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Sensory conduction velocity in the fast (beta) and slow (gamma) fibres
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related to force.had slightly lower values than that of controls,and the average curve of turns was as in controls. In 14 patients with neurogenie disorders the number of turns was the best indicator of neurogenic affection; it was decreased in two-thirds of patients at 20-30% of maximum force. The average curves of mean amplitude and ratio related to force were as in controls. A-3.05 SENSORY CONDUCTION VELOCITY IN THE FAST (BETA) AND SLOW (GAMMA) FIBRES. C.R. DeFaria, G.M. Manzano, M.A.S. Tolentino (Goisnia, Brazil) The effect of cold on the nerve fibres has been studied since 1921, when Adrian worked with alteration of the refractory period induced by cold, in animals. However, the results concerning nerve conduction velocities have been confusing. We studied human sensory conduction velocity of the median nerve, cooled by immersion of the prepared hand in ice. Stimulating electrodes were placed at,the tip of the 3rd finger with recording electrodes at the base of this finger. Supramaximal stimuli of 200 V were applied, and as the temperatures fell from 340 C to 16O C the amplitude of the response dropped from 34 DV to 2 pV and the velocity from 54 to 18 m/set. Conduction was blocked at about 15O C, so we increased the stimulus to 380-400 V and again we had a response, but now with two isolated comoonents of 15 uV with velocities of 30 m/se; and 19 m/se;. They were interpreted as belonging to fast (beta) and slow (gamma) fibres respectively. It became obvious that the small remaining response, at 18 m/set at 16O C, belonged to the gamma fibres. Repeating the test 24 hours later we reproduced the same results except for the amplitude of the first component (beta fibres) which was After 30 days there was comseverely reduced. This technique enabled us to plete recovery. studv seoaratelv fast and slow fibres. These results permit is to conclude that cold raises the threshold of nerve excitation, particularly of faster fibres, which are blocked at higher The lesion and slowing provoked temperature. by cold were particularly evident in the faster fibres, which were more sensitive to cold. B-7.03 PATTERN-EVOKED CHANGES IN TOXIC OPTIC NEUROPATHY. A. Kriss, W.M. Carroll, L.D. Blumhardt and A.M. Halliday (London, G.B.) The pattern-evoked potential to a reversing checkerboard stimulus comprised of 50' checks has been recorded in 23 patients with a diasnosis of toxic optic neuropathy. The response to full-field (O-16' radius) stimulation was typically of small amplitude and consisted of a positive-negative-positive (P75-N105-P135) complex usually best seen to either side of the Independent stimulation of occipital midline.
the half-fields (0-16O) for eawe showed that the major positive component (PlOO), derived mainly from the macular region, was usually of normal latency but attenuated. This component was commonly smaller following stimulation of the temporal half fields than following stimulation of the nasal half-fields. In contrast to what is seen in normals, the paramacular (m N105-P135) complexes were the outstanding feature in the responses from these patients. Responses following stimulation of the central fields (0-4O radius) were usually grossly abnormal, being either not detectable or exhibiting a very attenuated abnormal wave form. These findings parallel the centro-caecal scotomata characteristic of this condition. Clinical recovery was associated with an increase in amplitude but in most cases the pattern of abnormality remained. B-7.07 VISUAL AND SOMATOSENSORY EVOKED POTENTIAL STUDIES IN CHARCOT-MARIE-TOOTH DISEASE. A.M. Halliday, W.M. Carroll and S.J. Jones (London, G.B.) Fifteen cases of CMTD were studied using standard VEP (pattern reversal)and SEP (cortical and subcortical response) techniques. VEP abnormalities (mainly prolongation of latencv) were seen in 5 cases with wide-field and a furiher 3 cases with central-field stimulation, corresponding fairly well with neuroopthalmological findings (mainly disc pallor or mild colour vision impairment). Subcortical SEP components were generalCortical components were ly delayed or absent. identifiable in all cases. and delaved in all except 2 with normal motor conduction velocity The separation between cervic(Type II CMTD). al (where present) and cortical SEPs was normal in the majority of cases, but slightly increased for 5 arms (3 cases). Peripheral sensory conduction time (PCT) was estimated in all cases by extrapolating the wrist-elbow CT (change in cortical SEP latency with stimulation at the elbow instead of the wrist) to the spinal cord. The increase in PCT was sufficient to account for the delay in the cortical response (assuming normal cenral CT) for all except8 arms (7cases),for which there wasevidenceof additional delay. There was some evidence,therefore,ofcentral somatosensory pathway involvement in 8 cases,of whom 4 had evidence of visual pathway involvemelt, A-B.07 TWO DISTINCT TYPES OF ASYMMETRY IN THE PATTERN-EVOKED POTENTIALS OF HUMAN ALBINOS. A.M. Halliday, W.M. Carroll, B.S. Jay and W.I. McDonald (London, G.B.) In albinos each cerebral hemisphere receives a predominantly monocular input from the contralateral eye,-giving rise to an asymmetry of the visual evoked ootential (VEP) to whole-field stimulation which is similar.to that for
related to force.had slightly lower values than that of controls,and the average curve of turns was as in controls. In 14 patients with neurogenie disorders the number of turns was the best indicator of neurogenic affection; it was decreased in two-thirds of patients at 20-30% of maximum force. The average curves of mean amplitude and ratio related to force were as in controls. A-3.05 SENSORY CONDUCTION VELOCITY IN THE FAST (BETA) AND SLOW (GAMMA) FIBRES. C.R. DeFaria, G.M. Manzano, M.A.S. Tolentino (Goisnia, Brazil) The effect of cold on the nerve fibres has been studied since 1921, when Adrian worked with alteration of the refractory period induced by cold, in animals. However, the results concerning nerve conduction velocities have been confusing. We studied human sensory conduction velocity of the median nerve, cooled by immersion of the prepared hand in ice. Stimulating electrodes were placed at,the tip of the 3rd finger with recording electrodes at the base of this finger. Supramaximal stimuli of 200 V were applied, and as the temperatures fell from 340 C to 16O C the amplitude of the response dropped from 34 DV to 2 pV and the velocity from 54 to 18 m/set. Conduction was blocked at about 15O C, so we increased the stimulus to 380-400 V and again we had a response, but now with two isolated comoonents of 15 uV with velocities of 30 m/se; and 19 m/se;. They were interpreted as belonging to fast (beta) and slow (gamma) fibres respectively. It became obvious that the small remaining response, at 18 m/set at 16O C, belonged to the gamma fibres. Repeating the test 24 hours later we reproduced the same results except for the amplitude of the first component (beta fibres) which was After 30 days there was comseverely reduced. This technique enabled us to plete recovery. studv seoaratelv fast and slow fibres. These results permit is to conclude that cold raises the threshold of nerve excitation, particularly of faster fibres, which are blocked at higher The lesion and slowing provoked temperature. by cold were particularly evident in the faster fibres, which were more sensitive to cold. B-7.03 PATTERN-EVOKED CHANGES IN TOXIC OPTIC NEUROPATHY. A. Kriss, W.M. Carroll, L.D. Blumhardt and A.M. Halliday (London, G.B.) The pattern-evoked potential to a reversing checkerboard stimulus comprised of 50' checks has been recorded in 23 patients with a diasnosis of toxic optic neuropathy. The response to full-field (O-16' radius) stimulation was typically of small amplitude and consisted of a positive-negative-positive (P75-N105-P135) complex usually best seen to either side of the Independent stimulation of occipital midline.
the half-fields (0-16O) for eawe showed that the major positive component (PlOO), derived mainly from the macular region, was usually of normal latency but attenuated. This component was commonly smaller following stimulation of the temporal half fields than following stimulation of the nasal half-fields. In contrast to what is seen in normals, the paramacular (m N105-P135) complexes were the outstanding feature in the responses from these patients. Responses following stimulation of the central fields (0-4O radius) were usually grossly abnormal, being either not detectable or exhibiting a very attenuated abnormal wave form. These findings parallel the centro-caecal scotomata characteristic of this condition. Clinical recovery was associated with an increase in amplitude but in most cases the pattern of abnormality remained. B-7.07 VISUAL AND SOMATOSENSORY EVOKED POTENTIAL STUDIES IN CHARCOT-MARIE-TOOTH DISEASE. A.M. Halliday, W.M. Carroll and S.J. Jones (London, G.B.) Fifteen cases of CMTD were studied using standard VEP (pattern reversal)and SEP (cortical and subcortical response) techniques. VEP abnormalities (mainly prolongation of latencv) were seen in 5 cases with wide-field and a furiher 3 cases with central-field stimulation, corresponding fairly well with neuroopthalmological findings (mainly disc pallor or mild colour vision impairment). Subcortical SEP components were generalCortical components were ly delayed or absent. identifiable in all cases. and delaved in all except 2 with normal motor conduction velocity The separation between cervic(Type II CMTD). al (where present) and cortical SEPs was normal in the majority of cases, but slightly increased for 5 arms (3 cases). Peripheral sensory conduction time (PCT) was estimated in all cases by extrapolating the wrist-elbow CT (change in cortical SEP latency with stimulation at the elbow instead of the wrist) to the spinal cord. The increase in PCT was sufficient to account for the delay in the cortical response (assuming normal cenral CT) for all except8 arms (7cases),for which there wasevidenceof additional delay. There was some evidence,therefore,ofcentral somatosensory pathway involvement in 8 cases,of whom 4 had evidence of visual pathway involvemelt, A-B.07 TWO DISTINCT TYPES OF ASYMMETRY IN THE PATTERN-EVOKED POTENTIALS OF HUMAN ALBINOS. A.M. Halliday, W.M. Carroll, B.S. Jay and W.I. McDonald (London, G.B.) In albinos each cerebral hemisphere receives a predominantly monocular input from the contralateral eye,-giving rise to an asymmetry of the visual evoked ootential (VEP) to whole-field stimulation which is similar.to that for