86s C o m m u n i c a t i o n s a f f i c h 6 e s / P o s t e r s

P142 TRANSCBANIAL MAGNETIC STIMULATION OF FACIAL NERVE

Cocito D., De Mattei M. D.E,A. Neurologia

0spedale Molinette. Torino. Italia.

Aims of this study is clarify the mechanism of

transcranial facial nerve stimulation and asse~ the

clinical application of the method in patients with

Bell's palsy. Electromyographic responses were

elicited by electrical and magnetic transcranial

stimulation in 14 normal subjects and 33 patients

affected by Bell's palsy.

It has been possible to obtain a compound muscle

action potential (CMAP) by magnetic stimulation of

the affected side only in 7 of the 33 patients

examined: at the time of the neurophysiological

investigation they suffered from a peripheral palsy

of the facial nerve with different degrees of

involvement; thus it follows that the possibility

to record magnetic CMAPs not correlate with the

clinical stage Of palsy. We postulate that the magnetic stimulation might

excite the Facial nerve at the First tract of the

osseous duct, where,as known, the anatomical lesion

of Bell's palsy usually occurs:a lesional

hypoexcitable area might explain the difficulty to

obtain a CMAP even in patients who presented a good

functional outcome. Furthermore the presence in

some patients of CMAP5 by magnetic stimulation of

the affected side, might demonstrate a different

site off the nerve injury.

P144 MOTOR EVOKED RESPONSES AFTER CERVICAL SPINE

INJURIES. A.Landi, D.Curri, P.Cervellini, R.Bruno*. Dept. of Neurosurgery, Gen.Hosp. Vicenza and *FIDIA Clinical Res. Dept. Abano T. Italy.

Motor evoked poterltlals (MEPs) ctpon transcutaneous magnetic stJmttla~ ion were evaluated in~ 21 patients sufferirlq fr[im c e r v i c a l s p i n e i n j u t y ; t h e a i m o f t h e i n v e s t i g a t i o n w a s t o a s s e s s t h e d i a g n o s t ~ : ~ n d p r - o g n o s t i c r e l i a b i l i t y o f MEPs i n [ h i s p a r t i c u l a r d i s e a s e . M E P s u p o n c o r t i c a l , c e r v i c a l a n d l u m b a r - s t i m u l a t i o n w e r e r - e c o r d e d b o t h f r o m APB a n d EDL. b i l a t e r a l l y ; i n a d d i t i o n , F w a v e s w e r e o b t a i n e d f r o m m e d i a n n e r v e s , i n o r d e r t o a s s e s s p o s s i b l y r a d i c u l a r i m p a i r m e n t s a n d t o o b t a i n a m o r e e x a c t m e a s u r e m e n t o f CMCT ( C e n t r a l M o t o r C o n d u c t i o n T i m e ) . MEP r e c o r d i n g s w e r e p e r f o r m e d w i t h i n 4 8 hr"s f r o m t h e t r a u m a a n d 30 d a y s l a t e r . In a d d i t i o n , 1 0 p a t i e n t s w e r e t r e a t e d w i t h GMI ( I 0 0 r a g / d i e f o r 3 0 d a y s ) a n d t e s t e d w i t h MEPs before and after the treatment. MEF' restalts suggested to share out the patients in three groups, respectively: with a prevailing myelic damage, with a mixed myelo-radieular impairment and with a prevailing radicular impairment. MEPs were absent en 47 limbs (56% OT t h e t o t a l ) , 9 e f w h i c h p r e s e n t i n g o n l y h y p o r e f l e x i a , w i t h o u t s t r e n g t h i m p a i r m e n t . 3 0 d a y s l a t e r , M E P s s h o w e d a n i m p r o v e m e n t on 13 limbs (9 non-paretie and 4 paretic)~ preceeding a clinical amelioration; ne clinical improvement was observed in the other limbs. Patients treated with GMI presented with~further MEP and clinical improvement. In conclusion, MEF's showed to be reliable and useful in the early functional assessment of cervical spine injttries. The absence of MEP response in the acute stage suggests a poor prognosis.

P143 MAGNETIC BRAIN STIMULATION: EVIDENCE FOR FOCAL EFFECTS OF A FIGURE OF EIGHT COIL (8-COIL) COMPARED TO THE USUAL CIRCULAR COIL.

~-~i~Z@X, D. Claus, P. Brenner

Neurological Department,University Erlangen- Nuremberg, Schwabachanlage 6 8520 Erlangen, West-Germany Magnetic brain stimulation is usually carried out with a circular coil. The stimulus excites large areas of the human brain. To investigate focal lesions a more focalized stimulus could be of interest. Therefore surface electrodes were placed on distal and proximal muscles of both upper limbs in normal subjects. Compound muscle action potentials (CMAPs) were recorded from five muscles simultanously following magnetic brain stimulation (right abductor digiti minimi, right thenar, right biceps brachii, left abductor digiti minimi, and biceps muscle). With the target muscle contracted stimulation with the circular coil centered over Cz (clockwise current flow, 40% suprathreshold) evoked CMAPs in all muscles on both sides. In the relaxed condition the muscles of one side were excited preferentially The 8-coil was placed over the left hemisphere coil position was more critical. With the highest intensities only contralateral muscles were excited. No CMAPs could be recorded from the ipsi- lateral arm (target muscles contracted and relaxed). It is concluded that magnetic brain stimulation with the 8-coil excites circumscribed areas of the human brain. The eontralateral motor area is not stimulated. Investigation with the 8-coil would provide sensitive results in focal brain lesions.

This work was supported by the Sander Foundation.

P145 LOWER LIMB MUSCLE RESPONSES

TO TRANSCUTANEOUS ELECTRICAL STIMULATION OF THE SPINAL CORD

J. Zidar, T. Zgur Institute of Clinical Neurophysiology, University Medical Center, Ljubljana (Yugoslavia)

High voltage electrical st imulation on the neck preferentially activates spinal nerves at their exit from the spinal canal. At higher intensities responses from lower limb muscles could also be obtained. For this, long spinal tracts have to be excited.

We studied responses in tibialis anterior (TA) and gastrocnemius (GA) muscles after transcutaneous high voltage electrical stimulation on the neck (C7 vertebral level) and in the back (T6, T9 and L1 verte- bral level). Pre l iminary results of exper iments , a imed to study the mode of action of spinal stimulation, will be presented. Three healthy male volunteers (aged 29, 35, and 37 years) were examined. Digitimer D180 electrical s t imulator was used with the longer (100/~s) decay time constant. Stimulating electrodes consisted of saline soaked pads 2 cm in diameter. Electrodes were placed in the midline, with the anode always 5-7 cm cranially to the stimulating cathode.

Stimulation at C6 or T6 spinal processes gave on average by 471 % bigger responses, if the target muscle was slightly contracted. Such an increase was never observed, if L1 level was stimulated and only occasionally, if stimulation was performed at T9 level. It is thus likely that s t imulat ion at the spinal levels C7 and T6 activates leg lower motor neurons transsynaptically, while stimulation at L1 level activates them postsynaptically. Both types of action were observed at T9 level. Latencies of responses were the same in the resting and contracting muscles, what suggests that single stimulus in the back, in contrast to scalp stimulation, produces only single volley of impulses in the spinal tracts. Conduction velocities along the spinal cord were much higher (157 m/s, 115 m/s, 111 m/s), if latency differences of muscle responses between stimulation over C7 and T6 vertebrae were used for their calculation than in the case of latency differences between C7 and T9 (56 m/s, 59 m/s, 55 m/s) or C7 and L1 (58 m/s, 54 m/s, 67 m/s) stimulation sites. The former values are higher because it is likely that they do not include synaptic delays and conduction through proximal parts of the pe r iphe ra l motor axons. In conclusion, act ivat ion of several descending (not necessarily only the corticospinal) or even antidromic activation of the long ascending tracts may contribute to muscle responses in such experiments.