Brenda E. Benson

Frequency dependence of antidepressant response to left prefrontal repetitive transcranial magnetic stimulation (rTMS) as a function of baseline cerebral glucose metabolism.

BACKGROUND Recent studies suggest that both high frequency (10-20 Hz) and low frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS) have an antidepressant effect in some individuals. Electrophysiologic data indicate that high frequency rTMS enhances neuronal firing efficacy and that low frequency rTMS has the opposite effect. METHODS We investigated the antidepressant effects of 10 daily left prefrontal 1 Hz versus 20 Hz rTMS with the hypothesis that within a given subject, antidepressant response would differ by frequency and vary as a function of baseline cerebral glucose metabolism. After baseline PET scans utilizing [18F]-Fluorodeoxyglucose, thirteen subjects participated in a randomized crossover trial of 2 weeks of 20 Hz paired with 2 weeks 1 Hz or placebo rTMS. RESULTS We found a negative correlation between degree of antidepressant response after 1 Hz compared to 20 Hz rTMS (r = -0.797, p < .004). Additionally, better response to 20 Hz was associated with the degree of baseline hypometabolism, whereas response to 1 Hz rTMS tended to be associated with baseline hypermetabolism. CONCLUSIONS These preliminary results suggest that antidepressant response to rTMS might vary as a function of stimulation frequency and may depend on pretreatment cerebral metabolism. Further studies combining rTMS and functional neuroimaging are needed.

Effects of mood and subtype on cerebral glucose metabolism in treatment-resistant bipolar disorder.

BACKGROUND Functional brain imaging studies in unipolar and secondary depression have generally found decreased prefrontal cortical activity, but in bipolar disorders findings have been more variable. METHODS Forty-three medication-free, treatment-resistant, predominantly rapid-cycling bipolar disorder patients and 43 age- and gender-matched healthy control subjects had cerebral glucose metabolism assessed using positron emission tomography and fluorine-18-deoxyglucose. RESULTS Depressed bipolar disorder patients compared to control subjects had decreased global, absolute prefrontal and anterior paralimbic cortical, and increased normalized subcortical (ventral striatum, thalamus, right amygdala) metabolism. Degree of depression correlated negatively with absolute prefrontal and paralimbic cortical, and positively with normalized anterior paralimbic subcortical metabolism. Increased normalized cerebello-posterior cortical metabolism was seen in all patient subgroups compared to control subjects, independent of mood state, disorder subtype, or cycle frequency. CONCLUSIONS In bipolar depression, we observed a pattern of prefrontal hypometabolism, consistent with observations in primary unipolar and secondary depression, suggesting this is part of a common neural substrate for depression independent of etiology. In contrast, the cerebello-posterior cortical normalized hypermetabolism seen in all bipolar subgroups (including euthymic) suggests a possible congenital or acquired trait abnormality. The degree to which these findings in treatment-resistant, predominantly rapid-cycling patients pertain to community samples remains to be established.

Regional brain activity during transient self-induced anxiety and anger in healthy adults

BACKGROUND Several studies have demonstrated that transient self-induced sadness activates anterior paralimbic structures. To further examine the specificity of these findings and the neural substrates involved in anger and anxiety, we studied the neural correlates of the induction of anxiety and anger in healthy adults. METHODS We used H2(15)O and positron emission tomography (PET) to measure regional cerebral blood flow (rCBF) in 16 healthy adults during the induction of transient anxiety, anger, and neutral emotions. Subjects achieved differential emotions by recalling prior life events while viewing affect-appropriate faces. RESULTS Both the anxiety and anger conditions were associated with increased normalized rCBF in left inferior frontal and left temporal pole regions and decreased rCBF in right posterior temporal/parietal and right superior frontal cortex, compared to the neutral induction. Additionally, compared to neutral induction, anxiety was associated with increased rCBF in the left anterior cingulate and cuneus and decreased rCBF in right medial frontal cortex, while the anger induction was uniquely associated with increased rCBF in right temporal pole and thalamus. CONCLUSIONS Self-generated transient states of anxiety and anger are associated with both overlapping and distinct regional brain activity patterns and provide a template for further dissection of specific components of normal and pathologic emotions.

Regional cerebral glucose utilization in Patients with a range of severities of unipolar depression

BACKGROUND Patients with unipolar depression are most often reported to have decreased regional cerebral glucose metabolism (rCMRglu) in dorsal prefrontal and anterior cingulate cortices compared with healthy control subjects, often correlating inversely with severity of depression. METHODS We measured rCMRglu with fluorine-18 deoxyglucose positron emission tomography (PET) in 38 medication-free patients with unipolar depression and 37 healthy control subjects performing an auditory continuous performance task to further investigate potential prefrontal and anterior paralimbic rCMRglu abnormalities in patients attending to this task. RESULTS Compared with control subjects, the subgroup of patients with Hamilton depression scores of 22 or greater demonstrated decreased absolute rCMRglu in right prefrontal cortex and paralimbic/amygdala regions as well as bilaterally in the insula and temporoparietal cortex (right > left); they also exhibited increased normalized metabolic activity bilaterally in the cerebellum, lingula/cuneus, and brain stem. Severity of depression negatively correlated with absolute rCMRglu in almost the entire extent of the right cingulate cortex as well as bilaterally in prefrontal cortex, insula, basal ganglia, and temporoparietal cortex (right > left). CONCLUSIONS Areas of frontal, cingulate, insula, and temporal cortex appear hypometabolic in association with different components of the severity and course of illness in treatment-resistant unipolar depression.

Regional cerebral metabolism associated with anxiety symptoms in affective disorder patients

BACKGROUND We studied the relationship between regional cerebral metabolism and the severity of anxiety in mood disorder patients, controlling for depression severity. METHODS Fifty-two medication-free patients with unipolar or bipolar illness underwent positron emission tomography with [(18)F]-fluorodeoxyglucose. Hamilton Depression Rating Scale and Spielberger Anxiety-State Scale scores were obtained for the week of the scan. Analyses were performed on globally normalized images and were corrected for multiple comparisons. RESULTS After covarying for depression scores, age, and gender, Spielberger Anxiety-State Scale scores correlated directly with regional cerebral metabolism in the right parahippocampal and left anterior cingulate regions, and inversely with metabolism in the cerebellum, left fusiform, left superior temporal, left angular gyrus, and left insula. In contrast, covarying for anxiety scores, age, and gender, Hamilton Depression Rating Scale scores correlated directly with regional cerebral metabolism in the bilateral medial frontal, right anterior cingulate, and right dorsolateral prefrontal cortices. CONCLUSIONS Comorbid anxiety symptoms are associated with specific cerebral metabolic correlates that partially overlap with those in the primary anxiety disorders and differ from those associated with depression severity.

Intensity-dependent regional cerebral blood flow during 1-Hz repetitive transcranial magnetic stimulation (rTMS) in healthy volunteers studied with H215O positron emission tomography: i. effects of primary motor cortex rTMS

BACKGROUND Repetitive transcranial magnetic stimulation (rTMS) affects the excitability of the motor cortex and is thought to influence activity in other brain areas as well. We combined the administration of varying intensities of 1-Hz rTMS of the motor cortex with simultaneous positron emission tomography (PET) to delineate local and distant effects on brain activity. METHODS Ten healthy subjects received 1-Hz rTMS to the optimal position over motor cortex (M1) for producing a twitch in the right hand at 80, 90, 100, 110, and 120% of the twitch threshold, while regional cerebral blood flow (rCBF) was measured using H(2)(15)O and PET. Repetitive transcranial magnetic stimulation (rTMS) was delivered in 75-pulse trains at each intensity every 10 min through a figure-eight coil. The regional relationship of stimulation intensity to normalized rCBF was assessed statistically. RESULTS Intensity-dependent rCBF increases were produced under the M1 stimulation site in ipsilateral primary auditory cortex, contralateral cerebellum, and bilateral putamen, insula, and red nucleus. Intensity-dependent reductions in rCBF occurred in contralateral frontal and parietal cortices and bilateral anterior cingulate gyrus and occipital cortex. CONCLUSIONS This study demonstrates that 1-Hz rTMS delivered to the primary motor cortex (M1) produces intensity-dependent increases in brain activity locally and has associated effects in distant sites with known connections to M1.

Intrinsic Functional Connectivity of Amygdala-Based Networks in Adolescent Generalized Anxiety Disorder

OBJECTIVE Generalized anxiety disorder (GAD) typically begins during adolescence and can persist into adulthood. The pathophysiological mechanisms underlying this disorder remain unclear. Recent evidence from resting state functional magnetic resonance imaging (R-fMRI) studies in adults suggests disruptions in amygdala-based circuitry; the present study examines this issue in adolescents with GAD. METHOD Resting state fMRI scans were obtained from 15 adolescents with GAD and 20 adolescents without anxiety who were group matched on age, sex, scanner, and intelligence. Functional connectivity of the centromedial, basolateral, and superficial amygdala subdivisions was compared between groups. We also assessed the relationship between amygdala network dysfunction and anxiety severity. RESULTS Adolescents with GAD exhibited disruptions in amygdala-based intrinsic functional connectivity networks that included regions in medial prefrontal cortex, insula, and cerebellum. Positive correlations between anxiety severity scores and amygdala functional connectivity with insula and superior temporal gyrus were also observed within the GAD group. There was some evidence of greater overlap (less differentiation of connectivity patterns) of the right basolateral and centromedial amygdala networks in the adolescents with, relative to those without, GAD. CONCLUSIONS These findings suggest that adolescents with GAD manifest alterations in amygdala circuits involved in emotion processing, similar to findings in adults. In addition, disruptions were observed in amygdala-based networks involved in fear processing and the coding of interoceptive states.

Age, sex and laterality effects on cerebral glucose metabolism in healthy adults

Normal cerebral glucose metabolism (CMRglc) was assessed with positron emission tomography in 66 healthy adults (28 women, 38 men; mean age 39, range 20--69 years) to determine effects of age, sex and laterality on CMRglc using statistical parametric mapping. Significant age-related decreases in global metabolism (gCMRglc) were noted in the entire sample and in both sexes, as well as widespread and bilateral decreases in cortical absolute regional metabolism (rCMRglc) and more focal anterior paralimbic normalized rCMRglc. However, significant positive correlations of age with normalized rCMRglc were observed in cerebellum, thalamus and occipital areas. Although the declines in gCMRglc and rCMRglc with age did not significantly differ between sexes, men compared with women had significantly lower gCMRglc and widespread decreased cortical and subcortical absolute rCMRglc. In the entire sample, and similarly in both sexes, left greater than right asymmetry was observed in medial frontal gyrus, posterior thalamus, lingual gyrus, cuneus and superior cingulate. The opposite laterality appeared in mesio-anterior cerebellum, and lateral frontal and temporal regions. Few regions showed significant interactions of metabolic laterality with either age or sex. These findings contribute toward a convergence in the literature, and the regression models of CMRglc vs. age serve as a normative database to which patients may be compared.

Opposite effects of high and low frequency rTMS on mood in depressed patients: relationship to baseline cerebral activity on PET.

BACKGROUND Optimal parameters of rTMS for antidepressant efficacy in general, or within patients, have not been adequately delineated. METHODS Using a double-blind, sham-controlled, cross-over design, 22 adult patients with treatment refractory major depression (n=9; bipolar disorder, depressed phase) were randomized to active rTMS (20-Hz or 1-Hz) or sham rTMS conditions and given 5 rTMS treatments per week for two weeks. Repetitive TMS was administered at 100% of motor threshold for 1600 pulses over the left prefrontal cortex using a figure-eight coil. Patients initially randomized to sham rTMS were then exposed to two weeks of active rTMS with each frequency under blinded conditions. Those who received active 20-Hz and 1-Hz rTMS were crossed over to the opposite frequency for two weeks. Improvement in Hamilton Depression ratings were assessed after each two-week treatment phase. PET imaging was used to evaluate the patients baseline absolute regional cerebral activity (blood flow and metabolism) as potential predictor of clinical response. RESULTS Changes in depression severity on 1-Hz and 20-Hz rTMS were inversely correlated. PET scans with baseline hypoperfusion (but not hypometabolism) were associated with better improvement on 20-Hz rTMS as predicted. LIMITATIONS The magnitude of the clinical change with either frequency at 100% motor threshold was not robust, and larger studies with higher intensities of rTMS for longer durations of time should be explored. CONCLUSIONS High and low frequency rTMS exerts differential effects on depressed mood within individual subjects. The brain activity predictors and correlates of an optimal antidepressant response to rTMS remain to be better defined.

Left prefrontal-repetitive transcranial magnetic stimulation (rTMS) and regional cerebral glucose metabolism in normal volunteers

Repetitive transcranial magnetic stimulation (rTMS) holds promise as a probe into the pathophysiology and possible treatment of neuropsychiatric disorders. To explore its regional effects, we combined rTMS with positron emission tomography (PET). Fourteen healthy volunteers participated in a baseline 18-fluorodeoxyglucose (FDG) PET scan. During a second FDG infusion on the same day, seven subjects received 30 min of 1 Hz rTMS at 80% of motor threshold to left prefrontal cortex, and seven other subjects received sham rTMS under identical conditions. Global and normalized regional cerebral glucose metabolic rates (rCMRglu) from the active and sham conditions were compared to baseline and then to each other. Sham, but not active 1 Hz rTMS, was associated with significantly increased global CMRglu. Compared to baseline, active rTMS induced normalized decreases in rCMRglu in right prefrontal cortex, bilateral anterior cingulate, basal ganglia (L>R), hypothalamus, midbrain, and cerebellum. Increases in rCMRglu were seen in bilateral posterior temporal and occipital cortices. Sham rTMS compared to baseline resulted in isolated normalized decreases in rCMRglu in left dorsal anterior cingulate and left basal ganglia, and increases in posterior association and occiptal regions. Differences between the 1 Hz active versus sham changes from baseline revealed that active rTMS induced relative decrements in rCMRglu in the left superior frontal gyrus and increases in the cuneus (L>R). One Hertz rTMS at 80% motor threshold over the left prefrontal cortex in healthy subjects compared to sham rTMS in another group (each compared to baseline) induced an area of decreased normalized left prefrontal rCMRglu not directly under the stimulation site, as well as increases in occipital cortex. While these results are in the predicted direction, further studies using other designs and higher intensities and frequencies of rTMS are indicated to better describe the local and distant changes induced by rTMS.