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Paku M, Ando M, Itakura T, Sato S, Tani Y, Ishihara M, Adachi T, Taniguchi S, Kohara N, Saito T. Magnetoneurography to investigate the mechanisms underlying the P9 far-field potential. Clin Neurophysiol 2023; 150:197-204. [PMID: 37099870 DOI: 10.1016/j.clinph.2023.03.358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 03/07/2023] [Accepted: 03/26/2023] [Indexed: 04/28/2023]
Abstract
OBJECTIVE The mechanism underlying the generation of P9 far-field somatosensory evoked potentials (SEPs) is unresolved. Accordingly, we used magnetoneurography to visualize the current distribution in the body at the P9 peak latency and elucidate the origin of P9 generation. METHODS We studied five healthy male volunteers without neurological abnormalities. We recorded far-field SEPs after median nerve stimulation at the wrist to identify the P9 peak latency. Using magnetoneurography, we recorded the evoked magnetic fields in the whole body under the same stimulus conditions as the SEP recording. We analyzed the reconstructed current distribution at the P9 peak latency. RESULTS At the P9 peak latency, we observed the reconstructed current distribution dividing the thorax into two parts, upper and lower. Anatomically, the depolarization site at the P9 peak latency was distal to the interclavicular space and at the level of the second intercostal space. CONCLUSIONS By visualizing the current distribution, we proved that P9 peak latency originates in the change in volume conductor size between the upper and lower thorax. SIGNIFICANCE We clarified that magnetoneurography analysis is affected by the current distribution due to the junction potential.
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Affiliation(s)
- Masaaki Paku
- Department of Orthopedic Surgery, Graduate School of Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan.
| | - Muneharu Ando
- Department of Orthopedic Surgery, Graduate School of Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Takeshi Itakura
- Department of Orthopedic Surgery, Graduate School of Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Shinji Sato
- RICOH Futures BU, RICOH Company, Ltd., 2-3-10 Kandasurugadai, Chiyoda-ku, Tokyo 101-0062, Japan
| | - Yoichi Tani
- Department of Orthopedic Surgery, Graduate School of Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Masayuki Ishihara
- Department of Orthopedic Surgery, Graduate School of Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Takashi Adachi
- Department of Orthopedic Surgery, Graduate School of Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Shinichirou Taniguchi
- Department of Orthopedic Surgery, Graduate School of Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Nobuo Kohara
- Department of Orthopedic Surgery, Graduate School of Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Takanori Saito
- Department of Orthopedic Surgery, Graduate School of Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
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Dumitru D, Nandedkar SD, Barkhaus PE. Volume conduction: Extracellular waveform generation in theory and practice. Muscle Nerve 2023; 67:439-455. [PMID: 36815566 DOI: 10.1002/mus.27789] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Accepted: 01/09/2023] [Indexed: 02/24/2023]
Abstract
The extracellular waveform manifestations of the intracellular action potential are the quintessential diagnostic foundation of electrodiagnostic medicine, and clinical neurophysiology in general. Volume conduction is the extracellular current flow and associated voltage distributions in an ionic conducting media, such as occurs in the human body. Both surface and intramuscular electrodes, in association with contemporary digital electromyographic systems, permit very sensitive detection and visualization of this extracellular spontaneous, voluntary, and evoked nerve/muscle electrical activity. Waveform configuration, with its associated discharge rate/rhythm, permits the identification of normal and abnormal waveforms, thereby assisting in the diagnosis of nerve and muscle pathology. This monograph utilizes a simple model to explain the various waveforms that may be encountered. There are a limited number of waveforms capable of being generated in excitable tissues which conform to well-known volume conductor concepts. Using these principles, such waveforms can be quickly identified in real time during clinical studies.
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Affiliation(s)
- Daniel Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas
| | - Sanjeev D Nandedkar
- Department of Neurology, Medical College of Wisconsin, Milwaukee, Wisconsin.,Natus Medical Inc, Middleton, Wisconsin
| | - Paul E Barkhaus
- Department of Neurology, Medical College of Wisconsin, Milwaukee, Wisconsin
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Mendez Guerra I, Barsakcioglu DY, Vujaklija I, Wetmore DZ, Farina D. Far-field electric potentials provide access to the output from the spinal cord from wrist-mounted sensors. J Neural Eng 2022; 19. [PMID: 35303732 DOI: 10.1088/1741-2552/ac5f1a] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Accepted: 03/18/2022] [Indexed: 11/11/2022]
Abstract
OBJECTIVE Neural interfaces need to become more unobtrusive and socially acceptable to appeal to general consumers outside rehabilitation settings. APPROACH We developed a non-invasive neural interface that provides access to spinal motor neuron activities from the wrist, which is the preferred location for a wearable. The interface decodes far-field potentials present at the tendon endings of the forearm muscles using blind source separation. First, we evaluated the reliability of the interface to detect motor neuron firings based on far-field potentials, and thereafter we used the decoded motor neuron activity for the prediction of finger contractions in offline and real-time conditions. MAIN RESULTS The results showed that motor neuron activity decoded from the far-field potentials at the wrist accurately predicted individual and combined finger commands and therefore allowed for highly accurate real-time task classification. SIGNIFICANCE These findings demonstrate the feasibility of a non-invasive, neural interface at the wrist for precise real-time control based on the output of the spinal cord.
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Affiliation(s)
- Irene Mendez Guerra
- Department of Bioengineering, Imperial College London, 80 Wood Lane, London, W12 7TA, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Deren Yusuf Barsakcioglu
- Department of Bioengineering, Imperial College London, 80 Wood Lane, London, W12 7TA, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Ivan Vujaklija
- Department of Electrical Engineering and Automation, Aalto-yliopisto, Otakaari 3 (F306), Espoo, 00076, FINLAND
| | - Daniel Z Wetmore
- Meta Inc, 770 Broadway, New York City, New York, 10003, UNITED STATES
| | - Dario Farina
- Department of Bioengineering, Imperial College London, 80 Wood Lane, London, W12 7TA, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
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Gmel GE, Vollebregt PF, Thijssen MEG, Santos Escapa R, McAlees E, Mugan D, Parker JL, Knowles CH. Electrophysiological Responses in the Human S3 Nerve During Sacral Neuromodulation for Fecal Incontinence. Front Neurosci 2021; 15:712168. [PMID: 34707473 PMCID: PMC8545143 DOI: 10.3389/fnins.2021.712168] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 09/20/2021] [Indexed: 11/26/2022] Open
Abstract
Intra-operative electrode placement for sacral neuromodulation (SNM) relies on visual observation of motor contractions alone, lacking complete information on neural activation from stimulation. This study aimed to determine whether electrophysiological responses can be recorded directly from the S3 sacral nerve during therapeutic SNM in patients with fecal incontinence, and to characterize such responses in order to better understand the mechanism of action (MOA) and whether stimulation is subject to changes in posture. Eleven patients undergoing SNM were prospectively recruited. A bespoke stimulating and recording system was connected (both intraoperatively and postoperatively) to externalized SNM leads, and electrophysiological responses to monopolar current sweeps on each electrode were recorded and analyzed. The nature and thresholds of muscle contractions (intraoperatively) and patient-reported stimulation perception were recorded. We identified both neural responses (evoked compound action potentials) as well as myoelectric responses (far-field potentials from muscle activation). We identified large myelinated fibers (conduction velocity: 36–60 m/s) in 5/11 patients, correlating with patient-reported stimulation perception, and smaller myelinated fibers (conduction velocity <15 m/s) in 4/11 patients (not associated with any sensation). Myoelectric responses (observed in 7/11 patients) were attributed to pelvic floor and/or anal sphincter contraction. Responses varied with changes in posture. We present the first direct electrophysiological responses recorded from the S3 nerve during ongoing SNM in humans, showing both neural and myoelectric responses. These recordings highlight heterogeneity of neural and myoelectric responses (relevant to understanding MOA of SNM) and confirm that electrode lead position can change with posture.
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Affiliation(s)
| | - Paul F Vollebregt
- National Bowel Research Centre, Centre for Neuroscience, Surgery and Trauma, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom
| | | | | | - Eleanor McAlees
- National Bowel Research Centre, Centre for Neuroscience, Surgery and Trauma, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom
| | - Dave Mugan
- Saluda Medical Pty Ltd, Artarmon, NSW, Australia
| | | | - Charles H Knowles
- National Bowel Research Centre, Centre for Neuroscience, Surgery and Trauma, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom
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Day TJ. Optimal reference electrode placement for accessory and axillary nerve conduction studies. Muscle Nerve 2020; 61:632-639. [DOI: 10.1002/mus.26847] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Revised: 01/14/2020] [Accepted: 02/24/2020] [Indexed: 11/11/2022]
Affiliation(s)
- Timothy J. Day
- Department of Clinical NeurophysiologyRoyal Melbourne Hospital Parkville Victoria Australia
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Sonoo M. Far-field potentials in the compound muscle action potential. Muscle Nerve 2019; 61:271-279. [PMID: 31650553 DOI: 10.1002/mus.26743] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2019] [Revised: 10/12/2019] [Accepted: 10/18/2019] [Indexed: 11/09/2022]
Abstract
It has long been believed that the compound muscle action potential (CMAP) in motor-nerve conduction studies (MCSs) records the action potential beneath the active electrode over the muscle belly. However, recent studies have revealed the contribution of the reference electrode to the CMAP, most prominent in the tibial nerve, followed by the ulnar nerve. This "reference electrode potential" is recorded when the conventional reference electrode distal to the muscle belly is connected to a proximal reference. It must be a far-field potential (FFP) considering its distribution, although the precise mechanism of its generation has not been clarified. The conventional theory of termination of the action potential at the muscle-tendon junction is insufficient. Regarding the ulnar CMAP, interosseous muscles mostly contribute to the FFPs. New understanding of CMAP based on the FFP theory may provide new insights into the interpretation of MCSs and related techniques, including motor unit number estimation.
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Affiliation(s)
- Masahiro Sonoo
- Department of Neurology, Teikyo University School of Medicine, Itabashi-ku, Tokyo, Japan
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Muzyka IM, Estephan B. Somatosensory evoked potentials. HANDBOOK OF CLINICAL NEUROLOGY 2019; 160:523-540. [DOI: 10.1016/b978-0-444-64032-1.00035-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Volume conduction, waveform analysis, and near- and far-field potentials. ACTA ACUST UNITED AC 2019. [DOI: 10.1016/b978-0-444-64032-1.00002-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Finneran JJ, Mulsow J, Jones R, Houser DS, Accomando AW, Ridgway SH. Non-auditory, electrophysiological potentials preceding dolphin biosonar click production. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2018; 204:271-283. [PMID: 29222726 PMCID: PMC5816092 DOI: 10.1007/s00359-017-1234-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2017] [Revised: 11/16/2017] [Accepted: 11/20/2017] [Indexed: 12/03/2022]
Abstract
The auditory brainstem response to a dolphin’s own emitted biosonar click can be measured by averaging epochs of the instantaneous electroencephalogram (EEG) that are time-locked to the emitted click. In this study, averaged EEGs were measured using surface electrodes placed on the head in six different configurations while dolphins performed an echolocation task. Simultaneously, biosonar click emissions were measured using contact hydrophones on the melon and a hydrophone in the farfield. The averaged EEGs revealed an electrophysiological potential (the pre-auditory wave, PAW) that preceded the production of each biosonar click. The largest PAW amplitudes occurred with the non-inverting electrode just right of the midline—the apparent side of biosonar click generation—and posterior of the blowhole. Although the source of the PAW is unknown, the temporal and spatial properties rule out an auditory source. The PAW may be a neural or myogenic potential associated with click production; however, it is not known if muscles within the dolphin nasal system can be actuated at the high rates reported for dolphin click production, or if sufficiently coordinated and fast motor endplates of nasal muscles exist to produce a PAW detectable with surface electrodes.
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Insola A, Padua L, Mazzone P, Valeriani M. Low- and high-frequency subcortical SEP amplitude reduction during pure passive movement. Clin Neurophysiol 2015; 126:2366-75. [DOI: 10.1016/j.clinph.2015.03.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Revised: 03/01/2015] [Accepted: 03/04/2015] [Indexed: 12/15/2022]
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Sonoo M, Kurokawa K, Higashihara M, Kurono H, Hokkoku K, Hatanaka Y, Shimizu T. Origin of far-field potentials in the ulnar compound muscle action potential. Muscle Nerve 2011; 43:671-8. [PMID: 21484826 DOI: 10.1002/mus.21931] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
INTRODUCTION The compound muscle action potential (CMAP) following ulnar nerve stimulation receives a considerable contribution from far-field potentials (FFPs), although their origin is not entirely clear. We investigated this issue using voluntary contractions. METHODS In 7 control subjects, we placed multiple recording electrodes over the motor points of ulnar-innervated muscles. We asked the subjects to perform a weak movement corresponding to the action of each muscle, and identified the single motor unit potentials (MUPs) from that muscle. We summed the MUPs from each individual muscle and reconstructed the CMAPs. RESULTS The reconstructed CMAPs coincided well with the actual ones. The N1, P1, and early N2 components of the FFPs were generated primarily by palmar, but also by dorsal, interosseous muscles. The abductor digiti minimi muscle usually generated positive-negative biphasic FFPs, and the negative FFP generated the late N2 component. CONCLUSIONS These results should prompt a revision of the theory of FFP generation.
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Affiliation(s)
- Masahiro Sonoo
- Department of Neurology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 1738605, Japan.
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Wang FC. Can we accurately measure the onset latency to the first dorsal interosseous? Muscle Nerve 2011; 43:769-70; author reply 770. [DOI: 10.1002/mus.22030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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13
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Masakado Y, Kodama M, Takahashi O, Sasao Y, Kasahara T, Hyodo M, Hanayama K, Fujita Y. The origin of the premotor potential recorded from the second lumbrical muscle in normal man. Clin Neurophysiol 2011; 122:2089-92. [PMID: 21507714 DOI: 10.1016/j.clinph.2011.02.037] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Revised: 02/07/2011] [Accepted: 02/20/2011] [Indexed: 10/18/2022]
Abstract
OBJECTIVE When recording with a palm electrode, a premotor potential precedes the compound muscle action potential (CMAP), evoked from the second lumbrical (2L) muscle following median nerve stimulation. The purpose of this study was to determine the origin of the premotor potential from the 2L. METHODS We recorded potentials with multi-channel electrodes in the palm and finger in a bipolar or referential manner, stimulating the second digit or median nerve at the wrist. RESULTS We recorded the traveling nearfield sensory nerve action potential (SNAP) and stationary negative potential in the palm. The peak latency of the stationary negative potential was the same as the one of the near-field potential of the digital sensory fibers at the base of the second finger. The onset of the premotor potential from the 2L muscle is aligned to the palmar SNAP in a bipolar manner by antidromic stimulation. CONCLUSIONS We conclude that the premotor potential from the 2L muscle is composed of a SNAP arising from antidromically activated palm sensory branches and a far-field potential generated by the median digital nerve fibers as they pass from the palm into the second finger. SIGNIFICANCE Our results might be useful for evaluating the 2L-interossei test for diagnosing carpal tunnel syndrome.
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Affiliation(s)
- Yoshihisa Masakado
- Department of Rehabilitation Medicine, Tokai University School of Medicine, Kanagawa, Japan.
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Higashihara M, Sonoo M, Imafuku I, Ugawa Y, Tsuji S. Origin of ulnar compound muscle action potential investigated in patients with ulnar neuropathy at the wrist. Muscle Nerve 2010; 41:704-6. [DOI: 10.1002/mus.21620] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Hadoush H, Tobimatsu Y, Nagatomi A, Kimura H, Ito Y, Maejima H. Monopolar surface electromyography: a better tool to assess motoneuron excitability upon passive muscle stretching. J Physiol Sci 2009; 59:243-7. [PMID: 19340538 PMCID: PMC10717350 DOI: 10.1007/s12576-009-0027-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2008] [Accepted: 02/01/2009] [Indexed: 10/20/2022]
Abstract
Bipolar and monopolar surface electromyography (sEMG) are known procedures to measure the H-reflex. However, signal cancellation is a potential experimental problem of bipolar sEMG. The results of our study show that monopolar sEMG was the more sensitive procedure to differentiate motoneuron excitability at different passive muscle stretching speeds as it overcame signal cancellation.
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Affiliation(s)
- Hikmat Hadoush
- Graduate School of Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551 Japan
| | - Yoshiko Tobimatsu
- Graduate School of Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551 Japan
| | - Akiyoshi Nagatomi
- Department of Physical Medicine and Rehabilitation, Hiroshima University Hospital, Hiroshima, Japan
| | - Hiroaki Kimura
- Department of Physical Medicine and Rehabilitation, Hiroshima University Hospital, Hiroshima, Japan
| | - Yoshihiro Ito
- Department of Physical Medicine and Rehabilitation, Hiroshima University Hospital, Hiroshima, Japan
| | - Hiroshi Maejima
- Graduate School of Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551 Japan
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Sonoo M, Kobayashi M, Genba-Shimizu K, Mannen T, Shimizu T. Detailed analysis of the latencies of median nerve somatosensory evoked potential components, 1: selection of the best standard parameters and the establishment of normal values. ACTA ACUST UNITED AC 2007; 100:319-31. [PMID: 17441302 DOI: 10.1016/0168-5597(96)95035-2] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In order to objectively select the standard parameters best suited for the evaluation of somatosensory conduction in median nerve somatosensory evoked potentials (SEP), we performed a detailed statistical analysis of intersubject variability for the latencies of SEP components based on the recordings of 62 normal subjects. Multiple regression analyses for height, age, (age--20)2 and sex were performed for the latencies of 13 components and 78 intercomponent intervals, and the residual variance was used as an indicator of the stability of each parameter. As a result, N9 onset in EPi-NC lead, N11' onset in C6S-Fz lead, P13/14 onset in scalp-NC leads, for which N13' onset recorded in C6S-Fz lead may substitute, and N20 onset in CPc-Fz lead were the most stable time-points selected as standards. N11 onset in C6S-NC, which other authors have recommended as the standard point representing spinal entry, was not recorded consistently, and P11 onset in scalp-NC leads was also unstable. N20 peak and N13'-N20 interval (equivalent to conventional central conduction time) were extremely unstable. We presented the nomograms to find normal limits of the standard parameters corresponding to the given values of the predictor variables (height, age or sex). As the standard recording montage in routine clinical examinations, we recommended a simple method using Fz reference, for example (1) EPi-Fz, (2) C6S-Fz, (3) CPc-Fz, because this montage is sufficient to measure the stable standard parameters.
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Affiliation(s)
- M Sonoo
- Department of Neurology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 173, Japan
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17
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Dumitru D, Santa Maria DL. Positive sharp wave origin: Evidence supporting the electrode initiation hypothesis. Muscle Nerve 2007; 36:349-56. [PMID: 17487870 DOI: 10.1002/mus.20819] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
This investigation analyzes the temporal characteristics of maximal depolarization times for three waveforms: end-plate spikes, fibrillation potentials, and positive sharp waves (PSWs) to provide support for the electrode initiation hypothesis of PSW induction. The maximal depolarization times for PSWs are documented to comprise two distinct populations conforming to relatively short and comparatively longer maximal depolarization times. Those PSWs with short maximal depolarization times were found to be equivalent to end-plate spike maximal depolarization times, whereas those with longer times were comparable to fibrillation potentials. The PSW group with shorter maximal depolarization times was encountered more frequently. The combination of two distinct groups of PSWs with respective times comparable to end-plate spikes and fibrillation potentials supports the hypothesis that the majority of PSWs originate at the recording electrode during insertion, whereas a smaller population of PSWs arises as propagating fibrillation potentials that block at the recording electrode. Subcutaneous compared to intramuscular recordings from denervated muscle document that the recording electrode is necessary to both record and produce PSWs. Hence, this study confirms the proposed hypothesis that the majority of observed PSWs represent a suprathreshold single muscle-fiber discharge induced by, and originating in close proximity to, a perielectrode crushed membrane that then propagate away from the electrode; a smaller population of PSWs conform to that of a blocked fibrillation potential.
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Affiliation(s)
- Daniel Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900, USA.
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Sonoo M. Chapter 16 Generators of subcortical components of SEPs and their clinical applications. ACTA ACUST UNITED AC 2006; 59:113-20. [PMID: 16893101 DOI: 10.1016/s1567-424x(09)70020-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Affiliation(s)
- Masahiro Sonoo
- Department of Neurology, Teikyo University School of Medicine, Tokyo, Japan.
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Richerson S, Ingram M, Perry D, Stecker MM. Classification of the extracellular fields produced by activated neural structures. Biomed Eng Online 2005; 4:53. [PMID: 16146569 PMCID: PMC1239920 DOI: 10.1186/1475-925x-4-53] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2005] [Accepted: 09/07/2005] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Classifying the types of extracellular potentials recorded when neural structures are activated is an important component in understanding nerve pathophysiology. Varying definitions and approaches to understanding the factors that influence the potentials recorded during neural activity have made this issue complex. METHODS In this article, many of the factors which influence the distribution of electric potential produced by a traveling action potential are discussed from a theoretical standpoint with illustrative simulations. RESULTS For an axon of arbitrary shape, it is shown that a quadrupolar potential is generated by action potentials traveling along a straight axon. However, a dipole moment is generated at any point where an axon bends or its diameter changes. Next, it is shown how asymmetric disturbances in the conductivity of the medium surrounding an axon produce dipolar potentials, even during propagation along a straight axon. Next, by studying the electric fields generated by a dipole source in an insulating cylinder, it is shown that in finite volume conductors, the extracellular potentials can be very different from those in infinite volume conductors. Finally, the effects of impulses propagating along axons with inhomogeneous cable properties are analyzed. CONCLUSION Because of the well-defined factors affecting extracellular potentials, the vague terms far-field and near-field potentials should be abandoned in favor of more accurate descriptions of the potentials.
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Affiliation(s)
- Samantha Richerson
- Department of Biomedical Engineering, Bucknell University, Lewisburg, Pa 17837 USA
| | - Mark Ingram
- Department of Physics, Bucknell University, Lewisburg, Pa 17837 USA
| | - Danielle Perry
- Department of Physics, Bucknell University, Lewisburg, Pa 17837 USA
| | - Mark M Stecker
- Department of Neurology, Geisinger Medical Center, 100 N Academy Rd, Danville, Pa 17822 USA
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Mackert BM. Magnetoneurography: theory and application to peripheral nerve disorders. Clin Neurophysiol 2004; 115:2667-76. [PMID: 15546775 DOI: 10.1016/j.clinph.2004.07.028] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/23/2004] [Indexed: 11/23/2022]
Abstract
Magnetoneurography (MNG) is a non-invasive method to trace and visualize three-dimensionally the propagation path of compound action currents (CAC) along peripheral nerves. The basic physical and physiological principle is the mapping of extremely weak magnetic fields generated by the intraaxonal longitudinal ion flows of evoked nerval CAC using SQUID sensors (Superconducting Quantum Interference Devices). During recent years, MNG protocols have been established which allow for a non-invasive spatiotemporal tracing of impulse propagation along peripheral nerves in humans and in particular along proximal nerve segments in a clinical setting. Thereby, the three-dimensional path, the local nerve conduction velocity, the length and strength of the CAC de- and repolarization phase have been reconstructed. First recordings in patients demonstrated that the method is sensitive enough to detect and to localize nerve conduction anomalities along nerve roots, as, e.g. caused by lumbosacral disc herniation. This review on MNG will focus on those studies which provide data from humans and thereby reveal perspectives for its future clinical applications.
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Affiliation(s)
- Bruno-Marcel Mackert
- Neurophysics Group, Department of Neurology, Campus Benjamin Franklin, Charité-University Medicine Berlin, Hindenburgdamm 30, 12200 Berlin, Germany.
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Sonoo M, Hatanaka Y, Tsukamoto H, Tsai-Shozawa Y, Shimizu T. N10 component in median nerve somatosensory evoked potentials (SEPs) is not an antidromic motor potential. Clin Neurophysiol 2004; 115:2645-9. [PMID: 15465454 DOI: 10.1016/j.clinph.2004.06.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/04/2004] [Indexed: 11/28/2022]
Abstract
OBJECTIVE To test the hypothesis that the N10 far-field potential in median nerve somatosensory evoked potentials is generated by the motor axons by examining patients with amyotrophic lateral sclerosis (ALS). METHODS Subjects were 5 ALS patients showing pronounced or complete denervation of median-innervated small hand muscles. We evaluated N10 over scalp, and proximal plexus volleys (PPVs) at lateral or anterior cervical electrode. RESULTS N10 and PPVs were definitely preserved for every ALS subject. N10 amplitudes of ALS subjects were even significantly larger than control subjects. In one ALS patient completely lacking motor axons, N10 was larger than the largest one among control subjects. CONCLUSIONS Present results clearly indicate that N10 is not predominantly generated by motor axons but by the whole median nerve dominated by sensory axons. We propose a theory that N10 is a junctional potential generated by the entrance of the median nerve into bone at the intervertebral foramen, producing a positive pole at the non-cephalic reference electrode. Significantly larger N10 in ALS subjects may be due to the lack of cancellation by slower motor axons. SIGNIFICANCE The hypothesis that N10 is generated by motor axons is refuted, and a new theory of its generation is presented.
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Affiliation(s)
- M Sonoo
- Department of Neurology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 1738605, Japan.
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22
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Fukuoka Y, Komori H, Kawabata S, Ohkubo H, Shinomiya K, Terasaki O. Imaging of neural conduction block by neuromagnetic recording. Clin Neurophysiol 2002; 113:1985-92. [PMID: 12464338 DOI: 10.1016/s1388-2457(02)00345-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
OBJECTIVE For the clinical application of neuromagnetic recordings in neural conduction block, the patterns of magnetic fields in the region should be clarified. Using an experimental in vitro model, the spatiotemporal course of the neuromagnetic fields at the site of complete conduction block was examined. Additionally, the magnetic compound action fields (CAFs) and electric compound action potentials (CAPs) were compared and correlated. METHODS In a chamber containing Ringer's solution, 10 isolated sciatic nerves of rabbits were electrically stimulated. Both evoked CAPs and CAFs were measured before and after the ligation of the nerve. The sequential positions of the current dipoles and the location of the conduction block were estimated by the least-squares search. RESULTS The magnetic contour maps of the CAFs showed a characteristic quadrupolar pattern propagating along the nerve. The peak of the leading magnetic field ceased and disappeared at the position of the nerve ligation, while the trailing magnetic field became attenuated before reaching that position. The positions of the conduction blocks were localized by magnetic recordings within a difference of 2mm. CONCLUSIONS The neuromagnetic recordings could visualize the change of the magnetic fields at the site of the complete conduction block and closely localize that position. SIGNIFICANCE The neural conduction block was visualized and localized by neuromagnetic recordings.
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Affiliation(s)
- Yuko Fukuoka
- Section of Orthopedic Spinal Surgery, Department of Frontier Surgical Therapeutics, Division of Advanced Therapeutical Sciences, Graduate School of Tokyo Medical and Dental University, Tokyo, Japan.
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Dumitru D, Diaz CA, King JC. Prevalence of denervation in paraspinal and foot intrinsic musculature. Am J Phys Med Rehabil 2001; 80:482-90. [PMID: 11421515 DOI: 10.1097/00002060-200107000-00002] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE The primary purpose of this investigation was to determine the prevalence of abnormal spontaneous activity (positive sharp waves (PSWs) and fibrillation potentials (FPs)) in selected lumbosacral paraspinal and foot intrinsic muscles in an asymptomatic healthy population. DESIGN This was a prospective assessment of 50 individuals without history or physical findings suggestive of peripheral neuromuscular disease whereby a monopolar needle electrode was located in the unilateral L4 and L5 paraspinal as well as abductor hallucis and extensor digitorum brevis muscles. These muscles were extensively evaluated for the presence of PSWs, FPs, and fasciculation potentials. RESULTS Ten subjects per decade from 20-59 yr and ten subjects from 60-80 yr comprised the 50 participants (28 women), resulting in a mean age of 45+/-15.9 (range, 20-76) yr. A single individual (prevalence, 2%) demonstrated fibrillation potentials in the extensor digitorum brevis, and FPs and PSWs were detected in two subjects' (4% prevalence) L4/L5 paraspinal muscles. Ninety-four percent of the subjects had fasciculation potentials in the abductor hallucis, whereas 60% had these waveforms in the extensor digitorum brevis. Only 6% of subjects had fasciculation potentials in the L4 but not L5 paraspinal muscles. All subjects demonstrated both prototypical and "atypical" appearing endplate spikes in all of the muscles examined. CONCLUSIONS We failed to confirm the previously reported prevalence of FPs and PSWs in both the paraspinal and foot intrinsic musculature. Atypical appearing endplate spikes, however, display configurations similar to FPs and PSWs and were present in all subjects. Failure to pay close attention to the discharge rate and rhythm of endplate spikes can lead to misinterpreting these waveforms as FPs and PSWs. It is likely that the previously reported high prevalence of spontaneous activity in healthy persons resulted from not fully appreciating the similarity between innervated and denervated spontaneous single muscle fiber discharge configurations.
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, San Antonio 78229-3900, USA
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Sonoo M, Mochizuki A, Fukuda H, Oosawa Y, Iwata M, Hatanaka Y, Tsai-Shozawa Y, Okano M, Shimizu T. Lower cervical origin of the P13-like potential in median SSEPS. J Clin Neurophysiol 2001; 18:185-90. [PMID: 11435811 DOI: 10.1097/00004691-200103000-00011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The authors studied the origin of the scalp P13-like potential in median somatosensory evoked potentials, which have been reported to be preserved in patients with cervicomedullary lesions or in brain death. There were five patients with high to middle cervical lesions (C2/3 or C3/4 level). Small P13-like potentials after P11 were identified for all patients with a noncephalic reference but not with an ear reference. Their onset latencies were slightly earlier than the expected latency of the true P13/14 onset. In two patients, delayed true P13/14s followed by N18s were identified with both noncephalic and ear references. The authors argue that the P13-like potential observed in these patients is a different entity from scalp P13 in normal subjects. Because the C3/4 vertebral level corresponds to the C5 cord level, the origin of the P13-like potential must be below C5, contradicting the previous opinion that it is generated at the cervicomedullary junction or at the high cervical dorsal column. The authors named this potential lower cervical P13 (or lcP13), and present an opinion that it is generated by the beginning of the second spinal ascending volley, which has been described by direct-recording studies in humans.
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Affiliation(s)
- M Sonoo
- Department of Neurology, Teikyo University School of Medicine, Tokyo, Japan
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25
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Abstract
The extracellularly recorded configuration of a single muscle fiber discharge is generally appreciated to be triphasic with an initially positive deflection. However, careful attention to waveform appearance during the electrodiagnostic medicine examination reveals that both innervated and denervated muscle waveforms may display a pantheon of configurations. Further, despite the fact that innervated and denervated single muscle fiber discharges arise from distinctly different intracellular action potential (IAP) configurations, their extracellularly recorded waveforms can appear quite similar, leading to potential misidentification and, hence, the possibility of an erroneous diagnostic conclusion. The least appreciated, but nevertheless critical, aspect of explanations for muscle waveform configurations is the relationship between the muscle fiber and recording electrode. Additionally, it is important to appreciate both the near-field and far-field aspects of single fiber and compound muscle action potentials. In this review, the leading/trailing dipole model is used to explain muscle waveform configurations in both innervated and denervated tissues.
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900, USA.
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26
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Dumitru D. Configuration of normal and abnormal non-volitional single muscle fiber discharges. Clin Neurophysiol 2000; 111:1400-10. [PMID: 10904221 DOI: 10.1016/s1388-2457(00)00336-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
OBJECTIVE This investigation utilizes a single muscle fiber simulation to compare and contrast single muscle fiber waveform configurations arising from innervated and denervated tissue taking into account possible tissue-electrode interactions. METHODS Intracellular action potentials (IAPs) from innervated and denervated muscle tissue are simulated. The extracellular waveform configurations as recorded from the fiber's midpoint (endplate in innervated tissue), halfway between the midpoint and fiber termination, as well as fiber termination for both innervated and denervated single muscle fibers are examined. Further, two types of muscle fiber terminations are assessed: (1) sealed end effect; and (2) compressed end effect. RESULTS Irrespective of different types of IAPs, recordings from the fibers' middle, halfway between the midpoint and termination, as well as from the sealed end, revealed similar configurations. However, for the innervated fiber's compressed termination, a monophasic positive waveform was derived while the denervated fiber's compressed termination generated a prototypical positive sharp wave. CONCLUSIONS It is hypothesized that the needle electrode can no longer be considered a passive recording device but may interact with the fiber so as to generate a sealed end or compressed end effect. Depending upon the type of needle-fiber interaction and the electrode's location with respect to the IAP's generation site, a limited number of potentials with specific configurations will be recorded for both innervated and denervated tissue. Further, depending upon the type of needle-tissue interaction, innervated muscle fibers can generate non-volitional waveforms with configurations similar to those recorded from denervated tissue. It is no longer sufficient to merely consider waveform configuration when attempting to define positive sharp waves and fibrillation potentials, but it is important now also to consider firing rate and rhythm.
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
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27
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Abstract
Fibrillation potential configurations are characterized as initially positive triphasic waveforms, whereas positive sharp waves appear biphasic with an initial positive deflection. Careful observation of single muscle fiber discharges in denervated muscle, however, can reveal many different-appearing and stable firing waveforms that resemble a bifid positive sharp wave or some form of combined fibrillation potential and positive sharp wave. In this investigation, a number of atypical-appearing single muscle fiber discharges are hypothesized to arise from particular interactions between the muscle fiber and recording electrode. Single muscle fiber potentials are modeled as originating from a single denervated muscle fiber's former endplate and midfiber region as well as from the fiber's tendinous termination for both a compressed and sealed end effect. The modeled waveforms' appearance corresponds well to those obtained clinically and the necessary interpotential summated templates' temporal domains are feasible for action potential termination at the electrode with subsequent reinitiation beyond the proposed peri-electrode compressed region. It is hypothesized that the majority of hybrid waveforms are the result of a single muscle fiber action potential terminating at a recording electrode while also initiating a "skipped" activation of the muscle fiber past the electrode resulting in the summation of two distinct time-locked waveforms.
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, 78229-3900, USA.
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Sonoo M. Anatomic origin and clinical application of the widespread N18 potential in median nerve somatosensory evoked potentials. J Clin Neurophysiol 2000; 17:258-68. [PMID: 10928638 DOI: 10.1097/00004691-200005000-00004] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
N18 is a broad negativity, with a duration of approximately 20 msec after positive far-field potentials and is recorded widely over the scalp using a noncephalic reference. Its origin has been controversial but its preservation after pontine or upper medullary lesion while loss after high cervical lesions suggested its medullary origin. Comparison with animal studies and direct recording studies in humans leads the authors to conclude that N18 is most likely generated at the cuneate nucleus by primary afferent depolarization. Namely, dorsal column afferents send collaterals to interneurons within the cuneate nucleus, which in turn synapse on presynaptic terminals of dorsal column fibers and depolarize them as a mechanism of presynaptic inhibition. In this way, an electrical sink is formed on presynaptic terminals, whereas their dorsocaudally situated axons serve as a source. The ventrorostral negative pole of the resultant dipolar potential must correspond to N18. The authors obtained a measure to evaluate medullary function objectively, and therefore N18 may be useful as a diagnostic tool for brain death. Usage of a C2S reference is essential for the accurate estimation of N18. Origins of other somatosensory evoked potential components related to the cuneate nucleus are also discussed.
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Affiliation(s)
- M Sonoo
- Department of Neurology, Teikyo University School of Medicine, Tokyo, Japan
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29
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Dumitru D, King JC. Near field and far field source characteristics with respect to bioelectric source generators in volume conductors. Am J Phys Med Rehabil 1999; 78:595-8. [PMID: 10574176 DOI: 10.1097/00002060-199911000-00019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Abstract
OBJECTIVE Motor unit action potential (MUAP) recordings are modeled by means of a single muscle fiber simulation program, to define two key subcomponents comprising the complete physiologic MUAP duration. A number of defining properties of these subcomponents are further developed. METHODS A single muscle fiber simulation program is utilized with various muscle fiber lengths and conduction velocities to generate near-field and far-field waveforms. RESULTS Two key subcomponents to the total physiologic single muscle fiber and hence MUAP duration are identified. One, defined as the near-field component, is directly dependent upon muscle fiber hemi-length. The other, defined as the far-field component, is independent of fiber length, but matches the internal action potential in duration. Both the near-field and far-field components are inversely dependent upon intracellular action potential conduction velocity. Additionally, temporal dispersion among the individual fibers contributing to a MUAP must be included in the overall MUAP duration calculation. CONCLUSIONS It is hoped that this approach to MUAP duration may allow a more complete appreciation of the components contributing to the MUAP, than permitted by the empirically derived values for MUAP duration presently under clinical use.
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, 78284-7798, USA.
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31
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Abstract
Motor unit action potential (MUAP) components are investigated by means of single fiber computer simulations and clinical measurements. The single fiber simulations have essentially full bandwidth without noise, whereas the clinical measurements were made with a 3-10,000-Hz bandwidth utilizing approximately 1000 averages to reduce noise optimally. These parameters allow the recording of a MUAP's complete "physiologic" duration including its very slow onset and termination. The simulation results demonstrate a constant waveform onset regardless of the electrode's recording location along the fiber. A far-field potential is initiated when the action potential encounters the muscle fiber's termination. The simulated waveform's and clinically recorded MUAP's near-field component extends between the potential's onset and its corresponding far-field potential's onset. This near-field component's duration should vary with fiber length, and this prediction is clinically confirmed by measuring three different muscle lengths. The far-field potential reveals a constant duration, independent of fiber length, and appears to be associated with the muscle fiber's intracellular action potential duration. A more complete understanding of the components contributing to MUAP duration should provide a more fundamental basis for quantitative clinical MUAP duration measurements.
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Affiliation(s)
- D Dumitru
- University of Texas Health Science Center at San Antonio, Department of Rehabilitation Medicine, 7703 Floyd Curl Drive, San Antonio, Texas 78284-7798, USA
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Merletti R, Lo Conte L, Avignone E, Guglielminotti P. Modeling of surface myoelectric signals--Part I: Model implementation. IEEE Trans Biomed Eng 1999; 46:810-20. [PMID: 10396899 DOI: 10.1109/10.771190] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The relationships between the parameters of active motor units (MU's) and the features of surface electromyography (EMG) signals have been investigated using a mathematical model that represents the surface EMG as a summation of contributions from the single muscle fibers. Each MU has parallel fibers uniformly scattered within a cylindrical volume of specified radius embedded in an anisotropic medium. Two action potentials, each modeled as a current tripole, are generated at the neuromuscular junction, propagate in opposite directions and extinguish at the fiber-tendon endings. The neuromuscular junctions and fiber-tendon endings are uniformly scattered within regions of specified width. Muscle fiber conduction velocity and average fiber length to the right and left of the center of the innervation zone are also specified. The signal produced by MU's with different geometries and conduction velocities are superimposed. Monopolar, single differential and double differential signals are computed from electrodes placed in equally spaced locations on the surface of the muscle and are displayed as functions of any of the model's parameters. Spectral and amplitude variables and conduction velocity are estimated from the surface signals and displayed as functions of any of the model's parameters. The influence of fiber-end effects, electrode misalignment, tissue anisotropy, MU's location and geometry are discussed. Part II of this paper will focus on the simulation and interpretation of experimental signals.
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Affiliation(s)
- R Merletti
- Department of Electronics, Politecnico di Torino, Italy
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33
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Abstract
Motor unit action potentials (MUAPs) recorded from the same motor unit at two distances along the biceps brachii muscle with monopolar needle electrodes at high amplifier gains (20 microV/division) and averaged 2000-3000 times reveal total potential durations of 39.6 +/- 4.6 ms. In addition, the terminal segment for each of these two MUAPs contained a late far-field potential with a mean duration of 23.8 +/- 4.1 ms. Computer simulations of MUAPs suggest that this long-duration positive far-field mirrors the true morphology of the intracellular action potential (IAP), which is monophasic positive, possessing a terminal repolarization phase approaching 30 ms. This investigation suggests that the MUAP's physiologic duration is directly proportional to the muscle fiber length and the IAP's duration, which becomes manifest as a positive far-field potential when the IAP encounters the musculotendinous junction and slowly dissipates. The leading/trailing dipole model is used to explain qualitatively this study's quantitative clinical and computer simulation findings.
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Affiliation(s)
- D Dumitru
- University of Texas Health Science Center at San Antonio, Department of Rehabilitation Medicine, 78284-7798, USA
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Abstract
Motor artifact often interferes with recording of antidromic ulnar sensory responses from digit 5. In the belief that this artifact is due to a volume-conducted motor response, eight different recording electrode and finger positions were evaluated in 10 normal subjects in an attempt to reduce or eliminate it. Placement of the recording electrodes over the middle and distal phalanges of digit 5 while the fingers were extended and abducted reduced this artifact most effectively, with minimal decrease in amplitude of the sensory response. This finding has important implications for the routine performance of antidromic sensory conduction studies of the ulnar nerve.
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Affiliation(s)
- S B Rutkove
- Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA
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35
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Abstract
A finite muscle fiber simulation program which calculates the extracellular potential for any given intracellular action potential (IAP) was used to model a fibrillation potential and a positive sharp wave. This computer model employs the core conductor model assumptions for an active muscle fiber and allows two distinct types of end effects: a cut or a crush. A "cut end" is defined as a membrane segment with the termination of both active and passive ion channels. The "crush end" is simulated as a focal membrane segment which blocks action potential propagation, and is connected to a region of normal membrane on either side of it so that a normal transmembrane potential is maintained beyond the crush zone. A prototypical positive sharp wave of appropriate amplitude and duration could only be detected extracellularly by using an IAP of the configuration found in denervated rat muscle recorded from a muscle fiber terminating in a crush segment of membrane.
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, 78284-7798, USA
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36
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Abstract
The contributions of the various ulnar-innervated muscles of the hand to the hypothenar compound muscle action potential (CMAP) were estimated by directly stimulating individual muscles and by analyzing CMAP shape changes resulting from manipulations that changed individual muscle lengths. The results show that the first peak of the negative phase of the hypothenar CMAP comes from the hypothenar muscles, but that the second peak is due to a large volume-conducted potential from the interosseous muscles. The interosseous contribution affects both the amplitude and the area of the CMAP, and makes these parameters sensitive to changes in the configuration of the fingers and the temperature gradient in the hand. To reduce the interosseous contribution, a "balanced reference" consisting of two reference electrodes, one over each tendon, is proposed.
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Affiliation(s)
- K C McGill
- Rehabilitation Research and Development Center, VA Palo Alto Health Care System, California 94304-1200, USA
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Fujita Y, Yamada T, Inoue K, Sato A, Katayama M, Ofuji A, Fujita H, Yeh M. Origin of the "N10" stationary-field potential after median nerve stimulation. J Clin Neurophysiol 1999; 16:69-76. [PMID: 10082094 DOI: 10.1097/00004691-199901000-00007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The scalp far-field potentials after median nerve stimulation at the wrist consist of P9, P11, P13, and P14 positive components. Earlier, Emerson et al. (1984) identified the "N10" negative potential in-between the P9 and P11 and claimed that this was not merely a passive return to the baseline after the P9 positive deflection but a distinct component reflecting a proximal brachial plexus volley. They thought N10 was a far-field potential having widespread distribution with a fixed latency. In this study we found that N10 was of higher amplitude after median nerve stimulation at the elbow than after stimulation at the wrist. Indeed the N10 latency was fixed from the lower anterior neck to the scalp, and its amplitude was maximum at the anterior lower neck. The latency of N10 was about 0.3 milliseconds longer than the Erb's potential and 0.15 milliseconds longer than the potential recorded from the lateral neck on the side of stimulation. The N10 amplitude increased in parallel with increased stimulus intensity. In order to explore the origin of the N10 stationary field potential, we designed a paired stimuli paradigm applied to the wrist (S1) and to the elbow (S2). The interstimulus interval between S and S2 was adjusted so that the timing of S2 was immediately after the traveling impulse produced by the S1 stimulus as it passed through the S2 stimulus site. This technique allowed stimulation of the anterior interosseous nerve selectively at the elbow while the median nerve originating from the wrist was undergoing refractory period. The response of (S1 + S2) - S1 showed only the N10 with absence of cervical and cortical responses, implying that N10 was activated, predominantly by the interosseous nerve, i.e., an antidromic motor volley, when the median nerve was stimulated at the elbow.
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Affiliation(s)
- Y Fujita
- Department of Neurology, University of Iowa, College of Medicine, Iowa City 52242, USA
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38
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Mochizuki A, Sonoo M, Shimizu T, Iwata M. P9 in median nerve SEPs is a junctional potential generated by the change of the volume conductor size between trunk and neck. ELECTROENCEPHALOGRAPHY AND CLINICAL NEUROPHYSIOLOGY 1998; 108:584-7. [PMID: 9872430 DOI: 10.1016/s0168-5597(98)00039-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
OBJECTIVES We aimed to investigate the origin of P9 in median SEPs by applying the junctional potential theory. METHODS We studied the distribution over the body surface with contralateral shoulder reference in 4 normal subjects. RESULTS A stationary potential field P9/tN9 (=truncal N9) was recorded: P9 over head and neck (the smaller part), tN9 over trunk (the larger part), the boundary being located between trunk and neck. This polarity agreed with that expected from simulation studies. CONCLUSIONS P9 is a junctional potential generated by the change of the volume conductor size between trunk and neck.
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Affiliation(s)
- A Mochizuki
- Department of Neurology, Teikyo University School of Medicine, Tokyo, Japan
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39
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Abstract
Needle electromyographic insertional activity waveform morphology, and mechanisms of generation, have received little attention. This study analyzes the individual component waveforms that contribute to the burst of electrical activity known as insertional activity. One hundred monopolar needle insertions were slowly performed and high speed recorded to allow better separation of the contributing individual component waveforms. Analysis of the many waveforms recorded demonstrates several classes of potentials. All of these could be reconstructed by the summation of two basic or elementary waveform patterns: a biphasic initially negative spike with or without a "prepotential" similar to an end-plate spike, and the biphasic initially positive spike with a slowly declining negative phase, similar to a positive sharp wave, though shorter in duration. The relationship between these elementary waveforms and their hypothesized generator sources is discussed.
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio 78284-7798, USA
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40
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Dumitru D, King JC, Stegeman DF. Endplate spike morphology: a clinical and simulation study. Arch Phys Med Rehabil 1998; 79:634-40. [PMID: 9630141 DOI: 10.1016/s0003-9993(98)90036-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
OBJECTIVE To describe the various morphologic appearances of endplate spikes, define the theoretical volume conduction basis of these waveforms' morphologies, and simulate "atypical" endplate spike waveforms documented by other investigators. DESIGN Endplate spikes were recorded from the biceps brachii in healthy individuals using a monopolar needle electrode. The morphologies of these waveforms were compared with those obtained from a computer simulation. Previously documented endplate waveforms were simulated using two fundamental types of biphasic initially negative and positive waveform morphologies. SETTING University clinic outpatient electrodiagnostic medicine facility. SUBJECTS Five subjects without history or physical evidence of neuromuscular disease. MAIN OUTCOME MEASURES Endplate potential morphologies were assessed with respect to overall waveform shape and number of phases. Computer-generated waveforms for individual endplate spike waveforms were qualitatively compared with those recorded from the subjects. RESULTS Three fundamental waveforms were documented to arise from the endplate regions of all subjects and were successfully simulated: (1) biphasic initially negative potential from the endplate itself and up to 0.2mm from the endplate, (2) triphasic initially positive potential from within 0.2mm of the endplate up to 0.5mm from the musculotendinous junction, and (3) biphasic initially positive potential from the last 0.4mm of the fiber or from impulse blocking. Two biphasic endplate spike waveforms could be summated to generate all other endplate waveforms described in previously documented literature. CONCLUSION The combination of clinical and simulation studies suggests that endplate spike potentials can have quite varied morphologies. Triphasic initially positive and biphasic initially positive endplate spikes may be mistaken for fibrillation potentials and positive sharp waves, respectively. The triphasic waveforms most likely arise from an action potential propagating past the recording electrode adjacent to the endplate, while the biphasic initially positive potential is simulated to arise from the needle electrode blocking action potential propagation.
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, 78284-7798, USA
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Dumitru D, King JC. Concentric needle recording characteristics related to depth of tissue penetration. ELECTROENCEPHALOGRAPHY AND CLINICAL NEUROPHYSIOLOGY 1998; 109:124-34. [PMID: 9741803 DOI: 10.1016/s0924-980x(98)00003-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This study investigates the influence of tissue penetration depth as it relates to a concentric needle electrode, particularly delineating regions where the cannula potential predominates over the core potential. The regions of cannula predominance is studied by means of a standard and 20 times enlarged physical model of an electromyographic concentric needle electrode in a homogeneous volume conductor by delineating the zero isopotential which partitions where the core potential predominates versus where the cannula potential predominates. Clinical studies in muscle tissue are used to test and confirm results from the enlarged physical model. At shallow electrode insertions equivalent to 4 mm, the concentric needle model records a net negative potential, which is a region where the cannula predominates, from a distant positive dipole at the same depth compared with a net positive potential for penetration depths exceeding 4 mm. The clinical portion of this study verifies the bipolar nature of the concentric needle electrode in detecting motor unit action potentials (MUAPs) with primarily an initial positive onset irrespective of recording depth. Refinements to the conceptualization of the nature and detection of MUAPs are discussed which are consistent with all the findings of the clinical and model study.
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, 78284-7798, USA.
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Stegeman DF, Dumitru D, King JC, Roeleveld K. Near- and far-fields: source characteristics and the conducting medium in neurophysiology. J Clin Neurophysiol 1997; 14:429-42. [PMID: 9415390 DOI: 10.1097/00004691-199709000-00009] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
It is possible to appreciate the production of far-field potentials by considering constant current dipolar source voltage distributions in bounded volumes, especially when they are stretched in one direction, e.g., a cylinder. An essentially nondeclining voltage is detected when the recording electrodes are on opposite sides of, and relatively far from, the dipolar source. This voltage maintains its (a) latency, (b) amplitude, (c) morphology, and (d) polarity even if recordings are performed a whole body length away. These four criteria define far-field potentials. A propagating action potential (AP) can be conceptualized as a linear quadrupole or the summation of two dipoles "back-to-back" (+ - - +). The far-field components of the summated dipoles cancel resulting in the anticipated triphasic waveform for APs with only near-field characteristics, not meeting the first three criteria above. Far-field potentials can be transiently generated when any propagating AP constitutes a net "real" or "virtual" dipolar source. "Real" dipolar sources can occur if an AP encounters the termination of excitable tissue, an alteration in conduction velocity, curvature in excitable tissue resulting in a change in propagation direction, or an abrupt change in resistance of the excitable tissue. Virtual dipolar sources may be produced if an AP encounters a change in the size or shape of the extracellular medium or a transition in extracellular conductivity.
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Affiliation(s)
- D F Stegeman
- Department of Clinical Neurophysiology, Institute of Neurology, University Hospital Nijmegen, The Netherlands
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Sonoo M, Genba-Shimizu K, Mannen T, Shimizu T. Detailed analysis of the latencies of median nerve somatosensory evoked potential components, 2: Analysis of subcomponents of the P13/14 and N20 potentials. ELECTROENCEPHALOGRAPHY AND CLINICAL NEUROPHYSIOLOGY 1997; 104:296-311. [PMID: 9246067 DOI: 10.1016/s0168-5597(97)00035-x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Detailed analysis of P13/14 and N20 wavelets was performed for 62 normal subjects and patients with various lesions along the somatosensory pathway. A histogram of the latencies of all the identified P13/14 wavelets (measured from P13/14 onset) demonstrated three latency-groups, which were named P13, P14a and P14b subcomponents. The relationship between the three newly identified subcomponents and the conventional naming of P13 and P14 was inconstant, indicating the ambiguity of the latter. P14b was most prominent in the contralateral central region, and therefore a P15 positivity slightly after P14b was often recorded in the CPc-Fz and CPc-CPi leads (CPc and CPi are centroparietal electrodes contralateral and ipsilateral to the stimulation). P14b/P15 was lost even in patients with cortical lesions, and thalamocortical fibers were assumed for its origin. The CPc-Fz and CPi-Fz leads registered a low negativity named broad N13', suggesting frontal predominance of the overall P13/14 complex. Both P13 and P14a were identified in a patient with a pontine lesion, and a caudal brainstem origin for both was suspected due to the onset of two repetitive bursts of the ascending lemniscal volley. We refuted the presynaptic origin of the scalp P13 potential and pointed out that a prolonged and/or polyphasic P11 frequently observed in patients with high cervical lesions can be mistaken as scalp P13. A histogram of the latencies of all the identified negative wavelets of N20 in the CPc-Fz lead (measured from N20 onset) revealed five definite latency-groups, which were named N20a, N20b, N20c, N20d and N20e subcomponents. The highest peak of N20 actually corresponded to either N20b, N20c or N20d, and this uncertainty, which must be related to intracortical processes, resulted in a large instability of the N20 peak latency as well as the age and sex dependence of the N20 onset-peak interval, both of which were demonstrated by our preceding study (Sonoo, M., Kobayashi, M., Genba-Shimizu, K., Mannen, T. and Shimizu, T. Detailed analysis of the latencies of median nerve SEP components, 1: selection of the best standard parameters and the establishment of the normal values. Electroenceph. clin. Neurophysiol., 1996b, 100: 319-331). Negative subcomponents in the CPc-NC lead and positive subcomponents in the Fz-NC lead constituted mirror images of each other, which suggested that these subcomponents were generated within area 3b.
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Affiliation(s)
- M Sonoo
- Department of Neurology, Teikyo University School of Medicine, Tokyo, Japan
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Sonoo M, Hagiwara H, Motoyoshi Y, Shimizu T. Preserved widespread N18 and progressive loss of P13/14 of median nerve SEPs in a patient with unilateral medial medullary syndrome. ELECTROENCEPHALOGRAPHY AND CLINICAL NEUROPHYSIOLOGY 1996; 100:488-92. [PMID: 8980412 DOI: 10.1016/s0168-5597(96)96023-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Median nerve somatosensory evoked potentials (SEPs) in a patient with unilateral medial medullary syndrome of recent onset having an MRI-confirmed lesion at upper medulla were investigated. Cortical N20 following stimulation of the affected limb was extremely depressed and delayed, whereas widespread N18, which was best manifested by the CPi-C2S lead (CPi is centroparietal electrode ipsilateral to the stimulation), showed no significant difference regarding amplitude and duration between affected and non-affected sides. The result supported our previous opinion that the principal part of N18, the broad negativity lasting around 20 ms, originates from the cuneate nucleus at the medullary level. Less steep onset of N18 on the affected side suggested that some structures rostral to the cuneate nucleus, possibly the termination of the overall ascending volley, may contribute to the earliest part of N18. P13/14 on the affected side normally preserved at the first examination progressively declined and finally disappeared after 4 months, which suggested that the major part of P13/14 is generated within caudalmost medial lemniscus, as well as the occurrence of retrograde degeneration of lemniscal fibers.
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Affiliation(s)
- M Sonoo
- Department of Neurology, Teikyo University School of Medicine, Tokyo, Japan
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Affiliation(s)
- S B Rutkove
- Division of Neurology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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Park TA, Jurell KC, Del Toro DR. Generator sources for the early and late ulnar hypothenar premotor potentials: short segment electrophysiologic studies and cadaveric dissection. Arch Phys Med Rehabil 1996; 77:467-72. [PMID: 8629923 DOI: 10.1016/s0003-9993(96)90035-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
OBJECTIVE Determine the generator sources for the ulnar hypothenar premotor potentials (PMPs). DESIGN Observational. SETTING EMG laboratory. SUBJECTS Ten asymptomatic adult volunteers, three cadaver hands. MAIN OUTCOME MEASURE Far-field versus near-field characteristics of recorded PMPs as determined by bipolar and referential recording electrode montages. A possible anatomic basis for any observed differences between ulnar PMPs and previously studied median PMPs were explored through cadaveric dissection. RESULTS An early PMP (E-PMP) had a latency that varied with changes in the position of G1 only. A late PMP (L-PMP was seen only when G1 and G2 were on different volumes (palm vs fifth digit, or second digit vs fifth digit); its latency did not vary significantly with changes in the position of G1 and G2. CONCLUSIONS (1) E-PMP is a near-field potential generated by the ulnar nerve passing near the G1 electrode. (2) L-PMP represents a far-field potential generated by the ulnar digital nerves as they traverse from the hand volume containing G1 to the finger volume containing G2. (3) Greater L-PMP-to-CMAP separation in the median than in the ulnar nerve was explained by cadaveric dissection, which revealed that the motor branch (responsible for the trailing CMAP) is longer in the median nerve than in the ulnar nerve relative to each nerve's corresponding digital sensory branch (responsible for the preceding L-PMP). (4) The PMP that is typically recorded with G1 at the hypothenar motor point and G2 on the fifth digit most likely represents E-PMP. (5) Any proposed diagnostic use of the ulnar PMPs must take into consideration these generator sources.
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Affiliation(s)
- T A Park
- Department of Physical Medicine and Rehabilitation, Medical College of Wisconsin, Milwaukee 53226, USA
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Abstract
We measured somatosensory-evoked potentials in athletes to determine whether there were differences in somatosensory pathways related to sports performance or training. Seven sedentary subjects, 10 endurance runners, and seven elite gymnasts of similar height and weight were investigated. Peak latencies and amplitudes were measured of P9, P11, P13/14, N20, P25, and N30 waves, following electrical stimulation of the median nerve at the wrist. Central and peripheral conduction speeds of the sensory pathway were calculated. The subjects also completed a simple reaction test to a visual stimulus. There were no significant differences between the groups in any of the attributes we measured. The was a positive correlation between years of training undergone and the amplitude of N20, a negative correlation between the amplitudes of P11 and P13/14 and the number of hours of training undertaken per week, and a positive correlation between the amplitude of N30 and the simple visual reaction time. We conclude that the gymnasts, runners and sedentary subjects had no differences in somatosensory pathways, as measured using standard clinical procedures for evaluating somatosensory-evoked potentials.
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Affiliation(s)
- N G Thomas
- Department of Physiology, University of the Witwatersrand, Parktown, South Africa
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Abstract
The generator sources of the median thenar premotor potentials (PMPs) have remained elusive despite debate in the literature. By studying the median nerve in the hand with a variety of bipolar and referential recording montages, we systematically examined the possible near-field and far-field sources that may determine these potentials. The results suggest that the early PMP is a near-field potential recorded by G1 and generated by the median nerve traversing the distal carpal tunnel. The late PMP represents a far-field potential generated by the median digital nerve fibers as they pass from the palm volume into the thumb volume. Characteristics of the late PMP are explained using the leading/trailing dipole (L/TD) model of far-field potential generation. The diagnostic utility of these PMPs is questionable, since they are recorded from "regions" along the nerve rather than from more clearly defined sites.
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Affiliation(s)
- T A Park
- Department of Physical Medicine and Rehabilitation, Medical College of Wisconsin, Milwaukee, USA
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Xiao S, McGill KC, Hentz VR. Action potentials of curved nerves in finite limbs. IEEE Trans Biomed Eng 1995; 42:599-607. [PMID: 7790016 DOI: 10.1109/10.387199] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Previous simulations of volume-conducted nerve-fiber action-potentials have modeled the limb as semi-infinite or circularly cylindrical, and the fibers as straight lines parallel to the limb surface. The geometry of actual nerves and limbs, however, can be considerably more complicated. This paper presents a general method for computing the potentials of fibers with arbitrary paths in arbitrary finite limbs. It involves computing the propagating point-source response (PPSR), which is the potential arising from a single point source (dipole or tripole) travelling along the fiber. The PPSR can be applied to fibers of different conduction velocities by simple dilation or compression. The method is illustrated for oblique and spiralling nerve fibers. Potentials from oblique fibers are shown to be different for orthodromic and antidromic propagation. Such results show that the straight-line models are not always adequate for nerves with anatomical amounts of curvature.
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Affiliation(s)
- S Xiao
- Rehabilitation Research and Development Center, VA Medical Center, Palo Alto, CA 94304-1200, USA
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Abstract
A small negative waveform is known to precede the median and ulnar compound muscle action potentials when recorded with surface or concentric needle electrodes. This investigation documents that there are two distinct waveforms preceding the median compound muscle action potential (CMAP) depending upon the type of recording electrodes used (concentric needle versus surface) and their respective locations. The negative waveform originally described with a concentric needle electrode positioned within the substance of the distal thenar eminence and having a restricted zone of detection is referred to as the intramuscular nerve action potential (INAP). This potential is shown to be distinct from the premotor potential (the small negative waveform preceding surface recorded ulnar and median CMAPs). Detection of the median and ulnar premotor potentials at multiple locations about the hand with the same respective onset/peak latencies and amplitudes substantiates that this potential is a far-field potential. The median and ulnar premotor potentials most likely originate from a dipolar moment imbalance generated by digital sensory nerve action potentials as they cross the first and fifth metacarpophalangeal junctions, respectively. Applying far-field principles permits the documentation of additional far-field potentials as they are generated at the second through fourth metacarpophalangeal junctions following median nerve stimulation. Also, because the premotor potential is a far-field potential, caution must be exercised with respect to its diagnostic utility as joint position and other unknown factors may affect amplitude and onset/peak latency. The INAP following median nerve excitation, however, is documented to be a near-field potential distinct from the premotor potential arising from the recurrent branch of the median nerve.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center, San Antonio 78284-7798, USA
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