Somatosensory evoked potentials correlates of psychophysical magnitude estimates for tactile air-puff stimulation in man

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VIII CONGRESS OF EMG AND RELATED CLINICAL NEUROPHYS1OLOGY

trodes. The bipolar system has been implanted bilaterally into 3 tetraplegic patients, Follow-up time of the full-time electrophrenic respiration ranged from 2 to 4 years. The 4-pole electrode system has been implanted bilaterally into a patient with sleep apnea (Ondine's curse). Patients using the stimulators are weaned from the mechanical respirator. With both systems continuous, bilateral, fatigue-free electrophrenic respiration can be maintained by submaximal stimulation.

SY. Long-latency reflexes and motor control. - M. Hallett (NIH Clinical Center, Bldg. 10, Rm. 5N226, Bethesda, MID 20892, U.S.A.) Long-latency reflexes are those longer in latency than the monosynaptic stretch reflex (the 'short-latency' reflex). Some long-latency reflexes, whose pathways are restricted to the spinal cord, are short-loop and some, whose pathways go above the spinal cord, are tong-loop. Long-latency short-loop reflexes include flexor reflexes, group II mediated reflexes, and responses to segmented stimulation. Long-latency long-loop reflexes include the spino-bulbo-spinal reflex, some reflexes to stretch and, possibly, some reflexes to electrical and cutaneous stimulation. This review will emphasize the reflexes to stretch. There are at least two physiological roles of stretch reflexes: to help restore limb position after perturbation and to help regulate muscle stiffness. Lesions of the somatosensory pathways up to the level of cortex and of the corticospinal pathways lead to loss of longlatency stretch reflexes. Spasticity, often seen in these settings, is characterized by increased short-latency reflexes, but occasionally increased long-latency reflexes are found. Huntington's disease also is characterized by loss of long-latency stretch reflexes. The rigidity of Parkinson's disease can be explained by increase of long-latency reflexes. Stimulus-sensitive myoclonus also is characterized by hyperactivity of long-latency reflexes.

PS. Multiple level spinal SEP recorded from the epldoral space in man. - J.-P, Halonen, S J . Jones, M,A. Edgar and A.O. Ramford (The Medical Research Council and Royal National Orthopaedic Hospital, London, U.K.) The recordings were made from 28 neurologically normal patients admitted to the hospital for corrective scoliosis surgery. Spinal cord potentials were recorded from the epidural space at various levels from L3 to C5. Both pure cutaneous and mixed nerves were stimulated in the lower limb. A typical transformation of the ascending volley from a single large-amplitude potential at the lower lumbal level to a response with 3-4 small-amplitude peaks at the upper thoracic level was seen in all multiple level recordings. The amplitude of the responses was largest in recording sites close to the spinal tracts ipsilateral to the stimulation. This lateralization effect was obvious for all the peaks of the spinal response. However, at the segmental level T l l / 1 2 the response divided so that the ipsi-

lateral electrode recorded only one negative peak which was followed 1-1.5 msec later by another negative peak recorded at the contralateral side of the cord. The separate peaks of the response at the upper thoracic level had different stimulation thresholds so that the earlier peaks could be evoked with smaller intensities of peripheral stimulation compared to the later peaks, These results give new information concerning the physiology of the spinal cord in man and can also be used to evaluate the possible changes during spinal cord monitoring of scoliosis surgery.

PS. Peripheral nervous system involvement in multiple sclerosis. - S.R. Hammm~ and C, Yiannikus (Dept. of Medicine, University of Sydney, Sydney, NSW 2006, Australia) Somatosensory evoked potentials (SEPs) were recorded from median (MN) and posterior tibial nerve (PTN) stimulation in 32 and 42 control subjects respectively, and in 112 patients with clinically definite or probable multiple sclerosis (MS) who were all fully ambulant with mild to moderate disability at most. None of them showed any clinical evidence of peripheral neuropathy. Control and patients arm lengths (mean+ S.D.: controls 70.15 + 5.11 cm, patients 70.11 + 5.31 cm) and heights (controls 166.40+8.13 cm, patient 165.81_+ 8.91 cm) showed no significant differences. However, the mean latency to the potentials recorded over Erb's point (N10) from M N stimulation and over L1 (N20) from PTN stimulation were highly significantly longer ( P < 0.001) in the MS patients than in the controls (N10: controls 9.59+0.74 msec, patients 10.10+0.80 msec; N20: controls 20.19+1.72 msec, patients 21.96-+1.82 msec) whilst there were no significant interside differences (ISD) between the two groups for either parameter (N10 ISD: controls 0.13 _+0.13 msec, patients 0.17 _+0.14 msec; N20 ISD: controls 0.46 -+0.39 msec, patients 0.42 _+0.38 msec). These results suggest that there is subclinical symmetrical demyelination in the peripheral nervous system in MS, a disease which is generally considered to be confined to the central nervous system.

PS. Somatusensory evoked potentials correlates of psychophysical m a ~ t u d e estimates for tactile air-puff stimulation in man. - I. H u h i m o ~ (Dept. of Neurosm'gery, Tokyo Metropolitan Hospital of Fuchu, Fuchu City, Tokyo, Japan) Somatosensory evoked potentials (SEPs) elicited by tactile air-puff stimulation of the hand were recorded from the scalp over the contralateral primary projection area in man. The air puffs were generated by our recently developed high-speed air control system and provided constant and reproducible pressure wave forms that were varied continually. With air-puff stimulation, 6 components (N1, P1, N2, P2, N3 and P3) were consistently recorded within 100 msec after stimulus delivery. Six levels of stimulus intensity were applied to the palm of the fight hand at the base of the second digit. Magnitude estimation studies showed that the cutaneous sensation magnitude

ABSTRACTS produced by the stimuli increased linearly with increasing stimulus intensity. Amplitudes of the SEP components recorded under the same stimulus conditions systematically increased as a function of the stimulus function. These results suggest that SEP amplitudes can provide objective and quantitative measures of the subjective sensation magnitude in response to natural tactile stimulation.

SY. Natural versus electrical stimulation for eliciting somatosensory evoked potentials. I. Hashimoto (Dept. of Nemosurgery, Tokyo Metropolitan Hospital of Fuchu, Fuchu City, Tokyo, Japan) An extreme synchrony of nerve volleys foUowing intense electrical stimulation of nerve trunks results in an obviously increased signal-to-noise ratio in the recording of somatosensory evoked potentials (SEPs). These artificially synchronized volleys, however, are far from being physiological and are activated simply on the basis of size and electrical threshold of the nerve fibers, bypassing the peripheral receptors and terminal nerve fibers. Natural stimulation on the other hand has the advantages over electrical shocks that (1) one can limit and specify the location and type of sensory receptors, (2) by activating the peripheral receptors, the natural stimuli can generate a physiological pattern of impulses in the nerve fibers, (3) no discomfort to the subject, and (4) there is little or no contamination from the stimulus and muscle artifacts in the records. Among various types of natural stimuli, air-puffs have been shown to provide fairly constant and reproducible tactile stimuli without direct contact on the skin although the previous air-puffs have some inherent limitations in eliciting clear-cut SEPs. This report will examine SEPs elicited by sharp-fronted air-puffs (a rise-time of I msec) delivered to the face and hand in man and compare critically the natural SEPs with those evoked by electrical stimulation of the face and median nerve at the wrist.

PS. Analysis of short latency somatosensory evoked potentials (SSEPs) in 3 dimensions. - N.F. Hassan, A. Bromberg, L. Margari, P.J. Maceabee, R.Q. Craeco and J.B. Craeco (State University of New York Health Science Center, Brooklyn, NY 11203, U.S.A.) A mathematical algorithm was created to analyze evoked potentials in 3 dimensions. Utilizing short latency SSEP data, 3 dimensional computer projections were constructed such that different colors indicated different degrees of depth. These 3-dimensional projections could be rotated at various degrees of pitch and velocity when referenced to a horizontal plane. By selective digital filtering, distinct colors could be 'peeled away' providing approximate data on generator depth and localization. Preliminary analysis indicated that SSEP components may be distinguished by a combination of different dipole orientations. In patients with CAT-scan documented, focal CNS

$45 lesions, the evoked potential data revealed similarly localized color-coded 'holes' within the 3-dimensional projections. This mathematical model of investigation may significantly improve evoked potential localization.

SY. Motoneuron diseases in childhood. - I. l-lausmanowaPetrusewicz (Dept. of Neurology, Banacha la, 024197 Warsaw, Poland) The motoneuron disorders in childhood can be divided into (a) congenital diseases due allegedly to disturbed interaction between muscle and motoneuron during development, and (b) acquired ones occurring after maturation of motoneuron and muscle. The eiectrophysiological characteristics of various spinal muscular atrophies are given as an example of the congenital type of disorders and the cases of poliomyelitis and rare childhood amyotrophic lateral sclerosis as an example of acquired disorders. The electromyography gives insight into the compensatory mechanisms operating in chronic and mild disorders as well as into the dynamics of denervation in rapidly advancing diseases. The diagnostic yield of spontaneous activity, parameters of single motor unit potentials (MUPs) and effort pattern is discussed. Motor conduction velocity usually normal may be, however, slowed in motoneuron involvement. Somatosensory evoked potentials show that some congenital motoneuron diseases in children may also affect sensory pathways. EMG studies in children present some problems. First the properties of MUPs are undergoing continuous changes as the child develops. Secondly it is often not possible to obtain the cooperation of children. From this point of view the scope and limitations of conventional EMG, coherent EMG and other quantitative methods are discussed.

PS. The parallel NN classification rule and its application for an analysis of EMG data. - I. Hausmanowa-Petmsewicz and A. J6irwik (Dept. of Neurology, Banacha la, 02-097 Warsaw, and Instlt~te of Bioengineering, Polish Academy of Sciences, Warsaw, Poland) A method of parallel classification (diagnosis) for the multi-class problem is proposed and compared with the hierarchical and common classifications. It is assumed that the common classifications realize the ' k nearest neighbor' (k-NN) decision rule since the parallel and the hierarchical classifications are based on several k-NN rules. Each of these classification methods operates in a different feature space. The 3 above-mentioned methods of classification were applied to an analysis of EMG data concerning 3 selected forms of spinal atrophy in children up to the age of 4 years. The results indicate that the parallel classification gives the lowest rate of misclassification. The rate of misclassification was taken as a quality criterion. The geometrical interpretation in the feature space, as well as practical results, implies that the parallel classification is better than the hierarchical one, and that the hierarchical