No abstract

In addition to increased activation of the medial prefrontal cortex and right VLPFC, we observed altered connectivity between the amygdala or VLPFC and regions, which subserve mentalization (e.g. posterior cingulate cortex, precuneus, and medial prefrontal cortex). This suggests that structures that regulate emotion and affect interact abnormally with key structures that are involved in mentalization, a process known to be disrupted in GAD.

Adolescents with GAD, who are early in the course of their illness, exhibit abnormalities in neural structures that subserve threat appraisal, modulation of fear responses, attachment, and mentalization.

Although a variety of methods have been proposed to provide automated adjustment of shim homogeneity, these methods typically fail or require large numbers of iterations in vivo when applied to regions with poor homogeneity, such as the temporal lobe. These limitations are largely due to 1) the limited accuracy of single evolution time measurements when full B 0 mapping studies are used, and 2) inaccuracies arising from projectionbased methods when the projections pass through regions where the inhomogeneity exceeds the order of the fitted parameters. To overcome these limitations we developed a novel B 0 mapping method using multiple evolution times with a novel unwrapping scheme in combination with a user-defined ROI selection tool. We used these methods at 4T on 10 control subjects to obtain high-resolution spectroscopic images of glutamate from the bilateral hippocampi. A variety of rapid automated shim mapping methods for the human brain based on acquisition of a limited number of columnar projections using phase mapping have been described for small localized volumes (1,2). Shen and colleagues (3,4) demonstrated the need for alternate projection geometries when shimming planar volumes. Although these methods have been successfully applied in regions of good homogeneity, such as the occipital lobe for single volume measurements (1,2) and for slices above the corpus callosum (3), they can fail or require large numbers of iterations in vivo when applied to regions with very poor B 0 homogeneity adjacent to air-filled sinuses, such as the temporal lobes. Intrinsic to these maps is the assumption that the B 0 inhomogeneity present in the entire sample or region of interest (ROI) can be accurately represented by the limited number of columns acquired, and that the columns are sufficiently narrow for there to be negligible inhomogeneity across them. However, this assumption fails when the spatial order of the inhomogeneity present (i.e., the order of the spherical harmonic terms that characterize the spatial symmetry of the inhomogeneity) exceeds the spatial order that is used or measurable in the columnar analysis model, or when the inhomogeneity changes very rapidly in relationship to the cross-sectional width of the column (5). In this case lower-order corrections in localized regions are then used to attempt to compensate for higher-order corrections that do not have the same spatial symmetry. The calculated shim corrections can either over-or underestimate the size of the adjustments required to provide "optimal" homogeneity over the entire target volume given the available currents.Alternatively, shim methods that utilize complete maps (5-9) as opposed to columnar projections can provide accurate maps over large regions without assumptions regarding the order of the inhomogeneity present. In these cases the residual inhomogeneity is minimized by using information from sampling a much greater extent of the target volume. For B 0 mapping, typically a single, relatively short phase evolution time is used becau...