NEUROBIOLOGY OF THE INTEGRATIVE ACTIVITY OF THE BRAIN DYNAMICS OF INTERSTIMULUS INTERVALS IN THE ACTIVITY OF NEURONS OF THE SENS O R I M O T O R CORTEX DURING THE DEVELOPMENT OF A FOOD-PROCURING REFLEX IN THE RABBIT

UDC 612.821.6+612.822.3+612.825

D. V. Timoshin

The impulse activity of neurons of the sensorimotor cortx (SMC) during the formation of a food-procuring reflex in the rabbit, as well as in trained animals if reinforcement is discontinued and substituted, was investigated. In the process of training the neurons of the SMC acquire the capacity for anticipatory reactions. The sudden abolition and substitution of reinforcement elicits the appearance of activity which is characteristic for the process of discordance in the acceptor of the result of the action. Repeated substitutions lead to the appearance of activity which is characterized by a coordination process at the moment of the "recognition" of the substitution, despite the absence offood reinforcement. Numerous investigations devoted to the analysis of the processes of the formation of goal-directed alimentary behavior have demonstrated that the various stages of this form of behavior find their most complete reflection in the electrical activity of the sensorimotor cortex (SMC) of the brain [3, 7, 8, 11 14]. In this connection the aim of the present study was the investigation of the dynamics of the activity of neurons of the SMC in the process of the training of animals to a food-procuring reflex in free behavior conditions. METHODS

The investigations were carried out in eight chinchilla rabbits of both sexes, weighing from 2.5 to 3.5 kg, in 14 chronic experiments. The untrained animals were subjected to food deprivation over 24 h. Then the rabbits were trained to go to an automatically presented food dispenser in response to four auditory clicks and eat a portion of food (carrot, 2 g). The recording of the impulse activity of the neurons of the SMC was carried out out in the hungry animals and during training. The impulse activity of the neurons of the SMC was also investigated in trained animals in experiments with the sudden abolition and substitution of reinforcement. The coordinates of a stereotaxic atlas of the rabbit brain [18] were used to introduce the microelectrodes into the sensorimotor area of the cortex. In order to prevent pulsation of the brain tissue after the removal of the dura mater, the trephined opening was filled with agar-agar (warmed in isotonic solution). The pickup of the electrical activity of the neurons was carried out extracellularly by a glass electrode with a tip diameter of about 1 I.tm,filled with 3 M KCI. The microelectrode was introduced immediately before the beginning of the experiment by means of a mechanical micromanipulator (weight 5 g) fixed in the rabbit's skull [13]. The complex of electrophysiological apparatus included an amplifier in the microcircuit with an input resistance of 150 Mr2, fixed to the animal's skull, an amplifier and oscillograph. The recording of the electrical activity of the neurons was done on the magnetic tape by means of a 7003 Bruhl and Kjaer (Denmark) measuring tape recorder. The markers of the presentation of the food dispenser and the moment of the grasping of the food by the animal were automatically recorded in the process of the experiment. An NTA-1024 (Hungary) impulse analyzer was used for the analysis of the neuronograms obtained. Since the average frequencies of the impulse activity of the neurons in various forms of the animals' behavior vary insignificantly [12, 17], the statistical analysis of the results obtained was carried out by plotting percent histograms of the distribution of the interimpulse intervals using a piecewise-nonunilbrm time scale by means of an Apple-lI minicomputer. The

P. K. Anokhin Institute of Normal Physiology, Russian Academy of Medical Sciences, Moscow. Translated from Zhumal Vysshei Nervnoi Deyatel'nosti imeni 1. P. Pavlova, Vol. 41, No. 4, pp. 749-760, July-August, 1991. Original article submitted June 1, 1990; revision submitted January 1, 1991. 370

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INVESTIGATION RESULTS In the course of the experiment 66 neurons were investigated. In the hungry animals in the resting state 42 neurons of the SMC (63%) exhibited a bimodal distribution of the interimpulse intervals in the histogram within the limits of 5-20 and 100-200 msec in the background activity. A number of neurons with burst background activity, 16 (25%), exhibited a trimodal distribution of the interimpulse intervals of 5-20, t00-200 and greater than 1000 msec. Eight neurons (12%) were observed with a monomodal distribution of the intervals on the histogram within the limits of 20-30, 30--60, and 90-100 msec. The presentation of the acoustic signal for the first time in the untrained animals did not induce any changes in behavior. Changes were also not noticed when the impulse activity was analysed. At the moment of the seizure of the food, 56 neurons (83%) altered impulse activity. At the time only 100-200 msec interval was dominant on the histogram in 32 neurons (59%); such was the case in eight neurons (15%) which as a rule exhibited a distribution of the interimpulse intervals on the histogram of a monomodal character in the background activity, the 50-80 msec interval. Six neurons (9%) exhibited a different distribution of the interimpulse intervals (10--20, 70, 90 msec, etc.),while changes were not found in the activity in 10 neurons (17%) (Fig. 1). The most characteristic regularization was identified in neurons having a burst-like character of the initial activity (a trimodal distribution of the interimpulse intervals of 5-20, 100-200, and greater than 1000 msec). An orienting-investigatory reaction (OIR, exploratory behavior) appeared in the rabbit at the moment of the presentation of the four clicks at the second to third combination of the auditory signal and the unconditional food reinforcement; while when the histogram was analyzed, the distribution at this time of the interimpulse intervals was observed to be within the limits of 40-50 and 100-200 msec (Fig. 2). Subsequently, in the process of the training of the animal, the OIR and the changes in the histogram corresponding to it disappeared. The following time course of the behavioral continuum and of the impulse activity of the neurons of the SMC was identified. The development of the food-procuring skill took place at the 15th-20th combination. But stable changes in the character of the impulse activity, i.e., regularization at the moment of the presentation of the conditional auditory signal (the monomodal distribution of the interimpulse intervals on the histogram which is characteristic of reinforcement), appeared significantly earlier than the stable motoric reaction of the rabbit to the sound, namely, in response to the fifth to sixth combination. On this basis we hypothesized that the first associative connections had already formed, but all of the interneuronal interactions necessary for the formation of a functional system consisting of a large number of nerve elements and structures had not yet been established for the realization of the skill in the form of a specific behavioral act. With each successive reinforcement a gradual coinciding took place in time of the moment of the change in the character of the activity in response to the auditory signal and of the beginning of the motoric reaction of the rabbit. At the final stage of training, the reorganization of the impulse activity and the rabbit's run to the food dispenser already took place simultaneously in response to the first of the four clicks (Fig. 3). At late stages of training some neurons manifested an inhibitory type of reaction to the conditional auditory signal, and their discharge activity was renewed at the moment of the seizure of the food, with interval characteristics within the limits of 100-200 msec. In the following series of experiments, the trained animals were exposed, in addition to the food reinforcement, to its sudden one-time abolition, as well as, from time to time, to the replacement of the food with an inedible object - porolon (the "surprise" method [1]). It was observed in the experiments involving the abolition of reinforcement that a regularization of the impulse activity (distribution primarily of a monomodal character at 100-200 msec on the histogram) or inhibition lake place in response to the auditory signal. Since the animal is trained, the run to the food dispenser takes place at this point. A bimodal distribution of the interimpulse intervals within the limits of 40-50 and 100-200 msec (Fig. 4) is identified on the histogram at the moment of the lowering of the muzzle into the empty food dispenser, i.e., the same interval characteristics as at the beginning of training during the OIR (see Fig. 2). The appearance of the orienting-investigatory activity of the animal in this case reflects the noncoincidence of the expected and the actual result, which was caused by the sudden abolition of the food reinforcement. 377

The following results were obtained in the experiments involving the replacement of the food with an inedible object. At the time of the first presentation (it was usually the 40th to the 50th combination in the experiment), the rabbit always seized the porolon and tried to chew it. At that moment the impulse activity which is characteristic of the usual reinforcement was maintained (a monomodal distribution of the interimpulse intervals of the histogram, Fig. 5). The substitution alternated with the presentation of reinforcement without a specific sequence, every two to five combinations, on the average. As early as the second to third substitutions the rabbit manifested the signs of the OIR, and a bimodal distribution of the interimpulse intervals of 40-50 and 100-200 msec appeared in the histogram at the moment of the discovery of the substitution. When the substitution and the reinforcement were alternated further, that is, at the fourth to fifth discovery of the substitution when the rabbit approached the food dispenser it no longer seized its content, but at first sniffed it. When the substitution was discovered, the impulse activity of a number of the neurons took on the character of regular "activation" (Fig. 6, [6]). Other neurons responded with an inhibitory reaction in the same situation. The rabbit then retuned to the starting place, and at that time the impulse activity of the neurons of the SMC gradually acquired its background character.

DISCUSSION OF RESULTS It has been demonstrated in our investigations that the state of hunger is characterized by the presence of a specific organization of the impulse stream of the neurons under investigation, and organization which is formed under the influence of the dominant alimentary motivation, of the situational afferentation and memory of the animal [4, 6, 8, 9,12]. This organization is associated with the absence of a useful adaptive result, and is expressed in a primarily bi- and trimodal distribution of the interimpulse intervals on the histogram. The substantial number of neurons which discharge in this manner is evidently the result of the inclusion of these cells in the alimentary motivational excitation, and possibly reflects the cellular processes which are associated with the expectation of the reinforcement and with processes of the assessment of the parameters of the food reinforcement at the level of the receptor structures of the neuron [10, 15]. Thus the stage of prefiring integration at the level of the individual neuron, or more precisely, its interval characteristics carry within themselves the modal elements of the parameters of the expected result. The character of the impulse activity undergoes certain changes in the process of the food-procuring behavior of the animal, when the result (the food ) is achieved as well as in response to the action of the conditional auditory signal. The latter form of reacting appears in the course of the consolidation of the food-procuring skill. The majority of the neurons of the SMC change their activity when the rabbit is fed, and subsequently, as the repeated reinforcement progresses, they exhibit regularization even as soon as the animal approaches the food dispenser, i.e., as the consolidation of the food-procuring skill progresses, the neurons of the SMC acquire the capacity for anticipatory reactions, thus reflecting in their activity the processes of the achievement of a useful result and of the formation of positive emotions. The process of the formation of a functional system and the development of goal-directed behavior at the neuronal level are constructed on the principles of the anticipatory reflection of reality (as described by P. K. Anoldain), which is the basis for the successful achievement of a useful adaptive result. The presence of elements of the OIR [2], as well as the minimization of the discharge activity of individual neurons, characterize certain stages in the training of animals in any skill [6]. These experiments also revealed certain characteristics of the reorganization of the character of the impulse activity of the neurons when the reinforcement is discontinued and replaced. In this case, the process of discordance is reflected in the establishment of a bimodal (40-50 and 100-200 msec) distribution of the interimpulse intervals which is different from the initial distribution, and the alternation of the substitution and the usual reinforcement rapidly leads to the "incomplete learning" of the animal to recognize the substitution, which is manifested in the analysis of the impulse activity by the pattern of reinforcement (concordance). The above-described forms of reacting of the neurons of the SMC in the case of the alternation of replacement and reinforcement are characteristic for automatic alimentary behavior [ 13, 16], and are regarded as the reflection of processes of coordination in the CNS, in the light of anticipation and minimization in the discharge activity of the neurons [6]. The characteristic of the animals' behavioral reactions as well as neuronal activity in the described experiments define both the definite conservatism as well as the plasticity of the functional system which forms in the animals during short periods of training.

378

RESULTS 1. The state of hunger is characterized by the presence of a specific organization of the impulse stream of the neurons of the sensorimotor cortex primarily in the form of a bi- and trimodal distribution of the interimpulse intervals on the histogram. This organization undergoes dynamic changes in the course of the animals' alimentary behavior, as well as in response to the conditional auditory signal. The specific organization of the impulse stream of the neurons under investigation is associated with the processes of expectation and of the assessment of the parameters of the food reinforcement, and is reflected at the level of the individual nerve cell. 2. The development of goal-directed behavior is accompanied by the specific dynamics of the reorganization of the character of the impulse activity on the principle of the anticipatory reflection of reality. 3. In the instance of a sudden abolition, and especially with the irregular alternation of the usual reinforcement and replacement of the result, a high degree of the plasticity of the functional system and the rapid development of an additional skill in the recognition of the substitution are identified; this is reflected in the appearance of activity which is characteristic for the process of coordination at the level of the individual nerve cell. LITERATURE CITED I. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

13. 14. 15. 16. 17. 18.

P.K. Anokhin and E. Strezh, "A study of the dynamics of higher nervous activity. Report III. Disturbance of active choice as the result of substitution of the unconditional stimulus," Fiziol. Zh. SSSR, 16, No. 2, 280-294 (1933). P.K. Anokhin, "The role of the orienting-investigatory reaction in the formation of the conditioned reflex," in: The Orienting Reflex and Orienting-Investigatory Activity [in Russian], Izd-vo AMN SSSR, Moscow (1958), pp. 9-20. P.K. Anokhin, The Biology and Neurophysiology of the Conditioned Reflex [in Russian], Meditsina, Moscow (1968). P.K. Anokhin, The Physiology of Functional Systems [in Russian], Meditsina, Moscow (1975). B.V. Zhuravlev and N. N. Shamaev, "Analysis of the activity of neurons of the orbital cortex of rabbits in alimentary behavior," Zh. Vyssh. Nervn. Deyat., 31, No. 5, 1010-1017 (1985). B.V. Zhuravlev, "Systemic analysis of the activity of brain neurons during the food-procuring behavior of animals," in: Neurons in Behavior. SystemicAspects [in Russian], Nauka, Moscow (1986). A.I. Lakomkin and I. F. Myagkov, Hunger and Thirst (From the Physiological Perspective) [in Russian], Meditsina, Moscow (1975). K.V. Sudakov, Biological Motivations [in Russian], Meditsina, Moscow (1971). K.V. Sudakov, "The significance of motivational excitations in the integrative activity of brain neurons," Zh. Vyssh. Nervn. Deyat., 28, No. 1, 8-15 (1978). K.V. Sudakov and B. V. Zhuravlev, "Burst-like rhythmicity of neurons as a reflection of processes of hungry animals' expectation of a food reinforcement," Zh. Vyssh. Nervn. Deyat., 29, No. 3,643--646 (1979). K.V. Sudakov, "Systemic mechanisms of brain activity," in: Methodological Aspects of Brain Science [in Russian], Meditsina, Moscow (1983), pp. 102-116. Yu. A. Fadeev, "The dynamic alteration of the degrees of freedom of cortical neurons at different stages of the formation of an alimentary behavioral act," in: Systemic Analysis of Mechanisms of Behavior [in Russian], Nauka, Moscow (1979), pp. 287-298. V.B. Shvyrkov, The Neurophysiological Study of Systemic Mechanisms of Behavior [in Russian], Nauka, Moscow (1978). V.B. Shwrkov, "A study of the activity of neurons as a method of the psychophysiological investigation of behavior," in: Neurons in Behavior. SystemicAspects [in Russian], Nauka, Moscow (1986), pp. 6-25. A.I. Shumilina, B. V. Zhuravlev, and N. N. Shamaev, "Neuronal mechanisms of an animal's assessment of the results of behavioral activity," Vest. AMN SSSR, No. 2, 21-26 (1982). E.V. Evarts, "Pyramidal tract activity associated with a conditioned hand movement in the monkey," J. Neurophysiol., 29, No. 6, 1011-1021 (1966). V.B. Mountcastle, "Modality and topographic properties of single neuron of cat's somatic sensory cortex," J. Neurophysiol., 20, No. 4,408--434 (1957). C.H. Sawyer, J. W. Everett, and 1. D. Green, "The rabbit diencephalon in stereotaxic coordinates," J. Comp. Neurol., 101, No. 3, 801-824 (1954). 379