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Test–retest reliability of resting regional cerebral metabolic rate of glucose (rCMR) was examined in selected subcortical structures: the amygdala, hippocampus, thalamus, and anterior caudate nucleus. Findings from previous studies examining reliability of rCMR suggest that rCMR in small subcortical structures may be more variable than in larger cortical regions. We chose to study these subcortical regions because of their particular interest to our laboratory in its investigations of the neurocircuitry of emotion and depression. Twelve normal subjects (seven female, mean age = 32.42 years, range 21–48 years) underwent two FDG-PET scans separated by approximately 6 months (mean = 25 weeks, range 17–35 weeks). A region-of-interest approach with PET-MRI coregistration was used for analysis of rCMR reliability. Good test–retest reliability was found in the left amygdala, right and left hippocampus, right and left thalamus, and right and left anterior caudate nucleus. However, rCMR in the right amygdala did not show good test–retest reliability. The implications of these data and their import for studies that include a repeat-test design are considered. Hum. Brain Mapping 10:1–9, 2000. © 2000 Wiley-Liss, Inc.

Test–retest reliability of resting regional cerebral metabolic rate of glucose (rCMR) was examined in selected subcortical structures: the amygdala, hippocampus, thalamus, and anterior caudate nucleus. Findings from previous studies examining reliability of rCMR suggest that rCMR in small subcortical structures may be more variable than in larger cortical regions. We chose to study these subcortical regions because of their particular interest to our laboratory in its investigations of the neurocircuitry of emotion and depression. Twelve normal subjects (seven female, mean age = 32.42 years, range 21–48 years) underwent two FDG‐PET scans separated by approximately 6 months (mean = 25 weeks, range 17–35 weeks). A region‐of‐interest approach with PET‐MRI coregistration was used for analysis of rCMR reliability. Good test–retest reliability was found in the left amygdala, right and left hippocampus, right and left thalamus, and right and left anterior caudate nucleus. However, rCMR in the right amygdala did not show good test–retest reliability. The implications of these data and their import for studies that include a repeat‐test design are considered. Hum. Brain Mapping 10:1–9, 2000.© 2000 Wiley‐Liss, Inc.

THE role of the amygdala in major depression was investigated. Resting regional cerebral metabolic rate (rCMRglu) was measured with [18F]fluorodeoxyglucose positron emission tomography (PET) in two samples of subjects using two different PET cameras. The samples consisted of 10 and 17 medication-free depressives and 11 and 13 controls, respectively. Using coregistration of PET and magnetic resonance images, regions were individually delineated for the amygdala and thalamus, the latter of which was used as a control region. Within the depressed groups, right amygdalar rCMRgluwas positively correlated with negative affect. Thalamic rCMRgluwas not related to negative affect, and amygdalar rCMRgluaccounted for a significant portion of variance in depressives' negative affect scores over and above the contribution of thalamic rCMRglu.