Probably worth pointing out that normal people really are somewhat asymmetric in quantitative measures of flow and metabolism (small but consistent differences). I'm not the expert on it but I know there have been studies at least as far back as the ref below. ------------------------------------------------------------------------ Perlmutter JS, Powers WJ, Herscovitch P, Fox PT, Raichle ME Regional asymmetries of cerebral blood flow, blood volume, and oxygen utilization and extraction in normal subjects. J Cereb Blood Flow Metab 1987 Feb;7(1):64-7 Part of abstract: ... 32 right-handed subjects at rest. Mean left hemispheric CBF (46.2 +/- 6.8 ml/100 g/min) and CMRO2 (2.60 +/- 0.59 ml/100 g/min) were significantly lower than right hemispheric values (47.4 +/- 7.2 and 2.66 +/- 0.61 ml/100 g/min, respectively; p less than 0.0001 for both), whereas left and right hemispheric CBV and oxygen extraction were not significantly different. We further investigated these asymmetries by comparing left- and right-sided values for specific cortical and subcortical regions. We found that left-sided CBF and CMRO2 were significantly lower than right-sided values for sensorimotor, occipital, and superior temporal regions, whereas only left-sided CBF values were lower for anterior cingulum. CBV was asymmetric for the anterior cingulate and mid-frontal regions, and oxygen extraction was asymmetric for the sensorimotor area. No asymmetries were observed in inferior parietal cortex, thalamus, putamen, or pallidum. ... ------------------------------------------------------------------------ Kevin