D I T I O N E D STIMULZTS. II. I N H I B I T I O N I JORGE A . SOMMER-SMITH M , D . 2

Instituto de Investigaci6n de Ciencias Biol6gicas, Montevideo (Uruguay) (Accepted for publication: April 14, 1967)

INTRODUCTION

In a previous publication we described the use of cessation of a prolonged tone as the conditioned stimulus (Sommer-Smith et al. 1962) and concluded that the learned responses to tone cessation have behavioral and EEG characteristics of conditioned reflexes. This kind of conditioning has a special interest, because the tone cessation is a very labile signal which provokes small reactions, both behaviorally and EEG. It is difficult to be conditioned and it is easily inhibited. In this paper we describe the inhibitions in the Pavlovian sense: external inhibition, internal inhibition (i.e., extinction, differentiation, conditioned inhibition and delay) and disinhibitions. MATERIAL AND METHODS

The techniques of implantation and recording have been described already (Sommer-Smith et al. 1962). The EEG record was obtained from screws placed in the skull over the somatosensory areas. Eighteen cats were trained (12 with an avoidance conditioning routine and 6 by classical conditioning). During daily sessions 10 tones were applied and irregular intervals were used to avoid conditioning to time. Tones were of constant intensity (92 __+ 12 db) and of a variable duration (several seconds to several minutes). Electric shocks, a This paper was carried out in the Clinic for Nervous and Mental Diseases of the University of Siena. It was supported in part by grants from the Max Planck Institute for Psychiatry of Munich. 2 Present address: Clinica delle Malattie Nervose e Mentali dell'Universitg, Siena, Italy.

delivered through subcutaneous electrodes in the forepaw, provoked the movement of this forepaw and the retraction of the head. The shock was delivered only if the cat did not perform a certain response at the tone cessation in the avoidance conditioning and systematically in the classical conditioning. The conditioned stimulus (tone cessation) was presented when the cat was calm and the EEG showed an activity with spontaneous spindles (alpha type) (Hess et al. 1953). Movements of the head at the tone cessation were considered as a "general response", and the denomination "specific conditioned re~lctonse" was reserved for one which reproduced ,exactly the effect of the electric stimulus. Four categories of EEG arousal were,recognized (Fig. 1): type A: "activation" ,patterns with a substitution of the resting pattern by 20-40 c/sec waves of about 20 #V amplitude; type B : "activation" pattern with substitution of the resting pattern by an activity of lower frequency and higher voltage than type A, but clearly different from the previous control rhythm; type C: "activation" pattern like A, with a delay of 0.5-2 sec; type D: "activation pattern like type B with a delay of 0.5-2 sec. The duration of the arousal was measured and is shown in Fig. 4 and 5. After the stages of habituation and reinforcement, and when the cats showed a constant percentage of specific responses (over 70 or 80%) the inhibitory sessions were initiated. External inhibition was produced by an unexpected acoustical stimulus (clashing two small pieces of board) delivered some seconds before the cessation of the tone. Extinction (studied in 15 cats) was produced by presenting the tone without Electroeneeph. clin. NeurophysioL, 1967, 23:439-448

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reinforcement; criterion was the absence of behavioral response and the absence of arousal during a minimum of 10 sessions. Differentiation (studied in 10 cats) was obtained with 5 non-reinforced stimuli of a different frequency intercalated with the 5 reinforced stimuli. The same criterion was applied: absence of specific response and absence of EEG arousal to the differentiated tone during 10 sessions. The types of arousal and their duration were taken into account. Conditioned inhibition (studied in 5 cats) was obtained by a buzzer, added at the cessation of tone and never reinforced. This association was alternated irregularly with the tone alone which was always reinforced after its cessation. This inhibition was preceded by habituation to the buzzer. Criterion was the percentage of specific response and the duration of the E E G arousal. Delay (studied in 5 cats) was obtained, prolonging the interval between the tone cessation and the unconditioned stimulus. The delay of the conditioned response was observed when the interval was prolonged. The percentages of conditioned response must remain over 7 0 ~ and were controlled to determine that there was no extinction but a delay. Disinhibitions were provoked during the internal inhibitions by pre-

The external inhibition in the first sessions of the reinforcement always determined the disappearance of the conditioned response; in the latter sessions this inhibition provoked the delay or the modification of this response (the disappearance in a 30-50~). During extinction the effects of the conditioned stimulus (cessation of tone) disappeared very quickly in all fifteen cats after 2-3 sessions, when there was no reinforcement. Behavioral responses were initially inconstant, but were modified and finally completely abolished (Fig. 2). There were two stages in the evolution of the response: initially it was indicated by the disappearance of the behavioral response and by the short duration of the E E G arousal (2-5 sec); afterwards the inhibition was recognized by the complete abolition of the E E G response. After 5-6 sessions, all the cats showed a behavior and an EEG of sleep. This sequence is comparable with habituation, behaviorally and electroencephalographically (in the types and the duration of arousal) (Sommer-Smith et al. 1962). During differentiation the discrimination of tones of very different frequencies (300 and 1600, 1000 and 2000 c/sec) tested in all the ten cats was easily obtained after 12--40 trials and was evidenced by the absence of behavioral and EEG responses to the non-reinforced tone cessation (Fig. 3, left side). The discrimination of closer frequencies (300 and 400 c/sec) tested in six cats, was difficult even after 120-200 trials (Fig. 3, right side). The sequence: abolition behavioral response-abolition E E G response, followed a pattern similar to that of extinction (Fig. 4). Inhibition was manifested by the evident diminution of percentages of the behavioral response (under 20%) or by complete abolition, by the short duration of the E E G arousal or by its absence or by types B or D of E E G response (Fig. 4). Pavlovian "generalization" was observed: the conditioned response established to a certain Electroenceph. clin. Neurophysiol., 1967, 23:439--448

INHIBITION 1N CONDITIONING

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Electroenceph. clin. Neurophysiol., 1967, 23:439-448

INHIBITION IN CONDITIONING

stimulus was produced by another stimulus similar to the first one; generalization was observed in differentiation between 300 and 400 c/see. We also observed the contrary: by generalization of the inhibitory process, the effect of the reinforced tone was abolished or modified in the first 3-4 sessions of discrimination between similar and between very different frequencies. During cond/tioned inhibition the results were not constant. In three cases a very clear inhibition was obtained after 30-50 trials (buzzer-tone cessation). I n two cases the percentages ofbehavior~:l responses (75-100%) were practically identical and the inhibition was evidenced only by the shorter dur~.tion of the E E G arousal to the association buzzer-tone cessation, statistically significant for both cases (Fig. 5). A short arousal produced by the buzzer was always present (Fig. 6). SMCo "BUZZER" HABITUATION

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buzzer does not induce either behavioral response or EEG arousal. Cessation of the reinforced tone determines the behavioral and EEG responses. The association of the buzzer with tone cessation provokes a short arousal, but the behavioral conditioned response is abolished. During delay, three cases indicated inhibition by longer latency of the conditioned response (until40 sec); the percentages of this response were constant (60-100%) (Fig. 7). When the interval between tone cessation and unconditioned stimulus surpassed 40 sec, the percentages of the conditioned response were diminished (under 40 9/0) and sometimes abolished. In only one case with an interval of 100 sec the percentages were constant (70-100%), but the conditioned response did not show any delay.

Disinhibitions were obtained several times during extinction, differentiation, conditioned inhibition and delay. They were evidenced by the reappearance (during extinction, differentiation and conditioned inhibition) or by the shorter latency (during delay) of the inhibited response. The E E G showed a typical arousal. In the extinction the disinhibitions were easier to obtain during the first 4-5 sessions; in the other inhibitions that was not evidenced, because the disinhibitions were clearly provoked after hundreds of trials of the inhibited tone. DISCUSSION

In this series of experiments tone cessation was used as a conditioned stimulus. External inhibition was easily obtained during the first sessions, when reinforcement was provided, but before the conditioned response was well established. This "distracting" noise produced an orienting reaction and an E E G arousal, and was interpreted to induce a process of simple competition.When exceptionally (less than 15%) the conditioned response was performed after a Electroenceph. clin. NeurophysioL, 1967, 23:439-448

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delay prolonged several seconds, it would signify that the inhibitory process cart be overcome. Internal inhibition is characterized by the absence of behavioral and EEG effects, observed during differentiation and delay, or by "hypersynchronization", observed during extinction (Kogan 1960). Our results in extinction are similar to those of authors who employed other techniques (Jasper and Shagass 1941 ; Galambos et al. 1956; Jouvet 1956; Segundo et al. 1959), but they were much more quickly obtained. During "incomplete" extinction tone cessation provoked a short arousal. In "well established" extinction we observed hypersynchronization which we considered directly related to patterns and mechanisms of sleep (Motokawa and Huzimori 1949; Segundo et al. 1959). During differentiation, generalization of the inhibition, observed also by Jasper and Shagass (1941), induced a consistent diminution of the behavioral and EEG effects, elicited by the conditioned stimulus (cessation of tone); the percentage of responses to this stimulus is inferior to the reinforcement (Buendia et al. 1963). "Stable" differentiation, which follows the "unstable" former stage, is characterized by the absence of arousal and, exceptionally, by "hypersynchrony" localized over the cortical area where there is the representation of the unconditioned stimulus (Gastaut et al. 1957; Grasty~in et al. 1957; Yoshii 1957). In this type of conditioning it is very difficult to obtain a good behavioral discrimination between similar frequencies. In conditioned inhibition the addition of a buzzer to the conditioned stimulus had a very poorly inhibitory action. It seems that the addition of a sound against the substraction of another sound (conditioned stimulus) was not actually effective. During inhibition by delay, a short desynchronization to tone cessation was always present and was followed by spindles indicating the incomplete abolition of the EEG effects. The specific conditioned response was accomplished after a second EEG desynchronization (Motokawa and Huzimori 1949; Gluck and Rowland 1959); it seems to be a process in which mechanisms of an inhibitory extinction and the delayed actual reinforcement are present. The disinhibitions were easily obtained during

all the inhibitions. This would signify a process of inhibition that is more labile than the same reinforcement. During inhibitions, especially during extinction, the cats were asleep (slow wave sleep) in the conditioning cage; however, placing the cats into the cage would act as a stress (Corson et al. 1963), and at the beginning of the session the EEG showed a very prolonged desynchronization (Anokhin 1958). In our experiments (Sommer-Smith et al. 1964) the arousal was most evident over the somatosensory cortex; this is the area of representation of the unconditioned stimulus (Gastaut et al. 1957). The delayed responses (types C and D) were in time relation with the unconditioned stimulus which was delivered 2-5 sec after the tone cessation. Yoshii et al. (1959) have observed a similar phenomenon in the reticular formation (the "mnemonic trace"). This delay does not depend on the state of the EEG (alertness or calm) when the stimulus is applied (Lansing 1957; Calloway 1962). The arousal of type B was very frequently associated with inhibited tones. The duration of the arousal, reported also by others (Loomis et al. 1936, 1938; Travis and Knott 1936), is in accord with the significance of the stimulus, and was statistically analyzed during differentiation and conditioned inhibition. These experiments confirm that the cessation of a tone is a conditionable stimulus like the initiation of a tone; this type of conditioning is of particular interest because tone cessation is a very labile signal, as was shown in the conditioning process. Analysis of the results indicates a remarkable correspondence between type and duration of the EEG arousal and the significance of the stimulus in this conditioning. SUMMARY

Study of conditioning, using me cessation of tone as the conditioned stimulus in avoidance and classical conditioning proceedings, has enabled us to follow the evolution of behavioral responses. The latter were correlated with modifications in the EEG recorded from the somatosensory region, and were not complicated by interference from the unconditioned stimulus or by the tone per se.

Electroenceph. clin. Nearophysiol., 1967, 23:439-448

INHIBITION IN CONDITIONING Habituation, reinforcement, external and internal inhibition (differentiation, conditioned inhibition, delay and extinction) were obtained. Disinhibitions were also observed. These experiments show that the cessation of a tone can serve as an independent signal, and that there was a closer correspondence between tone cessation and the cortical responses than between this stimulus and the behavior o f the animal. RI~SUMI~ LA CESSATION DU SON COMME STIMULUS CONDITIONNEL. II. INHIBITION L'6tude du proc~s du conditionnement ~ la cessation du son (selon la m6thode de ' T a v o i d ance conditioning") a permis de suivre l'6volution de la r6ponse de c o m p o r t e m e n t en corr61ation avec les modifications produites au niveau du corticogramme sensori-moteur sans les interf6rences du stimulus inconditionnel et du son en soi. L'habituation, le renforcement et les inhibitions externe et interne (diff6rentiation, inhibition conditionnelle, retard et extinction) ont 6t6 observ6es. O n a aussi obtenu des d6sinhibitions. L' exp6rience a d6montr6 que la cessation du son agit c o m m e un signal ind6pendant. L'analyse des r6sultats a d6montr6 que les r6actions corticales refl~tent plus fid61ement que le c o m p o r t e m e n t la signification du stimulus pr6sent6. ZUSAMMENFASSUNG DAS ENDE DES TONES ALS BEDINGTESSTIMULUS. II. HEMMUNG Die Auswertung der Untersuchungsserie tiber das Ende des Reiztones (nach der M e t h o d e der "avoidance conditioning") liess uns die fortschreitende Entwicklung des Verhaltens in Bezug aufdie Ver/inderungen im E E G im somatomotorischen Cortex ohne die Interferenzen des unbedingten Reizes und des Tones verfolgen. Die Gew6hnung, die Verst~irkung und die ~iusserliche und innerliche H e m m u n g (Differenzierung, bedingte H e m m u n g , Verz6gerung und Aus16schung) sind beobachtet worden, WiT erhielten auch Enthemmungen.

447

Resultate hatten das Ende des Reiztones als ein unabh~tngiges Signal gezeigt. Die Analyse der Ergebnisse zeigte eine engere Beziehung der Reizes-Bedeutung zu den corticalen Antworten als z u m Verhalten. The interest and help of Professor M. Jouvet in the preparation of this manuscript is kindly acknowledged. REFERENCES ANOr,.HIN,P. K. Significance of the reticular formation for conditioned reflex. ActabhysioL poL, 1958, 9, 2: 131141. BUENDiA,N., SIERRA,G., GOODE,M. and SEGUNDO,J. P. Conditioned and discriminatory responses in wakeful and in sleeping cats. Electroenceph. clin. NeurophysioL, 1963, Suppl. 24: 199-218. CALLOWAY)E. Factors influencing the relationship between alpha activity and visual reaction time. Electroenceph. clin. Neurophysiol., 1962, 14: 674-682. CORSON, S. A., CORSON, E. O'L., PASAMANICK,B. and ENGLAND,J. M. The influence of restraint and isolation on physiologic baselines in conditioned reflex studies; the promise of telemetry. Bio-Telemetry. Pergamon, New York, 1963:311-320. GALAMBOS,R., SHEATZ,G. and VERNIER,V. G. Electrophysiological correlates of a conditioned response in cats. Science, 1956, 123: 376-377. GASTAUT,H., Jus, A., Jos, C., MORRELL,F., STORMVAN LEEUWEN,W., DONGIER,S., NAQUET,R., REGIS,H., ROGER, A., BEKKER1NG,D., KAMP,A. et WERRE,J. l~tude topographique des r6actions 61ectroenc6phalographiques conditionn6es chez l'homme. Electroenceph, clin. Neurophysiol., 1957, 9: 1-34. GLUCK, H. and ROWLAND,V. Defensive conditioning of electrographic arousal with delayed and differentiated auditory stimuli. Electroenceph. clin. Neurophysiol., 1959, 11 : 485-496. GRASTY.~N,E., HORI,Y, et ROGER,A. I~.tude61ectroenc6. phalographique temporo-spatiale d'un conditionnement moteur chez le chat. Proc. 1st intern. Congr. NeuroL Sci., Brussels. Pergamon, London, 1957, 111: 474-475. HESSJR., R., KOELLA,W. P. and AKERT, K. Cortical and subcortical recording in natural and artificially induced sleep in cats. Electroenceph. clin. Neurophysiol., 1953, 5" 75-90. JASPER, H. H. and SHAOASS,C. Conditioning of occipital alpha rhythm in man. J. exp. Psychol., 1941, 28: 373388. JOtrVET, M. Analyse 61ectroenc6phalographique de quelques aspects du conditionnement chez le chat. Acta neuroL lat.-amer., 1956, 2: 107-115. KOGAN, A. B. The manifestations of processes of higher nervous activity in the electrical potentials of the cortex during free behaviour of animals. Electroenceph. clin. Neurophysiol., 1960, Suppl. 13: 51-64. LANSING,R. W. Relation of brain and tremor rhythms to visual reaction time. Electroenceph. clin. NeurophysioL, 1957, 9: 497-504. Electroenceph. clin. Neurophysiol., 1967, 23:439--448

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LOOMIS, A. L., HARVEY, E. N. and HOBART, G. A. Brain potentials during hypnosis. Science, 1936, 83: 239241. LOOMIS, A. L,, HARVEY,E. N. and HOBART,G. A. Distribution of disturbance-patterns in the human electroencephalogram, with special reference to sleep. J. Neurophysiol., 1938,1: 413-430. MOTOKAWA,K. and HUZlMORI,B. Electroencephalograms and conditioned reflexes. TohokuJ. exp. Med., 1949, 50: 215-223. SEGUNDO, J. P., ROIG, J. A. and SOMMER-SMITH,J. A. Conditioning of reticular formation stimulation effects. Electroenceph. clin. Neurophysiol., 1959, 11: 471-484. SOMMER-SMITH,J. A., CREtrrZFELDT,O. y MOROCUTTI,C. Potenciales evocados corticales y subcorticales en el

condicionamiento. Comun. VL Congr. latinoamer. Cienc. fisioL, Vifia del Mar, 1964: 209. SOMMER-SMITH,J. A., GALEANO,C., PII~iEYRI~A,M., ROIG, J. A. and SEGUNDO,J. P. Tone cessation as conditioned signal. Electroenceph. clin. Neurophysiol., 1962, 14: 869-877. TRAVIS, L. E. and KNOTT, J. R. Brain potential studies of perseveration: I. Perseveration time to light. J. Psychol., 1936, 3: 87-100. YOSHn, N. Principes m6thodologiques de l'investigation 61ectroenc6phalographique du comportement conditionn6. Electroenceph. clin. Neurophysiol., 1957, Suppl. 6: 75-88. YOSHn, N., HASEGAWA,Y. and YAMAZAKI,H. Electroencephalographic study of defensive conditioned reflex in dog. Foliapsychiat. neurol.jap., 1959, 13: 320-367.

Reference: SOMM~R-SMrnt, J. A. Tone cessation as a conditioned stimulus, II. Inhibition. Electroenceph. clin. NeurophysioL, 1967, 23: 439-448,