The cerebral structures participating in motor preparation in humans: a
positron emission tomography study.
Deiber, Marie-Pierre, Vicente Iba[circumflex]uez, Norihiro Sadato, Mark
Hallett.
Human Motor Control Section, Medical Neurology Branch, National Institute
of Neurological Disorders and Stroke, National Institutes of Health, Bethesda,
MD 20892-1428, USA, INSERM (Institut National de la Sant[umlaut]a et de la
Recherche M[umlaut]adicale); CERMEP, 59 Boulevard Pinel, 69003 Lyon,
France.
APStracts 2:0264N, 1995.
SUMMARY AND CONCLUSIONS
1. Using positron emission tomography (PET) and measurement of regional
cerebral blood flow (rCBF) as an index of cerebral activity, we investigated
the central processing of motor preparation in thirteen healthy volunteers. 2.
We used a motor reaction-time paradigm with visual cues as preparatory and
response signals. A preparatory stimulus (PS) provided either full, partial or
no information regarding two variables of a forthcoming right finger movement:
finger type (index or little finger) and movement direction (abduction or
elevation). After a variable delay period, a response stimulus (RS) prompted
the movement. A condition was also tested in which the subject could freely
select any of the four possible movements during the preparation period
("Free" condition). The timing of events was designed to emphasize the motor
preparation phase over the motor execution component during the scanning time
of one minute. 3. Distinct preparatory processes, which depended on the
information contained in the PS, were demonstrated by significant differences
in reaction time between conditions. The reaction time was shorter in the
"Full" and "Free" conditions, intermediate in the two partial information
conditions ("Finger" and "Direction"), and longer when no preparatory
information was available ("None" condition). Conversely, movement time and
movement amplitude were similar between conditions, establishing the constancy
of the motor executive output. 4. In comparison with a "Rest" condition, which
had matched visual inputs, the different conditions of motor preparation were
associated with increased rCBF in a common set of cerebral regions: the
contralateral frontal cortex (sensorimotor, premotor, cingulate, and
supplementary motor cortex), the contralateral parietal association cortex
(anterior and posterior regions), the ipsilateral cerebellum, the
contralateral basal ganglia, and the thalamus. This observation substantiates
the participation of those cerebral structures in the preparation for
movement. Furthermore, the similarity of the activated areas among the
different conditions compared with the "Rest" condition suggests a single
anatomical substrate for motor preparation, independent of the movement
information context. 5. Differing amounts of movement information contained in
the PS affected rCBF changes in some cerebral regions. In particular, the rCBF
in the anterior parietal cortex (Brodmann's area 40) was significantly larger
in each of the Full, Finger and Direction conditions, individually, compared
with the None condition. This observation supports the hypothesis that the
anterior parietal association cortex plays a major role in the use of visual
instructions contained in the PS for partial or complete preparation to
perform a motor act. On the other hand, the posterior parietal association
cortex (Brodmann's area 7) was more activated in the Finger, Direction and
None conditions than in the Full condition. This increased activity with
restricted advance information suggests that the posterior region of the
parietal cortex is concerned with correct movement selection on the basis of
enhanced spatial attention to the RS. 6. In contrast with the parietal cortex,
the secondary motor areas (i.e, premotor cortex, cingulate cortex, and
supplementary motor area) showed similar activity regardless of the degree of
preparation allowed by the advance visual information. Thus, the parietal
cortex may play a more crucial role than the secondary motor areas in
integrating visual information in preparation for movement. 7. The effect on
brain activity of the internal (self-generated) versus the external (cued)
mode of movement selection was assessed by comparing the Free and Full
conditions, the preparatory component being matched in the two conditions. The
anterior part of the supplementary motor area (pre-SMA) was the main area
preferentially involved in the internal selection of movement, independently
of motor preparation processes.
Received 17 March 1995; accepted in final form 22 August 1995.
APS Manuscript Number J179-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.