9. i0. Ii. 12. 13. 14. 15. 16. 17. 18. 19.
V. Giguere and F. Labrie, Endocrinology, 111, 1752-1754 (1982). G. Gillies and P.J. Lowry, Nature, 278, 463-464 (1979). J. Z, Kiss, E. Mesey, and L. Sklrboll, Proc. Natl. Acad. Sci. USA, 81, 1854-1858 (1984). Z. S. Liposits, I. Lengvary, S. Vigh, et al., Peptides, ~, 941-953 (1983). G. B. Makara, E. Stark, M. K~rteszi, et al., Am. J. Physiol., 240, 441-446 (1981). G. C. Moriarty and N. S. Halmi, J. Histochem. Cytochem., 20, 590-604 (1972), C . H . Rhodes,~ J. I. Morrel, and D. W. Pfaff, J. Comp. Neurol., 198, 45-64 (1981). P. E. Sawchenko, L. W. Swanson, and W. W. Vale, Neuroscience, ~, 1118-1129 (1984). L. A. Sternberger and S. A. Josephs. J. Histochem. Cytochem., 27, 1424-1429 (1979). L. W. Sawnson and H. G. J. M. Kuypers, J. Comp. Neurol., 194, 555-570 (1980). W. W. Vale, J. Spiess, C. Rivier, and J. Rivier, Science, 213, 1394-1397 (1981).
LONG-LATENCY AUDITORY EVOKED POTENTIALS IN HUMANS AND THE LOCALIZATION OF A SOUND IMAGE UDC 612.85
Ya. A. Al'tman and S. F. Vaitulevich
In the article, we discuss data from an investigation concerning how boundary conditions for the creation of sound-image movement are reflected in long-latency auditory evoked potentials and discuss how an important feature associated with the human localizing function (resistance to interference during the localization of both a stationary and a moving sound image) appears in long-latency auditory evoked potentials. ~e establish that a change in the parameters of a signal creating a sensation of sound-image movement results in an exhaltation of the amplitudes of the N, and P= components. The effect of binaural freedom from masking is reflected in these same components of long-latency auditory evoked potentials during movement of spatially shifting signals. KEY WORDS: localization of a shifting sound source, human auditory evoked potentials, binaural freedom from masking.
Electrophysiological methods of evaluating the activities of the cortical and subcortical representations of visceral systems were widely used during a comprehensive and multifaceted study of these areas by Academician V. N. Chernigovskii and his co-workers; these methods were used, in particular, for recording evoked potentials in different parts of the brain [4]. The important role of late secondary electrical reactions reflecting processes associated with the final stage in the evaluation of diverse interoceptive signalizations by the brain should be especially emphasized in this regard. Additionally of interest, from this point of view, is the study of a special class of human evoked potentials also arising at significant time intervals following representations of stimuli in different sensory modalities~ Such investigations have become possible~ thanks to the use of modern methods for distinguishing these reactions in waking experimental subjects. The recent development of such investigations applicable to the human auditory system has allowed compilation of a broad range of data characterizing very diverse aspects of not only reflections of the parameters of an internal stimulus in so-called long-latency auditory evoked potentials (LAEP) [7], but also human mental functions, for example, attention to a stimulus, making a conceptual response to a stimulus, and stimulus recognition [6, 9, ii]. At the same time, one very important aspect of the activity of the auditory system has gone practically unstudied during investigation of LAEP. Speculation continues concerning how processes of sound-source localization in space are reflected in LAEP, particularly during movement of the sound source. Previous investigations were limited to data on differences between individual components of the LAEP during ipsi-, contralateral, and binaural stimulations only, these differences were discovered during a long series of experiments concerned Laboratory of the Physiology of Hearing (directed by Y. A. Al'tman). I. P. Pavlov Instituteof Physiology of the Academy of Sciences of the USSR, Leningrad. Translated from Fiziologlcheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 73, No. 2, pp. 260-268, February, 1987. Original article submitted July i~, 1986.
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with studying how the state of directed attention to an auditory stimulus was reflected in such responses [9, ii]. From the point of view of sound-source localization, the results of these studies can be considered as results obtained during stimulation imitating the positioning of a sound source to the right or lefto An investigation uniquely familiar to us concerns the process of alterning one of the components (N~) of the LAEP during different spatial positions of the sound source; this investigation carried out by Butler [8]. He demonstrated that the amplitude of the EP gradually increases by approximately 20% with an increase in distance between sound sources up to 90 ~ or more. In our present report, we present laboratory data on how the boundary conditions for the creation of sound-image movement are reflected in the LAEP and data on the appearance in the LAEP of another impor~ant feature of the human localizing function, resistance to interference during the localization of both a stationary and a moving sound source. Taking into consideration that the human auditory system requires a definite detection time for a shifting signal in order to localize the movement of a sound image, we investigated precisely those components of the LAEP which arise at a time approximating the indicated detection interval for the sound source. METHODS We employed the widely used method of dichotomous stimulation for studying spatial sound~ Presentation of sound signals through head phones to both ears of the subject is the basis for this method. Upon a delay (or intensification) of one signal relative to another, the sound image created is shifted from the midline of the subject's head (localization of an image during simultaneous presentations of signals differing in amplitude) to the side of an earlier (stronger) stimulation. If the interaural differences in stimulation are varied over time (as in our experiments on the effect of clicks, for example), then a distinct sense of sound-image movement imitating the displacement of a sound image in the horizontal plane arises [I]. While addressing ourselves to the first task in the research, we carried out a preliminary psychoacoustic investigation on man which demonstrated that the creation of the sense of sound-image movement (probability 0.95) occurs during repetition of clicks in series of Ii per sec, i.e., for an interval between clicks equalling approximately i00 msec (Fig. i). At lower frequencies of click succession, the probability of the appearance of a sense of movement is lowered and the subject can individually (i.e., discretely) localize each binaurally presented pair of clicks. As is well known [7], the early components (the N~ and P= complexes, Fig. 4), develop from the sequence of positive--negative waves composing the LAEP 90200 msec after the initiation of sound stimulation. We propose that it is precisely in these components that the correlation between the boundary conditions for the formation of the sense of sound-image movement and changes: in the LAEP are manifest to the greatest degree. The following three t y p e s 0 f signals were used in the experiments: I) a binaurally presented single sound pulsej a "click" (a rectilinear pulse of 0.2 msec duration); 2) series of binaurally presented auditory clicks with differentfrequencies of succession (in these two cases, the sound image was not moved; it was postioned along the midline of the head); 3) series of binaurally presented auditory clicks with the same frequency of succession and an interaural delay decreasing in a linear pattern from 0.8 msec to 0 (the sound image was shifted from the left ear to the midline of the subject's head). The frequency of click repetition in a series took on values of 6, 8, i0, 12, 15, 25, and 60 Hz during the course of the experiment. The duration of a series was I sec; the signal intensity was 50 dB over the hear294
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8 10 "I2 15 Z5 50 Hz Fig. 2. Changes in the summed amplitudes of N, and P= components at different frequencies of click repetition in a series for stimulation by "moving" (white columns) and "stationary" signals (hatched columns). Along the x-axis) frequency of repetition of clicks in a series, Hz; along the y-axis) average combined amplitudes of the Nx and P= components, ~Vo
ing threshold for each ear of the subject, measured at all frequencies of pulse repetition in the series. Thus, we actually studied one of the boundary conditions for the formation of a sense of a sound image in these experiments, namely, the change in the frequency of pulse succession in a series. Two other boundary conditions concerned with the minimum duration of a signal and the minimum number of pairs of pulses in a stimulus were automatically fulfilled when a signal with the parameters indicated above were used. The research was conducted on 4 experimental subjects (3 females and i male) 20 to 30 years of age and possessing normal hearing. Each subject participated in 5 experiments. The subjects were placed in a sound-proofed chamber in order to record LAEP. The active electrode was fastened to the skull over the right hemisphere at point C~. The reference electrode was placed on the ear lobe on the same side as an active, grounded electrode placed on the forehead. Recording of the potentials was carried out with the aid of a preamplifier (a passband of 0.3-30 Hz) with subsequent analog-digital conversion with~a sampling frequency of 200 Hz followed by averaging and accumulation on an "Electronika DZ-28" computer. Program control was realized in cross-averages [3]~ A 0.4-sec time of analysis was established for the auditory EP recordings. Averaging was carried out according to 50 realizations. RESULTS AND DISCUSSION Characteristic auditory EPs recorded during the influence of a single binaural click were similar to the wave configuration of response repeatedly described in the literature [7]. It is known from published data that an increase in the rhythm of auditory stimulation results in a decrease in the amplitudes of the N~ and P= components of the LAEP. This change in the LAEP amplitudes is not a linear function of the increase in the frequency of stimulation: a lowering of the amplitude by 20-30% occurs during rhythmic stimulation with a frequency from 0.I to 0.3 Hz, by 60% with a frequency of 1 H z , and by 70-80% with 2 Hz [7] of succession of pulses in a series was increased from 6 to 60 Hz during the creation of a stationary sound image. It was discovered that this high frequency of click succession results in peculiar changes in the LAEP different from those previously described in the literature: the combined peaks of the amplitudes of the N I-P= components are approximately equal at stimulation frequencies of 6-12 Hz. During a higher frequency of succession of impluses the combined amplitudes of these components increase and become maximum at ~0 Hz (Fig. 2). The introduction of variable interaural delays creating a shift in the sound image (discrete or continuous) results in an increase in the combined amplitude of the NI--P= components; it is consistently higher (p < 0.01) than during the effect of "stationary" signals, except at I0 and 15 Hz (Fig. 2). With regard to the amplitude of the N~ and P= components proper (measurements from the zero-line to the maximum value of each of them), the character of the changes discovered were as follows: an increase in the frequency of pulses in a series 295
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i Fig~ 3. Reactions of neurons of the auditory centers (I, A: internal genlculate body; B, C= posterior colliculus) and somatosensory cortex (II) for interaural differences in stimulation. In A) lateralization of a single click. Along the xaxis: interaural delay, msec; along the y-axis: number of pulses in a reaction (horizontal broken line in II: level of spontaneous activity); B) reaction during simultaneous binaural stimulation with series of clicks of 2 sec duration; C> imitation of sound-source movement (moments of change in direction of movement indicated by arrows). Along the y-axis in If, B, C: number of pulses. In drawings of a cat's head: the position and tracking of the movement of a sound image. The number 20 in I, B, C is the calibration bar for the number of pulses~ In I, B and II B, C) horizontal lines under the histograms: duration of stimulus 2 sec. results in an increase in Nz and P= and the introduction of an interaural delay results in a further increase in the amplitude of the LAEP. During the course of the experiments, we determined the boundary frequency for the formarion of a sense of sound movement in the subjects by a psychological method. A comparison of the threshold frequencies obtained with the curves of changes in the combined amplitudes of the Nz and P~ components indicate that an initial increase in the reaction did not always occur in each subject at frequencies below those obtained for the creation of a sense of sound-image movement. Note that the values of the threshold frequencies basically correspond to the data in Fig. i. Definite changes were detected in the latent periods of the LAEP components investigated. In the first place, the latent periods of the components have a tendency to increase during a gradual increase in the frequency of succession of clicks in series (from 15 Ez and higher: at lower frequencies, the latent periods do not change substantially). In the second place, the latent periods of the N, and P~ components increase (from 3 =o 12 msec) for all frequencies of clicks in series during the influence of a moving stimulus in comparison with the effect of a signal evoked by a stationary sound image localized along the midline of the head. However, the data obtained on the latent periods of both components is inconsistent in the majority of cases; and it is therefore difficult, at the present time~ to draw any final conclusions with regard to patterns reflecting conditions within them for the formation of a sense of movement associated with a continuous sound image. Thus, the investigation carried out allows us to establish that a change of two parameters in the signal, an increase in the frequency of succession of clicks in series and the
296
introduction of an interaural delay varying according to a regular pattern, results in an increase in the amplitudes of the N, and P~ components. The increase of reactions in the N~--P2 complex which we observed with an increase in the frequency of pulses in a series would seem to contradict the published data [7], However, it should be taken into account that a response was recorded in these reports to each auditory impulse or click varying in transmission frequency; in our experiment, an evoked potential was obtained not to a single pulse, but to an entire series of clicks lasting 1 sec. It can be therefore assumed that, during the effect of a "stationary" signal (a sound image localized along the midline of the head), an increase in the reaction of a complex of N, and P2 with increasing frequency could occur due to an increase in the energy level of the signal. The introduction of a second factor altering the amplitude of the NI--P2 complex (a time parameter) and, in specific, varying the interaural delay, results in an additional increase in the combined peak amplitude for all of the stimulation frequencies. It is apparent that a qualitative switch in the character of the perception of the spatial position of the sound source takes place during changes in the frequency of stimulation in this case. The sound images formed at low frequency (6-10 Hz) correspond to stationary sound sources spaced along the azimuth. With an increase in frequency (15-60 Hz), a transition toward the creation of a sound image corresponding t o an azimuthal movement of sound takes place. This may be a situation in which reactions of nerve elements facilitating the creation of individual stationary sound images decrease with an increase in the frequency, while the reaction of nerve elements facilitating the creation of a moving sound image increases. We find support for this proposition in electrophysiological experiments on animals. As is well known from numerous investigations at the Laboratory of Physiology of Hearing, a definite specificity exists in the reactions of individual neurons both to different spatial positions of the sound source and to definite directions of movement of this source in a horizontal plane. Both types of neurons were detected in the centers of the classical hearing pathway and in integrative brain structures located within the auditory system, including structures located in the associative areas of the cortex (Fig. 3) [I]. A reflection in the LAEP of the transition from reactions of neurons fixing the position of a stationary sound source to the inclusion of elements responding to a moving sound source is apparently confirmed by the presence of a definite zone of decrease in the components of the LAEF during the transition from perception of a stationary sound image to the perception of a moving sound image, i.e., at frequencies equaling 1012 Hz. The decrease of reactions in such a zone was shown applicable to the electrophysiological evaluation of other functions of the auditory system, the signal intensity, for example [5]. One of the features of spatial hearing important to the second stage of this research was the ability of hearing to distinguish a relevant signal against a background of noise. The phenomenon of binaural freedom from masking is well known from psychological investigations. This phenomenon, first described by Hirsh [i0], consists in the following: if a tonal (relevant) signal and variable (masking) noise is presented to the subject through head phones, the relevant signal ceases to be perceived at a certain intensity of noise. If one of the signals is transmitted to one ear in a phase opposite to that of the other at the same amplitude ratios of relevant signal to masking noise (the "masker"), the relevant signal again becomes audible and an additional increase in the intensity of the noise is required in order for the relevant signal to again cease to be perceived. The difference in the level of masking in these two situations has been called the difference in the level of binaural masking or binaural freedom from masking. Data accumulated at the present time describing binaural freedom from masking were obtained primarily during psychological investigations carried out on humans [2]. Only- in recent years have individual reports appeared in which binaural freedom from masking has been investigated with the aid of auditory evoked potentials; thus only recently has it become possible to make an objective evaluation of this effect. In these reports investigating the reflection of binural freedom from masking in LAEP. An oppositely phased insertion of either a signal or a mask was used. It is apparent that the oppositely phased insertion of a masked ("relevant") signal or a masking signal, although it creates interaural differences in stimulation, is, to a significant degree, an artificial laboratory technique. Investigating binaural freedom from masking during changes in interaural differences associated with stimulation (differences in time, for example) is more adequate~ As: is well known, this can characterize the spatial position of a sound source. We studied this phenomenon when recording LAEP in two situations: during a change in the localization of a stationary sound image and during movement of a sound image. In addition to the earlier suggested methodology, it should be pointed out that tonal pulses with a fre297
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N~~ +30 Fig. 4. Auditory evoked potentials recorded in one of the subjects during the effect of a tonal signal and noise. Numbers: the level of intensity of the signal, in dB relative to the psychological threshold; SoNo) signal and noise to both ears synphasally; STNo) noise transmitted synphasally but signal with an interaural delay of 500 msec. quency of 500 Hz and duration of 150 msec transmitted either to both ears simultaneously (the sound image located at the midline of the head) or with a time delay between pulses equal to 500 msec (the sound image shifted to the left ear) was used as the relevant signal in the first case~ Wide-band noise transmitted to both ears with a change in phase was used as a mark. The LAEP was recorded in these two situations (sound image at the center of the head and sound image shifted to the left ear) at six subthreshold signal intensities: from +5 to +30 dB over the threshold of detection for a tonal signal transmitted to both ears against a background of dichotomously presented noise at an intensity of 50 dB. Characteristic LAEP (data from a single subject) at different levels of intensity during localization of the signal along the midline of the head and during lateralization of the signal toward an ear are shown in Fig. 4. It is apparent that the N~ and P2 components become more pronounced at lower sound intensities under conditions where stimulations evoking a shift in the sound image. This tendency was maintained in all of the subjects. The peak amplitudes at all levels of intensity were greater in the presence of interaural differences in stimulation. The regression analysis carried out showed a satisfactory correspondence between these data and the given linear functional dependence of the recorded amplitudes of the components upon the intensities used for the signal~ In our experiments, steeper regression lines were obtained under conditions of oppositely phased stimulation evoking a shift of the sound image. The correlation coefficient turned out to be 0o755-0.641. The linear equations obtained for each subject during the two types of stimulation were used to calculate the extrapolated thresholds. The average values of these thresholdswere 0.7dB during localization of a sound image along the midline of the head and 6~ dB in the presence of interaural differences in stimulation. The latent periods of the N: component was also measured in the experiments we conducted~ Two circumstances should be noted: first, the latent periods of the N: component decreases
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with increasing stimulus intensity under two conditions of stimulation) secondly, under conditions involving an absence of interaural differences in stimulation, the latent periods were greater than in the presence of such differences at all levels of intensity (except +30 dB). Thus, the lateralization of the sound image achieved as a result of interaural time differences in stimulation is responsible for the effect of binaural freedom from masking in longlatency auditory EPs. Moreover, the latent periods of the N~ component change during binaural freedom from masking. In a second series of experiments, we investigated the effect of binaural freedom from masking during movement of a sound image. A series of binaurally presented clicks with a frequency of succession equaling 60 Hz was employed as the relevant signal. The series was transmitted either without an interaural delay (a sound image at the center of the head) or with a variable interaural delay (a sound image shifting from the left ear to the midline of the head). Broad-band noise served as the mask, The recording of the LAEP from the right and left hemispheres was carried out stimultaneously. Characteristic LAEP obtained at different levels of intensity of the relevant signal are shown in Fig. 5. In this series of experiments, we detected a large combined peak amplitude for N~ and P2 in the case of a moving sound image. When calculating the extrapolated thresholds for each subject, it was discovered that the extent of binaural freedom from masking equalled 2.9 dB. The value for the binaural freedom from masking obtained in this series of experiments is lower than when a lateral tonal signal is used. From our point of view, this is, to a large degree, caused by differences in the spectral characteristics of the relevant signals employed, since series of clicks have a higher-frequency spectral composition. It is known from psychological experiments that the greatest extent of binaural freedom from masking (from 5 to 15 dB) is encountered with low-frequency (from I00 to I000 Hz) relevant signals [2]. In conclusion, we note that the phenomenon of freedom from masking appearing in LAEP during the action of spatially shifted signals (lateralized and moving) is confirmed by numerous electrophysiological data on changing selectivities of nerve elements associated with various levels of the auditory system and other integrative brain structures to spatial position of the sound source~ On the basis of the data obtained, it can be asserted that the effect of binaural freedom from masking is well expressed at the level of the structures generating LAEP. In this connection, it is necessary to emphasize that, despite the absence of a unified point of view concerning the origin of LAEP, the majority of authors tend toward the opinion that these reactions are generated by the associative structures of the cerebral hemispheres in man. If this is so, then it is confirmation of our previously expressed point of view that the final stages in the discernment of the properties of auditory signals takes place within the centers of classical auditory pathways [i]. Since of the phenomenon of binaural freedom from masking characterizes the resistance to noise interference mainfested by the auditory system during the localization of a sound source, the effect obtained during the investigation of LAEP makes an objective evaluation of this phenomenon possible. The authors dedicate the article with deep respect to the memory of V. A. Chernigovskii, who had long ago foreseen the processing of information arriving along afferent systems of human and animal organisms reflected in late evoked potentials. LITERATURE CITED l.
2o 3. 4. 5.
6. 7.
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Ya. A. Al'tman, Localization of a Moving Sound Source [in Russian], Nauka, Leningrad (1983). Ya. Blauerm, Spatial Hearing [in Russian], Energiya, Moscow (1979). Bo I. Gekhman, I. A. Ravkin, and Vo Lo Temov, "Cross-system for the 'Electronika DE-28 Microcomputer," Series 9, ~, 52, 43-46 (1984). S. So Musyashchikova and V. N. Chernigovskii, Cortical and Subcortical Representation of Visceral Systems [in Russian], Nauka, Leningrad (1973). E~ A. Radionova, Functional Characterization of the Neurons of the Cochlear Nuclei and the Auditory Function [in Russian], Nauka, Leningrad (1971). E. M. Rutman, Evoked Potentials in Psychology and Psych,physiology [in Russian], Nauka, Leningrad (1979). S. N. Khechlnashvili and Z. Sh. Kevanishvili, Human Auditory Evoked Potentials [in Russian], Sabchota Sakartvelo, Tbilisi (1985).
8. 9. I0. ii.
Ya. A. Batler, "The influence of spatial separation of sound sources on the auditory evokes response," Neuropsychologiya, i0, 2, 219-225 (1972). S. A. Hillyard, R. F. Hink, V. L,:Schwent, and I. W. Picton, "Electrical signs of selective attention in human brain," Science, 182 , 4108, 177-180 (1973). I. J. Hirsh, "The influence of interaural phase on interaural summation and inhibition," J. Acoust. Soc. Am., 20, 4, 536-544 (1948). V. L. Schwent, E. Snyder, and S. A. Hillyard, "Auditory evoked potentials during multichannel selective listening role pitch and localization cures," J. Exp. Psychol. Human Percept. Perform., ~, 3, 313-325 (1976).
INFLUENCE OF SOME MONOAMINE OXIDASE INHIBITORS ON THE SLEEP--WAKEFULNESS CYCLE OF THE CAT T. N. Oniani and G. R. Akhvlediani
UDC 612.821.7
The influence of some monoamine oxidase inhibitors (phenelzine, transamin [tranylcypromine], nialamide) on the structure of the sleep--wakefulness cycle of the cat was studied. It was shown that these monoamine oxidase inhibitors elicit an increase in slow-wave sleep in the sleep--wakefulness cycle due to complete suppression of paradoxical sleep and a significant decrease in wakefulness. After the cessation of the action of the monoamine oxidase inhibitors, a selective rebound of wakefulness Is observed against the background of complete or partial absence of paradoxical sleep. This gives grounds for the hypothesis that during partial deprivation of wakefulness under the influence of monoamine oxidase inhibitors an intensification occurs on the accumulation of specific need for this physiological state, the satisfaction of which is accomplished as the result of its rebound in the post-deprivational cycle, i.e., after the termination of the EEG of the synchronizing effect of the monoamine oxidase inhibitors.
Pharmacological substances acting on the various neurotransmitter systems of the brain are often used to study the neurobiological mechanisms of regulation of the sleep-wakefulness cycle. Inhibitors of the enzyme, monoamine oxidase (MAO), which increases the amount of monoamine in the brain, belong to this type of agents. It has been shown that, as a function of their structure, different MAO inhibitors change the quantitative interrelationships of the monoamines in the brain in a non-identical manner [5, 12, 15]. Moreover, the same substances act differently in different species of animals. Consequently, the influence of MAO inhibitors on the sleep--wakefulness cycle must depend both on the species of the animal studied and on the structure of the substance itself. In fact, the majority of MAO inhibitors in the rat elicit active wakefulness and complete suppression of both phases of sleep [3, 7, ii, 19], while in cats the reverse is the case: they elicit the synchronization of the electrical activity of the cortex and an increase in the total duration of slow-wave sleep [5, 9, 13-15]. Common to all MAO inhibitors is their suppressive effect on paradoxical sleep, which has been demonstrated experimentally in rats [9, 13, 19], cats [5, 12, 15], and monkeys [18]. Similar data have also been obtained as the result of clinical investigations. In particular, it has been established that as a function of structure and dose MAO inhibitors sharply decrease or completely suppress paradoxir sleep in human beings [2, 4, 8, 16, 17]. Repeated injections of phenelzine [2, 8, 9], pargyllne and clorgyline [9] elicit suppression of paradoxical sleep after several days, and prior to that a dissociation between their individual components takes place (for example, movements of the eyeballs may develop without muscular atony). It is interesting that, according to the data of clinical investigations,
Laboratory of the Neurophysiology of the Wake-Sleep Cycle, I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Seehenova, Vol. 73, No. 3, pp. 332-337, March, 1987. Original article submitted July 30, 1986.
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