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Cerebellar influences on evoked cerebral responses
JOURNAL OF THE NEUROLOGICALSCIENCES
325
Cerebellar Influences on Evoked Cerebral Responses R. S. SNIDER*, K. SATO AND S. M I Z U N O * * Department of Anatomy, Northwestern University, Chicago, Ill. (U.S.A.); and Department of Physiology, University of Nagasaki, Nagasaki (Japan)
INTRODUCTION The concept that the cerebellum acts only in the proprioceptive sphere has been repeatedly challenged. Emphatic doubt was placed upon this concept when HENNEMAN et al. (1950) proved experimentally that the tactile, auditory and visual receiving areas of the cerebellum as demonstrated by SMDER AND STOWELL(1942, 1944), project to the tactile, auditory and visual areas of the cerebrum. Further doubt resulted from WHITESIDE AND SNIOER'S (1953) work showing that the cerebellum can exert influences not only on nucleus ventralis lateralis of the thalamus but also upon the so-called sensory relay group (ventralis posterolateralis; ventralis posteromedialis; geniculatum medialis) as well as some parts of the reticular activating system. Accordingly, the present experiments were undertaken in order to study possible cerebellar effects upon the evoked cerebral response. N o t only were changes observed on the primary response but repeatedly it was noted that there were alterations in the rhythmic after-effects which followed. This was of appropriate interest because, according to ADRIAN (1943), JARCHO (1949) and CHANG (1950), cerebral sensory areas under the action of afferent influences show rhythmic excitability which, according to the last named author, can be considered part of the cortico-thalamic reverberating circuit. On the other hand, BREMER AND BONNET (1951) have presented evidence to show that cortical rhythmicity may be autogenic. Therefore, in addition to observations on the primary response an attempt was made to study alterations in excitability of the auditory cortex when influenced by cerebellar stimulation.
MATERIALSAND METHODS Experiments on 72 normal adult cats, 53 used in experiments on surface recordings and 19 in stereotaxic recordings, comprise the basis of this report. In each animal, the brain was exposed quickly under light surgical levels of ethrr anesthesia. The ether was then discontinued and the preparation maintained under A preliminary report was read before the American Physiological Society in April 1958 [see Fed. Proc. (1958) 17: 152]. This research work was financed by the grant-in-aid program of the National Institutes of Health. * Present address: Center for Brain Research, University of Rochester, Rochester, N.Y. (U.S.A.) ** Present address: Kyoto Medical School, Kyoto (Japan). J. neurol. Sci. (1964) 1 : 325-339
326
R.S. SN1DER, K. SATO, S. MIZUNO
flaxedil (10 mg/kg) given intraperitoneally. Novocaine 5°/,] was repeatedly infiltrated beneath all incised tissues. The animals were artifically respired, a small amount of oxygen being added to the inspired air (approx. 50 ml/min). Care was taken to avoid any painful procedures such as harmful pinching, the skin, or incising it, or activating so-called pain endings in any way without preliminary medication. The common method of observing dilation of the pupils, as an index of painful procedures, was routinely
Fig. I. Composite charts which show stimulated points on the cerebellum and recording points on the ccrcbrurn (see text for details). employed. When such signs were positive the manipulations were altered immediately. Electrical stimuli were applied as conditioning shocks on the surface of the auditory areas of the cerebellum through bipolar silver wire electrodes beaded at the tips (see Fig. 1 for the location of the stimulating electrodes). Clicks as test stimuli were generated by a modified Grass ($3) stimulator and delivered through a 6-inch audio-speaker placed 6-10 inches in front of the head of the experimental animal equidistant between the two ears. Biphasic electrical stimuli were applied by means of Grass stimulators (Model S4-E) which permit independent variation of voltage, frequency, pulse duration, and delay of the test stimuli following the conditioning shock. The stimulation voltage at the pial surface of the cerebellum ranged between 3 and J. neurol. Sci.
(1964) 1:325-339
CEREBELLAR INFLUENCES ON EVOKED CEREBRAL RESPONSES
327
12 V (see figures for individual experiments) and the duration of the biphasic pulse ranged between 0. I and 0.5 msec. The usual threshold pulse was 6-8 V, duration 0.1 msec, delivered through silver-silver chloride electrodes having electrode-to-tissue resistance of approx. 6000 ohms. For the purpose of recording electrical responses from the cortical surface of the cerebral auditory areas, both monopolar and bipolar silver wire electrodes were employed. In the case of the former the so-called indifferent electrode was usually a coiled silver wire in the frontal sinus. During experiments in which stereotaxic procedures were used and the responses were recorded from the medial geniculate bodies, bipolar nichrome wires which were straightened, insulated and oriented side by side with approximately 0.5 mm tip separation were inserted by means of a Horsley-Clarke stereotaxic instrument irtto the structure to be examined. The recording electrodes were connected to the input of a Grass P6 preamplifier, the output of which was attached to a Du Mont cathode oscilloscope (Model 322). At the expiration of any critical experiment in which a stereotaxic instrument was used, the brain was perfused with 10% formalin via the carotid arteries, then the instrument carefully removed from the skull and the nervous tissues prepared by a frozen procedure for staining with a modified WElLmethod. Microscopic examination for the accuracy of electrode placement was done routinely and usually three-dimensional drawings were made. RESULTS
The accompanying figures depict as accurately as could be photographed electrical responses recorded from the auditory cortex and the medial geniculate nucleus (see subtitles for details). Recording f r o m cerebral cortex
Fig. 1 is a composite drawing of the lateral surface of the cerebral hemisphere showing individual recording sites within the auditory area as two dots connected by short line. When monopolar recording was used points of altered activity were taken from this same region and one or the other of the two electrodes were grounded. All the surfaces of the cerebellum shown in the adjacent diagram were stimulated but only those marked with dots and bars produced responses at sufficiently low stimulation voltage to be included with these data. Fig. 2 shows photographs of cathode ray sweeps under average experimental conditions when a folium of the second turn of tuber vermis was stimulated via bipolar electrodes with 6 V (duration of each pulse was 0.5 msec). The effects resulting from the conditioning stimulus alone are shown at Fig. 2C. The test stimulus produced the response shown in Fig. 2B. The recording site was located in the dorsal part of posterior ectosylvian gyrus (see insert). Fig. 2A represents background electrical activity of the cerebral area under identical recording conditions to that shown in the other photographs except electrical and/or click stimuli were not given. The other photographs (Figs. 2D-Q) represent cathode ray sweeps taken when the test stimulus was given at various intervals (10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, J. neurol. Sci. (1964) I: 325-339
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300 msec) after the conditioning stimulus. It is pointed out that at 80 msec (Fig. 2K) interval between conditioning and test stimuli, the amplitude of the response returned to approximately that of the control level (Fig. 2B). Following this interval it was not unusual for the preparation to show enhancement of the response for 50--100 msec (Fig. 2M, N) to be followed by some waxing and waning of amplitude during the next 80-100 msec when it may or may not return to baseline levels (see inset at right hand of Fig. 2). Fig. 3 shows a typical result when the conditioning stimulus (8 V, 0.5 msec duration, biphasic) was applied to the first turn of the tuber vermis. The recording site was located in the middle ectosylvian gyrus as shown in the inset. Fig. 3A shows spontaneous activity of the left ectosylvian gyrus while Fig. 3B illustrates the response to a 60 db click stimulus and Fig. 3C shows the ectosylvian response which resulted from electrical stimulation of the tuber vermis. Note, that although the cerebellar site of stimulation and cerebral recording site were changed from those shown in Fig. 2, the amplitude of the test responses varied below or above the control level depending upon the duration of the interval between the conditioning and test stimuli. Fig. 4 shows photographs of responses taken from the anterior ectosylvian gyrus of auditory area II when electrical pulses were applied (7.0 V, 0.5 msec) to the folia of the first turn of tuber vermis to produce the conditioning stimulus. The test stimuli were applied as noted above and the sequence of responses illustrated as in Figs. 2 and 3. Note that the alterations in amplitude of the test response (illustrated in the inset of Fig. 4) were similar to those illustrated in Figs. 2 artd 3. In summary, regardless of whether the recording site was in the anterior, middle, or posterior ectosylvian gyri, there was diminished response height for approx. 80-90 msec. Following this, there was a short period lasting for approx. 20 msec in which there was enhancement of the response; this was followed by another period of diminution which lasted a variable interval ranging from 50 to 200 msec. In many experiments it was not uncommon to observe that the second period of diminished amplitude was broken by a period of enhancement (see inset of Figs. 3 and 4). Because of limitations of the recording equipment it was not possible to observe phenomena beyond a 300 msec interval between conditioning and test stimuli.
Recording from medial geniculate nucleus In view of the effect.~ on responses in the auditory cortex produced by conditioning stimuli applied to the auditory receiving area of the cerebellum, it was of some interest to note what similar stimuli applied to the cerebellum might do to the activity of the medial geniculate nucleus. The following figures present these data. In Fig. 5A is shown the spontaneous background activity of the medial geniculate nucleus in the ventral portion at a Horsley-Clarke stereotaxic level of A5 (see inset). Fig. 5B shows a photograph of an evoked response following click stimulation while Fig. 5C shows the response resulting from electrical stimulation of the second turn of tuber vermis with art 8V biphasic pulse of 0.5 msec duration. Figs. 5D-Q show the effects of increasing the interval between conditioning and test stimuli from 10 to 300 msec. As shown in the small inset there was diminution of the test response by 50-60~ for 30 msec, then
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Fig. 8. Photograpbs of five superimposed cathode ray traces obtained from the pial surface of the middle ectosylvian gyrus by means of the monopolar recording technique. The stimulating electrodes were on the tuber vermis and the numbers indicate the interval in msec between conditioning and test stimuli. N o t e the 100 c/s time marks and the 200/~V amplitude marks in the lower right. The curves in the upper right represent the percent of threshold response and a ~ expressed in terms of an augmenting interval between conditioning and test stimuli in cats medicated with chloralosane or flaxedil. These data are to be compared with that presented in Figs. 2~1 which were obtained by bipolar recording technique.
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increased response height to a 90% level at 60 msec to be followed by reduction of response height to a 60~o level for more than 300 msec. This should be contrasted with similar curves shown in previous illustrations where the recordings were taken from the pial surface of the auditory cortex and the curve not only returns to a normal level but may oscillate above and below this level up to 300 msec later. Fig. 6 shows the effects on an evoked (from click) auditory response recorded from the A6 level of the medial geniculate nucleus at intervals varying from 10 to 300 msec following conditioning stimuli (8 V) applied to the second turn of the tuber vermis. Fig. 6A shows the spontaneous electrical background activity of the medial geniculate nucleus while Fig. 6B shows the response resulting from a click of 60 db intensity. Fig. 6C represents the electrical alterations resulting from the application of electrical conditioning stimuli to the cerebellum while Figs. 6D-Q show the effects of combining the stimuli when they were separated by intervals of 10-300 msec. Notice that there was greater diminution of the response than that illustrated in Fig. 5 since it was reduced to 40~o at 10 msec and never reached more than the 75~ level at 300 msec. The data shown in Fig. 7 were obtained under similar experimental conditions to those in Fig. 6 except the stimulating site for the conditioning stimuli was moved to the first part of the first turn of tuber vermis. As shown by the curve in the inset there was less depression of electrical activity and recovery was almost complete at the 50 msec interval. However, there was loss (down to 60~o) at 100 msec with some waxing and waning during the next 200 msec. The data shown in Fig. 8 are presented since they were obtained by means of the monopolar recording technique. These data were compared with those shown in Figs. 2-4 which were obtained with the bipolar recording technique. As can be seen the curve showing response height expressed in percent of threshold was similar (though not identical) to that plotted with bipolar recording when flaxedil is used despite the fact that the contours of the individual waves vary. As can be observed, chloralosane alters considerably the responsiveness of the preparation, but since this is part of another study it need not be discussed here. These data were obtained by applying electrical pulses (8 V, 0.5 msec duration) to the folia of first turn of tuber vermis. The work of STERIADE AND STOUPEL (1960) appeared in the literature while the present studies were being carried out; hence we are not reporting the data on the effects of lesions in auditory areas I or II on these responses. However, work in progress which involves destruction of pathways followed by electrical recording indicate that there may be a dual projection system, i.e., by way of the geniculate bodies as well as by way of the tegmentum.
DISCUSSION
The effects described here were not an unexpected finding in view of the earlier work by WHITESIDE AND SNIDER (1953) showing a cerebellar projection to the medial geniculate nuclei, the mesencephalic and the diencephalic tegmentum. If these areas are regions of convergence for ascending systems from peripheral end-organs as well as from the cerebellum, then it could be logically argued that reactional interference J. neurol. Sci. (1964) 1:325-339
338
R . S . SNIDER, K. SATO, S. MIZUNO
ADE AND STOUPEL (1960) except in animals in which the threshold of response was unusually high or in which a high stimulating voltage was used. The possibility that these differences in data are due to the use of medication is a worthy one since as shown by DEURA AND SNIDER (in press) the recovery cycle of cerebro-cerebellar systems is considerably longer when measured under chloralosane as contrasted with flaxedil. In view of the previous findings of HENNEMANe t al. (1950) it was hoped that observations could be made on localized effects within either the auditory area of the cerebellum or of the cerebrum. However, such effects could not be found and it was concluded t h a t - - s o far as these studies are c o n c e r n e d - - w h e n flaxedil was used, all cerebellar areas (lobus simplex and first and second turns of tuber vermis) projected to all parts of cerebral auditory areas I and II. O f course, this does not deny the presence of a localized projection if threshold values of stimulation are used under a wide variety of anesthetic conditions. The functional significance of the presently described system is unknown. However, it is tempting to consider it as a means to control levels of excitability in a sensory area of the cerebrum. This becomes even more plausible when interpreted in the light of SN1DER AND ELDRED'S (1952) studies on cerebro-cerebellar projections and the recent work of DEURA AND SNIDER (in press) showing that electrical effects in the cerebral auditory area can act back upon the cerebellar auditory area and alter its responsiveness. The earlier studies o f ALBE-FESSmtI>AND SZABO (1954) as well as those of GASTAUT et al. (1951) also indicated a cerebral influence on the so-called sensory areas of the cerebellum. This would be compatible with the newer concept of cerebellar function which maintains that this organ can and does act on both sensory and m o t o r systems to control levels of responsiveness.
SUMMARY
Electrical records were taken from the auditory area of the cerebrum of cats while click (test) stimuli were being administered and conditioning shocks (electrical) were being applied to the auditory area of the cerebellum. (1) Conditioning the response to a click by a preceding threshold electrical shock to the cerebellum resulted in marked diminution o f the response in intervals up to 80 msec which decreased progressively as the interval augnented. Following this diminution there was usually a period of enhancement after which there was a second period of diminution (not as prominent as the first). Occasionally a second period of enhancement followed. (2) The diminished responses could be induced in all parts of cerebral auditory areas I and II as a result of stimulation of any part of the cerebellar auditory areas. (3) Diminution of responses (following click stimuli), in the ventral and anterior parts of the medial geniculate body resulted when a conditioning stimulus was applied to the auditory area of cerebellum. (4) These data are interpreted to indicate that the cerebellum can alter levels of excitability of a cerebral sensory area and suggest that the medial geniculate nucleus may be involved as an intermediate center in which reactional interference occurs. J. neurol. Sci. (1964) 1 : 325-339
CEREBELLAR INFLUENCES ON EVOKED CEREBRAL RESPONSES
339
REFERENCES ADRIAN, E. D. (1943) Afferent areas in the cerebellum connected with the limbs, Brain, 66:289-315. ALBE. FESSARD, D. AND T. SZABO 0954) Observations sur l'interaction des aff6rences d'origines p6riph6rique et corticale destin6es a l'6corce c6r6belleuse du chat, J. Physiol. (Paris), 46: 225-229. BREMER, F. AND V. BONNET (1951a) Caract6res g6n6raux de la r6ponse du cervelet/t une voice d'influx aff~rents, J. Physiol. (Paris), 43 : 662-665. BREMER, F. AND V. BONNET (1951b) Convergence et interaction des influx aff6rents dans l'6corce c6r~belleuse, principe fonctionnel du cervelet, J. Physiol. (Paris), 43 : 665-667. CHANG, H. T. (1950) The repetitive discharges of cortico-thalamic reverberating circuit, J. Neurophysiol., 13 : 235-257. CLARE,M. H. AND G. H. BISHOP 0955) Properties of dendrites. Apical dendrites of the cat cortex, Electroenceph. clin. Neurophysiol., 7: 85-98. GASTAUT, H., R. NAQUET, M. BADIER, AND A. ROGER (1951) Signification de la r6ponse c6r6belleuse /t la stimulation lumineuse chez le chat, J. Physiol. (Paris), 43 : 737-740. HENNEMAN, E. M., P. M. COOKE AND R. S. SNIDER (1952) Cerebellar projections to the cerebral cortex, Res. Publ. Ass. Nerv. Ment. Dis., 30: 317-333. JARCHO, L. M. (1949) Excitability of cortical afferent systems during barbiturate anesthesia, J. Neurophysiol., 12: 447-457. SATO, K. (1957a) An interpretation concerning physiological significance of statistical nature of electroencephalogram, Folia psychiat, neurol, jap., 10: 283-294. SATO, K. (1957b) An introduction to the statistical theory of the brain wave, Appl. Stat. Meteorol., 7". 60-67. SNIDER, R. S. AND E. ELDRED 0952) Cerebro-cerebellar relationships in the monkey, J. Neurophysiol., 15 : 27-40. SNIDER,R. S. AND A. STOWELL (1942) Evidence of a projection of the optic system to the cerebellum, Anat. Rec., 82: 448--449. SNIDER,R. S. AND A. STOWELL 0944) Receiving areas of the tactile, auditory and visual systems in the cerebellum, J. Neurophysiol., 7: 331-357. STERIADE, M. AND N. STOUPEL (1960) Contribution/t l'6tude des relations entre rair¢ auditive du cervelet et l'6corce c6r6bra|e chez le chat, Electroenceph. clin. Neurophysiol., 12: 119-I 36. WHITESIDE, J. A. AND R. S. SNIDER (1953) Relation of cerebellum to upper brain stem, J. Neurophysiol., 16: 397-413.
J. neurol. Sci. (1964) 1 : 325-339
325
Cerebellar Influences on Evoked Cerebral Responses R. S. SNIDER*, K. SATO AND S. M I Z U N O * * Department of Anatomy, Northwestern University, Chicago, Ill. (U.S.A.); and Department of Physiology, University of Nagasaki, Nagasaki (Japan)
INTRODUCTION The concept that the cerebellum acts only in the proprioceptive sphere has been repeatedly challenged. Emphatic doubt was placed upon this concept when HENNEMAN et al. (1950) proved experimentally that the tactile, auditory and visual receiving areas of the cerebellum as demonstrated by SMDER AND STOWELL(1942, 1944), project to the tactile, auditory and visual areas of the cerebrum. Further doubt resulted from WHITESIDE AND SNIOER'S (1953) work showing that the cerebellum can exert influences not only on nucleus ventralis lateralis of the thalamus but also upon the so-called sensory relay group (ventralis posterolateralis; ventralis posteromedialis; geniculatum medialis) as well as some parts of the reticular activating system. Accordingly, the present experiments were undertaken in order to study possible cerebellar effects upon the evoked cerebral response. N o t only were changes observed on the primary response but repeatedly it was noted that there were alterations in the rhythmic after-effects which followed. This was of appropriate interest because, according to ADRIAN (1943), JARCHO (1949) and CHANG (1950), cerebral sensory areas under the action of afferent influences show rhythmic excitability which, according to the last named author, can be considered part of the cortico-thalamic reverberating circuit. On the other hand, BREMER AND BONNET (1951) have presented evidence to show that cortical rhythmicity may be autogenic. Therefore, in addition to observations on the primary response an attempt was made to study alterations in excitability of the auditory cortex when influenced by cerebellar stimulation.
MATERIALSAND METHODS Experiments on 72 normal adult cats, 53 used in experiments on surface recordings and 19 in stereotaxic recordings, comprise the basis of this report. In each animal, the brain was exposed quickly under light surgical levels of ethrr anesthesia. The ether was then discontinued and the preparation maintained under A preliminary report was read before the American Physiological Society in April 1958 [see Fed. Proc. (1958) 17: 152]. This research work was financed by the grant-in-aid program of the National Institutes of Health. * Present address: Center for Brain Research, University of Rochester, Rochester, N.Y. (U.S.A.) ** Present address: Kyoto Medical School, Kyoto (Japan). J. neurol. Sci. (1964) 1 : 325-339
326
R.S. SN1DER, K. SATO, S. MIZUNO
flaxedil (10 mg/kg) given intraperitoneally. Novocaine 5°/,] was repeatedly infiltrated beneath all incised tissues. The animals were artifically respired, a small amount of oxygen being added to the inspired air (approx. 50 ml/min). Care was taken to avoid any painful procedures such as harmful pinching, the skin, or incising it, or activating so-called pain endings in any way without preliminary medication. The common method of observing dilation of the pupils, as an index of painful procedures, was routinely
Fig. I. Composite charts which show stimulated points on the cerebellum and recording points on the ccrcbrurn (see text for details). employed. When such signs were positive the manipulations were altered immediately. Electrical stimuli were applied as conditioning shocks on the surface of the auditory areas of the cerebellum through bipolar silver wire electrodes beaded at the tips (see Fig. 1 for the location of the stimulating electrodes). Clicks as test stimuli were generated by a modified Grass ($3) stimulator and delivered through a 6-inch audio-speaker placed 6-10 inches in front of the head of the experimental animal equidistant between the two ears. Biphasic electrical stimuli were applied by means of Grass stimulators (Model S4-E) which permit independent variation of voltage, frequency, pulse duration, and delay of the test stimuli following the conditioning shock. The stimulation voltage at the pial surface of the cerebellum ranged between 3 and J. neurol. Sci.
(1964) 1:325-339
CEREBELLAR INFLUENCES ON EVOKED CEREBRAL RESPONSES
327
12 V (see figures for individual experiments) and the duration of the biphasic pulse ranged between 0. I and 0.5 msec. The usual threshold pulse was 6-8 V, duration 0.1 msec, delivered through silver-silver chloride electrodes having electrode-to-tissue resistance of approx. 6000 ohms. For the purpose of recording electrical responses from the cortical surface of the cerebral auditory areas, both monopolar and bipolar silver wire electrodes were employed. In the case of the former the so-called indifferent electrode was usually a coiled silver wire in the frontal sinus. During experiments in which stereotaxic procedures were used and the responses were recorded from the medial geniculate bodies, bipolar nichrome wires which were straightened, insulated and oriented side by side with approximately 0.5 mm tip separation were inserted by means of a Horsley-Clarke stereotaxic instrument irtto the structure to be examined. The recording electrodes were connected to the input of a Grass P6 preamplifier, the output of which was attached to a Du Mont cathode oscilloscope (Model 322). At the expiration of any critical experiment in which a stereotaxic instrument was used, the brain was perfused with 10% formalin via the carotid arteries, then the instrument carefully removed from the skull and the nervous tissues prepared by a frozen procedure for staining with a modified WElLmethod. Microscopic examination for the accuracy of electrode placement was done routinely and usually three-dimensional drawings were made. RESULTS
The accompanying figures depict as accurately as could be photographed electrical responses recorded from the auditory cortex and the medial geniculate nucleus (see subtitles for details). Recording f r o m cerebral cortex
Fig. 1 is a composite drawing of the lateral surface of the cerebral hemisphere showing individual recording sites within the auditory area as two dots connected by short line. When monopolar recording was used points of altered activity were taken from this same region and one or the other of the two electrodes were grounded. All the surfaces of the cerebellum shown in the adjacent diagram were stimulated but only those marked with dots and bars produced responses at sufficiently low stimulation voltage to be included with these data. Fig. 2 shows photographs of cathode ray sweeps under average experimental conditions when a folium of the second turn of tuber vermis was stimulated via bipolar electrodes with 6 V (duration of each pulse was 0.5 msec). The effects resulting from the conditioning stimulus alone are shown at Fig. 2C. The test stimulus produced the response shown in Fig. 2B. The recording site was located in the dorsal part of posterior ectosylvian gyrus (see insert). Fig. 2A represents background electrical activity of the cerebral area under identical recording conditions to that shown in the other photographs except electrical and/or click stimuli were not given. The other photographs (Figs. 2D-Q) represent cathode ray sweeps taken when the test stimulus was given at various intervals (10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, J. neurol. Sci. (1964) I: 325-339
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300 msec) after the conditioning stimulus. It is pointed out that at 80 msec (Fig. 2K) interval between conditioning and test stimuli, the amplitude of the response returned to approximately that of the control level (Fig. 2B). Following this interval it was not unusual for the preparation to show enhancement of the response for 50--100 msec (Fig. 2M, N) to be followed by some waxing and waning of amplitude during the next 80-100 msec when it may or may not return to baseline levels (see inset at right hand of Fig. 2). Fig. 3 shows a typical result when the conditioning stimulus (8 V, 0.5 msec duration, biphasic) was applied to the first turn of the tuber vermis. The recording site was located in the middle ectosylvian gyrus as shown in the inset. Fig. 3A shows spontaneous activity of the left ectosylvian gyrus while Fig. 3B illustrates the response to a 60 db click stimulus and Fig. 3C shows the ectosylvian response which resulted from electrical stimulation of the tuber vermis. Note, that although the cerebellar site of stimulation and cerebral recording site were changed from those shown in Fig. 2, the amplitude of the test responses varied below or above the control level depending upon the duration of the interval between the conditioning and test stimuli. Fig. 4 shows photographs of responses taken from the anterior ectosylvian gyrus of auditory area II when electrical pulses were applied (7.0 V, 0.5 msec) to the folia of the first turn of tuber vermis to produce the conditioning stimulus. The test stimuli were applied as noted above and the sequence of responses illustrated as in Figs. 2 and 3. Note that the alterations in amplitude of the test response (illustrated in the inset of Fig. 4) were similar to those illustrated in Figs. 2 artd 3. In summary, regardless of whether the recording site was in the anterior, middle, or posterior ectosylvian gyri, there was diminished response height for approx. 80-90 msec. Following this, there was a short period lasting for approx. 20 msec in which there was enhancement of the response; this was followed by another period of diminution which lasted a variable interval ranging from 50 to 200 msec. In many experiments it was not uncommon to observe that the second period of diminished amplitude was broken by a period of enhancement (see inset of Figs. 3 and 4). Because of limitations of the recording equipment it was not possible to observe phenomena beyond a 300 msec interval between conditioning and test stimuli.
Recording from medial geniculate nucleus In view of the effect.~ on responses in the auditory cortex produced by conditioning stimuli applied to the auditory receiving area of the cerebellum, it was of some interest to note what similar stimuli applied to the cerebellum might do to the activity of the medial geniculate nucleus. The following figures present these data. In Fig. 5A is shown the spontaneous background activity of the medial geniculate nucleus in the ventral portion at a Horsley-Clarke stereotaxic level of A5 (see inset). Fig. 5B shows a photograph of an evoked response following click stimulation while Fig. 5C shows the response resulting from electrical stimulation of the second turn of tuber vermis with art 8V biphasic pulse of 0.5 msec duration. Figs. 5D-Q show the effects of increasing the interval between conditioning and test stimuli from 10 to 300 msec. As shown in the small inset there was diminution of the test response by 50-60~ for 30 msec, then
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increased response height to a 90% level at 60 msec to be followed by reduction of response height to a 60~o level for more than 300 msec. This should be contrasted with similar curves shown in previous illustrations where the recordings were taken from the pial surface of the auditory cortex and the curve not only returns to a normal level but may oscillate above and below this level up to 300 msec later. Fig. 6 shows the effects on an evoked (from click) auditory response recorded from the A6 level of the medial geniculate nucleus at intervals varying from 10 to 300 msec following conditioning stimuli (8 V) applied to the second turn of the tuber vermis. Fig. 6A shows the spontaneous electrical background activity of the medial geniculate nucleus while Fig. 6B shows the response resulting from a click of 60 db intensity. Fig. 6C represents the electrical alterations resulting from the application of electrical conditioning stimuli to the cerebellum while Figs. 6D-Q show the effects of combining the stimuli when they were separated by intervals of 10-300 msec. Notice that there was greater diminution of the response than that illustrated in Fig. 5 since it was reduced to 40~o at 10 msec and never reached more than the 75~ level at 300 msec. The data shown in Fig. 7 were obtained under similar experimental conditions to those in Fig. 6 except the stimulating site for the conditioning stimuli was moved to the first part of the first turn of tuber vermis. As shown by the curve in the inset there was less depression of electrical activity and recovery was almost complete at the 50 msec interval. However, there was loss (down to 60~o) at 100 msec with some waxing and waning during the next 200 msec. The data shown in Fig. 8 are presented since they were obtained by means of the monopolar recording technique. These data were compared with those shown in Figs. 2-4 which were obtained with the bipolar recording technique. As can be seen the curve showing response height expressed in percent of threshold was similar (though not identical) to that plotted with bipolar recording when flaxedil is used despite the fact that the contours of the individual waves vary. As can be observed, chloralosane alters considerably the responsiveness of the preparation, but since this is part of another study it need not be discussed here. These data were obtained by applying electrical pulses (8 V, 0.5 msec duration) to the folia of first turn of tuber vermis. The work of STERIADE AND STOUPEL (1960) appeared in the literature while the present studies were being carried out; hence we are not reporting the data on the effects of lesions in auditory areas I or II on these responses. However, work in progress which involves destruction of pathways followed by electrical recording indicate that there may be a dual projection system, i.e., by way of the geniculate bodies as well as by way of the tegmentum.
DISCUSSION
The effects described here were not an unexpected finding in view of the earlier work by WHITESIDE AND SNIDER (1953) showing a cerebellar projection to the medial geniculate nuclei, the mesencephalic and the diencephalic tegmentum. If these areas are regions of convergence for ascending systems from peripheral end-organs as well as from the cerebellum, then it could be logically argued that reactional interference J. neurol. Sci. (1964) 1:325-339
338
R . S . SNIDER, K. SATO, S. MIZUNO
ADE AND STOUPEL (1960) except in animals in which the threshold of response was unusually high or in which a high stimulating voltage was used. The possibility that these differences in data are due to the use of medication is a worthy one since as shown by DEURA AND SNIDER (in press) the recovery cycle of cerebro-cerebellar systems is considerably longer when measured under chloralosane as contrasted with flaxedil. In view of the previous findings of HENNEMANe t al. (1950) it was hoped that observations could be made on localized effects within either the auditory area of the cerebellum or of the cerebrum. However, such effects could not be found and it was concluded t h a t - - s o far as these studies are c o n c e r n e d - - w h e n flaxedil was used, all cerebellar areas (lobus simplex and first and second turns of tuber vermis) projected to all parts of cerebral auditory areas I and II. O f course, this does not deny the presence of a localized projection if threshold values of stimulation are used under a wide variety of anesthetic conditions. The functional significance of the presently described system is unknown. However, it is tempting to consider it as a means to control levels of excitability in a sensory area of the cerebrum. This becomes even more plausible when interpreted in the light of SN1DER AND ELDRED'S (1952) studies on cerebro-cerebellar projections and the recent work of DEURA AND SNIDER (in press) showing that electrical effects in the cerebral auditory area can act back upon the cerebellar auditory area and alter its responsiveness. The earlier studies o f ALBE-FESSmtI>AND SZABO (1954) as well as those of GASTAUT et al. (1951) also indicated a cerebral influence on the so-called sensory areas of the cerebellum. This would be compatible with the newer concept of cerebellar function which maintains that this organ can and does act on both sensory and m o t o r systems to control levels of responsiveness.
SUMMARY
Electrical records were taken from the auditory area of the cerebrum of cats while click (test) stimuli were being administered and conditioning shocks (electrical) were being applied to the auditory area of the cerebellum. (1) Conditioning the response to a click by a preceding threshold electrical shock to the cerebellum resulted in marked diminution o f the response in intervals up to 80 msec which decreased progressively as the interval augnented. Following this diminution there was usually a period of enhancement after which there was a second period of diminution (not as prominent as the first). Occasionally a second period of enhancement followed. (2) The diminished responses could be induced in all parts of cerebral auditory areas I and II as a result of stimulation of any part of the cerebellar auditory areas. (3) Diminution of responses (following click stimuli), in the ventral and anterior parts of the medial geniculate body resulted when a conditioning stimulus was applied to the auditory area of cerebellum. (4) These data are interpreted to indicate that the cerebellum can alter levels of excitability of a cerebral sensory area and suggest that the medial geniculate nucleus may be involved as an intermediate center in which reactional interference occurs. J. neurol. Sci. (1964) 1 : 325-339
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J. neurol. Sci. (1964) 1 : 325-339