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

本研究旨在通过同时记录磁体感和小脑活动，阐明小脑活动的四种成分的生理机制以及大脑和小脑之间的功能关系。具体来说，我们试图定义来自外周的小脑输入，从小脑到大脑皮层的上升连接和从皮层到小脑的下降输入。我们得到了以下结果。小脑中的体位表征小脑中的体位表征已经在动物研究中得到了很好的证实。我们通过对上肢和下肢周围神经的6个点进行电刺激，研究了人类是否存在类似的表征，没有发现离散表征。结果表明，脑磁图的空间分辨率不足以研究人类小脑的体位表征。通过对正中神经进行8赫兹和16赫兹的有节奏刺激，可引起小脑对8赫兹刺激的稳态反应。用多偶极子估计方法估计小脑响应源我们仅能在三分之一的病例中用多偶极子估计方法估计小脑响应源。这是由于来自SI的强信号掩盖了小脑的反应，以及受环境磁噪声影响的低信噪比。

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.