Assessing both Primary Motor and Somatosensory Cortexes using Neuromagnetic Median Nerve Task (original) (raw)
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Clinical Neurophysiology, 2004
Objective: Hemiparesis due to damage by stroke in primary motor cortex (MI) or its underlying projections presents a problem for functional neuroimaging technologies that attempt to evaluate the neurophysiological basis for restoration of motor function. Traditional assessments of MI function require patients to move their fingers, hands, or limbs, which can be either impossible or markedly compromised after stroke. We recently demonstrated in normal subjects that magnetoencephalography (MEG), a non-invasive neuromagnetic functional imaging technique, detects neuronal response elicited by electrical median nerve stimulation in MI, as well as primary somatosensory cortex (SI). In the present study, we used the MEG response from median nerve stimulation to investigate the recovery of primary motor and somatosensory in acute ischemic stroke patients. Methods: Twelve patients with unilateral ischemic strokes that affected sensorimotor functions of their hand were studied in the acute stage (4.4^1.2 days, mean^SD) and during a 1-month follow-up (38.6^5.6 days, except for one patient's follow-up done 6 month after stroke). Results: Among the multiple cortical sources localized after median nerve stimulation, one source localized to SI and another localized to the vicinity of MI. Changes in the source strengths of the first component post-stimulus of MI and SI correlated with the extent of recovery of sensorimotor functions as determined by neurological exams. Conclusions: This study provides a novel way of indirectly assessing MI function using MEG during the acute stroke phase, when many patients often cannot perform motor tasks due to paralysis.
Brain sensorimotor hand area functionality in acute stroke: insights from magnetoencephalography
NeuroImage, 2004
An understanding of the functional readjustments that the brain undergoes during the early days after a stroke would give us a major insight into how and how much neurons are capable to react to an insult. Thirty-two patients affected by an acute monohemispheric ischemic stroke were enrolled in the study. Magnetoencephalography was used to record the somatosensory-evoked fields (SEF) generated in response to median nerve stimulation. Latency, strength, and position of the related early cortical components (M20 and M30) were studied both separately within each hemisphere, and in terms of interhemispheric differences. Interhemispheric cross-correlations among SEF waveshapes in the two hemispheres were also investigated. Overall, except for some source displacement possibly induced by the perilesional edema, results did not demonstrate any unusual neural recruitment. The severity of the clinical picture was found related to the sources' strengths (both as absolute values and as interhemispheric differences), to excessive interhemispheric differences in SEF waveshapes and in the M30 latencies. Signs of an enhanced excitability were present in the affected hemisphere (AH) following a cortical lesion, usually in combination with preserved hand functionality. An enhanced excitability of the unaffected hemisphere (UH) was paired with larger lesions with cortical involvement; signs compatible with an abnormal transcallosal transmission and intracortical function of inhibitory GABAergic interneurons in the AH were found subtending UH enhancement. Spared responsiveness from Brodmann's area (BA) 2 and posterior parietal areas despite an altered response from BA 3b was found in six patients, combined to high hand functionality. Present results in acute phase increase the knowledge of the mechanisms governing brain adaptation/reaction capabilities, for future efforts to establish therapeutic and rehabilitative procedures. D
Magnetoencephalography in Stroke Recovery and Rehabilitation
Frontiers in Neurology, 2016
Magnetoencephalography (MEG) is a non-invasive neurophysiological technique used to study the cerebral cortex. Currently, MEG is mainly used clinically to localize epileptic foci and eloquent brain areas in order to avoid damage during neurosurgery. MEG might, however, also be of help in monitoring stroke recovery and rehabilitation. This review focuses on experimental use of MEG in neurorehabilitation. MEG has been employed to detect early modifications in neuroplasticity and connectivity, but there is insufficient evidence as to whether these methods are sensitive enough to be used as a clinical diagnostic test. MEG has also been exploited to derive the relationship between brain activity and movement kinematics for a motor-based brain-computer interface. In the current body of experimental research, MEG appears to be a powerful tool in neurorehabilitation, but it is necessary to produce new data to confirm its clinical utility.
Ipsilateral activation of the unaffected motor cortex in patients with hemiparetic stroke
Clinical Neurophysiology, 2000
Background and purpose: Recent research has shown that following stroke patients can display ipsilateral activity re¯ecting a functional link between the undamaged hemisphere and the affected upper limb on the same side of the body. In the present study the capacity for ipsilateral activation is documented during recovery by using transcranial magnetic stimulation (TMS) and transcranial Doppler (TCD).
Somatosensory evoked magnetic fields from the primary somatosensory cortex (SI) in acute stroke
Clinical Neurophysiology, 1999
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.
Clinical Neurophysiology, 2003
Objective: Focal transcranial magnetic stimulation was used to test prospectively corticospinal excitability changes and reorganization of first dorsal interosseous (FDI) motor cortical representation in 31 patients who experienced a first ischemic stroke in the middle cerebral artery territory. All had severe hand palsy at onset. Methods: Patients were assessed clinically with the Medical Research Council, Rankin, the National Institutes of Health stroke scales and Barthel Index at days 1, 8, 30, 90, 180 and 360 after stroke. The following parameters of FDI motor evoked potential (MEPs) to focal transcranial magnetic stimulation were measured at the same delays: motor threshold, MEP amplitude, excitable cortical area, hot spot and center of gravity of FDI motor maps on affected and unaffected hemispheres. Correlations were sought between clinical and electrophysiological parameters. Results: In patients whose affected motor cortex remained excitable at day 1, motor thresholds were not significantly different between sides and were similar to those of controls. Persistence of MEP on the affected side at day 1 was a strong predictor of good recovery. If present at day 1, MEPs recorded in affected FDI were significantly smaller than of the opposite side or in normals and progressively recovered up to day 360. In these patients, area of excitable cortex remained stable throughout the entire study. At day 1, amplitudes of MEPs obtained in unaffected FDI were significantly larger than later. Between days 1 and 360, we observed a significant displacement of center of gravity of motor maps towards more frontal regions on the affected side while no change was noted on the unaffected side. Conclusions: Our data confirm the early prognosis value of transcranial magnetic stimulation in stroke. They indicate that the brain insult induces a transient hyperexcitability of the unaffected motor cortex. The evolution of FDI motor maps along the course of recovery mostly reflect corticospinal excitability changes but might also reveal some degree of brain plasticity. Most modifications observed occurred within 3 months of stroke onset.
After acute stroke several changes in cortical excitability occur involving affected (AH) and unaffected hemisphere (UH) but whether they contribute to motor recovery is still controversial. We performed transcranial magnetic stimulation mapping of several upper limb muscles over the two hemispheres in thirteen patients at 4e12 days from subcortical stroke and after 1 month. The occurrence of mirror movements (MMs) on the healthy side during contraction of paretic muscles was measured. At baseline, cortical excitability parameters over the AH decreased in comparison with controls, while excitability over the UH increased correlating with severity of motor deficits of the affected arm at baseline as well as with poor recovery. At follow-up, map parameters of the UH became closer to those of controls independently from recovery, while for the AH the number of responsive sites increased significantly. Ipsilateral motor evoked responses (iMEPs) in the affected arm were never elicited. We observed an early impairment in dexterity of the ipsilesional hand that recovered over-time but persistently differed in comparison with controls. MMs occurrence increased at baseline correlating with reduced cortical excitability of the AH as well as with increased map density over the UH. The acute increased excitability of the UH after stroke has a negative prognostic value on recovery and negatively affects motor performance of the ipsilesional hand. Moreover, the absence of iMEPs and the normalization of motor cortical excitability at follow-up indicate that the UH primary motor area does not contribute to recovery.
Specific changes in somatosensory evoked magnetic fields during recovery from sensorimotor stroke
Annals of Neurology, 2000
We studied recovery-induced changes in the responsiveness of the primary somatosensory cortex in stroke patients with sensory and/or motor symptoms. Somatosensory evoked magnetic fields, in response to median nerve stimulation, were recorded in 14 patients with their first symptomatic unilateral stroke 1 to 15 days from the first symptoms and again 2 to 3 months later. Neuronal activity at the contralateral primary somatosensory cortex was modeled with equivalent current dipoles at the peak latencies of the first two cortical deflections at about 20 msec (N1m) and at 28 to 91 msec (P1m). Twenty-three age-matched healthy volunteers, 9 of whom were tested also in serial recordings, served as control subjects. At follow-up, 6 patients showed a significant increase of P1m amplitude, whereas N1m increased only in 1. Clinical improvement of two-point discrimination ability, but not of other basic somatosensory skills, was significantly correlated with the increase of P1m. We conclude that the recovery of discriminative touch after stroke is paralleled by the growth of the P1m somatosensory evoked magnetic field deflection, and we propose that this may reflect reestablishment of lateral inhibitory functions at the primary somatosensory cortex.
Stroke, 1998
Background and Purpose —Studies of cerebral activation of motor function after ischemic stroke may enhance our understanding of the underlying mechanisms of motor functional recovery, including the role of the noninfarcted hemisphere. Methods —Eight right-handed recovering hemiparetic or hemiplegic patients were studied using functional MRI. Results were evaluated for each patient to consider individual variability in original functional organization, neuroanatomy, infarct size and extent, treatment, age, and sex. The results were also pooled as a group for comparison with a control group of eight right-handed normal subjects. Results —In six of eight stroke patients, extended activation in ipsilateral sensorimotor cortex was observed during paretic hand movements. Bilateral activation of the primary sensorimotor cortex was recorded in three of these six patients; ipsilateral activation alone was recorded in the remaining three patients. Only two patients had mild synkinesia. Furthe...