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Magnetoencephalographic Representation of the Sensorimotor 1649 J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.74.12.1649 on 24 November 2003. Downloaded from PAPER Magnetoencephalographic representation of the sensorimotor hand area in cases of intracerebral tumour M Oishi, M Fukuda, S Kameyama, T Kawaguchi, H Masuda, R Tanaka ............................................................................................................................... J Neurol Neurosurg Psychiatry 2003;74:1649–1654 Objective: To assess the clinical value of magnetoencephalography (MEG) in localising the primary hand motor area and evaluating cortical distortion of the sensorimotor cortices in patients with intracerebral tumour. Methods: 10 normal volunteers (controls) and 14 patients with an intracerebral tumour located around the central region were studied. Somatosensory evoked magnetic fields (SEFs) following median nerve stimulation, and movement related cerebral magnetic fields (MRCFs) following index finger extension, were measured in all subjects and analysed by the equivalent current dipole (ECD) method to ascertain the See end of article for authors’ affiliations neuronal sources of the primary sensory and motor components (N20m and MF, respectively). These ECD ....................... locations were defined as the primary hand sensory and motor areas and the positional relations between these two functional areas in controls and patients were investigated. Correspondence to: Dr M Oishi, Department of Results: The standard range of ECD locations of MF to N20m was determined in controls. In 11 of the 14 Neurosurgery, National patients, MRCFs could identify the primary motor hand area. ECD locations of MF were significantly closer Nishi-Niigata Central to the N20m in the medial-lateral direction in patients than in controls. In patients with a tumour located Hospital, 1-14-1 Masago, Niigata 950-2085, Japan; below the sensorimotor hand area, relative ECD locations of MF to N20m moved anteriorly over the [email protected] standard range determined in the control subjects. These MEG findings correlated well with radiological tumour locations. The mean estimated ECD strength of MF was significantly lower in patients than in Received 4 March 2003 controls. In revised form 17 April 2003 Conclusions: MRCF was useful in localising the primary motor hand area in patients with intracerebral Accepted 25 April 2003 tumour. The relative ECD locations of MF to N20m describe the anatomical distortion of the sensorimotor ....................... cortex. copyright. arly studies based on direct electrical stimulation of the sensorimotor areas in patients with intracerebral tumours. To cerebral cortices of awake neurosurgical patients estab- do this, we first determined the standard positional relation lished the somatotopic arrangement of the human motor between human hand motor and sensory areas using MEG in E 1 and sensory cortices. Recent neuroimaging modes such as normal subjects. We then recorded MRCFs from the patients functional magnetic resonance imaging (fMRI),2–7 positron with intracerebral tumours and evaluated whether the MEG emission tomography (PET),89and magnetoencephalography relation between hand motor and sensory areas corresponded (MEG)10–17 have allowed the non-invasive identification of to the anatomical findings in these patients. these functional areas and have confirmed the previously described sensory and motor homunculi. The hand area of METHODS http://jnnp.bmj.com/ each homunculus has been examined in relation to the Subjects anatomically characteristic landmark ‘‘knob’’ struc- Ten right handed normal volunteers (eight men, two women; 248912141618 ture. However, a direct relation between sensory age 20 to 41 years, mean 31.5) and 14 patients with and motor hand areas has never been described. intracerebral tumours adjacent to the sensorimotor area MEG is a non-invasive way of measuring extracranial (six men, eight women; age 20 to 66 years, mean 38.6) 19 magnetic fields generated by intraneuronal electric currents. participated in the study. Patients were evaluated for surgical As magnetic fields are relatively unaffected by the different treatment between June 2000 and January 2002. Thirteen of electrical conductivities of the brain, cerebrospinal fluid, the 14 patients were treated surgically. The final pathological on September 29, 2021 by guest. Protected skull, and skin, MEG can accurately localise the origin of diagnoses in these 13 patients were glial tumour (n = 8), intraneuronal electric currents that contribute to extracranial cavernous angioma (n = 4), and metastatic tumour (n = 1). magnetic fields by fitting to an equivalent current dipole The remaining patient with radiologically diagnosed caver- (ECD) model.20 The accuracy of MEG localisation has been nous angioma did not undergo surgery. Informed consent shown to be within a few millimetres of that obtained by was obtained from all controls and patients after the direct cortical mapping.21 The clinical value of MEG has been experimental procedures were explained. reported mainly in the identification of somatosensory, auditory, and visual areas in neurosurgical patients.11–13 15 22–24 Magnetoencephalography For the identification of the primary motor hand area by MEG recording was done in a magnetically shielded room at MEG, the movement related cerebral magnetic field (MRCF) the National Nishi-Niigata Central Hospital, Niigata, Japan. A generated by spontaneous finger movements is used.25–27 However, only a few investigators have reported clinical applications of the MRCF, mainly in patients with brain ................................................................ 17 28–30 tumours. Abbreviations: ECD, equivalent current dipole; MEG, In the present study, our main aim was to clarify the magnetoencephalography; MRCF, movement related cerebral magnetic clinical ability of MEG to evaluate the cortical distortion of field; SEF, somatosensory evoked magnetic field www.jnnp.com 1650 Oishi, Fukuda, Kameyama, et al J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.74.12.1649 on 24 November 2003. Downloaded from commercially available helmet shaped neuromagnetometer (Neuromag 204; 4D-Neuroimaging, San Diego, California, USA) consisting of 204 planar-type gradiometers was used. This gradiometer configuration is known to detect the largest signal at the site on the head immediately above the current source.31 Each subject was placed in a comfortable sitting position. Head position with respect to the helmet was determined using four indicator coils placed on the scalp that were referenced to three anatomical fiducial markers (nasion and bilateral preauricular points). The recorded data were analysed by fitting each component to a single ECD model in the three dimensional reference frame determined by the fiducial markers. ECDs with a goodness of fit better than 90% were accepted and were superimposed onto the patient’s three dimensional brain magnetic resonance (MR) images obtained with a 1.5 Tesla system (MAGNEX Epios15; Figure 1 The finger movement pad. When the small plate fixed to the Shimazu, Kyoto, Japan). index finger cuts off the light emitting diode because of finger extension, an input is triggered. Somatosensory evoked magnetic fields A median nerve was stimulated sequentially with an using a specific trigger board (finger movement pad; 4D- electrical square wave of 0.2 ms duration and 2.8 Hz neuroimaging) (fig 1). The input is triggered by this board repetition rate. The 350 ms period of a total of 200 epochs, and is averaged when the subject extends the index finger including a 50 ms prestimulus period for baseline setting, appropriately. Each subject was instructed to move the finger was averaged. Data were sampled at 1000 Hz with the low at self paced intervals of about five seconds with a sharp pass filter set at 300 Hz and analysed with the high pass filter movement that begins after the finger muscles are totally set at 10 Hz. The primary sensory area of the median nerve relaxed, and to avoid blinking and other eye movements was determined by localisation of an ECD for N20m, which is during the task. A total of 70 to 100 epochs and the 1000 ms a well known component indicating the earliest cortical prestimulus and 1000 ms poststimulus periods were aver- 32 response after stimulus. aged. The first 200 ms of the prestimulus period was used to obtain baseline data. Data were sampled at 500 Hz with the Movement related cerebral magnetic fields low pass filter set at 160 Hz and analysed with the bandpass The standard method for recording MRCFs has been filter set between 1 and 35 Hz. The MRCF waveform consists described in detail elsewhere.27 We modified the method of several major components (fig 2) for which functional copyright. http://jnnp.bmj.com/ on September 29, 2021 by guest. Protected Figure 2 Identification of the motor hand area by the movement related cerebral magnetic field (MRCF) in a normal volunteer. Upper panels: a typical waveform (left) and whole scalp waveforms (right) of MRCF in response to a right index finger extension task. RF, readiness field; MF, motor field; MEF- 1, movement evoked field 1. Lower left panel: isocontour map of the MF shows a clear dipole pattern. Lower middle and right panels: MF dipole superimposed onto axial (middle) and sagittal (right) MR images allows estimation of the neuronal source at the characteristic structure in the anterior wall of the central sulcus. The square and tail represent the dipole location and orientation,
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