Cortical mechanisms of human imitation

Science

Volumn 286, Issue 5449, 1999, Pages 2526-2528

  Iacoboni, Marco ^a,b   Woods, Roger P ^a,b   Brass, Marcel ^c   Bekkering, Harold ^c   Mazziotta, John C ^a,b   Rizzolatti, Giacomo ^d  

^a UNIVERSITY OF CALIFORNIA   (United States)

^b UNIVERSITY OF CALIFORNIA   (United States)

^c MAX PLANCK INSTITUTE FOR HUMAN COGNITIVE AND BRAIN SCIENCES   (Germany)

^d UNIVERSITY OF PARMA   (Italy)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; BRAIN SCINTISCANNING; FINGER; HAND MOVEMENT; IMITATION; MENTAL FUNCTION; MONKEY; MOTOR ACTIVITY; NEUROANATOMY; NONHUMAN; PRIORITY JOURNAL;

ADULT; BRAIN MAPPING; CUES; FEMALE; FINGERS; FRONTAL LOBE; HUMANS; IMITATIVE BEHAVIOR; MAGNETIC RESONANCE IMAGING; MALE; MOVEMENT; NEURONS; PARIETAL LOBE;

EID: 0033601380     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.286.5449.2526     Document Type: Article

References (49)

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17. Two recent behavioral studies demonstrated that movement observation strongly affects movement execution in a paradigm similar to the one adopted here (M. Brass, H. Bekkering, A. Wohlschlager, W. Prinz, Brain Cogn., in press; M. Brass, H. Bekkering, W. Prinz, Acta Psychol., in press). In both of these studies, as in this imaging study, a "mirror" configuration (right hand imitation of left hand action) was selected because it has been repeatedly shown that there is a natural tendency to imitate in the mirror configuration [H. Head, Brain, 43, 87 (1920); N. C. Kephart, The Slow Learner in the Classroom (Charles Merrill, Columbus, OH, 1971); W. N. Schofield, Q. J. Exp. Psychol. 28, 571 (1976)].
18. Two recent behavioral studies demonstrated that movement observation strongly affects movement execution in a paradigm similar to the one adopted here (M. Brass, H. Bekkering, A. Wohlschlager, W. Prinz, Brain Cogn., in press; M. Brass, H. Bekkering, W. Prinz, Acta Psychol., in press). In both of these studies, as in this imaging study, a "mirror" configuration (right hand imitation of left hand action) was selected because it has been repeatedly shown that there is a natural tendency to imitate in the mirror configuration [H. Head, Brain, 43, 87 (1920); N. C. Kephart, The Slow Learner in the Classroom (Charles Merrill, Columbus, OH, 1971); W. N. Schofield, Q. J. Exp. Psychol. 28, 571 (1976)].
19. Two recent behavioral studies demonstrated that movement observation strongly affects movement execution in a paradigm similar to the one adopted here (M. Brass, H. Bekkering, A. Wohlschlager, W. Prinz, Brain Cogn., in press; M. Brass, H. Bekkering, W. Prinz, Acta Psychol., in press). In both of these studies, as in this imaging study, a "mirror" configuration (right hand imitation of left hand action) was selected because it has been repeatedly shown that there is a natural tendency to imitate in the mirror configuration [H. Head, Brain, 43, 87 (1920); N. C. Kephart, The Slow Learner in the Classroom (Charles Merrill, Columbus, OH, 1971); W. N. Schofield, Q. J. Exp. Psychol. 28, 571 (1976)].
20. Two recent behavioral studies demonstrated that movement observation strongly affects movement execution in a paradigm similar to the one adopted here (M. Brass, H. Bekkering, A. Wohlschlager, W. Prinz, Brain Cogn., in press; M. Brass, H. Bekkering, W. Prinz, Acta Psychol., in press). In both of these studies, as in this imaging study, a "mirror" configuration (right hand imitation of left hand action) was selected because it has been repeatedly shown that there is a natural tendency to imitate in the mirror configuration [H. Head, Brain, 43, 87 (1920); N. C. Kephart, The Slow Learner in the Classroom (Charles Merrill, Columbus, OH, 1971); W. N. Schofield, Q. J. Exp. Psychol. 28, 571 (1976)].
21. Two recent behavioral studies demonstrated that movement observation strongly affects movement execution in a paradigm similar to the one adopted here (M. Brass, H. Bekkering, A. Wohlschlager, W. Prinz, Brain Cogn., in press; M. Brass, H. Bekkering, W. Prinz, Acta Psychol., in press). In both of these studies, as in this imaging study, a "mirror" configuration (right hand imitation of left hand action) was selected because it has been repeatedly shown that there is a natural tendency to imitate in the mirror configuration [H. Head, Brain, 43, 87 (1920); N. C. Kephart, The Slow Learner in the Classroom (Charles Merrill, Columbus, OH, 1971); W. N. Schofield, Q. J. Exp. Psychol. 28, 571 (1976)].
22. A total of 16 participants were studied, following the UCLA Human Subject Protection Committee guidelines. Four participants belonged to a pilot study, which was performed to evaluate the feasibility of the experiment in a fMRI setting. The four participants in the pilot study were three males and one female, and their mean age was 37.75 years (±15.84). The 12 participants in the experiment were nine males and three females, and their mean age was 25.42 years (±5.8). All participants were right-handed, as assessed with a questionnaire that was modified from the Edinburgh Handedness Inventory [R.C. Oldfield, Neuropsychohgia 9, 97 (1971)], and had no neurological abnormalities identified at the neurological examination that was performed just before the scanning procedure.
23. 2*-weighted gradient echo sequence [repetition time (TR) = 4000 ms; echo time (TE) = 70 ms; flip angle = 90°; 64 by 64 volume element (voxel) matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; interslice gap (skip) = 1 mm)]. We also acquired a coplanar high-resolution echo planar imaging (EPI) volume (TR = 4000 ms; TE = 54 ms; flip angle = 90°; 128 by 128 voxel matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; skip = 1 mm), to obtain anatomical data on our participants. The software program MacProbe [E. Zaidel and M. Iacoboni, Brain 119, 2155 (1996)] was used for stimulus presentation. Four fMRI scans of 5 min and 20 s each were performed on every participant. The six tasks were alternated with seven rest periods. Each task or rest period lasted 24 s, except for the last rest period, which lasted 36 s. Each trial lasted 3 s. Thus, each task period comprised eight trials. The task order was counterbalanced across participants. In-plane Gaussian filtering was applied to produce a final image resolution of 8.7 mm by 8.7 mm by 8.6 mm. Image registration for each participant was performed by aligning the functional volumes to the coplanar high-resolution EPI volume with a rigid-body linear registration algorithm [ R. P. Woods, S. T. Grafton, C. J. Holmes, S. R. Cherry, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 139 (1998) ]. Image registration for the group of participants was performed with fifth-order polynomial nonlinear warping (R. P. Woods, S. T. Grafton, J. D. G. Watson, N. L. Sicotte, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 153 (1998)] of each participant's images into a Talairach-compatible brain magnetic resonance (MR) atlas [ R. P. Woods, M. Dapretto, N. L. Sicotte, A. W. Toga, J. C. Mazziotta, Hum. Brain Mapp. 8, 73 (1999)]. Statistical analysis was performed with analysis of variance (ANOVA) [R. P. Woods, M. Iacoboni, S. T. Grafton, J. C. Mazziotta, in Quantification of Brain Function Using PET, R. Myers, V. Cunningham, D. Bailey, T. Jones, Eds. (Academic Press, San Diego, CA, 1996), pp. 353-358]. Participants (n = 12), fMRI scans (n = 4), task (n = 2: observation and observation-execution), and stimuli (n = 3: animated hand, static hand, and geometric figure) were included in the ANOVA, whereas rest periods were excluded. Because of the "blurred" hemodynamic response, the six brain volumes acquired per task period cannot be considered independent observations. Thus, we used the sum of the signal intensity at each voxel throughout each task period as the dependent variable. To account for the delayed hemodynamic response [R. S. Menon and S.-G. Kim, Trends Cogn. Sci. 3, 207 (1999)], we excluded the first brain volume of each task period and included the first brain volume of the following rest period. The statistical threshold, estimating variance at each voxel, was corrected for spatial multiple comparisons [K. J. Worsley et al., Hum. Brain Mapp. 4, 58 (1996)]. Although cluster size is reported here, duster size was not used in computing statistical significance; that is, even a single activated voxel would be statistically valid. The alpha level was also Bonferroni corrected for multiple comparisons. Given that we were interested in the cortical correlates of imitation, only cortical regions with motor properties were considered. Thus, our search region of interest was limited to the cerebral cortex of the frontal and parietal lobes.
24. 2*-weighted gradient echo sequence [repetition time (TR) = 4000 ms; echo time (TE) = 70 ms; flip angle = 90°; 64 by 64 volume element (voxel) matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; interslice gap (skip) = 1 mm)]. We also acquired a coplanar high-resolution echo planar imaging (EPI) volume (TR = 4000 ms; TE = 54 ms; flip angle = 90°; 128 by 128 voxel matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; skip = 1 mm), to obtain anatomical data on our participants. The software program MacProbe [E. Zaidel and M. Iacoboni, Brain 119, 2155 (1996)] was used for stimulus presentation. Four fMRI scans of 5 min and 20 s each were performed on every participant. The six tasks were alternated with seven rest periods. Each task or rest period lasted 24 s, except for the last rest period, which lasted 36 s. Each trial lasted 3 s. Thus, each task period comprised eight trials. The task order was counterbalanced across participants. In-plane Gaussian filtering was applied to produce a final image resolution of 8.7 mm by 8.7 mm by 8.6 mm. Image registration for each participant was performed by aligning the functional volumes to the coplanar high-resolution EPI volume with a rigid-body linear registration algorithm [ R. P. Woods, S. T. Grafton, C. J. Holmes, S. R. Cherry, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 139 (1998) ]. Image registration for the group of participants was performed with fifth-order polynomial nonlinear warping (R. P. Woods, S. T. Grafton, J. D. G. Watson, N. L. Sicotte, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 153 (1998)] of each participant's images into a Talairach-compatible brain magnetic resonance (MR) atlas [ R. P. Woods, M. Dapretto, N. L. Sicotte, A. W. Toga, J. C. Mazziotta, Hum. Brain Mapp. 8, 73 (1999)]. Statistical analysis was performed with analysis of variance (ANOVA) [R. P. Woods, M. Iacoboni, S. T. Grafton, J. C. Mazziotta, in Quantification of Brain Function Using PET, R. Myers, V. Cunningham, D. Bailey, T. Jones, Eds. (Academic Press, San Diego, CA, 1996), pp. 353-358]. Participants (n = 12), fMRI scans (n = 4), task (n = 2: observation and observation-execution), and stimuli (n = 3: animated hand, static hand, and geometric figure) were included in the ANOVA, whereas rest periods were excluded. Because of the "blurred" hemodynamic response, the six brain volumes acquired per task period cannot be considered independent observations. Thus, we used the sum of the signal intensity at each voxel throughout each task period as the dependent variable. To account for the delayed hemodynamic response [R. S. Menon and S.-G. Kim, Trends Cogn. Sci. 3, 207 (1999)], we excluded the first brain volume of each task period and included the first brain volume of the following rest period. The statistical threshold, estimating variance at each voxel, was corrected for spatial multiple comparisons [K. J. Worsley et al., Hum. Brain Mapp. 4, 58 (1996)]. Although cluster size is reported here, duster size was not used in computing statistical significance; that is, even a single activated voxel would be statistically valid. The alpha level was also Bonferroni corrected for multiple comparisons. Given that we were interested in the cortical correlates of imitation, only cortical regions with motor properties were considered. Thus, our search region of interest was limited to the cerebral cortex of the frontal and parietal lobes.
25. 2*-weighted gradient echo sequence [repetition time (TR) = 4000 ms; echo time (TE) = 70 ms; flip angle = 90°; 64 by 64 volume element (voxel) matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; interslice gap (skip) = 1 mm)]. We also acquired a coplanar high-resolution echo planar imaging (EPI) volume (TR = 4000 ms; TE = 54 ms; flip angle = 90°; 128 by 128 voxel matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; skip = 1 mm), to obtain anatomical data on our participants. The software program MacProbe [E. Zaidel and M. Iacoboni, Brain 119, 2155 (1996)] was used for stimulus presentation. Four fMRI scans of 5 min and 20 s each were performed on every participant. The six tasks were alternated with seven rest periods. Each task or rest period lasted 24 s, except for the last rest period, which lasted 36 s. Each trial lasted 3 s. Thus, each task period comprised eight trials. The task order was counterbalanced across participants. In-plane Gaussian filtering was applied to produce a final image resolution of 8.7 mm by 8.7 mm by 8.6 mm. Image registration for each participant was performed by aligning the functional volumes to the coplanar high-resolution EPI volume with a rigid-body linear registration algorithm [ R. P. Woods, S. T. Grafton, C. J. Holmes, S. R. Cherry, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 139 (1998) ]. Image registration for the group of participants was performed with fifth-order polynomial nonlinear warping (R. P. Woods, S. T. Grafton, J. D. G. Watson, N. L. Sicotte, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 153 (1998)] of each participant's images into a Talairach-compatible brain magnetic resonance (MR) atlas [ R. P. Woods, M. Dapretto, N. L. Sicotte, A. W. Toga, J. C. Mazziotta, Hum. Brain Mapp. 8, 73 (1999)]. Statistical analysis was performed with analysis of variance (ANOVA) [R. P. Woods, M. Iacoboni, S. T. Grafton, J. C. Mazziotta, in Quantification of Brain Function Using PET, R. Myers, V. Cunningham, D. Bailey, T. Jones, Eds. (Academic Press, San Diego, CA, 1996), pp. 353-358]. Participants (n = 12), fMRI scans (n = 4), task (n = 2: observation and observation-execution), and stimuli (n = 3: animated hand, static hand, and geometric figure) were included in the ANOVA, whereas rest periods were excluded. Because of the "blurred" hemodynamic response, the six brain volumes acquired per task period cannot be considered independent observations. Thus, we used the sum of the signal intensity at each voxel throughout each task period as the dependent variable. To account for the delayed hemodynamic response [R. S. Menon and S.-G. Kim, Trends Cogn. Sci. 3, 207 (1999)], we excluded the first brain volume of each task period and included the first brain volume of the following rest period. The statistical threshold, estimating variance at each voxel, was corrected for spatial multiple comparisons [K. J. Worsley et al., Hum. Brain Mapp. 4, 58 (1996)]. Although cluster size is reported here, duster size was not used in computing statistical significance; that is, even a single activated voxel would be statistically valid. The alpha level was also Bonferroni corrected for multiple comparisons. Given that we were interested in the cortical correlates of imitation, only cortical regions with motor properties were considered. Thus, our search region of interest was limited to the cerebral cortex of the frontal and parietal lobes.
26. 2*-weighted gradient echo sequence [repetition time (TR) = 4000 ms; echo time (TE) = 70 ms; flip angle = 90°; 64 by 64 volume element (voxel) matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; interslice gap (skip) = 1 mm)]. We also acquired a coplanar high-resolution echo planar imaging (EPI) volume (TR = 4000 ms; TE = 54 ms; flip angle = 90°; 128 by 128 voxel matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; skip = 1 mm), to obtain anatomical data on our participants. The software program MacProbe [E. Zaidel and M. Iacoboni, Brain 119, 2155 (1996)] was used for stimulus presentation. Four fMRI scans of 5 min and 20 s each were performed on every participant. The six tasks were alternated with seven rest periods. Each task or rest period lasted 24 s, except for the last rest period, which lasted 36 s. Each trial lasted 3 s. Thus, each task period comprised eight trials. The task order was counterbalanced across participants. In-plane Gaussian filtering was applied to produce a final image resolution of 8.7 mm by 8.7 mm by 8.6 mm. Image registration for each participant was performed by aligning the functional volumes to the coplanar high-resolution EPI volume with a rigid-body linear registration algorithm [ R. P. Woods, S. T. Grafton, C. J. Holmes, S. R. Cherry, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 139 (1998) ]. Image registration for the group of participants was performed with fifth-order polynomial nonlinear warping (R. P. Woods, S. T. Grafton, J. D. G. Watson, N. L. Sicotte, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 153 (1998)] of each participant's images into a Talairach-compatible brain magnetic resonance (MR) atlas [ R. P. Woods, M. Dapretto, N. L. Sicotte, A. W. Toga, J. C. Mazziotta, Hum. Brain Mapp. 8, 73 (1999)]. Statistical analysis was performed with analysis of variance (ANOVA) [R. P. Woods, M. Iacoboni, S. T. Grafton, J. C. Mazziotta, in Quantification of Brain Function Using PET, R. Myers, V. Cunningham, D. Bailey, T. Jones, Eds. (Academic Press, San Diego, CA, 1996), pp. 353-358]. Participants (n = 12), fMRI scans (n = 4), task (n = 2: observation and observation-execution), and stimuli (n = 3: animated hand, static hand, and geometric figure) were included in the ANOVA, whereas rest periods were excluded. Because of the "blurred" hemodynamic response, the six brain volumes acquired per task period cannot be considered independent observations. Thus, we used the sum of the signal intensity at each voxel throughout each task period as the dependent variable. To account for the delayed hemodynamic response [R. S. Menon and S.-G. Kim, Trends Cogn. Sci. 3, 207 (1999)], we excluded the first brain volume of each task period and included the first brain volume of the following rest period. The statistical threshold, estimating variance at each voxel, was corrected for spatial multiple comparisons [K. J. Worsley et al., Hum. Brain Mapp. 4, 58 (1996)]. Although cluster size is reported here, duster size was not used in computing statistical significance; that is, even a single activated voxel would be statistically valid. The alpha level was also Bonferroni corrected for multiple comparisons. Given that we were interested in the cortical correlates of imitation, only cortical regions with motor properties were considered. Thus, our search region of interest was limited to the cerebral cortex of the frontal and parietal lobes.
27. 2*-weighted gradient echo sequence [repetition time (TR) = 4000 ms; echo time (TE) = 70 ms; flip angle = 90°; 64 by 64 volume element (voxel) matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; interslice gap (skip) = 1 mm)]. We also acquired a coplanar high-resolution echo planar imaging (EPI) volume (TR = 4000 ms; TE = 54 ms; flip angle = 90°; 128 by 128 voxel matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; skip = 1 mm), to obtain anatomical data on our participants. The software program MacProbe [E. Zaidel and M. Iacoboni, Brain 119, 2155 (1996)] was used for stimulus presentation. Four fMRI scans of 5 min and 20 s each were performed on every participant. The six tasks were alternated with seven rest periods. Each task or rest period lasted 24 s, except for the last rest period, which lasted 36 s. Each trial lasted 3 s. Thus, each task period comprised eight trials. The task order was counterbalanced across participants. In-plane Gaussian filtering was applied to produce a final image resolution of 8.7 mm by 8.7 mm by 8.6 mm. Image registration for each participant was performed by aligning the functional volumes to the coplanar high-resolution EPI volume with a rigid-body linear registration algorithm [ R. P. Woods, S. T. Grafton, C. J. Holmes, S. R. Cherry, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 139 (1998) ]. Image registration for the group of participants was performed with fifth-order polynomial nonlinear warping (R. P. Woods, S. T. Grafton, J. D. G. Watson, N. L. Sicotte, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 153 (1998)] of each participant's images into a Talairach-compatible brain magnetic resonance (MR) atlas [ R. P. Woods, M. Dapretto, N. L. Sicotte, A. W. Toga, J. C. Mazziotta, Hum. Brain Mapp. 8, 73 (1999)]. Statistical analysis was performed with analysis of variance (ANOVA) [R. P. Woods, M. Iacoboni, S. T. Grafton, J. C. Mazziotta, in Quantification of Brain Function Using PET, R. Myers, V. Cunningham, D. Bailey, T. Jones, Eds. (Academic Press, San Diego, CA, 1996), pp. 353-358]. Participants (n = 12), fMRI scans (n = 4), task (n = 2: observation and observation-execution), and stimuli (n = 3: animated hand, static hand, and geometric figure) were included in the ANOVA, whereas rest periods were excluded. Because of the "blurred" hemodynamic response, the six brain volumes acquired per task period cannot be considered independent observations. Thus, we used the sum of the signal intensity at each voxel throughout each task period as the dependent variable. To account for the delayed hemodynamic response [R. S. Menon and S.-G. Kim, Trends Cogn. Sci. 3, 207 (1999)], we excluded the first brain volume of each task period and included the first brain volume of the following rest period. The statistical threshold, estimating variance at each voxel, was corrected for spatial multiple comparisons [K. J. Worsley et al., Hum. Brain Mapp. 4, 58 (1996)]. Although cluster size is reported here, duster size was not used in computing statistical significance; that is, even a single activated voxel would be statistically valid. The alpha level was also Bonferroni corrected for multiple comparisons. Given that we were interested in the cortical correlates of imitation, only cortical regions with motor properties were considered. Thus, our search region of interest was limited to the cerebral cortex of the frontal and parietal lobes.
28. 2*-weighted gradient echo sequence [repetition time (TR) = 4000 ms; echo time (TE) = 70 ms; flip angle = 90°; 64 by 64 volume element (voxel) matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; interslice gap (skip) = 1 mm)]. We also acquired a coplanar high-resolution echo planar imaging (EPI) volume (TR = 4000 ms; TE = 54 ms; flip angle = 90°; 128 by 128 voxel matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; skip = 1 mm), to obtain anatomical data on our participants. The software program MacProbe [E. Zaidel and M. Iacoboni, Brain 119, 2155 (1996)] was used for stimulus presentation. Four fMRI scans of 5 min and 20 s each were performed on every participant. The six tasks were alternated with seven rest periods. Each task or rest period lasted 24 s, except for the last rest period, which lasted 36 s. Each trial lasted 3 s. Thus, each task period comprised eight trials. The task order was counterbalanced across participants. In-plane Gaussian filtering was applied to produce a final image resolution of 8.7 mm by 8.7 mm by 8.6 mm. Image registration for each participant was performed by aligning the functional volumes to the coplanar high-resolution EPI volume with a rigid-body linear registration algorithm [ R. P. Woods, S. T. Grafton, C. J. Holmes, S. R. Cherry, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 139 (1998) ]. Image registration for the group of participants was performed with fifth-order polynomial nonlinear warping (R. P. Woods, S. T. Grafton, J. D. G. Watson, N. L. Sicotte, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 153 (1998)] of each participant's images into a Talairach-compatible brain magnetic resonance (MR) atlas [ R. P. Woods, M. Dapretto, N. L. Sicotte, A. W. Toga, J. C. Mazziotta, Hum. Brain Mapp. 8, 73 (1999)]. Statistical analysis was performed with analysis of variance (ANOVA) [R. P. Woods, M. Iacoboni, S. T. Grafton, J. C. Mazziotta, in Quantification of Brain Function Using PET, R. Myers, V. Cunningham, D. Bailey, T. Jones, Eds. (Academic Press, San Diego, CA, 1996), pp. 353-358]. Participants (n = 12), fMRI scans (n = 4), task (n = 2: observation and observation-execution), and stimuli (n = 3: animated hand, static hand, and geometric figure) were included in the ANOVA, whereas rest periods were excluded. Because of the "blurred" hemodynamic response, the six brain volumes acquired per task period cannot be considered independent observations. Thus, we used the sum of the signal intensity at each voxel throughout each task period as the dependent variable. To account for the delayed hemodynamic response [R. S. Menon and S.-G. Kim, Trends Cogn. Sci. 3, 207 (1999)], we excluded the first brain volume of each task period and included the first brain volume of the following rest period. The statistical threshold, estimating variance at each voxel, was corrected for spatial multiple comparisons [K. J. Worsley et al., Hum. Brain Mapp. 4, 58 (1996)]. Although cluster size is reported here, duster size was not used in computing statistical significance; that is, even a single activated voxel would be statistically valid. The alpha level was also Bonferroni corrected for multiple comparisons. Given that we were interested in the cortical correlates of imitation, only cortical regions with motor properties were considered. Thus, our search region of interest was limited to the cerebral cortex of the frontal and parietal lobes.
29. 2*-weighted gradient echo sequence [repetition time (TR) = 4000 ms; echo time (TE) = 70 ms; flip angle = 90°; 64 by 64 volume element (voxel) matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; interslice gap (skip) = 1 mm)]. We also acquired a coplanar high-resolution echo planar imaging (EPI) volume (TR = 4000 ms; TE = 54 ms; flip angle = 90°; 128 by 128 voxel matrix; 26 axial slices; 3.125-mm in-plane resolution; 4-mm thickness; skip = 1 mm), to obtain anatomical data on our participants. The software program MacProbe [E. Zaidel and M. Iacoboni, Brain 119, 2155 (1996)] was used for stimulus presentation. Four fMRI scans of 5 min and 20 s each were performed on every participant. The six tasks were alternated with seven rest periods. Each task or rest period lasted 24 s, except for the last rest period, which lasted 36 s. Each trial lasted 3 s. Thus, each task period comprised eight trials. The task order was counterbalanced across participants. In-plane Gaussian filtering was applied to produce a final image resolution of 8.7 mm by 8.7 mm by 8.6 mm. Image registration for each participant was performed by aligning the functional volumes to the coplanar high-resolution EPI volume with a rigid-body linear registration algorithm [ R. P. Woods, S. T. Grafton, C. J. Holmes, S. R. Cherry, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 139 (1998) ]. Image registration for the group of participants was performed with fifth-order polynomial nonlinear warping (R. P. Woods, S. T. Grafton, J. D. G. Watson, N. L. Sicotte, J. C. Mazziotta, J. Comput. Assisted Tomogr. 22, 153 (1998)] of each participant's images into a Talairach-compatible brain magnetic resonance (MR) atlas [ R. P. Woods, M. Dapretto, N. L. Sicotte, A. W. Toga, J. C. Mazziotta, Hum. Brain Mapp. 8, 73 (1999)]. Statistical analysis was performed with analysis of variance (ANOVA) [R. P. Woods, M. Iacoboni, S. T. Grafton, J. C. Mazziotta, in Quantification of Brain Function Using PET, R. Myers, V. Cunningham, D. Bailey, T. Jones, Eds. (Academic Press, San Diego, CA, 1996), pp. 353-358]. Participants (n = 12), fMRI scans (n = 4), task (n = 2: observation and observation-execution), and stimuli (n = 3: animated hand, static hand, and geometric figure) were included in the ANOVA, whereas rest periods were excluded. Because of the "blurred" hemodynamic response, the six brain volumes acquired per task period cannot be considered independent observations. Thus, we used the sum of the signal intensity at each voxel throughout each task period as the dependent variable. To account for the delayed hemodynamic response [R. S. Menon and S.-G. Kim, Trends Cogn. Sci. 3, 207 (1999)], we excluded the first brain volume of each task period and included the first brain volume of the following rest period. The statistical threshold, estimating variance at each voxel, was corrected for spatial multiple comparisons [K. J. Worsley et al., Hum. Brain Mapp. 4, 58 (1996)]. Although cluster size is reported here, duster size was not used in computing statistical significance; that is, even a single activated voxel would be statistically valid. The alpha level was also Bonferroni corrected for multiple comparisons. Given that we were interested in the cortical correlates of imitation, only cortical regions with motor properties were considered. Thus, our search region of interest was limited to the cerebral cortex of the frontal and parietal lobes.
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49. This work was supported by the International Human Frontier Science Program, the Brain Mapping Medical Research Organization, The Ahmanson Foundation, the Pierson-Lovelace Foundation, the Tamkin Foundation, and the Jennifer Jones-Simon Foundation.