- Email: [email protected]
Mechanical properties of motor units
$30
quently followed, 15 to 2o msec l a t e r , by C r e f l e x in the stimulated hand, which corresponds to an evoked myoclonus. Some patients show double c o r t i cal spikes and double C reflexes to a single s t i m u l a t i o n . The amplitude of the SEP and C r e f l e x diminishes by anticonvulsant medication. Backward averaging of EEG time-locked to myoclonus (jerk-locked averaging) demonstrates p o s i t i v e - n e g a t i v e , biphasic sharp potentials at the contralateral central region, occurring 7 to 18 msec before the myoclonus of an upper extremity. The high amplitude SEP and the myoclonus-related c o r t i c a l spike are s i m i l a r in terms of the wave form,:scalp topography, and the time r e l a t i o n s h i p to e i t h e r evoked or spontaneous myoclonus, suggesting an involvement of s i m i l a r physiological mechanisms. In addition, the C r e f l e x and the spontaneously occurring myoclonus show s i m i l a r pattern of spread to other muscles. I t is therefore suggested that the spontaneously occurring myoclonus in these cases is in fact generated by a c o r t i c a l r e f l e x mechanism. SEP is thus useful for i n v e s t i g a t i n g the mechanism of s t i m u l u s - s e n s i t i v e myoclonus and probably for choosing e f f e c t i v e treatment.
$33
AUDITORYNERVE-BRAINSTEMEVOKED RESPONSES
SOHMER H~ Department of Physiology, Hebrew U n i v e r s i t y , Hadassah Medical School, Israel Auditory evoked p o t e n t i a l s (AEP) are composed of a series of components representing e l e c t r i c a l a c t i v i t y generated along many parts of the auditory pathway recorded by skin electrodes in man using f i l t e r i n g , a m p l i f i c a t i o n and averaging techniques. Such components include responses generated by the cochlear h a i r c e l l s , by the auditory nerve, the brainstem auditory pathway, the cerebral cortex and even r e f l e x , myogenic responses to sound s t i m u l i . These various components can be isolated by proper choice of auditory stimulus, of recording electrode s i t e s , of recording f i l t e r bandpass and of averager parameters. Besides t h e i r use in auditory diagnosis, these AEP, p a r t i c u l a r l y the auditory nerve and brainstem evoked responses (ABR) also contribute to neurological diagnosis even when the lesion is not discernable using present day imaging techniques. An understanding of the basic neurophysiology of these responses and t h e i r mode of i n i t i a t i o n w i t h i n the cochlea is mandatory for the proper use of these techniques and for accurate neurological i n t e r p r e t a t i o n . The impact of ABR recordings on neurological diagnosis would be enhanced i f we had more i n formation concerning t h e i r exact sources w i t h i n the brainstem and concerning the possible d i f f e r e n t i a l effects of axonal versus synaptic lesions w i t h i n the brainstem auditory pathways. Such investigations are presently being conducted. In conclusion, even though ABR recordings are already making valuable c o n t r i b u t i o n s to diagnosis, present research is l i k e l y to enhance the diagnost i c capacity of ABR.
S34
MECHANICALPROPERTIES OF MOTORUNITS
STEIN,R.B., GORDON,T. and LEE,R.G., Departments of Physiology and Pharmacology, U n i v e r s i t y of Alberta, Edmonton and Department of C l i n i c a l Neuroscience, U n i v e r s i t y of Calgary, Calgary, Alberta, Canada I f a single motor u n i t is recorded together with the force f l u c t u a t i o n s of a whole muscle during voluntary contractions, the twitch contraction of that u n i t
$31
can be determined under some conditions by spike-triggered averaging. In normal subjects a r e l a t i o n s h i p exists between.the size (and often the speed) of the twitch contractions of single motor units and the threshold force level at which they begin to f i r e during increasing voluntary contractions. The same size re l a t i o n s h i p s are also observed a f t e r many insults to motoneurons such as pressure block of peripheral nerves or motoneuron disease. However, in e a r l i e r experiments the orderly pattern of recruitment was never observed a f t e r nerve section and resuture in human ulnar nerve patients. In cut and resutured cat nerves, we found that the i n i t i a l reconnection of motor units was random, but that over a period of months, the normal r e la t io n s hips redeveloped between the size of motor axons and the size and speed of the muscle units they innervated. In these animal studies, motoneurons were constrained to grow back to one or two closely synergistic muscles. In contrast, the severed ulnar nerves in pat i e n t s reinnervated many muscles in the hand, often with quite d i f f e r e n t functions and hence d i f f e r e n t patterns of voluntary a c t i v a t i o n . Evidence w i l l be presented that a substantial amount of misdirection of motor axons occurs, even with careful resuture of fascicles w i t h i n the nerve. Thus, reorganization of motor units according to size may also occur f o llo w in g reinnervation of human muscles, but the orderly pattern of recruitment is obscured.
S35
STEREOENCEPHALOTOMYAND MOTORCONTROL
STRUPPLER,A.~ Neurologische K l i n i k der Technischen U n i v e r s i t ~ t , Mbhlstra~e 28, 8000 MUnchen 80, FRG Stereotaxic interventions give the opportunity to investigate motor control in a l e r t cooperative human subjects. This technique has reached a new stage with the f o l l o w i n g developments: The development of neurodiagnostic imaging, l i k e CT-scan and NMR, give the p o s s i b i l i t y to v i s u a l i z e defined brain areas. Micros t i mu l a t i o n of discrete brain areas and simultaneous recording of the a f f e r e n t and e f f e r e n t a c t i v i t y t r a v e l l i n g through the target area allow to c o r r e l a t e anatomical substrate and function. This r e l a t i o n can be f u r t h e r processed with computer techniques in order to establish a brain mapping. The aim of the present study was to investigate patients f o l l o w i n g thalamoand subthalamotomy. Since these interventions produce hypotonia c o n t r a l a t e r a l l y to the l e s i o n , we were interested to test the change in motor control by applying torque pulse disturbances to the upper extremity. This kind of hypotonia shows an electromyographically recorded r e f l e x behaviour d i f f e r e n t from other types, such as hypotonia of peripheral or spinal o r i g i n . Since the target point can be anatomically and f u n c t i o n a l l y i d e n t i f i e d , i t is possible to redefine the c l i n i c a l manifestations. (Supported by DFG SFB 50 "Kybernetik".)
quently followed, 15 to 2o msec l a t e r , by C r e f l e x in the stimulated hand, which corresponds to an evoked myoclonus. Some patients show double c o r t i cal spikes and double C reflexes to a single s t i m u l a t i o n . The amplitude of the SEP and C r e f l e x diminishes by anticonvulsant medication. Backward averaging of EEG time-locked to myoclonus (jerk-locked averaging) demonstrates p o s i t i v e - n e g a t i v e , biphasic sharp potentials at the contralateral central region, occurring 7 to 18 msec before the myoclonus of an upper extremity. The high amplitude SEP and the myoclonus-related c o r t i c a l spike are s i m i l a r in terms of the wave form,:scalp topography, and the time r e l a t i o n s h i p to e i t h e r evoked or spontaneous myoclonus, suggesting an involvement of s i m i l a r physiological mechanisms. In addition, the C r e f l e x and the spontaneously occurring myoclonus show s i m i l a r pattern of spread to other muscles. I t is therefore suggested that the spontaneously occurring myoclonus in these cases is in fact generated by a c o r t i c a l r e f l e x mechanism. SEP is thus useful for i n v e s t i g a t i n g the mechanism of s t i m u l u s - s e n s i t i v e myoclonus and probably for choosing e f f e c t i v e treatment.
$33
AUDITORYNERVE-BRAINSTEMEVOKED RESPONSES
SOHMER H~ Department of Physiology, Hebrew U n i v e r s i t y , Hadassah Medical School, Israel Auditory evoked p o t e n t i a l s (AEP) are composed of a series of components representing e l e c t r i c a l a c t i v i t y generated along many parts of the auditory pathway recorded by skin electrodes in man using f i l t e r i n g , a m p l i f i c a t i o n and averaging techniques. Such components include responses generated by the cochlear h a i r c e l l s , by the auditory nerve, the brainstem auditory pathway, the cerebral cortex and even r e f l e x , myogenic responses to sound s t i m u l i . These various components can be isolated by proper choice of auditory stimulus, of recording electrode s i t e s , of recording f i l t e r bandpass and of averager parameters. Besides t h e i r use in auditory diagnosis, these AEP, p a r t i c u l a r l y the auditory nerve and brainstem evoked responses (ABR) also contribute to neurological diagnosis even when the lesion is not discernable using present day imaging techniques. An understanding of the basic neurophysiology of these responses and t h e i r mode of i n i t i a t i o n w i t h i n the cochlea is mandatory for the proper use of these techniques and for accurate neurological i n t e r p r e t a t i o n . The impact of ABR recordings on neurological diagnosis would be enhanced i f we had more i n formation concerning t h e i r exact sources w i t h i n the brainstem and concerning the possible d i f f e r e n t i a l effects of axonal versus synaptic lesions w i t h i n the brainstem auditory pathways. Such investigations are presently being conducted. In conclusion, even though ABR recordings are already making valuable c o n t r i b u t i o n s to diagnosis, present research is l i k e l y to enhance the diagnost i c capacity of ABR.
S34
MECHANICALPROPERTIES OF MOTORUNITS
STEIN,R.B., GORDON,T. and LEE,R.G., Departments of Physiology and Pharmacology, U n i v e r s i t y of Alberta, Edmonton and Department of C l i n i c a l Neuroscience, U n i v e r s i t y of Calgary, Calgary, Alberta, Canada I f a single motor u n i t is recorded together with the force f l u c t u a t i o n s of a whole muscle during voluntary contractions, the twitch contraction of that u n i t
$31
can be determined under some conditions by spike-triggered averaging. In normal subjects a r e l a t i o n s h i p exists between.the size (and often the speed) of the twitch contractions of single motor units and the threshold force level at which they begin to f i r e during increasing voluntary contractions. The same size re l a t i o n s h i p s are also observed a f t e r many insults to motoneurons such as pressure block of peripheral nerves or motoneuron disease. However, in e a r l i e r experiments the orderly pattern of recruitment was never observed a f t e r nerve section and resuture in human ulnar nerve patients. In cut and resutured cat nerves, we found that the i n i t i a l reconnection of motor units was random, but that over a period of months, the normal r e la t io n s hips redeveloped between the size of motor axons and the size and speed of the muscle units they innervated. In these animal studies, motoneurons were constrained to grow back to one or two closely synergistic muscles. In contrast, the severed ulnar nerves in pat i e n t s reinnervated many muscles in the hand, often with quite d i f f e r e n t functions and hence d i f f e r e n t patterns of voluntary a c t i v a t i o n . Evidence w i l l be presented that a substantial amount of misdirection of motor axons occurs, even with careful resuture of fascicles w i t h i n the nerve. Thus, reorganization of motor units according to size may also occur f o llo w in g reinnervation of human muscles, but the orderly pattern of recruitment is obscured.
S35
STEREOENCEPHALOTOMYAND MOTORCONTROL
STRUPPLER,A.~ Neurologische K l i n i k der Technischen U n i v e r s i t ~ t , Mbhlstra~e 28, 8000 MUnchen 80, FRG Stereotaxic interventions give the opportunity to investigate motor control in a l e r t cooperative human subjects. This technique has reached a new stage with the f o l l o w i n g developments: The development of neurodiagnostic imaging, l i k e CT-scan and NMR, give the p o s s i b i l i t y to v i s u a l i z e defined brain areas. Micros t i mu l a t i o n of discrete brain areas and simultaneous recording of the a f f e r e n t and e f f e r e n t a c t i v i t y t r a v e l l i n g through the target area allow to c o r r e l a t e anatomical substrate and function. This r e l a t i o n can be f u r t h e r processed with computer techniques in order to establish a brain mapping. The aim of the present study was to investigate patients f o l l o w i n g thalamoand subthalamotomy. Since these interventions produce hypotonia c o n t r a l a t e r a l l y to the l e s i o n , we were interested to test the change in motor control by applying torque pulse disturbances to the upper extremity. This kind of hypotonia shows an electromyographically recorded r e f l e x behaviour d i f f e r e n t from other types, such as hypotonia of peripheral or spinal o r i g i n . Since the target point can be anatomically and f u n c t i o n a l l y i d e n t i f i e d , i t is possible to redefine the c l i n i c a l manifestations. (Supported by DFG SFB 50 "Kybernetik".)