Muscle afferent inputs from the hand activate human cerebellum sequentially through parallel and climbing fiber systems.
OBJECTIVE
Spatio-temporal response characteristics of the human cerebellum to median nerve stimulation (MNS) were studied with the use of a whole-head magnetoencephalographic (MEG) system covering the cerebellum and upper cervical spine.


METHODS
Neuromagnetic responses from the cerebellum were recorded following electric stimulation of the right median nerve in 12 subjects. In 6 out of 12 subjects, the responses to the left median nerve and to the right index or middle finger stimulation were also recorded.


RESULTS
The medial part of the cerebellum (spinocerebellum) was activated by MNS. In contrast, there were no responses from the cerebellum to the finger stimulation, suggesting that muscle afferent inputs are the source of cerebellar activation for MNS. The cerebellar responses consisted of 3 or 4 components of alternating polarity within 90 ms post-stimulus: the current direction for the first component was from the depth to the surface of the anterior lobe.


CONCLUSIONS
From the timing and current direction, we speculate that the 4 components reflect, respectively, (1) excitatory postsynaptic potentials (EPSPs) of granule cells, (2) Purkinje cell EPSPs at the distal dendrites driven by parallel fibers, (3) Purkinje cell EPSPs at the soma and the proximal dendrites mediated by climbing fibers and (4) second Purkinje cell EPSPs at the distal dendrites driven by parallel fibers.


CONCLUSIONS
We first visualized serial activation of the human spinocerebellum following MNS noninvasively with MEG.
Human Information Systems Laboratory, Tokyo Office, Kanazawa Institute of Technology, 6-8-7 Akasaka, Minato-ku, Tokyo 107-0052, Japan. ihashi@ael.kanazawa-it.ac.jp
Isao
I
Hashimoto
Tomoaki
T
Kimura
Masato
M
Tanosaki
Yoshinobu
Y
Iguchi
Kensuke
K
Sekihara
D000328:Adult; D002531:Cerebellum / Q000166:cytology* / Q000502:physiology*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005260:Female; D006225:Hand / Q000294:innervation; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation*; D009412:Nerve Fibers / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology*; D011689:Purkinje Cells / Q000502:physiology; D011930:Reaction Time / Q000502:physiology