Time, frequency and volumetric differences of high-frequency neuromagnetic oscillation between left and right somatosensory cortices.

Hemispheric specialization or asymmetry in higher brain functions such as language is well accepted. This study was designed to quantitatively determine if the hemispheric asymmetry is measurable in the somatosensory system. Twenty-two participants were studied with magnetoencephalography (MEG) while their left and right index fingers were stimulated in randomized order. The finger representation in the cortex was volumetrically localized using a wavelet based beamformer. The strength of functional activity was estimated with an intensity volume while the waveforms of the virtual sensors were computed with a virtual sensor placed in the center of localized finger area. The results showed that the latency of the first identifiable response evoked by left finger stimulation was significantly shorter than that evoked by right finger stimulation (p<0.05). The left somatosensory cortex generated higher frequency neuromagnetic signals than did the right somatosensory cortex (p<0.05). Moreover, the volume of neuromagnetic activation elicited by right finger stimulation was significantly larger than that elicited by left finger stimulation in males (p<0.001). The neuromagnetic activation revealed by virtual sensors was more consistent than that revealed by physical sensors across participants. We conclude that neuromagnetic activities in the left and right somatosensory cortices have significant differences in terms of response latency, oscillation frequency and activation volume in high-frequency neuromagnetic signals. An investigation of the hemispheric specific features of neuromagnetic activation in the somatosensory cortex lays a foundation for the study of psychophysiologic asymmetries in the brain.