Brain Research, 91 (1975) 151-155
151
© Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
Effect of skin cooling on spontaneous EMG activity in triceps surae of the decerebrate cat
STEVEN L. WOLF AND WILLIAM D. LETBETTER Emory University Regional Rehabilitation Research and Training Center, and Department of Anatomy, Emory University, Atlanta, Ga. 30322 (U.S.A.)
(Accepted March 1lth, 1975)
Clinicians have reported a temporary reduction in muscle hyperactivity in man following intense cutaneous cold applications, usually in the form of ice9,12,14,15. These observations have led to the widespread clinical use of cryotechniques in therapeutic treatments designed to reduce spasticity and other motor abnormalities, but since little effort has been directed toward determining how thermal cutaneous stimulation might change underlying muscle activity, mechanistic details are still unknown. Accepted explanations for these changes in man seem to be based upon data from animal investigations in which muscle spindle afferent activity was seen to diminish when muscle was cooled directly6,13. Since cold-induced changes in cutaneous afferent activity might also contribute to observed motor changes during cooling, the present study was undertaken to evaluate the effects of a specific cutaneous cold stimulus on a form of hypermotor activity produced in cats by intercollicular decerebration. Ten animals of both sexes were made decerebrate under halothane anesthesia. Mean arterial blood pressure was maintained above 100 m m Hg and rectal temperature was held between 37 °C and 39.5 °C by a heating pad placed beneath the torso. The left hindlimb was shaved and fine wire bipolar electrodes z were inserted percutaneously into either the left medial gastrocnemius or soleus muscles. Location of electrode tips was verified by dissection following each experiment. Standard laboratory recording equipment was employed and data were stored on F M tape for subsequent analysis. An 8.6 sq. cm thermoelectric cooling module 2,zl was secured to the skin surface overlying medial gastrocnemius muscle several minutes prior to any recording session. When activated, the cold plate reduced skin-interface temperatures to as low as 10 °C at a rate of approximately 1 °C/sec. This mode of application was intended to stimulate only thermosensitive cutaneous structures and to eliminate any concomitant mechanical stimuli. Experiments lasted from 45 min to 7 h following decerebration. All recordings were made on animals in a prone position with the left hindlimb resting on a rolled towel (except for one in which the amount of extensor hypertonus was sufficient to enable the animal to support its own body weight with minimal assistance). The degree of extensor rigidity was evaluated periodically by
152
32" ~,,
f f - -
10" Fig. 1. Rectified and integrated E M G (in relative units) from medial gastrocnemius muscle (upper trace) integrated each sec at a sample rate of 500 Hz. Dashed line serves as a point to reference increasing (upward) and decreasing (downward) E M G levels. Lower trace: skin-cold plate interface temperature above recording site. Time marker: 10 sec.
examining the animal's responses to flexion withdrawal, pinna or crossed extensor reflexes, or by subjectively determining the amount of resistance to passive manipulation of forelimb or hindlimb joints. An experiment was terminated upon cessation of these reflexes or upon onset of flaccidity. In several experiments a needle thermistor (Victory Engineering, Model NM29-10-32-A) was positioned to measure subcutaneous temperatures beneath the cold plate. When the overlying skin surface was cooled to 10 °C, the average drop in subcutaneous temperatures was 2.7 °C. The maximum temperature drop observed within the substance of the medial gastrocnemius muscle itself was only 1.6 °C after 2 min of continuous cooling. Since these temperature changes were well below those reported by others as necessary to exert direct effects on muscle afferents themselves 6, all the effects reported below will be tentatively attributed to activity pattern changes in thermally sensitive cutaneous afferents. All rigid animals showed a reduction in integrated E M G activity following cutaneous cold stimulation. While this qualitative finding could be reproduced generally, the quantitative E M G changes varied from trial to trial and from animal to animal. Invariably, the most notable reduction in electromyographic activity occurred when animals displayed persistent rigid behavior in all 4 limbs as judged by the criteria stated above. Rigidity appeared to diminish 3-4 h following decerebration and it was at this time that muscle responses to skin cooling became less perceptible. Fig. 1 represents a typical motor response to skin cooling. E M G activity decreased within 1-5 sec after skin cooling had begun. This observation was consistent in cooling trials of various durations ranging from 30 sec to 5 min. Since afferent conduction of cold information is mediated by Ad and C fibers in the cat 4, 10,11 the long latency seen for changes in motor output must reflect, at least in part, the long afferent conduction times to the spinal cord over these pathways. However, long central delays due to spatial and temporal processing of the afferent information by spinal interneurons most likely account for the bulk of the reflex delays observed. The possibility of contributions from a spino-bulbospinal reflex mechanism 17,t8 cannot be excluded. It should be noted that when the cold stimulus was turned off, the integrated E M G activity showed a large transient increase before returning to the precooling control level. This increased level of motor activity always occurred between 1 and 10
153
%u 20
o z
t
10
8
16
24 TIME
80
88
96
104
(SEC)
Fig. 2. Single motor unit activity from the left medial gastrocnemius muscle during a cooling trial. Ordinate: discharge frequency plotted as number of discharges counted in successive 1-sec intervals. Break in abscissa represents a 54-sec interval in the skin cooling period during which time discharge frequency ranged from 4 to 9 Hz. Downward and upward arrows depict beginning and ending of cooling, respectively. Skin overlying this muscle was cooled from an ambient temperature of 36 °C to 11 °C.
sec following the end of cooling and is attributed to a release of motoneurons from the prevailing inhibitory influences resulting from activation of thermal afferents. This finding is deduced from an analysis z0 of preliminary data obtained in other experiments where increased excitatory post-synaptic potentials from triceps surae motoneurons or augmented test monosynaptic reflexes were observed upon terminating skin cooling. In a few instances we encountered single motor unit (SMU) activity from the medial gastrocnemius muscle during a cooling trial. These units displayed one of two specific firing patterns. The SMU depicted in Fig. 2 showed a resting frequency varying from 10 to 15 Hz and, despite the fact that the cooling interval was somewhat shorter than that seen in the previous figure, the behavior of this isolated unit generally paralleled the integrated activity of Fig. 1. The only apparent difference was that, unlike integrated responses, this isolated unit showed a post-cooling facilitatory response which developed over a 9 sec interval. A single motor unit recorded in another preparation (Fig. 3) had a considerably higher resting discharge frequency than the one in the previous figure. Its response to skin cooling further differed in that it showed an initial increased discharge but did not show a post-cooling facilitatory response. Differences observed in the units' responses to skin cooling may have been due to variations in the degree of existing rigidity in each preparation or to the duration of skin cooling. Alternatively, these responses may represent activity in tonic (Fig. 2) and phasic (Fig. 3) motor units since the resting discharges in these units correspond precisely with similarly classified muscle potentials seen in man during sustained but moderate contractions 8. Additionally, it has been shown that tonic motoneurons show predominantly inhibitory responses to electrical stimulation of the sural nerve in lightly anesthetized cats while motoneurons belonging to fast-twitch units show primarily excitatory responses to
154
°°1 I ud tt~
o z IX u.
2 TIME
(5EC)
Fig. 3. Single motor unit activity from the left medial gastrocnemius muscle during a cooling trial. Ordinate: discharge frequency plotted as number of discharges counted in successive 1-sec intervals. Downward and upward arrows depict beginning and ending of cooling, respectively. Skin overlying this muscle was cooled from an ambient temperature of 34 °C to 14 °C.
the same stimuli a. Other studies 5,16 suggest that electrical stimulation of sural afferents having diameters ranging from 4 to 9 # m can cause inhibition of ankle extensor motoneurons through at least one inhibitory interneuron in the decerebrate cat. In light of the above investigations it is suggested that in the present report the predominating inhibition, resulting from activation of flexor reflex afferents conveying cooling information (Figs. 1 and 2), is upon tonic motoneurons belonging to the ankle extensors of rigid cats. More precise electrophysiological data to substantiate this suggestion are being gathered and will be provided in future reports. The evidence presented here does suggest a skin-reflex relationship which is contrary to that presented by Hagbarth 7 in that a specific cutaneous cooling stimulus can cause an inhibition in underlying muscle responses without appreciably lowering intramuscular temperature. It should be noted that in Hagbarth's experiments heating sural nerve or skin overlying triceps surae resulted in augmented responses in ankle extensors when skin temperatures approached pain threshold while our cooling stimulus has never been considered painful when applied to human skin. The present study seems to corroborate recent observations made on lightly anesthetized cats in which polysynaptic reflex activity was reduced with skin cooling 19. Our data also suggest the possibility of differential motor responses from the same extensor motoneuron pool to a specific cutaneous thermal input.
155 This w o r k was s u p p o r t e d in p a r t by S R S 16-P-56808/4-08 f r o m the Social an d R e h a b i l i t a t i o n Service, D . H . E . W . , by a p r e d o c t o r a l fellowship (24-P-56921/4-03) a w a r d e d to Dr. W o l f f r o m the Social an d R e h a b i l i t a t i o n Service, an d by R e s e a r c h G r a n t NS-09735 f r o m N . I . N . D . S . a w a r d e d to Dr. Letbetter.
1 BASMAJIAN,J. V., Muscles Alive: Their Functions Revealed by Electromyography, Williams and Wilkins, Baltimore, Md., 1967, pp. 32-37. 2 BASMAJIAN,J. V., WOLF, S. L., AND SHINE, G. L., Device for controlled rapid localized cooling, Amer. J. phys. Med., 52 (1973) 65-67. 3 BURKE, R. E., JANKOWSKA,E., AND TEN BRHGGENCATE,G., A comparison of peripheral and rubrospinal synaptic input to slow and fast twitch motor units of triceps surae, J. Physiol. (Lond.), 207 (1970) 709-732. 4 DOUGLAS,W. W., RITCHIE,J. M., AND STRAt;B, R. W., Discharges in non-myelinated ((2) fibres in the cat's saphenous nerve in response to changing the temperature of the skin, J. Physiol. (Lond.), 146 (1959) 4~48P. 5 ECCLES, R. M., AND LUNDBERG,A., Supraspinal control of interneurones mediating spinal reflexes, J. Physiol. (Lond.), 147 (1959) 565-584. 6 ELDRED,E., LINDSLEY,D. F., AND BUCHWALD,J. S., The effect of cooling on mammalian muscle spindle, Exp. Neurol., 2 (1960) 144-157. 7 HAGBARTH,K.-E., Excitatory and inhibitory skin areas for flexor and extensor mononeurones, Actaphysiol. scand., 26, Suppl. 94 (1952) 1-58. 8 HANNERZ,J., Discharge properties of motor units in relation to recruitment order in voluntary contraction, Acta physiol, scand., 91 (1974) 374-384. 9 HARXVIKSON,K., Ice therapy in spasticity, Acta neuroL scand., 38, Suppl. 2 (1962) 79-84. 10 HENSEL, H., Electrophysiology of cutaneous thermoreceptors. In D. R. KENSHALO(Ed.), The Skin Senses, Thomas, Springfield, II1., 1968, pp. 384-399. 11 IGGO, A., Cutaneous heat and cold receptors with slowly conducting (C) afferent fibres, Quart. J. exp. PhysioL, 44 (1959) 362-370. 12 KNOTSSON,E., Topical cryotherapy in spasticity, Scand. J. rehab. Med., 2 (1970) 159-163. 13 LIPVOLD, O. C. J., NICHOLLS,J. G., AND REDFERN,J. W. T., A study of the afferent discharge produced by cooling a mammalian muscle spindle, J. Physiol. (Lond.), 153 (1960) 218-231. 14 MIGLmTTA,O., Action of cold on spasticity, Amer. J. phys. Med., 52 (1973) 198-205. 15 OLSON, J. E., AND STRAVINO,V. D., A review of cryotherapy, Phys. Ther., 52 (1972) 840-853. 16 ROSENBERG, M. E., Synaptic connexions of alpha extensor motoneurones with ipsilateral and contralateral cutaneous nerves, J. Physiol. (Lond.), 207 (1970) 231-255. 17 SHIMAMURA, M., Longitudinal coordination between spinal and cranial reflex systems, Exp. Neurol., 8 (1963) 505-521. 18 SHIMAMURA,M., AND AKERT, K., Peripheral nervous relations of proprio-spinal and spinobulbo-spinal reflex systems, Jap. J. Physiol., 15 (1965) 638-647. 19 TLEUUN,S. ZI~., KLEINBOCK,I. YA, ANDTS~TSURIN,V. I., Effect of peripheral heating and cooling on spinal reflex activity, Neirofiziol., 5 (1973) 181-185. 20 WOLF, S. L., The effect of a specific cutaneous cold stimulus on underlying gastrocnemius muscle motor activity, Dissert. Abstr. Intern., 34 (1974) 299. 21 WOLF, S. L., AND BASMAJIAN,J. V., A rapid cooling device for controlled cutaneous stimulation, Phys. Ther., 53 (1973) 25-27.
151
© Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
Effect of skin cooling on spontaneous EMG activity in triceps surae of the decerebrate cat
STEVEN L. WOLF AND WILLIAM D. LETBETTER Emory University Regional Rehabilitation Research and Training Center, and Department of Anatomy, Emory University, Atlanta, Ga. 30322 (U.S.A.)
(Accepted March 1lth, 1975)
Clinicians have reported a temporary reduction in muscle hyperactivity in man following intense cutaneous cold applications, usually in the form of ice9,12,14,15. These observations have led to the widespread clinical use of cryotechniques in therapeutic treatments designed to reduce spasticity and other motor abnormalities, but since little effort has been directed toward determining how thermal cutaneous stimulation might change underlying muscle activity, mechanistic details are still unknown. Accepted explanations for these changes in man seem to be based upon data from animal investigations in which muscle spindle afferent activity was seen to diminish when muscle was cooled directly6,13. Since cold-induced changes in cutaneous afferent activity might also contribute to observed motor changes during cooling, the present study was undertaken to evaluate the effects of a specific cutaneous cold stimulus on a form of hypermotor activity produced in cats by intercollicular decerebration. Ten animals of both sexes were made decerebrate under halothane anesthesia. Mean arterial blood pressure was maintained above 100 m m Hg and rectal temperature was held between 37 °C and 39.5 °C by a heating pad placed beneath the torso. The left hindlimb was shaved and fine wire bipolar electrodes z were inserted percutaneously into either the left medial gastrocnemius or soleus muscles. Location of electrode tips was verified by dissection following each experiment. Standard laboratory recording equipment was employed and data were stored on F M tape for subsequent analysis. An 8.6 sq. cm thermoelectric cooling module 2,zl was secured to the skin surface overlying medial gastrocnemius muscle several minutes prior to any recording session. When activated, the cold plate reduced skin-interface temperatures to as low as 10 °C at a rate of approximately 1 °C/sec. This mode of application was intended to stimulate only thermosensitive cutaneous structures and to eliminate any concomitant mechanical stimuli. Experiments lasted from 45 min to 7 h following decerebration. All recordings were made on animals in a prone position with the left hindlimb resting on a rolled towel (except for one in which the amount of extensor hypertonus was sufficient to enable the animal to support its own body weight with minimal assistance). The degree of extensor rigidity was evaluated periodically by
152
32" ~,,
f f - -
10" Fig. 1. Rectified and integrated E M G (in relative units) from medial gastrocnemius muscle (upper trace) integrated each sec at a sample rate of 500 Hz. Dashed line serves as a point to reference increasing (upward) and decreasing (downward) E M G levels. Lower trace: skin-cold plate interface temperature above recording site. Time marker: 10 sec.
examining the animal's responses to flexion withdrawal, pinna or crossed extensor reflexes, or by subjectively determining the amount of resistance to passive manipulation of forelimb or hindlimb joints. An experiment was terminated upon cessation of these reflexes or upon onset of flaccidity. In several experiments a needle thermistor (Victory Engineering, Model NM29-10-32-A) was positioned to measure subcutaneous temperatures beneath the cold plate. When the overlying skin surface was cooled to 10 °C, the average drop in subcutaneous temperatures was 2.7 °C. The maximum temperature drop observed within the substance of the medial gastrocnemius muscle itself was only 1.6 °C after 2 min of continuous cooling. Since these temperature changes were well below those reported by others as necessary to exert direct effects on muscle afferents themselves 6, all the effects reported below will be tentatively attributed to activity pattern changes in thermally sensitive cutaneous afferents. All rigid animals showed a reduction in integrated E M G activity following cutaneous cold stimulation. While this qualitative finding could be reproduced generally, the quantitative E M G changes varied from trial to trial and from animal to animal. Invariably, the most notable reduction in electromyographic activity occurred when animals displayed persistent rigid behavior in all 4 limbs as judged by the criteria stated above. Rigidity appeared to diminish 3-4 h following decerebration and it was at this time that muscle responses to skin cooling became less perceptible. Fig. 1 represents a typical motor response to skin cooling. E M G activity decreased within 1-5 sec after skin cooling had begun. This observation was consistent in cooling trials of various durations ranging from 30 sec to 5 min. Since afferent conduction of cold information is mediated by Ad and C fibers in the cat 4, 10,11 the long latency seen for changes in motor output must reflect, at least in part, the long afferent conduction times to the spinal cord over these pathways. However, long central delays due to spatial and temporal processing of the afferent information by spinal interneurons most likely account for the bulk of the reflex delays observed. The possibility of contributions from a spino-bulbospinal reflex mechanism 17,t8 cannot be excluded. It should be noted that when the cold stimulus was turned off, the integrated E M G activity showed a large transient increase before returning to the precooling control level. This increased level of motor activity always occurred between 1 and 10
153
%u 20
o z
t
10
8
16
24 TIME
80
88
96
104
(SEC)
Fig. 2. Single motor unit activity from the left medial gastrocnemius muscle during a cooling trial. Ordinate: discharge frequency plotted as number of discharges counted in successive 1-sec intervals. Break in abscissa represents a 54-sec interval in the skin cooling period during which time discharge frequency ranged from 4 to 9 Hz. Downward and upward arrows depict beginning and ending of cooling, respectively. Skin overlying this muscle was cooled from an ambient temperature of 36 °C to 11 °C.
sec following the end of cooling and is attributed to a release of motoneurons from the prevailing inhibitory influences resulting from activation of thermal afferents. This finding is deduced from an analysis z0 of preliminary data obtained in other experiments where increased excitatory post-synaptic potentials from triceps surae motoneurons or augmented test monosynaptic reflexes were observed upon terminating skin cooling. In a few instances we encountered single motor unit (SMU) activity from the medial gastrocnemius muscle during a cooling trial. These units displayed one of two specific firing patterns. The SMU depicted in Fig. 2 showed a resting frequency varying from 10 to 15 Hz and, despite the fact that the cooling interval was somewhat shorter than that seen in the previous figure, the behavior of this isolated unit generally paralleled the integrated activity of Fig. 1. The only apparent difference was that, unlike integrated responses, this isolated unit showed a post-cooling facilitatory response which developed over a 9 sec interval. A single motor unit recorded in another preparation (Fig. 3) had a considerably higher resting discharge frequency than the one in the previous figure. Its response to skin cooling further differed in that it showed an initial increased discharge but did not show a post-cooling facilitatory response. Differences observed in the units' responses to skin cooling may have been due to variations in the degree of existing rigidity in each preparation or to the duration of skin cooling. Alternatively, these responses may represent activity in tonic (Fig. 2) and phasic (Fig. 3) motor units since the resting discharges in these units correspond precisely with similarly classified muscle potentials seen in man during sustained but moderate contractions 8. Additionally, it has been shown that tonic motoneurons show predominantly inhibitory responses to electrical stimulation of the sural nerve in lightly anesthetized cats while motoneurons belonging to fast-twitch units show primarily excitatory responses to
154
°°1 I ud tt~
o z IX u.
2 TIME
(5EC)
Fig. 3. Single motor unit activity from the left medial gastrocnemius muscle during a cooling trial. Ordinate: discharge frequency plotted as number of discharges counted in successive 1-sec intervals. Downward and upward arrows depict beginning and ending of cooling, respectively. Skin overlying this muscle was cooled from an ambient temperature of 34 °C to 14 °C.
the same stimuli a. Other studies 5,16 suggest that electrical stimulation of sural afferents having diameters ranging from 4 to 9 # m can cause inhibition of ankle extensor motoneurons through at least one inhibitory interneuron in the decerebrate cat. In light of the above investigations it is suggested that in the present report the predominating inhibition, resulting from activation of flexor reflex afferents conveying cooling information (Figs. 1 and 2), is upon tonic motoneurons belonging to the ankle extensors of rigid cats. More precise electrophysiological data to substantiate this suggestion are being gathered and will be provided in future reports. The evidence presented here does suggest a skin-reflex relationship which is contrary to that presented by Hagbarth 7 in that a specific cutaneous cooling stimulus can cause an inhibition in underlying muscle responses without appreciably lowering intramuscular temperature. It should be noted that in Hagbarth's experiments heating sural nerve or skin overlying triceps surae resulted in augmented responses in ankle extensors when skin temperatures approached pain threshold while our cooling stimulus has never been considered painful when applied to human skin. The present study seems to corroborate recent observations made on lightly anesthetized cats in which polysynaptic reflex activity was reduced with skin cooling 19. Our data also suggest the possibility of differential motor responses from the same extensor motoneuron pool to a specific cutaneous thermal input.
155 This w o r k was s u p p o r t e d in p a r t by S R S 16-P-56808/4-08 f r o m the Social an d R e h a b i l i t a t i o n Service, D . H . E . W . , by a p r e d o c t o r a l fellowship (24-P-56921/4-03) a w a r d e d to Dr. W o l f f r o m the Social an d R e h a b i l i t a t i o n Service, an d by R e s e a r c h G r a n t NS-09735 f r o m N . I . N . D . S . a w a r d e d to Dr. Letbetter.
1 BASMAJIAN,J. V., Muscles Alive: Their Functions Revealed by Electromyography, Williams and Wilkins, Baltimore, Md., 1967, pp. 32-37. 2 BASMAJIAN,J. V., WOLF, S. L., AND SHINE, G. L., Device for controlled rapid localized cooling, Amer. J. phys. Med., 52 (1973) 65-67. 3 BURKE, R. E., JANKOWSKA,E., AND TEN BRHGGENCATE,G., A comparison of peripheral and rubrospinal synaptic input to slow and fast twitch motor units of triceps surae, J. Physiol. (Lond.), 207 (1970) 709-732. 4 DOUGLAS,W. W., RITCHIE,J. M., AND STRAt;B, R. W., Discharges in non-myelinated ((2) fibres in the cat's saphenous nerve in response to changing the temperature of the skin, J. Physiol. (Lond.), 146 (1959) 4~48P. 5 ECCLES, R. M., AND LUNDBERG,A., Supraspinal control of interneurones mediating spinal reflexes, J. Physiol. (Lond.), 147 (1959) 565-584. 6 ELDRED,E., LINDSLEY,D. F., AND BUCHWALD,J. S., The effect of cooling on mammalian muscle spindle, Exp. Neurol., 2 (1960) 144-157. 7 HAGBARTH,K.-E., Excitatory and inhibitory skin areas for flexor and extensor mononeurones, Actaphysiol. scand., 26, Suppl. 94 (1952) 1-58. 8 HANNERZ,J., Discharge properties of motor units in relation to recruitment order in voluntary contraction, Acta physiol, scand., 91 (1974) 374-384. 9 HARXVIKSON,K., Ice therapy in spasticity, Acta neuroL scand., 38, Suppl. 2 (1962) 79-84. 10 HENSEL, H., Electrophysiology of cutaneous thermoreceptors. In D. R. KENSHALO(Ed.), The Skin Senses, Thomas, Springfield, II1., 1968, pp. 384-399. 11 IGGO, A., Cutaneous heat and cold receptors with slowly conducting (C) afferent fibres, Quart. J. exp. PhysioL, 44 (1959) 362-370. 12 KNOTSSON,E., Topical cryotherapy in spasticity, Scand. J. rehab. Med., 2 (1970) 159-163. 13 LIPVOLD, O. C. J., NICHOLLS,J. G., AND REDFERN,J. W. T., A study of the afferent discharge produced by cooling a mammalian muscle spindle, J. Physiol. (Lond.), 153 (1960) 218-231. 14 MIGLmTTA,O., Action of cold on spasticity, Amer. J. phys. Med., 52 (1973) 198-205. 15 OLSON, J. E., AND STRAVINO,V. D., A review of cryotherapy, Phys. Ther., 52 (1972) 840-853. 16 ROSENBERG, M. E., Synaptic connexions of alpha extensor motoneurones with ipsilateral and contralateral cutaneous nerves, J. Physiol. (Lond.), 207 (1970) 231-255. 17 SHIMAMURA, M., Longitudinal coordination between spinal and cranial reflex systems, Exp. Neurol., 8 (1963) 505-521. 18 SHIMAMURA,M., AND AKERT, K., Peripheral nervous relations of proprio-spinal and spinobulbo-spinal reflex systems, Jap. J. Physiol., 15 (1965) 638-647. 19 TLEUUN,S. ZI~., KLEINBOCK,I. YA, ANDTS~TSURIN,V. I., Effect of peripheral heating and cooling on spinal reflex activity, Neirofiziol., 5 (1973) 181-185. 20 WOLF, S. L., The effect of a specific cutaneous cold stimulus on underlying gastrocnemius muscle motor activity, Dissert. Abstr. Intern., 34 (1974) 299. 21 WOLF, S. L., AND BASMAJIAN,J. V., A rapid cooling device for controlled cutaneous stimulation, Phys. Ther., 53 (1973) 25-27.
