Dopamine Modulates Effective Connectivity in Frontal Cortex.

There is increasing evidence that the left lateral frontal cortex is hierarchically organized such that higher-order regions have an asymmetric top-down influence over lower order regions. However, questions remain about the underlying neuroarchitecture of this hierarchical control organization. Within the frontal cortex, dopamine plays an important role in cognitive control functions, and we hypothesized that dopamine may preferentially influence top-down connections within the lateral frontal hierarchy. Using a randomized, double-blind, within-subject design, we analyzed resting-state fMRI data of 66 healthy young participants who were scanned once each after administration of bromocriptine (a dopamine agonist with preferential affinity for D2 receptor), tolcapone (an inhibitor of catechol-O-methyltransferase), and placebo, to determine whether dopaminergic stimulation modulated effective functional connectivity between hierarchically organized frontal regions in the left hemisphere. We found that dopaminergic drugs modulated connections from the caudal middle frontal gyrus and the inferior frontal sulcus to both rostral and caudal frontal areas. In dorsal frontal regions, effectivity connectivity strength was increased, whereas in ventral frontal regions, effective connectivity strength was decreased. These findings suggest that connections within frontal cortex are differentially modulated by dopamine, which may bias the influence that frontal regions exert over each other.

Assessing the Efficacy and Safety of a Digital Therapeutic for Symptoms of Depression in Adolescents: Protocol for a Randomized Controlled Trial.

BACKGROUND: Depression is a serious, prevalent, recurrent, and undertreated disorder in adolescents. Low levels of treatment seeking and treatment adherence in this age group, combined with a growing national crisis in access to mental health care, have increased efforts to identify effective treatment alternatives for this demographic. Digital health interventions for mental illness can provide cost-effective, engaging, and accessible means of delivering psychotherapy to adolescents. OBJECTIVE: This protocol describes a virtual randomized controlled trial designed to evaluate the efficacy and safety of a self-guided, mobile app-based implementation of behavioral activation therapy, SparkRx, for the adjunct treatment of symptoms of depression in adolescents. METHODS: Participants are recruited directly through web-based and print advertisements. Following eligibility screening and consenting, participants are randomly assigned to a treatment arm (SparkRx) or a control arm (assessment-enhanced usual care) for 5 weeks. The primary efficacy outcome, total score on the 8-item Patient Health Questionnaire (PHQ-8), is assessed at the end of the 5-week intervention period. Additional participant-reported outcomes are assessed at baseline, the postintervention time point, and 1-month follow-up. The safety of the intervention is assessed by participant report (and legal guardian report, if the participant is younger than 18 years) and by patterns of symptom deterioration on the PHQ-8, as part of a larger clinical safety monitoring protocol. The primary efficacy outcome, total PHQ-8 score at the postintervention time point, will be compared between SparkRx and enhanced usual care arms using mixed effect modeling, with baseline PHQ-8 and current antidepressant medication status included as covariates. Secondary efficacy outcomes, including the proportion of participants exhibiting treatment response, remission, and minimal clinically significant improvement (all derived from total PHQ-8 scores), will be compared between groups using chi-square tests. Symptom severity at 1-month follow-up will also be compared between arms. Planned subgroup analyses will examine the robustness of treatment effects to differences in baseline symptom severity (PHQ-8 score <15 or ≥ 15) and age (younger than 18 years and older than 18 years). The primary safety outcome, the number of psychiatric serious adverse events, will be compared between trial arms using the Fisher exact test. All other adverse events will be presented descriptively. RESULTS: As of May 2023, enrollment into the study has concluded; 223 participants were randomized. The analysis of the efficacy and safety data is expected to be completed by Fall 2023. CONCLUSIONS: We hypothesize that the results of this trial will support the efficacy and safety of SparkRx in attenuating symptoms of depression in adolescents. Positive results would more broadly support the prospect of using accessible, scientifically validated, digital therapeutics in the adjunct treatment of mental health disorders in this age range. TRIAL REGISTRATION: ClinicalTrials.gov NCT05462652; https://clinicaltrials.gov/study/NCT05462652. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/48740.

Striatal dopamine synthesis and cognitive flexibility differ between hormonal contraceptive users and nonusers.

In rodents and nonhuman primates, sex hormones are powerful modulators of dopamine (DA) neurotransmission. Yet less is known about hormonal regulation of the DA system in the human brain. Using positron emission tomography (PET), we address this gap by comparing hormonal contraceptive users and nonusers across multiple aspects of DA function: DA synthesis capacity via the PET radioligand 6-[18F]fluoro-m-tyrosine ([18F]FMT), baseline D2/3 receptor binding potential using [11C]raclopride, and DA release using methylphenidate-paired [11C]raclopride. Participants consisted of 36 healthy women (n = 15 hormonal contraceptive users; n = 21 naturally cycling/non users of hormonal contraception), and men (n = 20) as a comparison group. A behavioral index of cognitive flexibility was assessed prior to PET imaging. Hormonal contraceptive users exhibited greater DA synthesis capacity than NC participants, particularly in dorsal caudate, and greater cognitive flexibility. Furthermore, across individuals, the magnitude of striatal DA synthesis capacity was associated with cognitive flexibility. No group differences were observed in D2/3 receptor binding or DA release. Analyses by sex alone may obscure underlying differences in DA synthesis tied to women's hormone status. Hormonal contraception (in the form of pill, shot, implant, ring, or intrauterine device) is used by ~400 million women worldwide, yet few studies have examined whether chronic hormonal manipulations impact basic properties of the DA system. Findings from this study begin to address this critical gap in women's health.

Associations among locus coeruleus catecholamines, tau pathology, and memory in aging.

The locus coeruleus (LC) is the brain's major source of the neuromodulator norepinephrine, and is also profoundly vulnerable to the development of Alzheimer's disease (AD)-related tau pathology. Norepinephrine plays a role in neuroprotective functions that may reduce AD progression, and also underlies optimal memory performance. Successful maintenance of LC neurochemical function represents a candidate mechanism of protection against the propagation of AD-related pathology and may facilitate the preservation of memory performance despite pathology. Using [18F]Fluoro-m-tyrosine ([18F]FMT) PET imaging to measure catecholamine synthesis capacity in LC regions of interest, we examined relationships among LC neurochemical function, AD-related pathology, and memory performance in cognitively normal older adults (n = 49). Participants underwent [11C]Pittsburgh compound B and [18F]Flortaucipir PET to quantify ß-amyloid (n = 49) and tau burden (n = 42) respectively. In individuals with substantial ß-amyloid, higher LC [18F]FMT net tracer influx (Kivis) was associated with lower temporal tau. Longitudinal tau-PET analyses in a subset of our sample (n = 30) support these findings to reveal reduced temporal tau accumulation in the context of higher LC [18F]FMT Kivis. Higher LC catecholamine synthesis capacity was positively correlated with self-reported cognitive engagement and physical activity across the lifespan, established predictors of successful aging measured with the Lifetime Experiences Questionnaire. LC catecholamine synthesis capacity moderated tau's negative effect on memory, such that higher LC catecholamine synthesis capacity was associated with better-than-expected memory performance given an individual's tau burden. These PET findings provide insight into the neurochemical mechanisms of AD vulnerability and cognitive resilience in the living human brain.

Enhancing dopamine tone modulates global and local cortical perfusion as a function of COMT val158met genotype.

The cognitive effects of pharmacologically enhancing cortical dopamine (DA) tone are variable across healthy human adults. It has been postulated that individual differences in drug responses are linked to baseline cortical DA activity according to an inverted-U-shaped function. To better understand the effect of divergent starting points along this curve on DA drug responses, researchers have leveraged a common polymorphism (rs4680) in the gene encoding the enzyme catechol-O-methyltransferase (COMT) that gives rise to greater (Met allele) or lesser (Val allele) extracellular levels of cortical DA. Here we examined the extent to which changes in resting cortical perfusion following the administration of two mechanistically-distinct dopaminergic drugs vary by COMT genotype, and thereby track predictions of the inverted-U model. Using arterial spin labeling (ASL) and a double-blind, within-subject design, perfusion was measured in 75 healthy, genotyped participants once each after administration of tolcapone (a COMT inhibitor), bromocriptine (a DA D2/3 agonist), and placebo. COMT genotype and drug interacted such that COMT Val homozygotes exhibited increased prefusion in response to both drugs, whereas Met homozygotes did not. Additionally, tolcapone-related perfusion changes in the right inferior frontal gyrus correlated with altered performance on a task of executive function. No comparable effects were found for a genetic polymorphism (rs1800497) affecting striatal DA system function. Together, these results indicate that both the directionality and magnitude of drug-induced perfusion change provide meaningful information about individual differences in response to enhanced cortical DA tone.

Augmenting Frontal Dopamine Tone Enhances Maintenance over Gating Processes in Working Memory.

The contents of working memory must be maintained in the face of distraction, but updated when appropriate. To manage these competing demands of stability and flexibility, maintained representations in working memory are complemented by distinct gating mechanisms that selectively transmit information into and out of memory stores. The operations of such dopamine-dependent gating systems in the midbrain and striatum and their complementary dopamine-dependent memory maintenance operations in the cortex may therefore be dissociable. If true, selective increases in cortical dopamine tone should preferentially enhance maintenance over gating mechanisms. To test this hypothesis, tolcapone, a catechol-O-methyltransferase inhibitor that preferentially increases cortical dopamine tone, was administered in a randomized, double-blind, placebo-controlled, within-subject fashion to 49 participants who completed a hierarchical working memory task that varied maintenance and gating demands. Tolcapone improved performance in a condition with higher maintenance requirements and reduced gating demands, reflected in a reduction in the slope of RTs across the distribution. Resting-state fMRI data demonstrated that the degree to which tolcapone improved performance in individual participants correlated with increased connectivity between a region important for stimulus response mappings (left dorsal premotor cortex) and cortical areas implicated in visual working memory, including the intraparietal sulcus and fusiform gyrus. Together, these results provide evidence that augmenting cortical dopamine tone preferentially improves working memory maintenance.

Effects of Dopaminergic Drugs on Cognitive Control Processes Vary by Genotype.

Dopamine (DA) has been implicated in modulating multiple cognitive control processes, including the robust maintenance of task sets and memoranda in the face of distractors (cognitive stability) and, conversely, the ability to switch task sets or update the contents of working memory when it is advantageous to do so (cognitive flexibility). In humans, the limited specificity of available pharmacological probes has posed a challenge for understanding the mechanisms by which DA, acting on multiple receptor families across the PFC and striatum, differentially influences these cognitive processes. Using a within-subject, placebo-controlled design, we contrasted the impact of two mechanistically distinct DA drugs, tolcapone (an inhibitor of catechol-O-methyltransferase [COMT], a catecholamine inactivator) and bromocriptine (a DA agonist with preferential affinity for the D2 receptor), on the maintenance and switching of task rules. Given previous work demonstrating that drug effects on behavior are dependent on baseline DA tone, participants were stratified according to genetic polymorphisms associated with cortical (COMT Val158Met) and striatal (Taq1A) DA system function. Our results were partially consistent with an inverted-U-shaped relationship between tolcapone and robust rule maintenance (interaction with COMT genotype) and between bromocriptine and cued rule switching (interaction with Taq1A genotype). However, when task instructions were ambiguous, a third relationship emerged to explain drug effects on spontaneous task switching (interaction of COMT genotype and bromocriptine). Together, this pattern of results suggests that the effects of DA drugs vary not only as a function of the DA system component upon which they act but also on subtle differences in task demands and context.

Dopaminergic Mechanisms Underlying Normal Variation in Trait Anxiety.

Trait anxiety has been associated with altered activity within corticolimbic pathways connecting the amygdala and rostral anterior cingulate cortex (rACC), which receive rich dopaminergic input. Though the popular culture uses the term "chemical imbalance" to describe the pathophysiology of psychiatric conditions such as anxiety disorders, we know little about how individual differences in human dopamine neurochemistry are related to variation in anxiety and activity within corticolimbic circuits. We addressed this issue by examining interindividual variability in dopamine release at rest using [11C]raclopride positron emission tomography (PET), functional connectivity between amygdala and rACC using resting-state functional magnetic resonance imaging (fMRI), and trait anxiety measures in healthy adult male and female humans. To measure endogenous dopamine release, we collected two [11C]raclopride PET scans per participant. We contrasted baseline [11C]raclopride D2/3 receptor binding and D2/3 receptor binding following oral methylphenidate administration. Methylphenidate blocks the dopamine transporter, which increases extracellular dopamine and leads to reduced [11C]raclopride D2/3 receptor binding via competitive displacement. We found that individuals with higher dopamine release in the amygdala and rACC self-reported lower trait anxiety. Lower trait anxiety was also associated with reduced rACC-amygdala functional connectivity at baseline. Further, functional connectivity showed a modest negative relationship with dopamine release such that reduced rACC-amygdala functional connectivity was accompanied by higher levels of dopamine release in these regions. Together, these findings contribute to hypodopaminergic models of anxiety and support the utility of combining fMRI and PET measures of neurochemical function to advance our understanding of basic affective processes in humans.SIGNIFICANCE STATEMENT It is common wisdom that individuals vary in their baseline levels of anxiety. We all have a friend or colleague we know to be more "tightly wound" than others, or, perhaps, we are the ones marveling at others' ability to "just go with the flow." Although such observations about individual differences within nonclinical populations are commonplace, the neural mechanisms underlying normal variation in trait anxiety have not been established. Using multimodal brain imaging in humans, this study takes initial steps in linking intrinsic measures of neuromodulator release and functional connectivity within regions implicated in anxiety disorders. Our findings suggest that in healthy adults, higher levels of trait anxiety may arise, at least in part, from reduced dopamine neurotransmission.

Dopamine Synthesis Capacity is Associated with D2/3 Receptor Binding but Not Dopamine Release.

Positron Emission Tomography (PET) imaging allows the estimation of multiple aspects of dopamine function including dopamine synthesis capacity, dopamine release, and D2/3 receptor binding. Though dopaminergic dysregulation characterizes a number of neuropsychiatric disorders including schizophrenia and addiction, there has been relatively little investigation into the nature of relationships across dopamine markers within healthy individuals. Here we used PET imaging in 40 healthy adults to compare, within individuals, the estimates of dopamine synthesis capacity (Ki) using 6-[18F]fluoro-l-m-tyrosine ([18F]FMT; a substrate for aromatic amino acid decarboxylase), baseline D2/3 receptor-binding potential using [11C]raclopride (a weak competitive D2/3 receptor antagonist), and dopamine release using [11C]raclopride paired with oral methylphenidate administration. Methylphenidate increases synaptic dopamine by blocking the dopamine transporter. We estimated dopamine release by contrasting baseline D2/3 receptor binding and D2/3 receptor binding following methylphenidate. Analysis of relationships among the three measurements within striatal regions of interest revealed a positive correlation between [18F]FMT Ki and the baseline (placebo) [11C]raclopride measure, such that participants with greater synthesis capacity showed higher D2/3 receptor-binding potential. In contrast, there was no relationship between [18F]FMT and methylphenidate-induced [11C]raclopride displacement. These findings shed light on the nature of regulation between pre- and postsynaptic dopamine function in healthy adults, which may serve as a template from which to identify and describe alteration with disease.

Anticipatory and consummatory pleasure and displeasure in major depressive disorder: An experience sampling study.

Pleasure and displeasure can be parsed into anticipatory and consummatory phases. However, research on pleasure and displeasure in major depressive disorder (MDD), a disorder characterized by anhedonia, has largely focused on deficits in the consummatory phase. Moreover, most studies in this area have been laboratory-based, raising the question of how component processes of pleasure and displeasure are experienced in the daily lives of depressed individuals. Using experience sampling, we compared anticipatory and consummatory pleasure and displeasure for daily activities reported by adults with MDD (n = 41) and healthy controls (n = 39). Participants carried electronic devices for one week and were randomly prompted eight times a day to answer questions about activities to which they most and least looked forward. Compared to healthy controls, MDD participants reported blunted levels of both anticipatory and consummatory pleasure and elevated levels of both anticipatory and consummatory displeasure for daily activities. Independent of MDD status, participants accurately predicted pleasure but overestimated displeasure. These results are the first to provide evidence that, across both anticipatory and consummatory phases, individuals with MDD experience blunted pleasure and elevated displeasure for daily activities. Our findings clarify the disturbances in pleasure and displeasure that characterize MDD and may inform treatment for this debilitating disorder. (PsycINFO Database Record

Habenula responses to potential and actual loss in major depression: preliminary evidence for lateralized dysfunction.

The habenula has been implicated in predicting negative events and in responding to unexpected negative outcomes. Animal models of depression have supported the hypothesis that perturbations in habenula activity contribute to the pathophysiology of Major Depressive Disorder (MDD), a psychiatric illness characterized by abnormalities in responding to negative feedback and by pessimism in evaluating the likelihood of future events. No research to date, however, has examined human habenula responses to potential and experienced negative outcomes in MDD. In this study, depressed and healthy control participants performed a probabilistic guessing task for monetary rewards and penalties during high-resolution functional magnetic resonance imaging of the habenula. In healthy adults, we observed a pattern of habenula activation consistent with its hypothesized role in predicting future losses and responding to suboptimal outcomes. In contrast, in depressed participants the left habenula was not activated significantly during the prediction or experience of monetary penalty. Complementing this group difference, attenuated habenula activation to negative feedback in control participants was associated with levels of shame and rumination. The results of this study suggest that depressed individuals are characterized by dysfunction in a neural system involved in generating expectations and comparing expectations with objective outcomes.

Amygdala responses to salient social cues vary with oxytocin receptor genotype in youth.

Depression, anxiety, and posttraumatic stress disorder are linked to altered limbic morphology, dysregulated neuroendocrine function, and heightened amygdala responses to salient social cues. Oxytocin appears to be a potent modulator of amygdala reactivity and neuroendocrine responses to psychosocial stress. Given these stress regulatory effects, there is increasing interest in understanding the role of oxytocin in vulnerability to stress-related clinical disorders. The present study examines the impact of a common functional variant within the oxytocin receptor (OXTR) gene (rs2254298) on structure and function of the amygdala in a high-risk sample of urban, low-income, minority youth with a high incidence of early life stress (ELS). Compared to G/G homozygotes, youth carrying the OXTR A-allele showed increased amygdala volume, reduced behavioral performance, and heightened amygdala response during two functional magnetic resonance imaging (fMRI) tasks that involved viewing socially-relevant face stimuli. Higher amygdala response was related to ELS in A-allele carriers but not G/G homozygotes. These findings underscore a series of relations among a common oxytocin system gene variant, ELS exposure, and structure and function of the amygdala in early life. Heightened amygdala response to salient social cues in OXTR A-allele carriers may elevate risk for emotional psychopathology by increasing amygdala involvement in disambiguating environmental cues, particularly for individuals with ELS.

Memory for novel positive information in major depressive disorder.

Major depressive disorder (MDD) is associated with biases in memory, including poor memory for positive stimuli. It is unclear, however, if this impaired memory for positive stimuli in MDD is related to difficulties in the initial processing of stimuli, or alternatively, reflects a decreased ability to draw on memories of positive stimuli after they have been formed. Using two versions of a word-matching task that featured a mixture of novel and practiced emotionally valenced words, we found that depressed individuals experienced greater difficulty learning positively valenced information than did their nondepressed peers. This difficulty seemed to be specific to initial encounters with the novel, but not the practiced, positive stimuli. These findings suggest that memory deficits for positive information associated with depression are related to how this information is initially processed. Implications of these findings for interventions are discussed and directions for future research are advanced.

Activation of the medial prefrontal and posterior cingulate cortex during encoding of negative material predicts symptom worsening in major depression.

Considerable research indicates that depressed individuals have better memory for negative material than do nondepressed individuals, and that this bias is associated with differential patterns of neural activation. It is not known, however, whether these aberrant activation patterns predict illness course. Using functional neuroimaging, we examined whether change in depressive symptoms is predicted by baseline patterns of neural activation that underlie negative memory biases in major depressive disorder. Depressed participants viewed negative and neutral pictures during functional MRI at baseline and completed an incidental memory task for these pictures 1 week later. Depression severity was assessed by administering the Beck Depression Inventory both at baseline (Time 1) and at Time 2, an average of 18 months later. Contrast maps of activation for subsequently remembered negative versus subsequently remembered neutral pictures were regressed against change in Beck Depression Inventory scores between Time 1 and Time 2, controlling for initial symptom severity. Results from this analysis revealed no associations between memory sensitivity for negative stimuli and symptom change. In contrast, whole brain analyses revealed significant positive associations between within-subject changes in depressive symptoms and baseline neural activation to successfully recalled negative pictures in the posterior cingulate cortex and medial prefrontal cortex. These findings indicate that neural activation in cortical midline regions is a better predictor of long-term symptomatic outcome than is memory sensitivity for negative material.

Interoceptive awareness, positive affect, and decision making in major depressive disorder.

BACKGROUND: Little work has examined the relation between interoceptive awareness and symptoms of Major Depressive Disorder (MDD). Existing research suggests that depressed individuals exhibit impaired heartbeat perception, though the results of this research have been equivocal. Importantly, depressed participants in these studies have had comorbid anxiety disorders, making it difficult to draw inferences about interoceptive awareness in MDD. The current study addresses this issue by assessing heartbeat perception in depressed women without current anxiety disorders and exploring the relation between interoception and perturbations in both affective intensity and decision making, components of MDD postulated to be related to bodily awareness. METHODS: Depressed women without concurrent anxiety disorders (n=25) and never-disordered controls (n=36) performed a heartbeat perception task. Participants completed the self-report Affect Intensity Measure (AIM), and decision-making difficulty was assessed in MDD participants using the Structured Clinical Interview for DSM-IV. RESULTS: Depressed women exhibited poorer heartbeat perception accuracy than did control participants. Impaired accuracy in MDD participants was associated with reduced positive affectivity and difficulty in decision making. LIMITATIONS: Our sample was composed exclusively of females and was heterogeneous with respect to treatment status, thereby limiting our ability to generalize results to depressed males and to exclude the contribution of exogenous factors to the observed group differences. CONCLUSIONS: Results of this study suggest that for depressed individuals without anxiety comorbidities, disrupted perception of bodily responses reduces both the experience of positive arousal and the ability to use interoceptive feedback to inform decision making.

Functional neuroimaging of major depressive disorder: a meta-analysis and new integration of base line activation and neural response data.

OBJECTIVE: Functional neuroimaging investigations of major depressive disorder can advance both the neural theory and treatment of this debilitating illness. Inconsistency of neuroimaging findings and the use of region-of-interest approaches have hindered the development of a comprehensive, empirically informed neural model of major depression. In this context, the authors sought to identify reliable anomalies in baseline neural activity and neural response to affective stimuli in major depressive disorder. METHOD: The authors applied voxel-wise, whole-brain meta-analysis to neuroimaging investigations comparing depressed to healthy comparison groups with respect to baseline neural activity or neural response to positively and/or negatively valenced stimuli. RESULTS: Relative to healthy subjects, those with major depression had reliably higher baseline activity, bilaterally, in the pulvinar nucleus. The analysis of neural response studies using negative stimuli showed greater response in the amygdala, insula, and dorsal anterior cingulate cortex and lower response in the dorsal striatum and dorsolateral prefrontal cortex in individuals with major depressive disorder than in healthy subjects. CONCLUSIONS: The meta-analytic results support an elegant and neuroanatomically viable model of the salience of negative information in major depressive disorder. In this proposed model, high baseline pulvinar activity in depression first potentiates responding of the brain's salience network to negative information; next, and owing potentially to low striatal dopamine levels in depression, this viscerally charged information fails to propagate up the cortical-striatal-pallidalthalamic circuit to the dorsolateral prefrontal cortex for contextual processing and reappraisal.

Default-mode and task-positive network activity in major depressive disorder: implications for adaptive and maladaptive rumination.

BACKGROUND: Major depressive disorder (MDD) has been associated reliably with ruminative responding; this kind of responding is composed of both maladaptive and adaptive components. Levels of activity in the default-mode network (DMN) relative to the task-positive network (TPN), as well as activity in structures that influence DMN and TPN functioning, may represent important neural substrates of maladaptive and adaptive rumination in MDD. METHODS: We used a unique metric to estimate DMN dominance over TPN from blood oxygenation level-dependent data collected during eyes-closed rest in 17 currently depressed and 17 never-disordered adults. We calculated correlations between this metric of DMN dominance over TPN and the depressive, brooding, and reflective subscales of the Ruminative Responses Scale, correcting for associations between these measures both with one another and with severity of depression. Finally, we estimated and compared across groups right fronto-insular cortex (RFIC) response during initiations of ascent in DMN and in TPN activity. RESULTS: In the MDD participants, increasing levels of DMN dominance were associated with higher levels of maladaptive, depressive rumination and lower levels of adaptive, reflective rumination. Moreover, our RFIC state-change analysis showed increased RFIC activation in the MDD participants at the onset of increases in TPN activity; conversely, healthy control participants exhibited increased RFIC response at the onset of increases in DMN activity. CONCLUSIONS: These findings support a formulation in which the DMN undergirds representation of negative, self-referential information in depression, and the RFIC, when prompted by increased levels of DMN activity, initiates an adaptive engagement of the TPN.

Variant in oxytocin receptor gene is associated with amygdala volume.

The oxytocin system plays a significant role in modulating stress responses in animals and humans; perturbations in this system may contribute to the pathogenesis of psychiatric disorder. Attempts to identify clinically relevant genetic variants in the oxytocin system have yielded associations between polymorphisms of the oxytocin receptor (OXTR) gene and both autism and major depression. To date, however, little is known about how such variants affect brain structures implicated in these disorders. Applying a manual tracing procedure to high-resolution structural magnetic resonance images, amygdala volumes were measured in 51 girls genotyped on OXTR rs2254298(G>A), a single nucleotide polymorphism associated with psychopathology. Results of this study indicate that despite having greater gray matter volume, participants homozygous for the G allele were characterized by smaller volumes of both left and right amygdala than were carriers of the A allele. A subsequent whole-brain voxel-based morphometry analysis revealed additional genotype-mediated volumetric group differences in the posterior brain stem and dorsomedial anterior cingulate cortex. These findings highlight one neurobiological pathway by which oxytocin gene variants may increase risk for psychopathology. Further research is needed to characterize the mechanism by which this polymorphism contributes to anatomical variability and to identify functional correlates of these alterations in regional brain volume.

Altered timing of amygdala activation during sad mood elaboration as a function of 5-HTTLPR.

A functional variant of the serotonin transporter gene (5-HTTLPR) has been associated with increased risk for major depression in the context of stress. In attempting to understand the mechanisms underlying this relation, we tested the hypothesis that 5-HTTLPR genotype affects the speed with which amygdala is recruited during emotional processing in young girls with no history of psychiatric disorder. We used functional magnetic resonance imaging to compare the rise time to peak amygdala activation in 5-HTTLPR short-allele carriers and long-allele homozygotes during enhancement of sad mood. Relative to long-allele homozygotes, participants with at least one copy of the 5-HTTLPR short allele showed both stronger and earlier activation in left amygdala as they increased a sad mood state. Individuals carrying the short allele appear to exhibit a neural 'readiness' to engage and enhance negative affect. Future research should examine how exposure to negative life events and more chronic sadness modify the time course of amygdala activity during the experience of negative emotion.

Frontostriatal functional connectivity in major depressive disorder.

BACKGROUND: Abnormalities of the striatum and frontal cortex have been reported consistently in studies of neural structure and function in major depressive disorder (MDD). Despite speculation that compromised connectivity between these regions may underlie symptoms of MDD, little work has investigated the integrity of frontostriatal circuits in this disorder. METHODS: Functional magnetic resonance images were acquired from 21 currently depressed and 19 never-disordered women during wakeful rest. Using four predefined striatal regions-of-interest, seed-to-whole brain correlations were computed and compared between groups. RESULTS: Compared to controls, depressed participants exhibited attenuated functional connectivity between the ventral striatum and both ventromedial prefrontal cortex and subgenual anterior cingulate cortex. Depressed participants also exhibited stronger connectivity between the dorsal caudate and dorsal prefrontal cortex, which was positively correlated with severity of the disorder. CONCLUSIONS: Depressed individuals are characterized by aberrant connectivity in frontostriatal circuits that are posited to support affective and cognitive processing. Further research is required to examine more explicitly the link between patterns of disrupted connectivity and specific symptoms of depression, and the extent to which these patterns precede the onset of depression and normalize with recovery from depressive illness.