Quantification of activity in chimpanzee regions homologous to those that contain mirror neurons in macaques. A, ROI activation in individual conditions. Percentage of ROIs active in each condition were averaged across subjects. An initial repeated-measures ANOVA showed no effect of hemisphere, so data were averaged bilaterally for each ROI. Activation was greater in execution, transitive observation, and intransitive observation relative to rest, as measured with a repeated-measures ANOVA (main effect of task condition, F(3,9) = 14.185, p < 0.001; individual comparisons, p = 0.004, 0.007, and 0.026, respectively). In addition, the FCBm was more active than PFD/PF (main effect of region, F(1,3) = 17.386, p = 0.014). B, ROI activation in conjunction analyses. Percentage of voxels in top 1% of execution condition which were also in top 1% of transitive observation or intransitive observation conditions in FCMb and PF, averaged across subjects. A repeated-measures ANOVA revealed no effect of condition, but a main effect of region (F(1,3) = 16.076, p = 0.028); the frontal ROI was more active than the parietal ROI.