Magnetic measurements of human cerebellar activity- noninvasive study of cerebro-cerebellar interaction

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The aims of this study are to elucidate physiological mechanisms of the four components in cerebellar activity and functional relations between cerebrum and cerebellum by recording magnetic somatosensory and cerebellar activity simultaneously. Specifically, we attempted to define the cerebellar input from periphery, ascending connection from the cerebellum to cerebral cortex and descending input from the cortex to cerebellum. We obtained the following results.1.Somatotopic representations in the cerebellumSomatotopic representations in the cerebellum have been well established in animal studies. We examined whether similar representations are present in humans by delivering electric stimuli over 6 points in peripheral nerves of upper and lower limbs and discrete representations are not found. The results suggest that the spatial resolution of MEG is not sufficient for studying somatotopic representations in the human cerebellum.2.Steady state response from the cerebellumBy delivering rhythmic 8 Hz and 16 Hz stimulation of the median nerve, steady state response from the cerebellum was elicited to 8 Hz stimulus.3.Source estimation of the cerebellar response by multi-dipole estimation methodWe were able to estimate cerebellar sources in only one third of the cases by multi-dipole estimation method. This is due to strong signals from SI which overshadow the cerebellar response and to low signal-to-noise ratio influenced by environmental magnetic noise.