Brain-Behavior Relationships: Evidence from Practice Effects in Spatial Stimulus-Response Compatibility. 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.
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