Magnetoencephalography And Magnetic Source Imaging In The Somatosensory, Auditory, And The Epileptic Focus Localization

Objective To investigate the gender differences of M20 response in latency, amplitude and location of primary somatosensory cortex in healthy subjects by magnetoencephalography. Methods forty healthy subjects volunteers for the study. There were 20 males and 20 females, mean age 40.5 ± 18.5 years old. The bilateral median nerves were stimulated with bipolar surface electrodes at the wrist. Constant current pulses 0.3ms.The interstimulus interval (ISI) was 0.5s. Magnetic resonance images (MRIs) of head were acquired by spoiled gradient recalled sequence at 1.5T unit, slices of 1.5mm thinkness, with no space. The brain primary somatosensory responses were evaluated by equivalent current dipoles (ECDs). Combining the M20 gained by MEG with co-registered MRI, we canget MSI. Results : According to the differences in latency after giving the electrical stimuli, we can get the M20, M35 and M60 somatosensory evoked fields from the primary somatosensory cortex. We only analyzed the gender difference of M20 response in latency, amplitudes and location because M35 and M60 were apt to affect by interstimulus interval. The results as follows (l)M20 latency in left and right hemisphere are 20.6±1.0ms,20.7± 1.2ms in males and 20.1 ± 0.9ms, 20.2+0.9ms in females. There is no significant difference between males and females(P>0.05). (2) M20 amplitudes in left and right hemisphere in males are 23.6+ 11.2nAm , 25.4+ 11.2nAm in males and 25.8 + 10.5nAm , 27.6+7.8nAm in females. M20 source strength was not different in the isolateral hemisphere between males and females(P>0.05). (3)There is significant difference in X axial in left hemisphere in location of M20 between males and females(P<0.05 =, The higher x-coordinate values in males than females'. There are no significant differences in x axial in right hemisphere and y-,z-coordinate values of bilateral hemispheres (P>0.05).(4) MSI shows all the peak value of M20 localized in central postcentral gyrus.Conclusion M20 latency, amplitude and location of primary somatosensory cortex in males and females could be defined by MEG MSI shows the peak values of M20 were localized in postcentral gyrus of somatosensory cortex of hand area..