Instrumental alimentary conditioned reflexes ( CR ) in response to the electrostimulation of the hippocampus were developed in experiments on dogs with ...
INTRALIMBIC EVOKED POTENTIALS DURING THE FORMATION OF AN ALIMENTARY CONDITIONED REFLEX IN RESPONSE TO THE ELECTROSTIMULATION OF THE HIPPOCAMPUS OF DOGS
L,, I. Chilingaryan and G. A. Grigor'yan
UDC 612.821.6+612.822.3+612.822.6
Instrumental alimentary conditioned reflexes ( CR ) in response to the electrostimulation of the hippocampus were developed in experiments on dogs with electrodes implanted in various divisions of the hippocampus, the amygdala, the septum, and the hypothalamus. During their development the evoked potentials (EP) were investigated in the hippocampus itself and in other limbic structures, as well as in the hippocampus during the testing of the latter for the purpose of verifying generalization. The formation and extinction of the CR was accompanied by changes in the amplitude-temporal characteristics primarily of late components of the EP picked up from the lateral hypothatamus and the amygdaloid complex in response to the hippocampal electrostimulation. During the carrying out of this stimulation of signal functions (pedal pressing to obtain food), the average amplitude of the trace positivity and of the late negative wave were found to be lower than by the end of extinction in the presence of ineffectiveness of the signal. The average amplitudes of the late components of the hippocampal EP which arose in response to electrostimulation of the amygdala were lower in those tests in which the instrumental movement appeared when the generalization of the CR was tested. The placement of a function on the structural canvas is important for the elucidation of the mechanism of formation and functioning of conditioned reflexes (CR). When EP and conditioned reflex movements are elicited by one and the same stimulus, it is evident that which formations of the brain are obligatory components of the complex constellations of structures assuring the execution of a specific CR can be judged on the basis of changes in EP. As is well known, the formation and functioning of the CR correlate in a specific manner with the changes in the amplitude-temporal characteristics of EP initiated by the signal stimulus. This has been demonstrated mainly in experiments in which light or sound stimuli served as the signal [1, 2]. In a smaller number of studies of this kind changes were found for EP arising in response to signal electrostimulation (ES) of the cerebral cortex [12, 13] or of subcortical structures {8, 9]. It has been shown that the specific character of the conditioned reflex transformations of the EP depends on a multiplicity of factors: the level of wakefulness and the degree of emotional tension associated with the stage of development and the type (classical or instrumental), and nature (alimentary or defensive) of the CR, as well as on the type of animal, the parameters, modality, or site of stimulation, and the region of pickup of the EP. On the other hand, motivations and emotions, the most complex vitally important unconditioned reflexes, on the basis of which CR are formed, are linked to the function of the limbic system (LS) of the brain [5, 6, 11]. Therefore the structures of the LS must, it would appear, occupy one of the central positions in the constellation of structures which is specific for each CR, the activation of which assures its functioning. The fact that the hippocampus is included in the constellation of structures of various CR was found in experiments involving the recording of the total electrical and neuronal activity [4, 7], as well as of the EP arising in response to a tone [14, 15], or to a combination of a tone with ES of the hippocampal formation [23, 25]. In these studies changes in the amplitude-temporal characteristics of the hippocampal EP at various stages of the formation of a drinking CR in rats [14], during the extinction of a food-procuring CR in rabbits, as well as a function of the placement of the tone [16], were analyzed. In studies [23, 25], in which a complex conditional stimulus, consisting of a tone and ES of the hippocampus were used in developing the CR, the EP of another one of its divisions on the side of the stimulation or of the same area but on the opposite side were investigated. Thus, in experiments on rabbits [25], a significant increase in the population spike of the EP picked up in the dentate fascia in response to ES, coinciding with a tone, of the perforant tract was demonstrated during Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow. Translated from Zhumal Vysshei Nervnoi Deyatel' nosti imeni I. P. Pavlova, Vol. 41, No. 5, pp. 926-936, September-October, 1991. Original article submitted May 5, 1991; revision submitted May 15, 1991. 0097-0549/92/2206-0495512.50 9
Plenum Publishing Corporation
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the development of an eyeblink drinking CR in them. An attempt was made to investigate the conditioned reflex influences on the transmission of excitation in this element of the hippocampal formation by forming a two-sided avoidance reflex in rats in response to the ES of the perforant tract and by recording EP in the dentate fascia [18, 21, 22]. As the development of the CR progressed, the amplitude of the slow component of the EP which is associated with the summary EPSP increased, and the amplitude of the population spike decreased [21]. An abbreviation of the peak latent period of the hippocampal EP also took place [22]. A decrease in the population spike was also found when EP were recorded in the dentate fascia during the development of an alimentary instrumental CR in response to a single stimulation of the perforant tract [24], and when recording from the contralateral dorsal hippocampus (DHp) during the development of a drinking instrumental CR in response to a commissural ES [3]. The EP of the sensorimotor cortex of the cat during the formation and extinction of CR using ES of the LH as the conditional stimulus has also been investigated [9]. Thus, in the studies known to us, only intrahippocampal or hypothalamocortical EP have been investigated during the formation of CR. At the same time, the role of other limbic structures in associative learning has been identified by means of the recording of cell activity [19, 20]. In this context it seemed to be of interest to clarify the nature of the changes to which intralimbic EP are subjected during the formation of CR, and thus to attempt to elucidate the degree of involvement of the hippocampal-amygdalar or hippocampal-hypothalamic element of their LS in this process. In its turn, the discovery of the structures activated in this case will facilitate the elucidation of the mechanism of the formation of CR. The purpose of the present study is a comparison with one another of the degree and directionality of the changes in the EP of various limbic structures which arise in response to signal ES of the hippocampus, and in the hippocampal EP recorded during the stimulation of these structures during the testing of generalization of the reflex. METHODS Concentric stainless steel electrodes (diameter 0.6 mm) were implanted stereotaxically in accordance with the atlas of Lira, et al. [17] into the hippocampus, amygdala, hypothalamus, and septum of the brain of three dogs. Three weeks after the operation we proceeded to the sequential development of three alimentary instrumental CR: a basic, or situational, reflex in response tO light flashes and to ES of the hippocampus. In the first case the dog received each time, in response to pressing a pedal, a dish with 30 g of ground meat; in the second and third the food was presented only when the pedal presses were accomplished during the time of action of the conditional stimuli. The light flashes were presented at a frequency of 50 Hz, while the stimulation of the hippocampus (in Tishka and Peggy of the dorsal hippocampus, and in Flin(of the ventral hippocampus) was carried out at a frequency of 2 Hz. In the course of an experiment 15-20 combinations of stimuli were presented at the interval between them of 3-5 min. Stimulation of the brain was accomplished by biphasic rectangular pulses of current: duration 0.5 msec; duration of stimulation 8-9 sec; and current strength 0.2-1.0 mA. During the course of the development of CR in response to ES of the hippocampus, EP were recorded from the lateral hypothalamus (LH) and the central nucleus of the amygdala (CA) in Tishka, and from the medial septum (MS) and the contralateral (DHp) in Peggy. In addition, the EP of the hippocampus were recorded also in tests for generalization during testing low-frequency stimulation of the amygdala. The pickup of the potentials was accomplished from the cylinder of the concentric electrode in relation to an indifferent electrode (silver wire, diameter 1 ram) located on the occipital protuberance or in the bone above the frontal sinus. The EP of the limbic structures in response to ES of the hippocampus were investigated as a function of the character of the behavioral reactions elicited by the signal stimulus and at various stages of the development and consolidation of the instrumental CR. In the tests for generalization EP in the initially signal structure were investigated in response to test ES. The EP were averaged across 15 individual EP by means of an Atak-501-10 analyzer; the analysis epoch was 400 or 200 msec. The average EP was subjected to further statistical analysis by means of a laboratory microcomputer. The amplitudetemporal characteristics of all of the components of the EP, and their mean square deviations were calculated, and the degree of significance of the differences of the corresponding components of the EP, obtained in the combination or the tests, in which an instrumental movement was accomplished was found on a basis of the Student test as compared with those in which it was absent. The location of the tips of the electrodes in the above-indicated structures were established by morphological investigation carried out by V. N. Mats, senior scientific worker of the laboratory of CNS morphology, for which the authors 496
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Fig. 2. Dynamics of the amplitude changes on the EP in the DHp (I) and MS (II) in response to ES of the contralateral DHp during the development in response to the stimulation of the alimentary CR, The dog Peggy. Along the horizontal, days of the experiment; along the vertical, amplitude of the components of the EP, ~tV. Circles, the EP prior to tests for generalization; squares, after them. A-D) Components of the EP. Designations as in Fig. 1.
express their appreciation. INVESTIGATION RESULTS The number of components and the amplitude-temporal parameters of the intralimbic EP depended both on the intensity and site of stimulation and on the structure from which they were picked up. The most constant components of the intralimbic EP were the initial negativity (Fig. 1C, N1), the trace positivity (P2), and the late negative wave (N3). Initial positivity preceding the initial negativity, an additional negative wave superimposed on the latter, as well as a late positive wave were encountered more rarely. They, along with the more constant components of the intralimbic EP, will be described in another article in connection with change in the level of motivation and with the accomplishment of unconditioned reflexes. During the development of the CR to the ES of the hippocampus, the EP recorded in response to it in the limbic structures of the brain underwent substantial changes. These changes were associated both with the character of the behavioral reactions arising in response to the signal stimulus and with the degree of specialization and consolidation of the CR. The averaged EP recorded in the LH (A) and the CA (B) when the dog pressed the pedal during the signal stimulation (a) or immediately after it (b), as well as when there was no instrumental movement either during or after this stimulation (c), are shown in Fig. 1, I. It can be seen that the EP differ from one another substantially depending upon the presence or absence of the instrumental movement (or series of movements). The trace positivity (P2) and the late negative wave (N 3) of the EP picked up from the LH (A) changed statistically significantly during the accomplishment of the conditioned reflex motoric reaction. The amplitude of the trace positivity was least when the instrumental reaction occurred during signal stimulation (a) and greatest in the complete absence of movement (c). Moreover, the difference between the amplitude of the trace positivity in 498
these two states was significant (p < 0.05). When the instrumental movement was completed following the termination of the stimulation of the brain (b), the amplitude of the trace positivity was also higher than in those cases in which the pedal presses were accomplished during the action of the conditional stimulus. However, the difference was not significant. The amplitude of the late negative wave also was found to be lowest when the EP from the LH were recorded in the combinations in which the pedal presses were accomplished during the signal stimulation (Fig. 1, I, A, a). In comparison with these cases, it was found to be significantly greater (p < 0.05) in combinations with a delayed motoric reaction (b) and only showed a tendency to increase in the absence of an instrumental movement (c). The EP of the central nucleus of the amygdala were similar in form to the EP picked up from the LH; however, they were lower in amplitude (compare C and B in Fig. 1, I). The changes in the amplitude of the trace positivity of the EP picked up from the CA exhibited the same directionality as that described for EP recorded from the LH (N3, in A, B, Fig. 1, I). In this case as well the P2 wave was least in the presence of the movement during the signal stimulation and greatest in its absence (p < 0.05). However, the changes in the late negative wave were found to be insignificant. The peak latent periods of the components of the EP in the LH and the CA in the presence of the above-described differences in behavioral reactions appearing in response to the signal stimulus remained essentially unchanged. The changes in the amplitude of the hypothalamic EP during the extinction of the CR, as compared with the period of its development, were similar to those described above. The amplitude of the trace positivity (Fig. 1, II, A, P2) and of the slow negative wave (N 3) were found to be least prior to the extinction of the CR (a) increasing significantly in the period of its extinction (b, c). However, for the trace positivity, the difference between the period of partial extinction when the instrumental reaction was still preserved (b) and the time preceding it (a) was significant (p < 0.05). For the late negative wave, a significant increase in amplitude (p < 0.01) took place only in the presence of complete extinction of the CR (c), although a tendency toward its increase was noted already in the initial period of the extinction of the CR (b). The peak latent periods of the EP were not changed substantially, with the exception of the significant decrease of the latent period of the trace positivity during the transition from the period preceding extinction (18.5 + 2.0 msec) to the time of partial (14.4 + 1.7) and complete extinction of the CR (13.3 +_ 1.0 msec). The amplitude characteristics of the components of the EP of the central amygdala, not counting the late negative wave, did not changed substantially. The amplitude of this wave increased (p < 0.05) during the complete extinction of the CR (Fig. 1, II, B, N 3, c) as compared with the period preceding extinction. The peak latent period of the early negative wave (N 1) and of the trace positivity also increased during the extinction of the CR. Thus, the peak latent period in the early negative wave was 13.5 + 1.5 msec prior to extinction, while during extinction it was 18.6 _+ 1.6 msec. The corresponding values for the trace positivity were: 42.5 + 2.8 msec and 47.6 + 2.7 msec. Thus, the presence or absence of an instrumental reaction to the stimulus signalizing the possibility of obtaining food correlated in different ways with the amplitude-temporal characteristics of the EP picked up from the LH. This circumstance was reflected least in EP recorded in response to the signal ES of the hippocampus in the CA. Specific dynamics of the changes of the various components of the EP arising in response to this stimulation in the DHp of the contralateral side (Fig. 2, I) and in the MS (II) were identified during the development of the alimentary instrumental conditioned reflex in response to the ES of the DHp. It can be seen that as the increase in the number of combinations of the conditional and unconditional stimuli progresses, changes in different directions take place in some components of the EP. First and foremost, a progressive increase in the early negative wave of the hippocampal response (Fig. 2, I, A), the amplitude of which increased up to 90 ~tV by the seventh day of the experiments, is noteworthy. The same, although less distinct dynamics were characteristic for its late negative wave (I, C), which, ignoring the first day of the experiments, increased by factor of two. The trace positivity, the amplitude of which, unlike those of the negative waves, decreased progressively starting with the second experiment (I, B) was subjected to substantial changes in the course of the development and consolidation of the CR. The dynamics of the changes in the components of the EP which arise in the MS in response to signal ES, showed a less distinct tendency to change during the consolidation of the CR. Only the amplitude of the negative wave (N 1) in the late stages of the development of the CR was significantly (p < 0.05) greater, than at the early stages (Fig. 2II, A). Judging by Fig. 3, I, a significant (p < 0.05) increase in the amplitude of the early negative wave was observed in the responses of the LH from the beginning of the development to the moment of consolidation of the instrumental CR, as in the preceding cases. Significant differences were not identified when it was compared in related experiments. A clear tendency in the changes in one direction or another was not found in the dynamics of the changes in the amplitude of the trace 499
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Fig. 3. Dynamics of the amplitude changes in the EP in the LH in response to the ES of the DHp during the development of the alimentary CR in the dog Tishka (T) and the EP in the VHp in response to test ES of the MS in tests for generalization of the CR in the dog Flint (II). Along the vertical, amplitudes of the components, gV. In I: circles, presses during signal stimulation; squares, after it; first cross, before test for the generalization of CR; second, after them. Remaining designations as in Fig. 2. In II: along the horizontal, components of EP (a, pedal presses; b, misses during the attempts at pressing; c, series of presses; d, single press).
positivity and the late negative wave (B, D), whereas the amplitude of the late negative wave (C) showed a tendency to decrease. In Fig. 3, I differences can be seen between the amplitudes [sic] of EP during pedal presses during signal stimulation (circles) or after it (squares). As already mentioned, in the first case the amplitude of the trace positive (B) and late negative (C) waves was less than in the second case. Up until now we have been dealing with change in the EP of the limbic structures in response to signal ES of the hippocampus and with the correlation of these changes with the presence or absence of a motor instrumental reaction. Let us now move on to a comparison of the latter with changes in the hippocampal EP arising in response to test stimulations of the amygdala for the purpose of testing the generalization of the CR. It is shown in Fig. 3, II that, in the presence of a full-fledged instrumental reaction in the form of a pedal press (a), as compared with incomplete (b) reactions (misses during attempts to press), the amplitude of the late negative wave (N3) was substantially lower (p < 0.05). In addition, the amplitude of the late positive wave (P3) of the hippocampal EP proved to be significantly lower during multiple presses on the pedal in response to the signal ES (c) as compared with single presses (d) (p < 0.05). The amplitude of the other waves of the EP changed insignificantly. DISCUSSION OF RESULTS
We had previously found that intralimbic EP change during the accomplishment of unconditioned reflex reactions, such as eating, drinking, and the lifting of a paw in response to its electrodermal stimulation. In the present study hippocampal stimulation which elicited EP in the limbic structures of the brain signalized that the dog will receive food in response to a pedal press. 500
In this case, probably, the amplitude-temporal parameters of the EP were determined not only by the physical (capacity to excite the nervous elements), but also by the signal properties of the hippocampal stimulation. Due to its physical properties, the ,excitation of hippocampal neurons, its transmission to the neurons of other limbic structures, and the occurrence of EP in them take place even in the conditions of sleep and anesthesia. In becoming a signal stimulation, hippocampal stimulation evidently sets in motion the entire sequence of goal-directed behavior, by intensifying alimentary motivation~ changing the emotional state of the dog, and initiating pedal pressing. This is probably achieved by the simultaneous and sequential excitation ,of a number of brain structures including limbic structures which is reflected in the amplitude-temporal parameters of the intralimbic EP. Significant differences were found in our experiments between the intralimbic EP in the case of the performance and nonperformance by hippocampal stimulation of its signal functions. This could take place for two reasons: due to the intensification of the volley of excitation in response to the hippocampal stimulation, which carries the signal information, and due to the interaction of it at the site of the pickup of the EP with the streams of impulses arising from other brain structures which are involved in the organization of goal-directed behavior. Probably an interaction of this sort may be both summational as well as occlusive, depending upon the specific conditions of the experiment (the site and parameters of stimulation, the site of pickup, the characteristics of the instrumental reaction, etc.). In our experimental conditions, when the hippocampal ES elicited the instrumental movement, the interaction of excitations was evidently occlusive. t~robably the first impulses of the signal hippocampal ES, by conditioned reflexes exciting the structure from which the EP were picked up and other motivatiogenic and emotiogenic limbic structures interacting with it strongly depolarized the neurons at the site of pickup, due to which they responded to succeeding impulses with a lesser degree of depolarization, in turn reflected in a decrease in the amplitude of the EP. Judging by the fact that the late components of the EP changed mainly, the genesis of which has been linked to secondary involvement of the neuron in various processes through excitory or inhibitory intermediate neurons, an occlusive interaction of this kind evidently takes place in them. Thus, the amplitude of the trace positivity and of the late negative wave was significantly less when the hippocampal stimulation, in fulfilling its signal function, elicited an effective reaction, than when it was ineffective or elicited a trace delayed reaction. The same was characteristic for the process of extinction of the CR. The loss of the signal function by the signal stimulus in the process of extinction led to an increase in the amplitude of the late negative wave, probably in connection with the decrease in the contribution of conditioned reflex excitation to the formation of EP. When this pattern was preserved, the amplitude of the late negative wave of the intralimbic EP increased as the consolidation of the CR progressed. This fact may have a dual explanation. First of all, with consolidation of the CR automatization takes place of the instrumental movements which possibly are actuated by weaker excitation of a smaller number of structures. Second, an inhibitory phase precedes the "excitatory conditioned reflex" contribution to the initiation of the EP due to the development of the delayed CR; during this phase, as during extinction, the amplitude of the late negative wave of the intralimbic EP increases. Thus, judging by our data, the interaction of excitations in the process of the formation and functioning of alimentary instrumental CR took place in intermediate neurons of the limbic structures, in particular in the LH, and to a lesser degree in the nuclei of the amygdaloid complex. When it was effective for the initiation of movement the amplitude of the late components of the hippocampal EP induced by test stimulation of the amygdala also decreased. It can be hypothesized on this basis that movements are elicited during the testing of the generalization of the CR in a mediated fashion, due to secondary activation of neurons at the site of the application of the signal in the hippocampal formation, with involvement of its intermediate neurons. Thus, when the EP and the conditioned reflex behavior reactions are elicited by the same stimulus, a judgment can be made on a basis of the changes in the intracerebral EP as to which structures of the brain are included in the constellation of structures achieving one behavioral reaction or another. On the basis of our data, the lateral hypothalamus and the central nucleus of the amygdaloitd complex represent such structures for the alimentary instrumental CR. Moreover, judging by the changes of the EP, we are left with the impression that the stronger their activation the more complete is the behavioral reaction of the dog to the conditional stimulus. CONCLUSIONS 1. The amplitude-temporal characteristics of intralimbic EP arising in response to electrostimulation of hippocampus change in different directions during development in it of instrumental alimentary CR and during its extinction. 2. During the fulfillment by hippocampal stimulation of signal functions (presses on a pedal to obtain food), the average amplitudes of the trace positivity and of the late negative wave are lower than when these functions are lost by the end of extinction. 501
3. The late components of the EP of the lateral hypothalamus and of the nuclei of the amygdaloid complex change in the greatest degree. 4. When the generalization of the CR is tested, the average amplitude of the late components of the hippocampal EP arising in response to ES of the amygdala is lower in tests in the presence of instrumental movements as compared with negative tests. LITERATURE CITED .
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CERTAIN METHODS OF BIOMECHANICAL DESCRIPTION OF VARIOUS POSTURAL ADJUSTMENT PATTERNS DURING MOTORIC LEARNING IN DOGS
A. V. Aleksandrov, O. N. Vasireva, M. E. Ioffe, and A. A. Frolov
UDC 612.821.6+612.825+612.76
Methods for the biomechanical description of spatial displacements of the center of mass of a quadruped animal (dog), developed by the authors on the basis of an assessment of the vertical constituents of support pressures, as well as methods for the assessment of the postural adjustment pattern (coefficient of diagonality), are presented in this paper. The results are presented of an investigation of the role of the motor cortex in the accomplishment of the postural adjustment pattern of dogs, reorganized during learning, in the performance of an instrumental movement.
In the process of motoric learning, i.e., the formation of new movements, certain synergies or coordinations enter the picture of a developed movement; however, more often they are modified, and a portion of them which is integrated with the developed movement is inhibited. It has been shown previously [4] that the formation of a specialized descending message which accomplishes the inhibition of integrated coordinations is associated with the motor area of cortex (MC) and the pyramidal system. This is a specific function of the MC, in addition to the control of the fineness and precision of movements. Injury to the MC or pyramidotomy leads to disinhibition and to domination of the initial (suppressed in the process of learning) synergies and coordinations. However, the degree to which the MC carries out the function of the suppression of interfering coordinations in the case of the reorganization of postural synergies has remained unclear. It is known that in animal [9] and man [1] movements of the extremities are anticipated and accompanied by reorganization of posture which achieves a shift in the center of gravity (CG), and the maintenance of equilibrium during movement. It has been demonstrated [4, 5, 9] that injury to the MC mainly affects local movements of the extremities and has relatively little influence on the character of postural adjustment. It was therefore important to investigate whether the MC has a specific role of its own at the inhibition of interfering synergies during change in the postural adjustment pattern during the process of motoric learning. However, it was first necessary to develop a sufficiently good quantitative description of postural adjustment in dogs, a description which permits the comparison of the characteristic postural adjustment patterns (PAP) before and after their reorganization, as well as the disengagement of various supraspinal structures. Methods for the description of postural adjustment in dogs are presented in the present paper, and the results of an experimental investigation of the role of the MC in the reorganization of PAP are also presented briefly. These methods and results were previously described in part [2, 8, 10-14].
Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow. Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni 1. P. Pavlova, Vol. 41, No. 5, pp. 937-947, September--October, 1991. Original article submitted May 14, 1991; revision submitted May 15, 1991. 0097-0549/92/2206-0503512.50 9
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