Wednesday, September 06, 2006

Neural operations that give rise to a unitary sense of self.

An interesting article by Moran et. al. in Journal of Cognitive Neuroscience: They examined whether the cognitive and affective components of self-reflection can be dissociated using functional magnetic resonance imaging. Using a simple paradigm in which subjects judged the personal relevance of personality characteristics that were either favorable (e.g., "honest") or unfavorable (e.g., "lazy"), they found that distinct neural circuits in adjacent regions of the prefrontal cortex subserve cognitive and emotional aspects of self-reflection. The medial prefrontal cortex responded only to material that was self-descriptive, and this did not differ as a function of the valence of the trait. When material was judged to be self-relevant, the valence of the material was resolved in an adjacent region of ventral anterior cingulate.

Figure Legend: Whole-brain ANOVA analysis revealed a main effect of self-relevance (top left) in the medial prefrontal cortex (MPFC) and posterior cingulate cortex (pCC), a main effect of valence (top right) in the ventral anterior cingulate cortex (vACC), and a self-relevance by valence interaction (bottom left) in the vACC, the dorsal anterior cingulate cortex (dACC), and the supplementary motor area (SMA). To qualitatively identify whether brain regions identified in the ANOVA analysis showed a strong bias toward one of the two main effects, a self-relevance/valence sensitivity measure (F ratio) was computed on a voxel-by-voxel basis by dividing the self-relevance F score for each voxel by the valence F score. Voxels that did not yield a significant main effect of either self-relevance or valence were excluded from further analysis to avoid spurious F ratio effects. To facilitate visualization of this sensitivity measure, F ratios were transformed to a logarithmic scale. Voxels that were more sensitive to trait valence yielded negative values (blue color scale), whereas voxels that were more sensitive to self-relevance yielded positive values (yellow color scale). Voxels at the tail end of the color scales were those voxels that exhibited the greatest bias toward trait valence and self-relevance, respectively. Voxels in the MPFC (BA 10) and two regions of the pCC (BA 29/30 and BA 23) demonstrated greater sensitivity to self-relevance, whereas voxels in the vACC (BA 25) demonstrated greater sensitivity to trait valence.

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