- Email: [email protected]
P33-25 Activated area of imagined movement: MEG study
S304
Posters
P33-21 Human cortical response to parametric passive finger movement an MEG study
P33-23 Visualization of the sensitivity of the MEG sensor array based on the realistic signal generation modeling on standardized space
M. Matsuhashi1 , T. Mima1 , T. Nagamine2 , H. Shibasaki3 , H. Fukuyama1 Human Brain Research Center, Kyoto University, Kyoto, Japan, 2 Department of System Neuroscience, Sapporo Medical University, Sapporo, Japan, 3 Takeda General Hospital, Kyoto, Japan
S. Iwaki1 1 National Institute of Advanced Industrial Science and Technology (AIST), Japan
1
Objective: To clarify the cerebral mechanism of proprioceptive sensation in human Methods: Thirteen right handed healthy volunteers participated. We used a newly developed device to produce brisk but accurately controlled passive flexion of the PIP joint of the right index finger in the magnetically shielded room. The motion stimuli of varying parameters, with travel angle and time of 15/30, 15/50, 15/80, 15/120, 9/50 and 23/120 (degrees/ms), were delivered at 1 3 s random intervals while cerebral activities were recorded using 122 channel whole-head neuromagnetometer (Neuromag 122) with 0.03 300 Hz passband. The data were analyzed for the source strength of the equivalent current dipole (ECD) of averaged response and also the event related synchronization/desynchronization (ERS/ERD) as the mean power change of the left central channels. The effects of motion velocity and travel angle were tested in constant travel (15/30, 15/50, 15/80 and 15/120) and constant velocity (9/50, 15/80 and 23/120) conditions using Friedman test. Results: Three major response peaks were observed, all located in the left central area: early peak at 39±6 ms after the motion onset (mean ± s.d.), middle peak at 71±13 ms after the motion onset, and late peak at 95±28 ms after the motion offset. The ECD of these peaks were all estimated in and around the left primary sensorimotor cortex. The effect of motion velocity was significant only on the source dipole moment of the early peak (p < 0.05). The effect of travel angle was significant (p < 0.05) on the ERD of 18 24 Hz band. Conclusions: This result suggests differential physiological significance of ‘evoked response’ which reflects time-locked cortical inputs and ‘induced response’ representing local cortical oscillation in the perception of passive finger movement in the human sensorimotor cortex. P33-22 Advances in analysis of spontaneous EEG/MEG activity by independent component analysis A. Hyvarinen1 , P. Ramkumar2 , R. Hari2 1 Dept of Mathematics and Statistics, University of Helsinki, Finland, 2 Brain Research Unit, LTL, Aalto University, Espoo, Finland Objective: We develop new methods for exploratory analysis of spontaneous EEG/MEG activity. Currently, the analysis is quite difficult and existing methods need to be improved. In particular, novel methods might be able to find and analyze default-mode networks, which have been defined with fMRI but are more elusive in EEG/MEG. Methods: We use the framework of independent component analysis (ICA) which has had some success in the analysis of spontaneous activity. First, we improve the capability of ICA to analyze brain sources by introducing a new spatial variant similar to the way ICA is used with fMRI. This is possible by first computing the minimum norm solution to the inverse problem. We further combine this spatial ICA with our Fourier-domain method (Hyvarinen et al, NeuroImage, 2010). Second, we introduce a new testing method for finding components which are consistently similar over subjects. The novelty here is that we formulate a null hypothesis, under which the components are obtained as random orthogonal rotations of whitened data. Most other work has relied on heuristically chosen thresholds instead of a null hypothesis, and thus has not been able to control the false positive rate. Results: We applied the methods on MEG recordings from ten healthy subjects who were either resting or received alternating naturalistic visual, auditory, and tactile stimulation. Both temporal and spatial ICA found rhythmic narrow-band sources (networks) which were consistent across subjects. Networks with statistically significant consistency typically corresponded to early sensory areas. Some of the identified networks seem to be related to default-mode networks, especially in the spatial ICA. Conclusions: Analysis of spontaneous EEG/MEG activity is possible within the framework of independent component analysis. The spatial version of ICA provides new information compared with the temporal version of ICA. The statistical significance tests provide intuitively reasonable results.
Magnetoencephalography (MEG) has been used as a tool for investigating human brain functions non-invasively. Although MEG has excellent temporal resolution up to 1 ms, it is generally difficult to reconstruct the distribution of the neural current in the brain from the magnetic field distribution outside of the head due to the non-uniqueness of the neuromagnetic inverse problem, especially under such condition where the neural current has complex spatial distribution. Under those conditions, simple methods are required (1) to approximately visualize the source of MEG components appeared at specific sensor sets, and (2) to determine the “sensor-set of interest (SOI)” once the cortical area-ofinterest is determined either in the standardized 1 or in the subjectspecific coordinate system, especially in the clinical application. Here we present a system to visualize (i) the distribution of the sensitivity of arbitrary selected group of MEG sensors on the subject-specific cortical surface, and (ii) the distribution of MEG signal strength predicted from a realistic MEG signal generation model (forward model). The current results suggest that (a) our methods to predict MEG field distribution from a priori information about the possible “active” cortical regions obtained from standardized fMRI results is useful for determining the sensorsets of interest in the MEG studies for a specific subject under specific measurement condition, and that (b) visualization of the sensitivity of sensor groups could provide the approximate distribution of the signal sources without solving the MEG inverse problem. P33-24 Correlations between the development of cognitive functions and spontaneous MEG responses of healthy 3- to 4-year-old infants K. Nagao1,2 , Y. Yoshimura2 , G.B. Remijn2 , M. Kikuchi2 , H. Kojima2 , T. Tsubokawa2 , T. Munesue1,2 , Y. Minabe2 1 United Graduate School of Child Development, Osaka University, Kanazawa University and Hamamatsu University School of Medicine; Osaka University, Japan, 2 Kanazawa University, Japan Objective: This study examined the correlations between the development of cognitive functions and the spontaneous magnetoencephalogram (MEG) responses in 3 4 year old healthy infants. Although MEG is noninvasive and suitable to measure infant cortex, there have been no previous studies relating cognitive development and MEG data of preschool infants. Method: The cognitive functions of 22 healthy 3- to 4-year-old infants were evaluated by the Japanese adaptation of the Kaufman Assessment Battery for Children (K-ABC test). The head coil unit of the MEG system (Yokogawa Electric Co., Kanazawa, Japan) to fit the infants’ head was specially developed to measure the infants’ brain activity. The spontaneous brain response during rest and a closed eye period was measured. Results: Relative spectral power value was calculated for the MEG data. There was a positive correlation (r = 0.70) between the infants’ theta power value and their chronological age. Furthermore, the infants’ theta power value was positively correlated to their raw score on the sequential processing scale of the K-ABC (r = 0.44). By contrast, there was a negative correlation (r = 0.54) between the infants’ alpha power value and their raw score on the simultaneous processing scale of the K-ABC. Conclusions: Taken together, the results suggest that the relative spectral power of the MEG data reflected the development of the infants’ cognitive processing abilities. P33-25 Activated area of imagined movement: MEG study N. Tsuyuguchi1 , T. Uda1 , Y. Shigihara2 , K. Ohata1 Department of Neurosurgery, Osaka City Univercity Graduate School of Medicine, Osaka, Japan, 2 Department of Physiology, Osaka City University Graduate School of Medicine, Japan
1
Objective: To detect the activated area in motor imaginary using magnetoencephalography. Materials and Methods: Twenty healthy volunteers participated in this study. The subjects attempted to clench their right hand on a visual
29th International Congress of Clinical Neurophysiology cue. The timing of the cue was used as the trigger and 50 trials were performed. The data were analyzed by the equivalent current dipole (ECD) procedure and b band event-related desynchronization (ERD). The estimated location of the ECD, peak of the distribution of b-band ERD sources, and hand motor cortex in MRI were compared in a threedimensional coordinate system. To compare the motor imaginary and motor execution, the hand clenching task was assigned consecutively in the same subjects and analyzed by the same methods. Results: In motor imaginary, event-related activations were recognized in the contralateral frontal cortex approximately 50 250 ms after the cue in ECD and 0 600 ms after the cue in b band ERD. These activated areas were well-matched with the motor cortex in MRI, and considered to show activation in the primary motor area. There were no differences in the coordinate axis in comparing with the motor execution task. However, both of the analyses had low sensitivities for detection of the primary motor area. The low sensitivity in ECD was thought to be because the timing of the cue and the execution of motor imaginary could not be matched precisely. In ERD, this was because there were some cases in which significant ERD did not emerge, and widespread ERD in the occipital area by the visual stimulus masked the ERD around the motor cortex. Conclusion: We detected the activated area by two different methods of analysis in magnetoencephalography, i.e., ECD and ERD. The location of the area matched that of the primary motor cortex. This corresponded well with the results of previous functional MRI studies. P33-26 Neuromagnetic field measurement in the lumbar spine S. Ishii1 , S. Kawabata1 , K. Sakaki1 , S. Tomizawa1 , K. Shinomiya1 , A. Okawa1 , Y. Adachi3 , Y. Kawada2 , R. Nakamura2 , S. Fujii2 , K. Sekihara2 1 Department of Orthopedic and Spinal Surgery, Graduate School of Tokyo Medical and Dental University, Tokyo, Japan, 2 Department of Systems Design and Engineering, Tokyo Metropolitan University, Hino, Japan, 3 Applied Electronics Laboratory, Kanazawa Institute of Technology, Kanazawa, Japan Objective: We previously reported the usefulness of neuromagnetic recording for the diagnosis of disorders of the cervical spinal cord. In the case of lumbar spine disease too, the development of a functional examination is desirable. While there are some reports of neuromagnetic field measurement in the lumbar spine, these do not cover the spinal canal in detail. In this study, we measured and estimated nerve activity in the spinal canal in detail using neuromagnetic recording. Methods: The tibial nerves of 5 healthy males in supine position were electrostimulated at the ankle. The neuromagnetic field was measured over the surface of the lower back using a Superconducting Quantum Interference Device (SQUID) fluxmeter. A spatial filter method (UGMN) was applied to the obtained magnetic field data in order to estimate the current source. In addition, we inserted a catheter-type electrode into the lumbar epidural space percutaneously in two subjects and measured the cauda equina action potential after tibial nerve stimulation, comparing it with the estimated source current. Results: Biphasic magnetic fields could be recorded in all subjects. Conduction velocity based on peak latency was in the range of 43.2 69.6 m/s, which agrees with physiological nerve conduction velocity. Isomagnetic field maps of the obtained neuromagnetic fields showed a quadrupolar pattern propagating in the caudal to cranial direction along the lumbar spinal canal at the L3-L5 level. Waveforms of the estimated signal sources corresponded exactly to that of the cauda equina action potential. Conclusions: We successfully measured the neuromagnetic field originating in the lumbar cauda equina over the skin surface in healthy individuals. Thus, nerve conduction, which can be estimated in detail through highly invasive epidural potential measurement, can now be achieved through non-invasive neuromagnetic field measurement. The application of this technique to patients with lumbar spine disease shows promise in the near future.
S305 P34. EMG, Myopathy, Neuromuscular junction disorders P34-1 Human botulism: stimulated single fiber EMG at different frequencies J.M. Fernandez1 , C. Dieguez1 , M.N. Pereira-Martinez1 , S. Mederer2 , J.V. Trontelj3 1 Dept. Clinical Neurophysiology, University Hospitals of Vigo, Vigo, Spain, 2 Neurology Service, Complejo Hospitalario de Pontevedra, Pontevedra, Spain., 3 Institute of Clinical Neurophysiology, University Medical Center, Zalovska, 7, Ljubljana, Slovenia Background and Objectives: The low safety factor of neuromuscular transmission typical of presynaptic disorders (e.g. Lambert Eaton myasthenic syndrome) when studied with Single Fiber EMG is known to improve by increasing the voluntary activation frequency or by high frequency (>10 Hz) micro-stimulation resulting in lower jitter values and less frequent blocking. However, stimulated Single Fiber EMG has not been systematically used to test the function of end-plates in clinical botulism. Patients and Methods: Five patients aged 30 to 54 (mean 43) with typical acute clinical botulism were studied using Single Fiber EMG with axonal microstimulation in addition to the conventional methods. Stimulated SFEMG studies were performed in the frontalis muscles in all of them by applying rectangular pulses of 0.04 ms at frequencies ranging from 1 3 to 20 Hz with a monopolar needle and recording with a Single Fiber EMG electrode. We succesfully collected sufficient data from the whole protocol in 28 end-plates. Results: Most end-plates showed higher degrees of neuromuscular disturbance at lower rates of stimulation (1 3 Hz) improving at higher frequencies (7 10 Hz). At higher rates (20 Hz or more) only two end-plates showed deterioration with increased jitter values and higher degrees of blocking. Conclusions: Our results suggest that most end-plates typical a presynaptic disturbance. However, at higher frequencies of stimulation a small proportion of end-plates do not necessarily do so. P34-2 Correlation of single fiber EMG findings in Lambert-Eaton myasthenic syndrome with clinical and repetitive nerve stimulation findings S. Oh1 , M. Ohira2 , D. Jeong3 1 Department of Neurology, University of Alabama at Birmingham, Birmingham, Alabama, USA, 2 Keiyo University Medical School, Tokyo, Japan, 3 Soonchunhang University Medical School, Chun-An, Korea Objectives: Correlation of SFEMG in LEMS with clinical and RNS findings was not extensively studied. This study reports the correlation of SFEMG in LEMS with clinical and RNS findings in 31 LEMS patients. Methods and Materials: We analyzed 82 SFEMG tests in 31 LEMS patient at the UAB.SFEMG was done all in the extensor digitorum communis (EDC) muscle. Mean consecutive difference (MCD), SF potential pair (PP) > 53 ms, and SFPP with blocking were compared with clinical classification, compound muscle action potential (CMAP) ampitude and 50 Hz responses in the RNS test in the abductor digitii quinti (ADQ) muscle. Results: In 31 cases, the fiber density was normal in all cases except one. The first test showed a marked abnormality in jitter: man MCD, 132 ms, 93% of SFPPs > 53 ms MCD, and 63% of SFPPs with blocking. With clinical severity, mean MCD and percentage of SFPP > 53 ms MCD and with blocking increase. However, jitter was abnormal in asymptomatic stage. There is a good inverse correlation between MCD value and ADQ CMAP amplitude and a good correlation between MCD value and logarhythmic scale of 50 Hz response in the ADQ muscle. In three cases, the MCD values are analyzed in relationship with firing rates in five SPPPs. MCV values decreases with increasing firing rate. Conclusion: SFEMG in EDC muscle is markedly abnormal in all cases in EDC muscle. This is in contrast to myasthenia gravis in which SFEMG in EDC muscle is abnormal in 82 91% of cases. P34-3 A comparison between recordings obtained using reusable and disposable single fiber needle electrodes E.S. Papathanasiou1 , E. Zamba-Papanicolaou1 Clinical Sciences, The Cyprus Institute of Neurology & Genetics, Nicosia, Cyprus
1
Objectives: Stimulated single fiber EMG (SSFEMG) is a sensitive method to detect neuromuscular junction dysfunction. Until recently, only reusable
Posters
P33-21 Human cortical response to parametric passive finger movement an MEG study
P33-23 Visualization of the sensitivity of the MEG sensor array based on the realistic signal generation modeling on standardized space
M. Matsuhashi1 , T. Mima1 , T. Nagamine2 , H. Shibasaki3 , H. Fukuyama1 Human Brain Research Center, Kyoto University, Kyoto, Japan, 2 Department of System Neuroscience, Sapporo Medical University, Sapporo, Japan, 3 Takeda General Hospital, Kyoto, Japan
S. Iwaki1 1 National Institute of Advanced Industrial Science and Technology (AIST), Japan
1
Objective: To clarify the cerebral mechanism of proprioceptive sensation in human Methods: Thirteen right handed healthy volunteers participated. We used a newly developed device to produce brisk but accurately controlled passive flexion of the PIP joint of the right index finger in the magnetically shielded room. The motion stimuli of varying parameters, with travel angle and time of 15/30, 15/50, 15/80, 15/120, 9/50 and 23/120 (degrees/ms), were delivered at 1 3 s random intervals while cerebral activities were recorded using 122 channel whole-head neuromagnetometer (Neuromag 122) with 0.03 300 Hz passband. The data were analyzed for the source strength of the equivalent current dipole (ECD) of averaged response and also the event related synchronization/desynchronization (ERS/ERD) as the mean power change of the left central channels. The effects of motion velocity and travel angle were tested in constant travel (15/30, 15/50, 15/80 and 15/120) and constant velocity (9/50, 15/80 and 23/120) conditions using Friedman test. Results: Three major response peaks were observed, all located in the left central area: early peak at 39±6 ms after the motion onset (mean ± s.d.), middle peak at 71±13 ms after the motion onset, and late peak at 95±28 ms after the motion offset. The ECD of these peaks were all estimated in and around the left primary sensorimotor cortex. The effect of motion velocity was significant only on the source dipole moment of the early peak (p < 0.05). The effect of travel angle was significant (p < 0.05) on the ERD of 18 24 Hz band. Conclusions: This result suggests differential physiological significance of ‘evoked response’ which reflects time-locked cortical inputs and ‘induced response’ representing local cortical oscillation in the perception of passive finger movement in the human sensorimotor cortex. P33-22 Advances in analysis of spontaneous EEG/MEG activity by independent component analysis A. Hyvarinen1 , P. Ramkumar2 , R. Hari2 1 Dept of Mathematics and Statistics, University of Helsinki, Finland, 2 Brain Research Unit, LTL, Aalto University, Espoo, Finland Objective: We develop new methods for exploratory analysis of spontaneous EEG/MEG activity. Currently, the analysis is quite difficult and existing methods need to be improved. In particular, novel methods might be able to find and analyze default-mode networks, which have been defined with fMRI but are more elusive in EEG/MEG. Methods: We use the framework of independent component analysis (ICA) which has had some success in the analysis of spontaneous activity. First, we improve the capability of ICA to analyze brain sources by introducing a new spatial variant similar to the way ICA is used with fMRI. This is possible by first computing the minimum norm solution to the inverse problem. We further combine this spatial ICA with our Fourier-domain method (Hyvarinen et al, NeuroImage, 2010). Second, we introduce a new testing method for finding components which are consistently similar over subjects. The novelty here is that we formulate a null hypothesis, under which the components are obtained as random orthogonal rotations of whitened data. Most other work has relied on heuristically chosen thresholds instead of a null hypothesis, and thus has not been able to control the false positive rate. Results: We applied the methods on MEG recordings from ten healthy subjects who were either resting or received alternating naturalistic visual, auditory, and tactile stimulation. Both temporal and spatial ICA found rhythmic narrow-band sources (networks) which were consistent across subjects. Networks with statistically significant consistency typically corresponded to early sensory areas. Some of the identified networks seem to be related to default-mode networks, especially in the spatial ICA. Conclusions: Analysis of spontaneous EEG/MEG activity is possible within the framework of independent component analysis. The spatial version of ICA provides new information compared with the temporal version of ICA. The statistical significance tests provide intuitively reasonable results.
Magnetoencephalography (MEG) has been used as a tool for investigating human brain functions non-invasively. Although MEG has excellent temporal resolution up to 1 ms, it is generally difficult to reconstruct the distribution of the neural current in the brain from the magnetic field distribution outside of the head due to the non-uniqueness of the neuromagnetic inverse problem, especially under such condition where the neural current has complex spatial distribution. Under those conditions, simple methods are required (1) to approximately visualize the source of MEG components appeared at specific sensor sets, and (2) to determine the “sensor-set of interest (SOI)” once the cortical area-ofinterest is determined either in the standardized 1 or in the subjectspecific coordinate system, especially in the clinical application. Here we present a system to visualize (i) the distribution of the sensitivity of arbitrary selected group of MEG sensors on the subject-specific cortical surface, and (ii) the distribution of MEG signal strength predicted from a realistic MEG signal generation model (forward model). The current results suggest that (a) our methods to predict MEG field distribution from a priori information about the possible “active” cortical regions obtained from standardized fMRI results is useful for determining the sensorsets of interest in the MEG studies for a specific subject under specific measurement condition, and that (b) visualization of the sensitivity of sensor groups could provide the approximate distribution of the signal sources without solving the MEG inverse problem. P33-24 Correlations between the development of cognitive functions and spontaneous MEG responses of healthy 3- to 4-year-old infants K. Nagao1,2 , Y. Yoshimura2 , G.B. Remijn2 , M. Kikuchi2 , H. Kojima2 , T. Tsubokawa2 , T. Munesue1,2 , Y. Minabe2 1 United Graduate School of Child Development, Osaka University, Kanazawa University and Hamamatsu University School of Medicine; Osaka University, Japan, 2 Kanazawa University, Japan Objective: This study examined the correlations between the development of cognitive functions and the spontaneous magnetoencephalogram (MEG) responses in 3 4 year old healthy infants. Although MEG is noninvasive and suitable to measure infant cortex, there have been no previous studies relating cognitive development and MEG data of preschool infants. Method: The cognitive functions of 22 healthy 3- to 4-year-old infants were evaluated by the Japanese adaptation of the Kaufman Assessment Battery for Children (K-ABC test). The head coil unit of the MEG system (Yokogawa Electric Co., Kanazawa, Japan) to fit the infants’ head was specially developed to measure the infants’ brain activity. The spontaneous brain response during rest and a closed eye period was measured. Results: Relative spectral power value was calculated for the MEG data. There was a positive correlation (r = 0.70) between the infants’ theta power value and their chronological age. Furthermore, the infants’ theta power value was positively correlated to their raw score on the sequential processing scale of the K-ABC (r = 0.44). By contrast, there was a negative correlation (r = 0.54) between the infants’ alpha power value and their raw score on the simultaneous processing scale of the K-ABC. Conclusions: Taken together, the results suggest that the relative spectral power of the MEG data reflected the development of the infants’ cognitive processing abilities. P33-25 Activated area of imagined movement: MEG study N. Tsuyuguchi1 , T. Uda1 , Y. Shigihara2 , K. Ohata1 Department of Neurosurgery, Osaka City Univercity Graduate School of Medicine, Osaka, Japan, 2 Department of Physiology, Osaka City University Graduate School of Medicine, Japan
1
Objective: To detect the activated area in motor imaginary using magnetoencephalography. Materials and Methods: Twenty healthy volunteers participated in this study. The subjects attempted to clench their right hand on a visual
29th International Congress of Clinical Neurophysiology cue. The timing of the cue was used as the trigger and 50 trials were performed. The data were analyzed by the equivalent current dipole (ECD) procedure and b band event-related desynchronization (ERD). The estimated location of the ECD, peak of the distribution of b-band ERD sources, and hand motor cortex in MRI were compared in a threedimensional coordinate system. To compare the motor imaginary and motor execution, the hand clenching task was assigned consecutively in the same subjects and analyzed by the same methods. Results: In motor imaginary, event-related activations were recognized in the contralateral frontal cortex approximately 50 250 ms after the cue in ECD and 0 600 ms after the cue in b band ERD. These activated areas were well-matched with the motor cortex in MRI, and considered to show activation in the primary motor area. There were no differences in the coordinate axis in comparing with the motor execution task. However, both of the analyses had low sensitivities for detection of the primary motor area. The low sensitivity in ECD was thought to be because the timing of the cue and the execution of motor imaginary could not be matched precisely. In ERD, this was because there were some cases in which significant ERD did not emerge, and widespread ERD in the occipital area by the visual stimulus masked the ERD around the motor cortex. Conclusion: We detected the activated area by two different methods of analysis in magnetoencephalography, i.e., ECD and ERD. The location of the area matched that of the primary motor cortex. This corresponded well with the results of previous functional MRI studies. P33-26 Neuromagnetic field measurement in the lumbar spine S. Ishii1 , S. Kawabata1 , K. Sakaki1 , S. Tomizawa1 , K. Shinomiya1 , A. Okawa1 , Y. Adachi3 , Y. Kawada2 , R. Nakamura2 , S. Fujii2 , K. Sekihara2 1 Department of Orthopedic and Spinal Surgery, Graduate School of Tokyo Medical and Dental University, Tokyo, Japan, 2 Department of Systems Design and Engineering, Tokyo Metropolitan University, Hino, Japan, 3 Applied Electronics Laboratory, Kanazawa Institute of Technology, Kanazawa, Japan Objective: We previously reported the usefulness of neuromagnetic recording for the diagnosis of disorders of the cervical spinal cord. In the case of lumbar spine disease too, the development of a functional examination is desirable. While there are some reports of neuromagnetic field measurement in the lumbar spine, these do not cover the spinal canal in detail. In this study, we measured and estimated nerve activity in the spinal canal in detail using neuromagnetic recording. Methods: The tibial nerves of 5 healthy males in supine position were electrostimulated at the ankle. The neuromagnetic field was measured over the surface of the lower back using a Superconducting Quantum Interference Device (SQUID) fluxmeter. A spatial filter method (UGMN) was applied to the obtained magnetic field data in order to estimate the current source. In addition, we inserted a catheter-type electrode into the lumbar epidural space percutaneously in two subjects and measured the cauda equina action potential after tibial nerve stimulation, comparing it with the estimated source current. Results: Biphasic magnetic fields could be recorded in all subjects. Conduction velocity based on peak latency was in the range of 43.2 69.6 m/s, which agrees with physiological nerve conduction velocity. Isomagnetic field maps of the obtained neuromagnetic fields showed a quadrupolar pattern propagating in the caudal to cranial direction along the lumbar spinal canal at the L3-L5 level. Waveforms of the estimated signal sources corresponded exactly to that of the cauda equina action potential. Conclusions: We successfully measured the neuromagnetic field originating in the lumbar cauda equina over the skin surface in healthy individuals. Thus, nerve conduction, which can be estimated in detail through highly invasive epidural potential measurement, can now be achieved through non-invasive neuromagnetic field measurement. The application of this technique to patients with lumbar spine disease shows promise in the near future.
S305 P34. EMG, Myopathy, Neuromuscular junction disorders P34-1 Human botulism: stimulated single fiber EMG at different frequencies J.M. Fernandez1 , C. Dieguez1 , M.N. Pereira-Martinez1 , S. Mederer2 , J.V. Trontelj3 1 Dept. Clinical Neurophysiology, University Hospitals of Vigo, Vigo, Spain, 2 Neurology Service, Complejo Hospitalario de Pontevedra, Pontevedra, Spain., 3 Institute of Clinical Neurophysiology, University Medical Center, Zalovska, 7, Ljubljana, Slovenia Background and Objectives: The low safety factor of neuromuscular transmission typical of presynaptic disorders (e.g. Lambert Eaton myasthenic syndrome) when studied with Single Fiber EMG is known to improve by increasing the voluntary activation frequency or by high frequency (>10 Hz) micro-stimulation resulting in lower jitter values and less frequent blocking. However, stimulated Single Fiber EMG has not been systematically used to test the function of end-plates in clinical botulism. Patients and Methods: Five patients aged 30 to 54 (mean 43) with typical acute clinical botulism were studied using Single Fiber EMG with axonal microstimulation in addition to the conventional methods. Stimulated SFEMG studies were performed in the frontalis muscles in all of them by applying rectangular pulses of 0.04 ms at frequencies ranging from 1 3 to 20 Hz with a monopolar needle and recording with a Single Fiber EMG electrode. We succesfully collected sufficient data from the whole protocol in 28 end-plates. Results: Most end-plates showed higher degrees of neuromuscular disturbance at lower rates of stimulation (1 3 Hz) improving at higher frequencies (7 10 Hz). At higher rates (20 Hz or more) only two end-plates showed deterioration with increased jitter values and higher degrees of blocking. Conclusions: Our results suggest that most end-plates typical a presynaptic disturbance. However, at higher frequencies of stimulation a small proportion of end-plates do not necessarily do so. P34-2 Correlation of single fiber EMG findings in Lambert-Eaton myasthenic syndrome with clinical and repetitive nerve stimulation findings S. Oh1 , M. Ohira2 , D. Jeong3 1 Department of Neurology, University of Alabama at Birmingham, Birmingham, Alabama, USA, 2 Keiyo University Medical School, Tokyo, Japan, 3 Soonchunhang University Medical School, Chun-An, Korea Objectives: Correlation of SFEMG in LEMS with clinical and RNS findings was not extensively studied. This study reports the correlation of SFEMG in LEMS with clinical and RNS findings in 31 LEMS patients. Methods and Materials: We analyzed 82 SFEMG tests in 31 LEMS patient at the UAB.SFEMG was done all in the extensor digitorum communis (EDC) muscle. Mean consecutive difference (MCD), SF potential pair (PP) > 53 ms, and SFPP with blocking were compared with clinical classification, compound muscle action potential (CMAP) ampitude and 50 Hz responses in the RNS test in the abductor digitii quinti (ADQ) muscle. Results: In 31 cases, the fiber density was normal in all cases except one. The first test showed a marked abnormality in jitter: man MCD, 132 ms, 93% of SFPPs > 53 ms MCD, and 63% of SFPPs with blocking. With clinical severity, mean MCD and percentage of SFPP > 53 ms MCD and with blocking increase. However, jitter was abnormal in asymptomatic stage. There is a good inverse correlation between MCD value and ADQ CMAP amplitude and a good correlation between MCD value and logarhythmic scale of 50 Hz response in the ADQ muscle. In three cases, the MCD values are analyzed in relationship with firing rates in five SPPPs. MCV values decreases with increasing firing rate. Conclusion: SFEMG in EDC muscle is markedly abnormal in all cases in EDC muscle. This is in contrast to myasthenia gravis in which SFEMG in EDC muscle is abnormal in 82 91% of cases. P34-3 A comparison between recordings obtained using reusable and disposable single fiber needle electrodes E.S. Papathanasiou1 , E. Zamba-Papanicolaou1 Clinical Sciences, The Cyprus Institute of Neurology & Genetics, Nicosia, Cyprus
1
Objectives: Stimulated single fiber EMG (SSFEMG) is a sensitive method to detect neuromuscular junction dysfunction. Until recently, only reusable