Post-reinforcement electrocortical synchronization and facilitation of cortical somato-sensory evoked potentials during instrumentally conditioned appetitive behavior in the cat

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

POST-REINFORCEMENT ELECTROCORTICAL SYNCHRONIZATION AND FACILITATION OF CORTICAL SOMATO-SENSORY EVOKED POTENTIALS D U R I N G INSTRUMENTALLY CONDITIONED APPETITIVE BEHAVIOR IN THE CAT 1 T. J. MARCZYNSKI AND J. T. HACKETT 2 Department of Pharmacology, College of Medicine, University of 1[lino&, Chicago, Ill. 60680 (U.S.A.) (Accepted for publication: May 27, 1968)

In an illuminated test cage the ECoG recorded from the visual cortex, in the food-deprived cat trained to press a lever for milk reward, displays a sudden shift from a desynchronized to highly synchronized pattern (large amplitude waves at about 6-9 c/sec) after the presentation and during the consumption of the reinforcement. Clemente et al. (1964) termed these ECoG phenomena post-reinforcement synchronization (PRS). These bursts of PRS activity depend not only on the visual input but also on the quality, appropriateness and taste of food reward (Sterman and Wyrwicka 1967; Marczynski et al. 1968) suggesting that they may reflect a pleasurable experience. The amplitude of cortical evoked potentials (EPs) induced by a meaningless tone or click is conspicuously augmented during PRS. It was suggested that this post-reinforcement facilitation of EPs results from an active transient inhibition of certain components of the reticular activating system (Marczynski et al. 1968). The present study on the cortical somatosensory EPs was undertaken to shed more light on PRS phenomena and on the effect of positive reinforcement on sensory input to the cortex. The ECoG correlates of instrumentally conditioned alimentary behavior, cortical somatosensory EPs induced by mild and meaningless electrical stimuli applied to the skin were recorded: (a) after non-rewarded lever pressing (NOR); (b) after rewarded lever pressing in the presence 1 This work was supported by G r a n t N B 06385 from National Institutes of Health. 2 Pre-doctoral fellow (Training G r a n t G M 81-09 from National Institutes of Health).

of light in the test cage; i.e., during bursts of PRS; (c) after presentation of reward in the dark cage (RD); i.e., while the PRS activity was suppressed. These ECoG correlates and EPs were compared to those obtained during: (i) waking but relaxed state after satiation (REL); (ii) emotional excitement (EXC); and (iii) spindle slow wave sleep after satiation (SL). METHODS

From a total of sixteen adult mongrel cats trained to press a lever for 0.5 ml of milk reward five animals (3-4 kg) which showed most consistent PRS patterns served as subjects in 52 experimental sessions. The experimental set-up, training of the animals, surgery and recording techniques of averaged EPs using CAT computer were previously described (Marczynski et al. 1968)3. The somato-sensory EPs were recorded over posterior and anterior marginal, posterior, medial and anterior suprasylvian, posterior and anterior sigmoid gyri. In order to obtain somato-sensory EPs two stainless steel sutures provided with miniature connectors were attached 2-3 cm apart to the skin of the back in the midline at the level of the third to fifth thoracic vertebra. The subjects were habituated to mild manually triggered electrical stimuli delivered through an isolation unit from a Grass S-4 stimulator. The voltage and duration of stimuli were kept 25 below the threshold voltage which interfered a The computed data will be referred to as averages, although the Computer of Average Transients performs a summation process.

Electroenceph. clin. Neurophysi¢l., 1969, 26:41-49

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T. J. MARCZYNSKI AND J. T. HACKETT

either with the occurrence of E C o G patterns of physiological sleep, PRS activity or the animal's operant behavior. During the first experiments 3 weeks after surgery the required voltage and duration of electrical impulses were relatively low (5-8 V; 0.02-0.05 msec). However, after 2 or 3 months the threshold voltage significantly increased; this was probably due to the development of scar tissue around the skin electrodes. In most experiments the threshold voltage did not appreciably change during 15 days. During this period a sufficient number of computer averaged EPs could be accumulated for statistical analysis. The amplitude of EPs was measured peak to peak. The differences between the mean amplitudes of series of averaged EPs accumulated for each behavioral state were evaluated by using the two-tailed Student's t test. As shown by Boneau (1960), this test does not lose its validity even when the distribution of variance is not symmetrical provided that the number of samples in each category is the same. The difference between the means was considered significant when P < 0.05. An equal number of 20 averaged EPs was accumulated during several experimental sessions for each behavioral category using the same stimulus parameters. In about 15 % of EPs the electrostatic cable artifacts obliterated or markedly distorted their characteristic components. Such EPs were excluded from statistical analysis. For illustration purposes single averaged EPs were carefully retraced on a transparent paper and superimposed.

in Fig. 1 and 2. Each tracing is a summation of twenty single EPs. The composite Fig. 3 is a summary of amplitude measurements and statistical evaluation of differences between sets of EPs. Primary components were measured peak to peak from " a " to " b " , and the secondary ones from " c " to " d " over somatic projections,

PM-ASS

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Electrocorticogram Mild electrical impulses delivered to the skin had no appreciable effect on the ECoG, or on subject's performance and physiological sleep. Only occasionally one or two large amplitude waves (100-160 #V) of the PRS bursts were prevented from occurring (see Fig. 1 and 2), a phenomenon similar to that observed previously in the study on click-induced cortical EPs (Marczynski et al. 1968). Somato-sensory averaged evoked potentials Representative sets of superimposed computer averaged EPs obtained either referentially or bipolarly during six behavioral states are shown

sensory cortical evoked potentials (EPs) in cat 15. They were recorded bipolarly from the left hemisphere between posterior marginal and anterior suprasylvian (PM-ASS), posterior marginal and posterior sigmoid (PM-PS), and posterior marginal and anterior sigmoid gyri (PM-AS), after non-rewarded lever pressing (NOR), during bursts of post-reinforcement synchronization (PRS), consumption of reward in the dark (RD), relaxed state (REL), emotional excitement (EXC), and physiological sleep (SL). Each tracing is a summation of 20 single responses. On the right the corresponding ECoG activity over the left PM gyrus recorded from a separate electrode. Downward arrows marked: N - non-reinforced lever press; R - reinforced lever press; S - electrical stimulus delivered to the skin for eliciting EPs. Note poorly developed EPs dining NOR and EXC, and conspicuous facilitation of both "primary" and "secondary" components of EPs during PRS. Note also a tendency to differential suppression of secondary components during RD, and their differential enhancement during SL.

Electroenceph. clin, Neurophysiol., 1969, 26:41-49

REINFORCEMENT AND SOMATO-SENSORYEPS

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Fig. 2 On the left superimposed computer averaged somatosensory EPs in cat 19 recorded referentially over posterior sigmoid (PS) and posterior marginal gyri (PM) of the right hemisphere during non-rewarded lever pressing (NOR), post-reinforcement synchronization (PRS), consumption of reward in the dark (RD), relaxed state after

satiation (REL), excitement (EXC)~ and spindle slow wave sleep (SL). Each tracing is an average of 20 single responses. On the right the corresponding ECoG over PS and PM of the same hemisphere; N - non-rewarded; R - rewarded lever press; S - electrical stimulus delivered to the skin. Note the conspicuous augmentation of EPs during PRS and SL. A comparable enhancement of PRS EPs can be observed over both PS and PM although the PRS activity is confined to PM, and there is little or no change in the ECoG over PS. Note also much larger amplitude of the secondary components during PRS than that observed during REL and RD. Positive deflection is downward. and from " e " to " f " over non-specific projections. a. Early ("primary") components. Nine "prim a r y " EPs were studied. Four referentially recorded averaged EPs were positive or negativepositive waves; they could be observed over posterior and anterior sigmoid, and anterior

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suprasylvian gyri. The latencies of the first deflection varied from 10 to 15 msec, and those of the positive peaks from 20 to 30 msec. The latter remained within the lower limits during operant behavior (NOR, RD, PRS) as well as during EXC; they shifted towards the upper limits during SL and REL. As shown in Fig. 3, the mean amplitudes of the averaged EPs obtained during N O R showed no significant differences when compared to the corresponding responses recorded during EXC in the eight series of EPs. Only in one series of EPs recorded bipolarly between posterior marginal and anterior suprasylvian gyri was the early component obtained during N O R significantly larger than that observed during EXC. During R E L the mean amplitudes of the early components were larger than the same recorded either during EXC or N O R in eight series of EPs. Only one series of EPs recorded between posterior marginal and anterior sigmoid gyri showed no significant difference in these three situations. In three series of EPs the mean amplitudes of the primary components obtained during SL were significantly larger than the corresponding ones recorded during REL, N O R and EXC. When compared only to those recorded during N O R or EXC EPs, four SL EPs were larger: referentially recorded from anterior and posterior sigmoid gyri, and two bipolarly obtained between anterior marginal and posterior sigmoid, and between posterior marginal and posterior sigmoid gyri. Four SL EPs showed no significant differences when compared to either N O R or EXC EPs, and one SL EPs obtained between posterior marginal and anterior suprasylvian gyri was significantly larger than the corresponding one obtained during EXC. It should be pointed out that amplitude measurements in some SL EPs were difficult because the primary components showed a tendency to merge with the secondary ones which displayed a conspicuous amplitude enhancement during SL; the peak latencies of the latter ranged from 100 to 140 msec. The same responses recorded during PRS, R D and R E L showed easily separable and well developed short and long latency peaks. The primary EPs recorded during R D were larger than those obtained during either N O R Eleetroeneeph. elin. Neurophysiol., 1969, 26:41-49

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Fig. 3 Mean amplitudes (with standard errors) of 14 different somato-sensoryEPs (comprising 9 primary and 14 secondary components) obtained over specific and non-specific cortical projections in response to mild electrical stimulation of the skin in cats 12, 15, 19, 20 and 25 during six behavioral states: consumption of 0.5 ml milk reward in the illuminated cage; i.e., during bursts of PRS; consumption of reward in the dark (RD); spindle slow wave sleep in a satiated subject (SL); relaxed state after satiation (REL); after non-reinforced lever pressing (NOR); and during emotional excitement caused by confrontation with a mouse (EXC). Each bar is based on measurements of a set of 20 averaged EPs. Hatched bars represent the amplitude of the primary and the empty ones that of the secondary components. Note the conspicuous enhancement of both primary and secondary wave forms during PRS in almost all EPs, especially over anterior sigmoid (subject 12), anterior marginal (subject 20) as well as in bipolarly recorded EPs between posterior marginal and anterior suprasylvian, posterior marginal and anterior sigmoid (both subject 15), and between anterior marginal and anterior sigmoid gyri (subject 20). Note a preferential reduction of secondary components during RD, and their preferential enhancement during SL in subjects 15, 20 and 25. Most primary and secondary EPs during PRS were larger than those during RD, REL, NOR and EXC. Most primary EPs during PRS were larger than those during SL, and most secondary PRS EPs were comparable to those recorded during SL. The remaining abbreviations: ASS, MSS, and PSS - anterior, medial and posterior suprasylvian gyrus. Calibration (50 #V) refers to the height of the bars.

Electroenceph. clin. Neurophysiol., 1969, 26:41-49

REINFORCEMENT AND SOMATO-SENSORY EPS

or EXC in seven series of EPs. Two series of RD EPs showed no significant differences in these three situations. Two series of RD EPs showed significant increase in amplitude when compared to the corresponding REL EPs: bipolarly obtained between posterior marginal and anterior sigmoid, and between anterior marginal and posterior sigmoid gyri. The remaining seven series of EPs showed no significant differences in these two situations. Four RD EPs were larger than the same recorded during SL: two of them obtained referentially from anterior marginal and posterior sigmoid gyri, and two recorded bipolarly between posterior marginal and anterior sigmoid, and between anterior marginal and anterior sigmoid gyri. Four RD EPs showed no significant differences in these two situations, and one series of RD EPs recorded referentially from posterior sigmoid gyrus was significantly smaller than the corresponding EPs obtained during SL. All nine studied primary EPs obtained during PRS were significantly increased when compared to those recorded either during NOR or EXC. Five PRS EPs were larger than the same recorded during REL: one obtained referentially from anterior marginal gyrus, and four recorded bipolarly between posterior marginal and anterior suprasylvian, posterior marginal and anterior sigmoid, anterior marginal and posterior sigmoid, and between anterior marginal and anterior sigmoid gyri. The remaining four sets of PRS EPs showed no significant differences in these two situations. The primary components of six PRS EPs were larger than the same obtained during SL: from anterior marginal, anterior and posterior sigmoid gyri (referential recording), and in EPs obtained between posterior marginal and anterior suprasylvian, posterior marginal and anterior sigmoid gyri, and between anterior marginal and anterior sigmoid gyri (bipolar recording). Two series of PRS EPs showed no significant differences in these two situations, and one series of PRS EPs from posterior sigmoid gyrus was significantly smaller than the same recorded during SL (referential recording). PRS EPs were larger than the same responses recorded during RD in three series: from anterior and posterior sigmoid gyri (referential

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recording) and in one obtained between anterior marginal and anterior sigmoid gyri (bipolar recording). The remaining six series of EPs showed no significant differences in these two situations. b. Long latency ("secondary")EPs. A total of fourteen long latency "secondary" components of averaged EPs were studied. Eight of them were recorded referentially over anterior and posterior sigmoid, anterior and posterior marginal and medial and posterior suprasylvian gyri. They were negative-positive or positive waves of 25-30 msec latency; their positive peak latencies ranged from 50 to 130 msec; they remained within the lower limits in EPs recorded during RD, PRS, NOR and EXC, and shifted to upper limits during SL. The remaining six EPs were obtained in bipolar recordings between the afore-mentioned cortical areas. The secondary EPs recorded during NOR or EXC were poorly developed; in several series they were hardly discernible. The mean amplitudes of all NOR EPs showed no significant differences when compared to the corresponding responses obtained during EXC, except one recorded bipolarly between posterior marginal and anterior suprasylvian gyri which was significantly larger during NOR. During REL all fourteen series of secondary EPs showed significant amplitude increase when compared to the corresponding responses obtained either during EXC or NOR. SL EPs were larger than those recorded during RD, REL, NOR or EXC in twelve series of studied responses. The remaining two series of SL EPs obtained over medial suprasylvian, posterior marginal gyri showed no difference from corresponding RD EPs but were larger than REL, NOR and EXC EPs. RD EPs were comparable to REL EPs in eight series obtained from: posterior and anterior marginal, medial and posterior suprasylvian, and anterior sigmoid gyri (referential recording), and between posterior marginal and medial suprasylvian, anterior marginal and posterior sigmoid, and between anterior marginal and anterior sigmoid gyri (bipolar recording). Three RD EPs were smaller than the corresponding REL EPs obtained between posterior marginal and posterior sigmoid, posterior marginal and Electroenceph. clin. Neurophysiol., 1969, 26:41-49

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T . J . MARCZYNSKI AND J. T. HACKETT

anterior suprasylvian, posterior marginal and anterior sigmoid gyri (bipolar recording). The remaining three RD EPs were larger than REL EPs obtained over posterior sigmoid, medial suprasylvian and posterior marginal gyri (referential recording). All fourteen series of RD EPs were larger than the corresponding ones recorded during EXC. Twelve RD EPs were larger than NOR EPs. The remaining two series obtained between posterior marginal and anterior suprasylvian, posterior marginal and posterior sigmoid gyri showed no differences in these two behavioral states. PRS EPs were significantly larger than NOR, EXC, or RD EPs in twelve series. The remaining two series of PRS EPs recorded referentially over posterior marginal and medial suprasylvian gyri, i.e., over the area where PRS activity was most conspicuous, were smaller than the same responses obtained during RD. (This may indicate that in some instances the large amplitude PRS activity may interfere with the summation process carried out by the CAT computer.) All PRS EPs were larger than REL EPs except one series obtained between posterior marginal and medial suprasylvian gyri which showed no difference in these two behavioral states. Eight series of PRS EPs were comparable to those obtained during SL. The remaining six responses were smaller: recorded between anterior marginal and posterior sigmoid, posterior marginal and posterior sigmoid, and posterior marginal and medial suprasylvian gyri (bipolar recording), and over posterior marginal, posterior sigmoid, and posterior suprasylvian gyri (referential recording). DISCUSSION

In four out of five cats the facilitation of somato-sensory EPs observed during PRS, was more pronounced than that previously reported on the auditory (Marczynski et al. 1968) and visual EPs (Hackett and Marczynski 1968). Similar to the generalization of auditory EPs, the facilitation of somato-sensory EPs during PRS was not topographically restricted to the visual cortex (posterior marginal gyrus); i.e., to the area of PRS activity. A comparable facilitation could be observed over anterior and posterior sigmoid gyri, and even greater over anterior

marginal and suprasylvian gyri where PRS could not be obtained, and where instead, the ECoG patterns showed low voltage fast activity during bursts of PRS. The widespread and dramatic character of the reward-induced facilitation of EPs is a common feature shared with the generalization phenomena described by John and Killam (1959) and others (cf, John 1967). After habituation to a biologically irrelevant stimulus the cortical EPs are significantly reduced in amplitude and topographically restricted to the proper projection area. These responses show facilitation and wide distribution during generalization; i.e., when a subject performs a previously acquired conditioned response upon the presentation of a modified conditioned stimulus which contains some novel characteristics when compared to the previous stimulus used during training (e.g., change in frequency of flicker stimuli). We believe that there are three main differences between the generalization phenomena and those occurring during PRS: (1) the presentation of food reinforcement presumably does not have any elements of novelty which is required to produce generalization, since our subjects were performing the same responses in the same environment, and on the same reinforcement schedule for more than one year; (2) any novel environmental stimuli (including a change in quality or quantity of food reinforcement) had to be carefully avoided in order to obtain well developed PRS activity; (3) the reward-induced facilitation of EPs is of a very transient nature; and (4) it is repeatable thousands of times in the same experimental situation as long as the subject is motivated to press the lever to obtain food, whereas the generalization phenomena may show relatively rapid extinction after several trials using the same stimulus parameters. The significant reduction in amplitude of the long latency secondary components in most RD EPs as compared to those recorded during PRS indicates that visual input may play a role in the enhancement of somato-sensory cortical responses, particularly, when they are actively facilitated by reinforcement. This may be a phenomenon similar to that reported by Chang (1952) on auditory EPs. However, before such a conclusion can be drawn one must exclude a Electroenceph. clin. Neurophysiol., 1969, 26:41--49

REINFORCEMENT AND SOMATO-SENSORY EPS

possibility that turning off the light for only about one-fifth of the subject's performance in the test cage (NOR, PRS, EXC, REL and RD) does not constitute a novel environmental stimulus which may be responsible for a shift in the arousal level. Assuming that transient and phasic facilitation of "irrelevant" sensory inputs triggered by positive reinforcement is a general phenomenon occurring in higher mammals, it can be postulated that it plays a role in complex adaptational psychodynamic processes through an influence opposite to that of habituation. As pointed out by Eccles (1966), perception of environmental stimuli is much more synthetic than we imagine. An overwhelming indirect evidence indicates that this synthesis is an outcome of convergence of all sensory modalities although the spectrum of conscious perception may be very limited. It is conceivable that "flashes" of "irrelevant" inputs triggered by positive reinforcement maintain a tonic activity of neuronal pools which in turn produce systems of subliminally excited "fringe neurons", thus providing a necessary background for correct integration of relevant inputs. This general concept on the physiological significance of the reward-induced facilitation of sensory input is further supported by: (1) many clinical observations on the functional relationship between the tonus of positive reinforcement systems and adaptational psychodynamic processes (Heath 1964; Rado 1962, 1964); and (2) sensory deprivation experiments in man which lead to a variety of perceptual and cognitive disturbances caused by the elimination of "irrelevant" sensory inputs (Freedman et al. 1961; Vernon et al. 1961 ; and others). SUMMARY

Five cats bearing chronically implanted cortical electrodes were trained to press a lever for 0.5 ml of milk reward. They displayed characteristic bursts of high voltage slow wave (6-9 c/sec) activity; i.e., post-reinforcement synchronization (PRS) over the visual cortex (posterior marginal gyrus) after the presentation and during consumption of milk reward. Computer averaged somato-sensory evoked potentials (EPs) induced by mild electrical stimuli delivered to the skin were recorded over the specific and non-specific

47

cortical projections during the following behavioral states: (1) after non-rewarded lever pressing (NOR); (2) after presentation of reward in the illuminated environment; i.e., during bursts of PRS; (3) during consumption of reward in the dark (RD); i.e., during complete suppression of PRS activity; (4) in a waking but relaxed subject after satiation (REL); (5) during emotional excitement (EXC); and (6) during the early stage of spindle slow wave sleep (SL). The subjects were habituated to mild skin stimuli whose intensity was kept 2 5 ~ below the threshold which interfered with the occurrence of PRS. These stimuli were neither disrupting the subject's performance nor physiological sleep. The irrelevant character of the stimuli was maintained by their presenting at random during aforementioned six behavioral states. Most of the fourteen EPs (comprising 9 primary and 14 secondary c~mponents) recorded over frontal and parieto-occipital cortex were conspicuously augmented during bursts of PRS and during SL as compared to the corresponding EPs obtained during NOR, EXC, REL and RD. The primary responses in all PRS EPs and in six SL EPs were larger than those obtained during NOR or EXC; they were also larger in six PRS EPs as compared to those recorded during SL (two of them showed no difference and one PRS EPs was smaller); five PRS EPs were larger than those obtained during REL. All fourteen secondary responses showed a conspicuous augmentation during SL, PRS and REL as compared to the corresponding responses obtained during NOR and EXC. The amplitude of eight PRS EPs was comparable to that obtained during SL (the remaining 6 were smaller). All except one PRS EPs were larger than REL EPs (one showed no difference). Twelve PRS EPs were significantly larger than the corresponding ones recorded during RD suggesting that the visual input may play a role in the reward-induced facilitation of long latency somatosensory cortical EPs recgrded over primary and secondary visual projections, and even beyond the classical visual cortex over the anterior marginal, and anterior and posterior sigmoid gyri. A possible physiological significance of the phasic facilitation of "irrelevant" sensory input Electroenceph. olin. NeurophysioL, 1969, 26:41-49

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T . J . MARCZYNSKI AND J~ T. HACKETT

caused by positive reinforcement has been discussed. RESUMI~ SYNCHRONISATION ET FACILITATION I~LECTROCORTICALES POST-RENFORCEMENT DES POTENTIELS 1~VOQU}~S CORTICAUX SOMATO-SENSITIFS AU COURS DU COMPORTEMENT APPI~TITIF CONDITIONNI~ DU CHAT

Cinq chats porteurs d'Slectrodes corticales implantSes chroniques ont 6tS entralnSs h presser un levier pour une gratification de 0,5 ml de lait. Ils montrent des bouffSes caractSristiques d'activitS lente (6 5. 9 c/see) de haut voltage, i.e. une synchronisation post-renforcement (PRS) sur le cortex visuel (gyrus marginal postSrieur) apr6s la prSsentation du lait et pendant sa eonsommation. Les potentiels Svoqu6s somato-sensitifs (EPs) moyennSs par un calculateur, induits par des stimuli Slectriques d'intensit6 moyenne appliquSs la peau ont 6t6 enregistrSs au niveau des projections eorticales spSeifiques et non spScifiques pendant les Stats comportementaux suivants: (1) apr~s avoir press6 le levier sans gratification (NOR); (2) aprbs prSsentation d'une gratification dans un environnement 6clairS, i.e. pendant les bouffSes de PRS; (3) pendant la eonsommation de la gratification dans l'obseurit6 (RD), i.e. pendant la suppression complete de l'aetivit6 PRS; (4) ehez un sujet 6veill6 mais dStendu apr6s la sati6t6 (REL); (5) pendant 1'excitation 6motionnelle (EXC); et (6) au eours du stade prScoce du sommeil avec fuseaux d'ondes lentes (SL). Les sujets sont habituSs ~t des stimuli cutanSs faibles dont l'intensit6 est maintenue 5. 25% au-dessous du seuil qui interf6re avec la survenue de PRS. Ces stimuli n'ont jamais interrompu l'efficienee des sujets, ni le sommeil physiologique. Le caract~re alSatoire des stimuli est assurS par le fait qu'ils sont prSsentSs au hasard pendant les 6 Stats eomportementaux mentionnSs ci-dessus. La plupart des 14 EPs (comportant 9 composantes primaires et 14 composantes secondaires) enregistrSs au niveau du cortex frontal et pari6tooccipital sont de faqon tr~s nette, augment6s pendant les bouff6es d'activit6 PRS et pendant le SL par comparaison aux EPs correspondants obtenus au eours des p6riodes NOR, EXC, REL

et RD. Les r6ponses primaires de tous les potentiels 6voqu6s PRS et dans 6 potentiels 6voqu6s SL sont plus grandes que celles obtenues au cours des p6riodes NOR ou EXC; pour 6 potentiels Svoqu6s PRS elles sont Sgalement plus grandes que celles enregistrSes pedant SL (2 d'entre elles ne montraient pas de diffSrence et 1 potentiel Svoqu6 PRS Stait plus petit); 5 potentiels SvoquSs PRS Staient plus grands que ceux obtenus an cours des REL. La totalitS des 14 rSponses secondaires montre une augmentation indiscutable pendant SL, PRS et REL par comparaison aux rSponses correspondantes obtenues pendant NOR et EXC. L'amplitude de 8 potentiels Svoqu6s PRS Stait comparable h celle obtenue pendant SL (les 6 restants Stant plus petits). Tous les potentiels SvoquSs PRS sauf un Staient plus grands que les potentiels SvoquSs REL (I ne montrait aucune diffSrence). Douze potentiels SvoquSs PRS Staient de fa¢on significative plus grands que les potentiels SvoquSs correspondants enregistrSs pendant RD; ceci suggbre que les affSrences visuelles peuvent jouer un r61e darts la facilitation induite par la gratification des potentiels Svoqu6s corticaux somato-sensitifs ~t longue latence enregistrSs au niveau des aires de projections visuelles primaires et secondaires, dSbordant m~me le cortex visuel classique au-delS. de la ligne antSrieure, et des gyri sigmoides antSrieur et postSrieur. Les auteurs discutent la signification physiologique possible de la facilitation phasique d'affSrences sensorielles alSatoires provoquSe par le renforcement positif. REFERENCES BONEAU, C. A. The effects of violations of assumptions underlying the t-test. Psychol. Bull., 1960, 57: 49-64. CHANG,H-T. Cortical response to stimulation of lateral geniculate body and the potentiation thereof by continuous illumination of retina. J. Neurophysiol., 1952, 15: 5-26. CLEMENTE,D. C., STERMAN,M. B. and WYRWICKA,W. Post-reinforcement EEG synchronization during alimentary behavior. Electroenceph. clin. Neurophysiol., 1964, 16: 355-365. ECCLES, J. C. Conscious experience and memory. In J. C. ECCLES CEd.), Brain and conscious experience. Springer, New York, 1966: 314-344. FREEDMAN, S. J., GRUNEBAUM,H. V. and GREENBLATT, M. Perceptual and cognitive changes in sensory depriva-

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REINFORCEMENT AND SOMATO-SENSORY EPS tion. In P. SOLOMON (Ed.), Sensory deprivation. Harvard University Press, Cambridge, Mass., 1961: 58-71. HACKETT, J. T. and MARCZYNSKI,T. J. Scopolamine and post-reinforcement facilitation of somatosensory and visual evoked potentials in the cat. Fed. Proc., 1968, 27 (2) : 571. HEATH, R. G. Pleasure response of human subjects to direct stimulation of the brain: Physiologic and psychodynamic considerations. In R. G. HEATI4 (Ed.), The role of pleasure in behavior. Grune and Stratton, New York, 1964: 219-247. JOHN, E. R. Mechanisms of memory. Academic Press, New York, 1967, 468 p. JOHN, E. R. and KILLAM, K. F. Electrophysiological correlates of avoidance conditioning in the cat. J. Pharmacol. exp. Ther., 1959, 125: 252-274. MARCZYNSKI,T. J., ROSEN, A. J. and HACKETT,J. T. Post-reinforcement electrocortical synchronization

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and facilitation of cortical auditory evoked potentials in appetitive instrumental conditioning. Electroenceph. clin. Neurophysiol., 1968, 24: 227-241. RADO, S. Theory and therapy: the theory of schizotypal organization and its application to the treatment of decompensated schizotypal behavior. In collected papers, Psychoanalysis of behavior. Grune and Stratton, New York, 1962: 127-140. RADO, S. Hedonic self-regulation of the organisms. In R. G. HEATH (Ed.), The role of pleasure in behavior. Harper and Row, New York, 1964: 257-264. STERMAN,M. B. and WYRWICKA,W. EEG correlates of sleep: evidence for separate forebrain substrates. Brain Res., 1967, 6: 143-163. VEF.NON, J. A., MCGILL, T. E., GULICK, W. L. and CANDLAND,D. R. The effect of human isolation upon some perceptual and motor skills. In P. SOLOMON (Ed.), Sensory deprivation. Harvard University Press, Cambridge, Mass., 1961: 41-57.

Reference: MARCZYNSKI,T. J. and HACKETT,J. T. Post-reinforcement electrocortical synchronization and facilitation of cortical somato-sensory evoked potentials during instrumentally conditioned appetitive behavior in the cat. Electroenceph. clin. Neurophysiol., 1969, 26: 41-49.