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Separating mental arithmetic from working memory: An fMRI-study
NemoImage
11, Number
5, 2000,
Part 2 of 2 Parts 1 D E ,[@
MEMORY
- LEARNING
Separating mental arithmetic from working memory: An fMRI-study Kenneth Hugdahl*$, Tormod Thomsen *, Nils Inge Landrat, Lars Ersland*$, Alf Inge SmievollS, Arvid Lundervold*$, Roger BarndonS, HIkan Sundherg*, Jarle K. Iverse& Bjarne Roscher# *University of Bergen, Bergen, Norway IUniversity of Oslo, Oslo, Norway SHaukeland University Hospital, Bergen, Norway Lesion studies have implicated the role of the left parietal cortex in mental arithmetic operations, like subtraction and addition”. Brain imaging studies on healthy individuals have however reported increased activation in both parietal and frontal cortex, and on both the left and right side’.“. A possible explanation for the discrepant findings between lesion and imaging studies may be that demands on working memory interact with number processing, which causes activation in frontal areas. In the present study, we compared brain activation in 12 healthy individuals when they viewed brief presentations of single digits during a memory task, and when they had to add two and two successive digits. Method Functional MRI was performed with a 1.5 T Siemens Vision Plus scanner equipped with 25 mT/m gradients. Initial scanning of anatomy was done with a TlW 3D FLASH pulse sequence. Thereafter, serial imaging with 90 BOLD sensitive EPI whole brain measurements were done during each of the two tasks. Each measurement of 4 s consisted of 40 axial slices (Fmthickl FOV/matrix = 90”/0.6ms/60ms/3mm/22Omm/64x64) which gives a voxel size of (3.0 x 3.4 x 3.4) mm3. The measurement interval was 6 s. Digit stimuli were presented with the MEL software for 36 trials for each ON block. There were 3 ON and 3 OFF blocks for each task, presented in a boxcar design. During the memory task, the subjects were instructed to press a button placed on their chest whenever “number 7 appeared after number 5”. During the mental arithmetic task, they were instructed to “add two and two digits, and press the button whenever the sum was 10”. Each digit was shown 2.5 s through fiber optic video glasses (Magnetic Resonance Technology, Inc.) Group as well as single-subject analyses were performed using contrasts according to the “General Linear Model” as implemented in the SPM99b analysis software package (http://www.fil.ion.ucl.ac.uk). Voxels were identified as significantly activated if they passed a height threshold of p < ,001 or p < .05, corrected for multiple comparisons. Results
and Conclusions
Within-task subtractions for the memory task showed significant bilateral activations in the occipital cortex (BA 1708). and in the left and right prefrontal cortex (BA 44/45/46), with more intense activation on the right side. There was also a smaller cluster in the right parietal lobule. The corresponding aubtractions for the mental arithmetic task also showed significant activations in the occipital and prefrontal cortex, equally intense on the left and right side. In addition, there were significant activations bilaterally in the inferior parietal lobule (BA 39/40). Between-task subtractions showed residual activation bilaterally in the parietal cortex, and in the left prefrontal cortex during the mental arithmetic task. During the memory task, residual activation was observed in the prefrontal cortex. predominantly on the right side. For both tasks, there were very few response errors. We conclude that prefrontal activation during a mental arithmetic task is driven by demands for keeping information in working memory during number processing. Parietal lobe activation is more directly related to mental arithmetic and number processing. which also fit with previous lesion data. Working Mental
memory
task
arithmetic
task
References I ) Leaak, M.D. ( 1994). 2) Chochon. F., Cohen. 3) Dehaene, S., Spelke.
assessment. New York: Oxford University Press. L., van de Moortele, P.F.. Dehane, S. .I. Cogn. Nrurosci., 1999, II, 617-630. E., Stanescu,R., Pincl. P. et al., Science. 1999. 284. 970-974.
Nrurops~chologictrl
S384
11, Number
5, 2000,
Part 2 of 2 Parts 1 D E ,[@
MEMORY
- LEARNING
Separating mental arithmetic from working memory: An fMRI-study Kenneth Hugdahl*$, Tormod Thomsen *, Nils Inge Landrat, Lars Ersland*$, Alf Inge SmievollS, Arvid Lundervold*$, Roger BarndonS, HIkan Sundherg*, Jarle K. Iverse& Bjarne Roscher# *University of Bergen, Bergen, Norway IUniversity of Oslo, Oslo, Norway SHaukeland University Hospital, Bergen, Norway Lesion studies have implicated the role of the left parietal cortex in mental arithmetic operations, like subtraction and addition”. Brain imaging studies on healthy individuals have however reported increased activation in both parietal and frontal cortex, and on both the left and right side’.“. A possible explanation for the discrepant findings between lesion and imaging studies may be that demands on working memory interact with number processing, which causes activation in frontal areas. In the present study, we compared brain activation in 12 healthy individuals when they viewed brief presentations of single digits during a memory task, and when they had to add two and two successive digits. Method Functional MRI was performed with a 1.5 T Siemens Vision Plus scanner equipped with 25 mT/m gradients. Initial scanning of anatomy was done with a TlW 3D FLASH pulse sequence. Thereafter, serial imaging with 90 BOLD sensitive EPI whole brain measurements were done during each of the two tasks. Each measurement of 4 s consisted of 40 axial slices (Fmthickl FOV/matrix = 90”/0.6ms/60ms/3mm/22Omm/64x64) which gives a voxel size of (3.0 x 3.4 x 3.4) mm3. The measurement interval was 6 s. Digit stimuli were presented with the MEL software for 36 trials for each ON block. There were 3 ON and 3 OFF blocks for each task, presented in a boxcar design. During the memory task, the subjects were instructed to press a button placed on their chest whenever “number 7 appeared after number 5”. During the mental arithmetic task, they were instructed to “add two and two digits, and press the button whenever the sum was 10”. Each digit was shown 2.5 s through fiber optic video glasses (Magnetic Resonance Technology, Inc.) Group as well as single-subject analyses were performed using contrasts according to the “General Linear Model” as implemented in the SPM99b analysis software package (http://www.fil.ion.ucl.ac.uk). Voxels were identified as significantly activated if they passed a height threshold of p < ,001 or p < .05, corrected for multiple comparisons. Results
and Conclusions
Within-task subtractions for the memory task showed significant bilateral activations in the occipital cortex (BA 1708). and in the left and right prefrontal cortex (BA 44/45/46), with more intense activation on the right side. There was also a smaller cluster in the right parietal lobule. The corresponding aubtractions for the mental arithmetic task also showed significant activations in the occipital and prefrontal cortex, equally intense on the left and right side. In addition, there were significant activations bilaterally in the inferior parietal lobule (BA 39/40). Between-task subtractions showed residual activation bilaterally in the parietal cortex, and in the left prefrontal cortex during the mental arithmetic task. During the memory task, residual activation was observed in the prefrontal cortex. predominantly on the right side. For both tasks, there were very few response errors. We conclude that prefrontal activation during a mental arithmetic task is driven by demands for keeping information in working memory during number processing. Parietal lobe activation is more directly related to mental arithmetic and number processing. which also fit with previous lesion data. Working Mental
memory
task
arithmetic
task
References I ) Leaak, M.D. ( 1994). 2) Chochon. F., Cohen. 3) Dehaene, S., Spelke.
assessment. New York: Oxford University Press. L., van de Moortele, P.F.. Dehane, S. .I. Cogn. Nrurosci., 1999, II, 617-630. E., Stanescu,R., Pincl. P. et al., Science. 1999. 284. 970-974.
Nrurops~chologictrl
S384