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The brain areas involved in the executive control of task switching as revealed by PET
ABSTRACTS
The Brain Areas Involved in the Executive Control of Task Switching as Revealed by PET E. J. Lauber 1, D. E. Meyer 2, J. E. Evans 2, J. Rubinstein 3, L. Gmeindl 2, L. Junck 2, R. A. Koeppe 2
1=University of Georgia, 2=University of Michigan, 3=University of California, Davis. The executive mental processes needed to switch between two simple tasks were examined using both behavioral and PET methodologies. It was discovered that relative to performing single tasks continuously (i.e. without switching), certain additional brain areas were activated during task alternation, including the left dorsolateral prefrontal cortex, the left anterior premotor cortex, and the anterior cingulate. It is proposed these areas subserve executive-like operations already proposed by us and other cognitive researchers (e.g. ref 1).
Method Both behavioral and PET data were collected for each of ten subjects (5 male/5 female: age 21-30 yrs old) in each of five conditions (2 scans each). Two Single-Task conditions required subjects to press an assigned key on a three-button mouse to either the Color or Shape of visually presented stimuli (colors=red, green, blue; shapes=square, triangle, cross). Two Dual-Task conditions required subjects to alternate between these two tasks. A Baseline condition required only a middle button keypress to sequentially presented black circles. Stimulus presentation rate was held constant (2 items per 2.25 sec) and subjects responded with the first three fingers of their right hand. Subjects received one training session the day before and written informed consent was obtained. Condition order was counterbalanced across subjects. 60 second PET scans were acquired after a 39 mCi bolus of O15-water was administered through an intravenous catheter. Analysis of the PET data consisted of a modified SPM procedure (ref 2, 3). Images were transformed into a standard anatomical space (ref 4) and subtractions were made after appropriate averaging, t-scores have been adjusted for multiple comparisons (Bonferroni corrected).
Results Previous behavioral work has confirmed that task switching requires executive-like operations distinct from taskspecific processes. Subtraction of the activation images obtained in the average of the Single-Task conditions from the average of the Dual-Task conditions revealed peak activation foci in left dorsolateral prefrontal cortex (significant activation in Brodmann Areas 9,44,45,46; peak t-score=7.04; p<.001), left posterior parietal cortex (BA 7, 39, 40; t-6.71; p<.001), left premotor cortex (BA 6; t=5.03; p<.01), right cerebellum (t=4.85; p<.01) and left anterior cingulate gyms (BA 32; t=4.30; p<. 10). Subtraction of the Baseline condition from the average of the Single-Task conditions revealed significant activation in left inferior parietal lobule (BA 40; t=7.00; p<.001), left precentral gyms (BA 4; t=6.48; p<.001), left superior parietal lobule (BA 7, t=5.50; p<.001), left cerebellum (t=5.11; p<.01; t=4.45; p<.05), left inferior occipital gyms (BA 18; t=4.61; p<.01), and right and left inferior and middle occipital gyri (BA 18, 19; t=4.22 (right), t=4.20 (left); p<.10).
Conclusions The regions activated by the Single-Task conditions can be understood as representing a sequence of operations~ such as color or shape discrimination (lateral occipital cortex), selection of the appropriate response in space or body-centered coordinates (parietal cortex), and execution of the chosen response (precentral gyms). The additional regions activated by Dual-Task (switching) performance may reflect processes engaged in context updating or task designation (left prefrontal cortex), accuracy monitoring and response inhibition (anterior cingulate cortex), and movement preparation (premotor cortex). These inferences are consistent with longstanding claims that regions of the frontal lobes are differentially involved in higher-level, executive-like operations. 1. 2. 3. 3.
Meyer, D. E. & Kieras, D. E. PsychologicalRev. In Press. Minoshima, S., Berger, K. L., Lee, K. S. & Minam, M. J. Nucl.Med. 1992, 33; 1579. Minoshima, S. et al., ibid. 1993, 34; 322. Talairach, J., Tournoux, P. 1988.
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The Brain Areas Involved in the Executive Control of Task Switching as Revealed by PET E. J. Lauber 1, D. E. Meyer 2, J. E. Evans 2, J. Rubinstein 3, L. Gmeindl 2, L. Junck 2, R. A. Koeppe 2
1=University of Georgia, 2=University of Michigan, 3=University of California, Davis. The executive mental processes needed to switch between two simple tasks were examined using both behavioral and PET methodologies. It was discovered that relative to performing single tasks continuously (i.e. without switching), certain additional brain areas were activated during task alternation, including the left dorsolateral prefrontal cortex, the left anterior premotor cortex, and the anterior cingulate. It is proposed these areas subserve executive-like operations already proposed by us and other cognitive researchers (e.g. ref 1).
Method Both behavioral and PET data were collected for each of ten subjects (5 male/5 female: age 21-30 yrs old) in each of five conditions (2 scans each). Two Single-Task conditions required subjects to press an assigned key on a three-button mouse to either the Color or Shape of visually presented stimuli (colors=red, green, blue; shapes=square, triangle, cross). Two Dual-Task conditions required subjects to alternate between these two tasks. A Baseline condition required only a middle button keypress to sequentially presented black circles. Stimulus presentation rate was held constant (2 items per 2.25 sec) and subjects responded with the first three fingers of their right hand. Subjects received one training session the day before and written informed consent was obtained. Condition order was counterbalanced across subjects. 60 second PET scans were acquired after a 39 mCi bolus of O15-water was administered through an intravenous catheter. Analysis of the PET data consisted of a modified SPM procedure (ref 2, 3). Images were transformed into a standard anatomical space (ref 4) and subtractions were made after appropriate averaging, t-scores have been adjusted for multiple comparisons (Bonferroni corrected).
Results Previous behavioral work has confirmed that task switching requires executive-like operations distinct from taskspecific processes. Subtraction of the activation images obtained in the average of the Single-Task conditions from the average of the Dual-Task conditions revealed peak activation foci in left dorsolateral prefrontal cortex (significant activation in Brodmann Areas 9,44,45,46; peak t-score=7.04; p<.001), left posterior parietal cortex (BA 7, 39, 40; t-6.71; p<.001), left premotor cortex (BA 6; t=5.03; p<.01), right cerebellum (t=4.85; p<.01) and left anterior cingulate gyms (BA 32; t=4.30; p<. 10). Subtraction of the Baseline condition from the average of the Single-Task conditions revealed significant activation in left inferior parietal lobule (BA 40; t=7.00; p<.001), left precentral gyms (BA 4; t=6.48; p<.001), left superior parietal lobule (BA 7, t=5.50; p<.001), left cerebellum (t=5.11; p<.01; t=4.45; p<.05), left inferior occipital gyms (BA 18; t=4.61; p<.01), and right and left inferior and middle occipital gyri (BA 18, 19; t=4.22 (right), t=4.20 (left); p<.10).
Conclusions The regions activated by the Single-Task conditions can be understood as representing a sequence of operations~ such as color or shape discrimination (lateral occipital cortex), selection of the appropriate response in space or body-centered coordinates (parietal cortex), and execution of the chosen response (precentral gyms). The additional regions activated by Dual-Task (switching) performance may reflect processes engaged in context updating or task designation (left prefrontal cortex), accuracy monitoring and response inhibition (anterior cingulate cortex), and movement preparation (premotor cortex). These inferences are consistent with longstanding claims that regions of the frontal lobes are differentially involved in higher-level, executive-like operations. 1. 2. 3. 3.
Meyer, D. E. & Kieras, D. E. PsychologicalRev. In Press. Minoshima, S., Berger, K. L., Lee, K. S. & Minam, M. J. Nucl.Med. 1992, 33; 1579. Minoshima, S. et al., ibid. 1993, 34; 322. Talairach, J., Tournoux, P. 1988.
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