Individual variability in the inferior prefrontal cortex is fundamentally important to both experimental and clinical neuroscience. Numerous studies have examined intersubject anatomical and functional variability in the inferior frontal gyrus (IFG). However, few studies have attempted to relate the two sources of individual variability, and to our knowledge no study has looked for quantitative correlations. In the present study, we evaluated methods of qualitatively and quantitatively relating anatomical and functional variability for a semantic generation task. Positron emission tomography (PET) and anatomical magnetic resonance imaging (MRI) were used to assess intersubject anatomical and functional variability in 7 normal subjects who underwent a synonym generation task. The IFG was parcellated into three regions of interest: the pars opercularis (POp), pars triangularis (PTr), and pars orbitalis (POr). Location, intensity, extent, and lateralization of functional activity were assessed. Activations were qualitatively described relative to surface anatomy, and the correlation between structural and functional variability was examined using Euclidean distances and lateralization indices. Activations were found to occur at the intersection of two sulci, most often the inferior frontal sulcus and the ascending ramus of the lateral fissure. The strongest correlations between anatomical and functional variability occurred within the POp and the weakest correlations within the PTr. We concluded that functional activity is most accurately described relative to anatomical landmarks rather than with Talairach coordinates and that more sophisticated methods are needed to quantitatively relate structure and function in the IFG.
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