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Physiological basis of the effects of motor cortex stimulation
ABSTRACTS SY. Physiological basis of the effects of motor cortex stimulation. - R.Q. Crac¢o (State University of New York, Health Science Center, Depm'tment of Neurology, Brooklyn, NY 11203, U.S.A.) The motor cortex can be stimulated transcranially and evoked motor action potentials can be recorded from limb muscles in man. The physiological basis of these motor effects is complex. Shocks delivered to area 4 in monkeys elicit a series of positive D and I waves in corticospinal tract. The first is called a D (direct) wave because its latency is too short to allow for an interposed synapse. It results from excitation of pyramidal cell IS segments or first or deeper nodes. The subsequent I (indirect) waves are transsynaptically generated by presynaptic cortical fibers. I waves are probably preferentially activated when magnetic coils are used to induce currents. Both D and I waves are conducted (50-70 m/sec) primarily in fast pyramidal tract neurons. In anesthetized monkeys and probably in relaxed humans a train of repetitive activity (D and I wayes) is required to depolarize spinal motor neurons. However, D waves alone may be sufficient to depolarize spinal motor neurons when they are facilitated by voluntary muscle contraction. Abnormalities in central motor conduction time have been described in patients with CNS disease. The pathophysiological basis of these abnormalities will be discussed and problems in interpretation emphasized. Additionally, callosally mediated cortical potentials to transcranial stimulation will be described. PS. Peripheral and central conduction times in alcoholi c s . - V. Crespi, G. Bogiiun and M.L. Delodovici 0Divisione Neurologica, Ospedale S. Gerardo, 20052 Monza,
l~y) Seventeen alcoholic patients, age range 45-71, suffering from ethylic liver cirrhosis, were submitted to median nerve SEP determination, with standard technique. N o patient had overt peripheral neuropathy or clinical evidence of other dismetabolic disease. All patients had detectable Erb's point potential (N9), spinogram (N13), parietal controlateral N20. The following conduction times could be calculated (mean + S.D.): wrist-Erb 11.23 + 0.87 msec; Erb-spine 3.8 5=0.86 msec; central conduction time (N13-N20) 6.1 5=0.86 msec. Wrist-Erb conduction showed a highly significant difference from agematched controls ( P <0.001), whereas no significant difference was found for other values. Moreover, nearly 50% of individual wrist-Erb conductions were above normal limits; on the contrary Erb-spine and central conduction were rarely affected in single cases. This peripheral, mainly distal, conduction impairment is in keeping with clinical and histopathological data about ethylic peripheral neuropathy, subclinical in our patients. We did not find any evidence to support central axonopathy in the same cases. No difference in conduction times was found between 8 patients with and 9 patients without hepatic encephalopathy; therefore, we think that these values are unaffected by the metabolic derangement typical of this state.
$23 PS. Downbeat nystngmns: an electro-oculographic study. L. Crevita (Dept. of Neurology, Academic Hospital, B-9000 Ghent, Belgium) An electrc~ocniographic study of the different oculomotor subsystems in 4 patients with downbeat nystagmus is presented. Some uncommon or atypical features are illustrated and discussed in the light of the pathophysiological hypotheses of downbeat nystagmus. The question arises whether different subtypes of downbeat nystagmus exist or whether they represent different expressions of a dysfunction in the complex eye stabilizing network. The need for further quantitative and accurate eye movement studies is stressed.
PS. L-Acetyl-carnitine in cerebrovascular lesions.- C. Crisci, B. Laneillo, R. Massini, L. Trolano, L. Pelosi, M. Pappone and G. Caruso 0Fondazinne Clin. Lavoro, Centro Medico, Campnii M.T., Dept. Clin. Neurophysinl. and Neurolngic Clinic, 2nd School of Medicine, University of N O e s , Naples, Italy) Ten selected patients with signs and symptoms of acute cerebrovascular damage (hemiparesis, aphasia, dementia) were treated with L-acetyl-camitine in an oral dose of 200 mg 3 times/day for 3 months. Each month, the patients were submitted to a battery of clinical, electrophysiological and neuropsychological tests, and the results were compared with those obtained in another group of age-matched untreated patients. Rehabilitation and other drug treatment started before the L-acetyl-carnitine administration was continued in both groups. The results of the tests showed a significantly improved performance in the group of treated patients compared with the untreated group.
PS. Tapering of myelinated fibers as a possible cause of distal slowing in peripheral nerve conduction velocity. - C. Crisci, R. Massini, P. Russo, G. Vacchiano, L. Santoro and G. Caruso 0Fondazione Gin. del Lavoro, Centro Medico, Campoli M.T., Dept. Clin. Neurophysiol. and Forensic Med. Inst., 2nd School of Medicine, Univ. of Naples, Naples, Italy) Within the framework of a study on the causes of distal slowing of nerve conduction velocity in peripheral nerves of the arms, samples of median and ulnar nerves were taken at different levels (finger, palm, wrist and elbow) in 3 young healthy males who had met a violent death at the age 18, 24 and 33 years, respectively. The hypothesis of tapering in myelinated fibers has been tested by evaluating on a statistically significant sample the area of the fibers in toto, of the myelin sheath, and of the axon, with a computer-aided system (Kontron Videoplan). Frequency distributions of areas of the various parameters evaluated at the different levels were fitted into ganssian curves and compared to one another. No significant tapering was observed for the areas of fibers
l~y) Seventeen alcoholic patients, age range 45-71, suffering from ethylic liver cirrhosis, were submitted to median nerve SEP determination, with standard technique. N o patient had overt peripheral neuropathy or clinical evidence of other dismetabolic disease. All patients had detectable Erb's point potential (N9), spinogram (N13), parietal controlateral N20. The following conduction times could be calculated (mean + S.D.): wrist-Erb 11.23 + 0.87 msec; Erb-spine 3.8 5=0.86 msec; central conduction time (N13-N20) 6.1 5=0.86 msec. Wrist-Erb conduction showed a highly significant difference from agematched controls ( P <0.001), whereas no significant difference was found for other values. Moreover, nearly 50% of individual wrist-Erb conductions were above normal limits; on the contrary Erb-spine and central conduction were rarely affected in single cases. This peripheral, mainly distal, conduction impairment is in keeping with clinical and histopathological data about ethylic peripheral neuropathy, subclinical in our patients. We did not find any evidence to support central axonopathy in the same cases. No difference in conduction times was found between 8 patients with and 9 patients without hepatic encephalopathy; therefore, we think that these values are unaffected by the metabolic derangement typical of this state.
$23 PS. Downbeat nystngmns: an electro-oculographic study. L. Crevita (Dept. of Neurology, Academic Hospital, B-9000 Ghent, Belgium) An electrc~ocniographic study of the different oculomotor subsystems in 4 patients with downbeat nystagmus is presented. Some uncommon or atypical features are illustrated and discussed in the light of the pathophysiological hypotheses of downbeat nystagmus. The question arises whether different subtypes of downbeat nystagmus exist or whether they represent different expressions of a dysfunction in the complex eye stabilizing network. The need for further quantitative and accurate eye movement studies is stressed.
PS. L-Acetyl-carnitine in cerebrovascular lesions.- C. Crisci, B. Laneillo, R. Massini, L. Trolano, L. Pelosi, M. Pappone and G. Caruso 0Fondazinne Clin. Lavoro, Centro Medico, Campnii M.T., Dept. Clin. Neurophysinl. and Neurolngic Clinic, 2nd School of Medicine, University of N O e s , Naples, Italy) Ten selected patients with signs and symptoms of acute cerebrovascular damage (hemiparesis, aphasia, dementia) were treated with L-acetyl-camitine in an oral dose of 200 mg 3 times/day for 3 months. Each month, the patients were submitted to a battery of clinical, electrophysiological and neuropsychological tests, and the results were compared with those obtained in another group of age-matched untreated patients. Rehabilitation and other drug treatment started before the L-acetyl-carnitine administration was continued in both groups. The results of the tests showed a significantly improved performance in the group of treated patients compared with the untreated group.
PS. Tapering of myelinated fibers as a possible cause of distal slowing in peripheral nerve conduction velocity. - C. Crisci, R. Massini, P. Russo, G. Vacchiano, L. Santoro and G. Caruso 0Fondazione Gin. del Lavoro, Centro Medico, Campoli M.T., Dept. Clin. Neurophysiol. and Forensic Med. Inst., 2nd School of Medicine, Univ. of Naples, Naples, Italy) Within the framework of a study on the causes of distal slowing of nerve conduction velocity in peripheral nerves of the arms, samples of median and ulnar nerves were taken at different levels (finger, palm, wrist and elbow) in 3 young healthy males who had met a violent death at the age 18, 24 and 33 years, respectively. The hypothesis of tapering in myelinated fibers has been tested by evaluating on a statistically significant sample the area of the fibers in toto, of the myelin sheath, and of the axon, with a computer-aided system (Kontron Videoplan). Frequency distributions of areas of the various parameters evaluated at the different levels were fitted into ganssian curves and compared to one another. No significant tapering was observed for the areas of fibers