Study of neuronal plasticity in children by biomagnetism

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Neuronal plasticity is that the damage to the neuron will recover and/or a cirtain brain region will contain other function. The plasticity will occur more dramatically in immature brain. The purpose of this project is to determine the function of injured brain in childhood and whether some area of the brain other than original region possess functioning. We evaluated the distribution of the brain function in cortical dysplasias using magnetoencephalography (MEG).The subjects included 2 cases of focal cortical dysplasia, 2 cases of band heterotopia, each one case of hemimegalencephaly and periventricular nodular heterotopia, 2 cases of hemispheric cortical dysplasia, and other 3 cases of cartical displasia, Sensory evoked fields (SEF) induced by left and right median nerve stimulation were recorded in a magnetically shielded room using a 122-channel whole head MEG system (Neuromag-122, Neuromag Ltd.)The central sulci were identified according to the signal sourse of SEF in 6 out of the 11 cases cortical dysplasia and abnormal patterm of gyri around the central sulcus.In the 4 cases, the latency, amplitude and direction of the electric current of N20m showed abnormal. The abnormal direction of the electric current implies that the fomation of neurons were distorted during neuronal migration period. In cases of migration disorders, the electrophysiological parameters show variable changes. This heterogeueity is likely due to distortion of neuronal arrangement during migrating period.Signal sourse analysis of epileptic activity in cases of hemispheric cortical dysplasia with abnormal pattern of gyri and sulci decreased volume in the affected side. Epileptic activity was found in the affected hemisphere in 2 cases. In one case, another epileptic activity was also observed in the non-affected hemisphere in which EEG could not detected epileptic discharges. The MEG has superiority for detection of scarce epileptic activity.