Somatosensory evoked magnetic fields from the primary somatosensory cortex (SI) in acute stroke

We recorded somatosensory evoked magnetic fields (SEFs) to median nerve stimulation from 15 patients in the acute stage (1-15 days from the onset of the symptoms) of their first-ever unilateral stroke involving sensorimotor cortical and/or subcortical structures in the territory of the middle cerebral artery (MCA). Neuronal activity corresponding to the peaks of the N20m, P35m and P60m SEF deflections from the contralateral primary somatosensory cortex (SI) was modelled with equivalent current dipoles (ECDs), the locations and strengths of which were compared with those of an age-matched normal population. Four patients with pure motor stroke had symmetric SEFs. In one of the 4 patients with pure sensory stroke, and in 5 of the 7 patients with sensorimotor paresis, the SEFs were markedly attenuated or missing. All except one patient with abnormal SEFs had deficient two-point discrimination ability; especially the attenuation of N20m was more clearly correlated with two-point discrimination than with joint-position or vibration senses. Of the different SEF deflections, P35m and P60m were slightly more sensitive indicators of abnormality than N20m, the former being affected in two patients with symmetric N20m. Three patients with pure sensory stroke and lesions in the opercular cortex had normal SEFs from SI. We conclude that the SEF deflections N20m, P35m and P60m from SI are related to cutaneous sensation, in particular discriminative to touch. The results also demonstrate that basic somatosensory perception can be affected by lesions in the opercular cortex in patients with functionally intact SI.

[1]  T. Yoshimoto,et al.  Neuromagnetic evidence of pre- and post-central cortical sources of somatosensory evoked responses. , 1996, Electroencephalography and clinical neurophysiology.

[2]  R. Ilmoniemi,et al.  Magnetoencephalography-theory, instrumentation, and applications to noninvasive studies of the working human brain , 1993 .

[3]  G. Donnan,et al.  A comparison of somatosensory evoked and motor evoked potentials in stroke , 1989, Annals of neurology.

[4]  R. Hari,et al.  Functional Organization of the Human First and Second Somatosensory Cortices: a Neuromagnetic Study , 1993, The European journal of neuroscience.

[5]  R. Ilmoniemi,et al.  Somatosensory evoked magnetic fields to median nerve stimulation: interhemispheric differences in a normal population. , 1997, Electroencephalography and clinical neurophysiology.

[6]  C C Wood,et al.  Human cortical potentials evoked by stimulation of the median nerve. II. Cytoarchitectonic areas generating long-latency activity. , 1989, Journal of neurophysiology.

[7]  V Pizzella,et al.  On the reorganization of sensory hand areas after mono-hemispheric lesion: a functional (MEG)/anatomical (MRI) integrative study , 1998, Brain Research.

[8]  W W Orrison,et al.  Somatosensory evoked magnetic fields in patients with stroke. , 1994, Electroencephalography and clinical neurophysiology.

[9]  L. Parkkonen,et al.  122-channel squid instrument for investigating the magnetic signals from the human brain , 1993 .

[10]  H. Lüders,et al.  The Somatosensory Evoked Potential in Patients with Cerebrovascular Diseases , 1971, Folia psychiatrica et neurologica japonica.

[11]  M Hämäläinen,et al.  Early deflections of cerebral magnetic responses to median nerve stimulation. , 1989, Electroencephalography and clinical neurophysiology.

[12]  L Leinonen,et al.  Cerebral magnetic responses to stimulation of ulnar and median nerves. , 1987, Electroencephalography and clinical neurophysiology.

[13]  F Mauguière,et al.  Astereognosis and dissociated loss of frontal or parietal components of somatosensory evoked potentials in hemispheric lesions. Detailed correlations with clinical signs and computerized tomographic scanning. , 1983, Brain : a journal of neurology.

[14]  R. J. Ilmoniemi,et al.  Human somatosensory cortical activation strengths: comparison between males and females and age-related changes , 1999, Brain Research.

[15]  T. Allison,et al.  Somato-sensory evoked responses in patients with unilateral cerebral lesions. , 1970, Electroencephalography and clinical neurophysiology.

[16]  R. Emerson,et al.  Median nerve somatosensory evoked potentials in patients with lacunar and other small subcortical strokes , 1991, Journal of the Neurological Sciences.

[17]  O. Witte,et al.  Extended brain disinhibition following small photothrombotic lesions in rat frontal cortex , 1997, Neuroreport.

[18]  M. Merzenich,et al.  Reorganization of neocortical representations after brain injury: a neurophysiological model of the bases of recovery from stroke. , 1987, Progress in brain research.

[19]  H. Tsukagoshi,et al.  Somatosensory evoked potentials in patients with selective impairment of position sense versus vibration sense , 1991, Acta neurologica Scandinavica.

[20]  F Mauguière,et al.  Focal capsular vascular lesions can selectively deafferent the prerolandic or the parietal cortex: Somatosensory evoked potentials evidence , 1991, Annals of neurology.

[21]  C C Wood,et al.  Electrical sources in human somatosensory cortex: identification by combined magnetic and potential recordings. , 1985, Science.

[22]  S. Tsuji,et al.  Topography of somatosensory evoked potentials to median nerve stimulation in patients with cerebral lesions. , 1988, Electroencephalography and clinical neurophysiology.

[23]  P M Rossini,et al.  Analysis of interhemispheric asymmetries of somatosensory evoked magnetic fields to right and left median nerve stimulation. , 1994, Electroencephalography and clinical neurophysiology.

[24]  T. Tsumoto,et al.  Cerebrovascular disease: changes in somatosensory evoked potentials associated with unilateral lesions. , 1973, Electroencephalography and clinical neurophysiology.

[25]  T. Allison,et al.  Functional magnetic resonance imaging of sensory and motor cortex: comparison with electrophysiological localization. , 1995, Journal of neurosurgery.

[26]  R. Caselli,et al.  Ventrolateral and dorsomedial somatosensory association cortex damage produces distinct somesthetic syndromes in humans , 1993, Neurology.

[27]  V. Hömberg,et al.  Reorganization of motor output in the non-affected hemisphere after stroke. , 1997, Brain : a journal of neurology.

[28]  C. Kase,et al.  Somatosensory evoked potentials in pure sensory stroke and related conditions. , 1985, Stroke.

[29]  J. Dichgans,et al.  The significance of somatosensory evoked potentials for localization of unilateral lesions within the cerebral hemispheres , 1983, Journal of the Neurological Sciences.

[30]  C. Nicholson,et al.  Distortion of magnetic evoked fields and surface potentials by conductivity differences at boundaries in brain tissue. , 1990, Biophysical journal.

[31]  K. Nakashima,et al.  Somatosensory evoked potentials over the non-affected hemisphere in patients with unilateral cerebrovascular lesions , 1985, Journal of the Neurological Sciences.

[32]  F. Reisecker,et al.  Somatosensory evoked potentials (SSEPs) in various groups of cerebro-vascular ischaemic disease. , 1986, Electroencephalography and clinical neurophysiology.

[33]  J Hyvärinen,et al.  Receptive field integration and submodality convergence in the hand area of the post‐central gyrus of the alert monkey. , 1978, The Journal of physiology.

[34]  J. Kaas.  The functional organization of somatosensory cortex in primates. , 1993, Annals of anatomy = Anatomischer Anzeiger : official organ of the Anatomische Gesellschaft.