Thursday, December 31, 2009

Inhibited behavior and our right frontal cortex.

Another interesting piece of work from Richie Davidson and colleagues at the University of Wisconsin.  Continuing their general catalog of correlations of left versus right frontal lobe activation with outgoing versus protective behaviors they find  that individuals with greater tonic (resting) activity in right-posterior dorsolateral prefrontal cortex rate themselves as more behaviorally inhibited. (The authors point out some limitation of the study: It is done with only female subjects and self reports of inhibition, so this clearly needs to be expanded. Their conclusions rest on a model, not a direct measurement, of the cerebral sources underlying the EEG, and the study did not address the degree to which individual differences in behavioral inhibition reflect altered functional connectivity between right-posterior DLPFC and other structures thought to underlie the behavioral inhibition system - e.g., amygdala, PAG, or ACC). Here is their abstract followed by a graphic from the article:
Individuals show marked variation in their responses to threat. Such individual differences in behavioral inhibition play a profound role in mental and physical well-being. Behavioral inhibition is thought to reflect variation in the sensitivity of a distributed neural system responsible for generating anxiety and organizing defensive responses to threat and punishment. Although progress has been made in identifying the key constituents of this behavioral inhibition system in humans, the involvement of dorsolateral prefrontal cortex (DLPFC) remains unclear. Here, we acquired self-reported Behavioral Inhibition System Sensitivity scores and high-resolution electroencephalography from a large sample (n= 51). Using the enhanced spatial resolution afforded by source modeling techniques, we show that individuals with greater tonic (resting) activity in right-posterior DLPFC rate themselves as more behaviorally inhibited. This observation provides novel support for recent conceptualizations of behavioral inhibition and clues to the mechanisms that might underlie variation in threat-induced negative affect.

Figure - Relations between individual differences in behavioral inhibition and tonic activity in right-posterior dorsolateral prefrontal cortex (DLPFC). The images in (a) depict the results of the electroencephalography source modeling analyses. The cluster lies at the intersection of the precentral and inferior frontal sulci, encompassing the right-posterior midfrontal and inferior-frontal gyri and including the inferior frontal junction (cluster-corrected p= .02). The crosshair shows the location in right-posterior DLPFC of the peak correlation in the sagittal (green outline), coronal (cyan outline), and axial (yellow outline) planes. The magnitude of voxel-wise correlations is depicted using a red-yellow scale; lighter shades of yellow indicate stronger correlations. "L" and "R" indicate the left and right hemispheres, respectively. The scatter plot (b) depicts the peak correlation between scores on the Behavioral Inhibition System (BIS) scale and standardized activity in right-posterior DLPFC (area 9/46v), r(48) =−.37, uncorrected p= .003. Standardized activity is in units of z-transformed cortical current density, log10(A/m2). Lines depict the regression line and 95% confidence envelope.

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