PS. A new method for recording short latency evoked potentials by using EKG artifact elimination procedure

ABSTRACTS PS. A statistical method to evaluate rite EMG voluntary activity: isoelectrie and spike deosity. - G. Serra, M. Carreras, G. Sclarretta * and D. De Grandis * (Nenrolngieal Clinics of the Universities of Ferrara and * Verona, Italy) In 1984 Hermens et al. found that a gaussian curve, around the zero value, described in healthy subjects the statistical amplitude distribution of motor unit potential negative and positive peaks in a surface EMG registration. The authors studied, by using computerized methods, the peak amplitude distribution histogram, by using different sampling intervals in a needle EMG recording, following the consideration that, if the sampling windows, where the computer recognizes the peaks and isoelectric tracts, become longer, the probability of finding spikes changes. The authors, in fact, found a gaussian curve with brief intervals, but with longer intervals the histogram was progressively divided into two curves because the zero value probability was diminished. The quantitative analysis of the phenomenon may be used as a method to analyze the probability density of EMG signals. Furthermore, the typical gaussian distribution tended to be present for relatively long intervals in neurogenic disorders, where the isoelectric EMG trace was more probable; the opposite situation was found in myogenic patterns. This quantitative method is similar to the classic subjective evaluation of the isoelectric intervals in maximal effort EMG pattern.

PS. Ulnar nerve imlsy localized to the distal brachial plexus. R. Sethi and C. Krarup (Dept. of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, U.S.A.) A 23-year-old male with marked weakness (2/5) in ulnar innervated muscles and loss of touch and pin-prick sense in the ulnar distribution was examined. EMG of the ADM showed severe loss of motor units. Conduction studies showed normal amplitudes of the MAP in the ADM and of the SAP at wrist. Conduction velocities along the forearm, across the elbow, and along the upper arm were normal. There was severe conduction block in ulnar but not in median motor fibers between Erb's point and axilla. The sensory response from dig. V decreased from 5 ttV in the axilla to 0.6 /tV at Erb's point and the conduction velocity was 36 m/see. The response from dig. III remained constant (3/~V) in the axilla and at Erb's point and the conduction velocity was 69 m/see. Two weeks later, improvement of the conduction block was apparent. The findings localize the lesion to the ulnar nerve at the division of the medial cord. No focal injury or entrapment of the plexus had occurred and he had no evidence of systemic disease associated with mononeuropathy. One week before the onset of the weakness he had suffered a mild whip-lash injury and a post-traumatic brachial plexopathy is a possible etiology.

$95 SY. Electrophysioiogical studies of tics, chorea and myodonus. - H. Shibasaki (Dept. of Internal Medicine, Saga Medical Sehunl, Saga 840-01, Japan) Tics, chorea and myoclonus can be recognized by clinical observation, but the study of their pathophysiology requires electrophysiological investigations. EEG correlates of these involuntary movements can be investigated by the simuhaneous recording of EEGs and EMGs from various muscles, as well as by the back averaging of EEGs with respect to the involuntary movement. Simple tics of Gilles de la Tourette's syndrome have been reported not to be preceded by any negative slow cortical potential. With the exception of choreaacanthocytosis, chorea is not preceded by any cortical activity. Cortical myoclonus is preceded by a cortical spike localized at the contralateral central region. In somatosensory cortical reflex myoclonus, the early cortical components of SEPs are extremely enhanced and are frequently followed by a long latency reflex in the peripheral muscles. There seem to be some common constituents between the myoclonus-related cortical spike and the giant SEP. Scalp distribution of the giant SEP was found to be similar to that of the normal SEE Photosensitive myoclonus seems to involve the cortical reflex mechanism. PS. A new method for recording short latency evoked potenrials by using EKG artifact elimination procedure. H. Shibasaki, M. Nakamtwa *, S. Nishida * and R. Kakigi (Dept. of Int. Med., Saga Medical School, and * Dept. of Elect. Eng., Saga Univ., Saga, Japan) This is the first trial to apply the EKG artifact elimination procedure to evoked potential (EP) recording with the noncephalic reference derivation. The method consists of 3 separate steps: data acquisition, EKG artifact elimination and EP averaging. Based on the simultaneously recorded EEG, EKG and stimulus pulse, EKG artifacts in the raw EEG were eliminated by using our new procedure which consists of 4 basic operations: synchronized partition of the raw EEG, EKG averaging, synchronized repetition and sychronized subtraction of the EKG estimate from the raw EEG. Then the average EPs are obtained by averaging the processed EEG using the stimulus pulse as a trigger. Using SEP records recorded with the hand reference derivation, data obtained by proposed method were compared with those obtained by 2 conventional averaging methods, and were shown to be more accurate than those obtained by the latter. The advantage of the proposed method is that it requires a smaller number of sweeps and hence it takes much less time to record short latency EPs with noncephalic reference derivation than other methods. PS. Scalp topography of photic evoked potentials. Application of the wave form decomposition technique. - H. Shibasaki, M. Nakamura * and S. Nishida * (Dept. Int. Med., Saga Medical School, and *Dept. Elect. Eng., Saga Univ., Saga, Japan) The components of the scalp-recorded photic evoked potential and their generator sources in man have not been