Brain-Behavior Relationships: Evidence from Practice Effects in Spatial
Iacoboni, Marco, Roger P. Woods, John C. Mazziotta.
Division of Brain Mapping, Dept. of Neurology (MI, RPW, JCM), Psychology
(MI), Pharmacology (JCM), and Radiological Sciences (JCM), Reed Neurological
Research Center, Neuropsychiatric Institute, UCLA School of Medicine,
Laboratory of Nuclear Medicine, 710 Westwood Blvd., Los Angeles, CA 90095.
APStracts 3:0035N, 1996.
SUMMARY AND CONCLUSIONS
1. We measured relative cerebral blood flow (rCBF) changes with positron
emission tomography (PET) and H 2 15 O in six normal subjects repeatedly
performing a spatial stimulus-response compatibility task. Subjects had two
motor response conditions. They were instructed to respond with the left hand
to a left visual field light stimulus and with the right hand to a right
visual field light stimulus (compatible condition), and with the right hand to
a left visual field light stimulus and with the left hand to a right visual
field light stimulus (incompatible condition). Six rCBF measurements per
condition were performed in each subject. 2. Reaction times were faster
(p<0.0005) in the compatible (287 ms) rather than the incompatible (339 ms)
condition (spatial stimulus-response compatibility effect). A bilateral
increase (p<0.05) in rCBF in the superior parietal lobule of the two
hemispheres was observed during the incompatible condition when compared to
the compatible one. No rCBF decreases were observed. Reaction times correlated
(p<0.0001) with the rCBF in the two activated superior parietal lobule areas.
3. Reaction times decreased with practice according to a linear trend
(p<0.05). Practice-related linear rCBF increases (p<0.05) were observed in the
dorsolateral prefrontal, premotor, and primary motor cortex of the left
hemisphere. No significant rCBF decreases were observed. 4. Practice did not
affect the spatial stimulus-response compatibility effect. A parallel
shortening of reaction times was observed in both compatible and incompatible
conditions, in both left and right response hands, and in both left and right
visual fields. Accordingly, when rCBF was analyzed, the spatial stimulus-
response compatibility by practice interaction did not show any significant
activated area. 5. These findings suggest that the two activated areas in the
left and right superior parietal lobules subserve the mapping of the visual
stimulus spatial attributes onto the motor response spatial attributes and
that the rCBF increases in the incompatible response condition represent the
more complex computational re-mapping required when stimuli and response do
not match spatially. 6. The dorsolateral prefrontal, premotor and motor rCBF
linear increases in the left hemisphere seem to reflect the effect of practice
on cortical processes common to both compatible and incompatible response
conditions. These cortical processes presumably strengthen the links between
stimuli and responses under different stimulus-response compatibility
conditions. The lateralization of the rCBF increases suggests a left
hemisphere superiority in these processes.
Received 20 September 1995; accepted in final form 30 January 1996.
APS Manuscript Number J624-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 14 February 96