Comparison of regional cerebral blood flow (rcbf) with transcranial
magnetic stimulation (tms) at different forces.
Dettmers, Christian, Michael C Ridding, Klaus M Stephan, Roger N
Lemon, John C Rothwell, Richard Sj Frackowiak.
Wellcome Department of Cognitive Neurology, Leopold M[umlaut]uller
Functional Imaging Laboratory, Institute of Neurology, London, UK;
MRC Human Movement and Balance Unit, Institute of Neurology, London,
UK; Sobell Department of Neurophysiology, Institute of Neurology,
APStracts 3:0191A, 1996.
This study's objective was to investigate regional cerebral blood flow
(rCBF) within the primary motor cortex (M1) and to compare it with
thresholds of transcranial magnetic stimulation (TMS) and
electromyographic (EMG) recordings during exertion of different force
levels with the right index finger. Quantitative EMG recordings, TMS
and positron emission tomography (PET) scans were performed while 5
and 6 volunteers respectively pressed a Morse-key repetitively or
with constant force with the right hand at five different force
levels: 5%, 10%, 20%, 40% and 60% of the individual's maximum
voluntary contraction (MVC). While at 5% MVC muscle activity was
restricted to the first dorsal interosseus muscle (FDI), superficial
finger flexors and extensors, there was progressive involvement of
proximal muscles during finger flexion with increasing force. rCBF
increased logarithmically in the contralateral M1 with increasing
force. In ipsilateral M1 rCBF decreased at 5% MVC and then increased
logarithmically at higher force levels. TMS thresholds in the
contralateral hemisphere declined logarithmically to reach a plateau
at high force levels. The threshold in the ipsilateral hemisphere
decreased slightly at high force levels. The logarithmic increase of
rCBF and decrease of TMS thresholds in the contralateral hemisphere
suggest related underlying physiological phenomena; increased
cortical synaptic activity and increased excitability. It is
suggested that the pronounced ipsilateral rCBF alterations reflect
transcallosal inhibition and are more prominent during repetitive
movements (as used in the PET study) than during the generation of a
constant force (as exerted during TMS).
Received 21 March 1995; accepted in final form 27 February 1996.
APS Manuscript Number A306-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96