Topographic analyses of somatosensory evoked potentials following stimulation of tibial,sural and lateral femoral cutaneous nerves |
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| Affiliation: | 1. Division of Clinical Electrophysiology, Department of Neurology, University of Iowa, College of Medicine, Iowa City, IA 52242, USA;2. Department of Orthopedic Surgery, Kansai Medical University, Osaka, Japan;3. Department of Orthopedic Surgery, Yamaguchi University, Yamaguchi, Japan;1. Instituto de Envejecimiento, Pontificia Universidad Javeriana, Bogotá, Colombia;2. Departamento Neurociencias, Área de Neurocirugía, Hospital Universitario San Ignacio y Pontificia Universidad Javeriana, Bogotá, Colombia;3. Semillero de Neurociencias y Envejecimiento, Facultad de Medicina, Pontificia Universidad Javeriana, Bogotá, Colombia;4. Hospital Universitario San Ignacio, Bogotá, Colombia;1. Universidad Pontificia Bolivariana - Hospital Pablo Tobón Uribe, Medellín, Colombia;2. Universidad Pontificia Bolivariana, Medellín, Colombia;1. Departamento de Anatomía Patológica, Hospital Universitario Central de Asturias, Oviedo, España;2. Departamento de Anatomía Patológica, Hospital Universitario del Henares, Madrid, España;3. Departamento de Anestesia y Reanimación, Hospital Universitario San Agustín, Avilés, España;1. Department of Epileptology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan;2. Department of Neurology and Stroke Medicine, Yokohama City University Graduate School of Medicine, Yokohama, Kanagawa, Japan;1. Department of Epileptology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan;2. Department of Collaborative Laboratory of Electromagnetic Neurophysiology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan;3. Institute of Development, Aging and Cancer, Tohoku University, Sendai, Miyagi, Japan |
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| Abstract: | Using topographic maps, we studied the scalp field distribution of somatosensory evoked potentials (SEPs) in response to the stimulation of the tibial (TN), sural (SN) and lateral femoral cutaneous (LFCN) nerves in 24 normal volunteers. Cortical peaks, i.e., N35, P40, N50 and P60 were generally dominant in the contralateral hemisphere for the LFCN-SEP, whereas all peaks except N35 had dominance in the ipsilateral hemisphere for TN- and SN-SEPs. The findings imply that ipsilateral or contralateral peak dominance for the lower extremity SEP is determined by where the cortical leg representation occurs. As a result, mesial hemisphere representation results in peak dominance projected to the hemisphere ipsilateral to stimulation. Representations at the superior lip of the interhemispheric fissure or lateral convexity lead to midline or contralateral peak dominance. These findings also suggest that the paradoxically lateralized P40 is not the result of a positive field dipole shadow generated by the primary negative wave in the mesial hemisphere, but is the primary positive wave, analogous to P26 of the median nerve SEP. Accordingly, contralaterally dominant N35 is likely equivalent to the first cortical potential of N20 in the median nerve SEP. The difference in vector directions of potential fields between N35 and P40 may account for the opposite hemispheric dominance for these peaks in TN- and SN-SEPs. |
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