Differential modulation of emotion processing brain regions by noradrenergic and serotonergic antidepressants

The effect and safety of probiotics on depression: a systematic review and meta-analysis of randomized controlled trials

PURPOSE

With the escalating social pressures, there has been a continuous rise in the prevalence of depression among the population, leading to substantial healthcare burdens. Moreover, conventional pharmacological interventions still exhibit certain limitations. Therefore, the primary objective of this study is to systematically evaluate the clinical efficacy of probiotics in the treatment of depression.

METHODS

Randomized controlled trials of probiotics in treating depressive symptoms were retrieved from Pubmed, Cochrane Library, Web of Science, Wan Fang database, and CNKI between the establishment of the database and March 2022. The primary outcome was Beck's depression rating scale (BDI) scores, while the secondary outcomes were depression scores on the DASS-21 scale, biochemical indicators (IL-6, NO, and TNF-α levels), and adverse events. In addition, Revman 5.3 was used for Meta-analysis and quality evaluation, and Stata 17 was used for the Egger test and Begg's test. A total of 776 patients, including 397 and 379 patients in the experimental and control groups, respectively, were included.

RESULTS

The total BDI score of the experimental group was lower than that of the control group (MD = - 1.98, 95%CI - 3.14 to - 0.82), and the score of DASS (MD = 0.90, 95%CI - 1.17 to 2.98), the IL-6 level (SMD = - 0.55, 95%CI - 0.88 to - 0.23), the NO level (MD = 5.27, 95% CI 2.51 to 8.03), and the TNF-α level (SMD = 0.19, 95% CI - 0.25 to 0.63).

CONCLUSION

The findings substantiate the therapeutic potential of probiotics in mitigating depressive symptoms by significantly reducing Beck's Depression Inventory (BDI) scores and alleviating the overall manifestation of depression.

Self-blame-selective hyper-connectivity between anterior temporal and subgenual cortices predicts prognosis in major depressive disorder

BACKGROUND

Self-blame-related fMRI measures were shown to predict subsequent recurrence in remitted major depressive disorder (MDD). Their role in current MDD, however, is unknown. We hypothesised that these neural signatures reflect a highly recurrent but remitting course of MDD and therefore predict favourable outcomes over a four-month follow-up period in current MDD.

METHODS

Forty-five participants with current MDD and non-responders to at least two serotonergic antidepressants, were encouraged to optimise their medication and followed up after receiving four months of primary care treatment-as-usual. Prior to their medication review, participants completed an fMRI paradigm in which they viewed self- and other-blame emotion-evoking statements. Thirty-nine participants met pre-defined fMRI data minimum quality thresholds. Psychophysiological interaction analysis was used to determine baseline connectivity of the right superior anterior temporal lobe (RSATL), with an a priori BA25 region-of-interest for self-blaming vs other-blaming emotions, using Quick Inventory of Depressive Symptomatology (16-item) percentage change as a covariate.

RESULTS

We corroborated our pre-registered hypothesis that a favourable clinical outcome was associated with higher self-blame-selective RSATL-BA25 connectivity (Family-Wise Error-corrected p <.05 over the a priori BA25 region-of-interest; rs(34) = -0.47, p =.005). This generalised to the sample including participants with suboptimal fMRI quality (rs(39) = -0.32, p =.05).

CONCLUSIONS

This study shows that neural signatures of overgeneralised self-blame are relevant for prognostic stratification of current treatment-resistant MDD. Future studies need to confirm whether this neural signature indeed represents a trait-like feature of a fully remitting subtype of MDD, or whether it is also modulated by depressive state and related to treatment effects.

A pharmacological challenge paradigm to assess neural signatures of script-elicited acute dissociation in women with post-traumatic stress disorder

BACKGROUND

There is limited experimentally controlled neuroimaging research available that could explain how dissociative states occur and which neurobiological changes are involved in acute post-traumatic dissociation.

AIMS

To test the causal hypothesis that acute dissociation is triggered bottom-up by a selective noradrenergic-mediated increase in amygdala activation during the processing of autobiographical trauma memories.

METHOD

Women with post-traumatic stress disorder (n = 47) and a history of interpersonal childhood trauma underwent a within-participant, placebo-controlled pharmacological challenge paradigm (4.0 mg reboxetine versus placebo) employing script-driven imagery (traumatic versus neutral autobiographical memory recall). Script-elicited brain activation patterns (measured via functional magnetic resonance imagery) were analysed by means of whole-brain analyses and a pre-registered region of interest (i.e. amygdala).

RESULTS

Self-reported acute dissociation increased significantly during trauma (versus neutral) recall but did not differ between pharmacological conditions. The pharmacological manipulation was also unsuccessful in eliciting increased amygdala activation following script-driven imagery in the reboxetine (versus placebo) condition. In the reboxetine condition, trauma retrieval resulted in similar activation patterns as in the placebo condition (e.g. elevated brain activation in the middle occipital gyrus and supramarginal gyrus), albeit with different peaks.

CONCLUSIONS

Current (null) findings cast doubt on the suggested role of the amygdala in subserving dissociative processing of trauma memories. Alternative pharmacological manipulation approaches (e.g. ketamine) and analysis techniques (e.g. event-related independent component analysis) might provide better insight into the spatiotemporal dynamics and network shifts involved in dissociative experiences and autobiographical trauma memory recall.

The effects of transient receptor potential cation channel inhibition by BI 1358894 on cortico-limbic brain reactivity to negative emotional stimuli in major depressive disorder

Abnormal emotional processing in major depressive disorder (MDD) has been associated with increased activation to negative stimuli in cortico-limbic brain regions. The authors investigated whether treatment with BI 1358894, a small-molecule inhibitor of the transient receptor potential cation channel subfamily C leads to attenuated activity in these areas in MDD patients. 73 MDD patients were randomized to receive a single oral dose of BI 1358894 (100 mg), citalopram (20 mg), or matching placebo. Brain responses to emotional faces and scenes were investigated using functional magnetic resonance imaging. Primary endpoints were BOLD signal changes in response to negative faces in cortico-limbic brain regions, i.e. bilateral amygdala (AMY), dorsolateral prefrontal cortex, anterior insula (AI), and anterior cingulate cortex. Secondary endpoints were BOLD signal changes in response to negative scenes. For each region, separate ANOVA models were computed for the comparison of treatments (BI 1358894 or citalopram) vs. placebo. The adjusted treatment differences in the % BOLD signal changes in the faces task showed that BI 1358894 induced signal reduction in bilateral AMY and left AI. In the scenes task, BI 1358894 demonstrated significant signal reduction in bilateral AMY, AI, anterior cingulate cortex and left dorsolateral prefrontal cortex. Citalopram failed to induce any significant reductions in BOLD signal in both tasks. BI 1358894-mediated inhibition of the transient receptor potential cation channel subfamily resulted in strong signal reduction in cortico-limbic brain regions, thereby supporting development of this mechanism of action for MDD patients.

Hippocampal BMP signaling as a common pathway for antidepressant action

The benefits of current treatments for depression are limited by low response rates, delayed therapeutic effects, and multiple side effects. Antidepressants affect a variety of neurotransmitter systems in different areas of the brain, and the mechanisms underlying their convergent effects on behavior have been unclear. Here we identify hippocampal bone morphogenetic protein (BMP) signaling as a common downstream pathway that mediates the behavioral effects of five different antidepressant classes (fluoxetine, bupropion, duloxetine, vilazodone, trazodone) and of electroconvulsive therapy. All of these therapies decrease BMP signaling and enhance neurogenesis in the hippocampus. Preventing the decrease in BMP signaling blocks the effect of antidepressant treatment on behavioral phenotypes. Further, inhibition of BMP signaling in hippocampal newborn neurons is sufficient to produce an antidepressant effect, while chemogenetic silencing of newborn neurons prevents the antidepressant effect. Thus, inhibition of hippocampal BMP signaling is both necessary and sufficient to mediate the effects of multiple classes of antidepressants.

Selective serotonin reuptake inhibitor treatment retunes emotional valence in primate ventral striatum

Selective serotonin reuptake inhibitors (SSRIs) are widely used to treat psychiatric disorders with affective biases such as depression and anxiety. How SSRIs exert a beneficial action on emotions associated with life events is still unknown. Here we ask whether and how the effectiveness of the SSRI fluoxetine is underpinned by neural mechanisms in the ventral striatum. To address these issues, we studied the spiking activity of neurons in the ventral striatum of monkeys during an approach-avoidance task in which the valence assigned to sensory stimuli was manipulated. Neural responses to positive and negative events were measured before and during a 4-week treatment with fluoxetine. We conducted PET scans to confirm that fluoxetine binds within the ventral striatum at a therapeutic dose. In our monkeys, fluoxetine facilitated approach of rewards and avoidance of punishments. These beneficial effects were associated with changes in tonic and phasic activities of striatal neurons. Fluoxetine increased the spontaneous firing rate of striatal neurons and amplified the number of cells responding to rewards versus punishments, reflecting a drug-induced positive shift in the processing of emotionally valenced information. These findings reveal how SSRI treatment affects ventral striatum neurons encoding positive and negative valence and striatal signaling of emotional information. In addition to a key role in appetitive processing, our results shed light on the involvement of the ventral striatum in aversive processing. Together, the ventral striatum appears to play a central role in the action of SSRIs on emotion processing biases commonly observed in psychiatric disorders.

Approach and Avoidance Behavior in Female Patients With Borderline Personality Disorder

Objectives

Borderline personality disorder (BPD) is portrayed by unstable relationships, fears of abandonment and heightened sensitivity to social rejection. Research has shown that these characteristics may lead to inappropriate social behavior including altered approach-avoidance behavior. However, it has remained unclear how social exclusion may affect approach-avoidance behavior in patients with BPD.

Design

We assessed social approach-avoidance behavior and the impact of social exclusion in a sample of 38 patients with BPD and 40 healthy control participants.

Methods

We used an explicit joystick-based approach-avoidance task (AAT) after playing a virtual ball-tossing game (Cyberball), which simulates the exclusion of the participant by two other players. In the AAT, participants were required to push or pull emotional stimuli, more specifically happy and angry facial expressions, with either direct or averted gaze direction.

Results

Patients with BPD approached happy stimuli less and showed overall less differential approach-avoidance behavior toward individuals expressing positive or negative facial emotions compared to healthy participants, who showed more approach behavior for happy compared to angry facial expressions. Moreover, borderline symptom severity correlated inversely with the AAT score for happy facial expressions and positively with subjective unpleasantness during social exclusion as well as rejection sensitivity. However, social exclusion did not influence approach-avoidance tendencies.

Conclusion

Patients with BPD showed altered approach-avoidance behavior, which might affect social interactions in the patient’s everyday lives and may therefore impede social interaction.

Baseline Perfusion Alterations Due to Acute Application of Quetiapine and Pramipexole in Healthy Adults

BACKGROUND

The dopaminergic system is implicated in many mental processes and neuropsychiatric disorders. Pharmacologically, drugs with dopamine receptor antagonistic and agonistic effects are used, but their effects on functional brain metabolism are not well known.

METHODS

In this randomized crossover, placebo-controlled, and rater-blinded study, 25 healthy adults received an acute dose placebo substance (starch), quetiapine (dopamine receptor antagonist), or pramipexole (dopamine agonist of the nonergoline class) 1 hour before the experiment. Background-suppressed 2D pseudo-continuous arterial spin labeling was used to examine whole-brain baseline cerebral blood flow differences induced by the 3 substances.

RESULTS

We found that quetiapine reduced perfusion in the occipital (early visual areas) and bilateral cerebellar cortex relative to placebo. In contrast, quetiapine enhanced cerebral blood flow (relative to placebo) in the striatal system (putamen and caudate nucleus) but also in the supplementary motor area, insular-, prefrontal- as well as in the pre- and postcentral cortex. Pramipexole increased cerebral blood flow compared with placebo in the caudate nucleus, putamen, middle frontal, supplementary motor area, and brainstem (substantia nigra), but reduced cerebral blood flow in the posterior thalamus, cerebellum, and visual areas. Pramipexole administration resulted in stronger cerebral blood flow relative to quetiapine in the hypothalamus, cerebellum, and substantia nigra.

CONCLUSIONS

Our results indicate that quetiapine and pramipexole differentially modulate regional baseline cerebral blood flow. Both substances act on the dopaminergic system, although they affect distinct regions. Quetiapine altered dopaminergic function in frontal, striatal, and motor regions. In contrast, pramipexole affected cerebral blood flow of the nigrostriatal (striatum and substantia nigra) dopaminergic, but less the fronto-insular system.

Facilitation of emotion regulation with a single dose of escitalopram: A randomized fMRI study

Acute antidepressant administration modulates neural activity consistent with decreases in negative emotion processing bias. However, studies are yet to examine whether treatment facilitates neural activity during reappraisal, an adaptive emotion regulation strategy associated with behavioral treatment response. Here we examine the impact of acute administration on reappraisal of negative stimuli using pharmaco-fMRI. Thirty-six healthy female participants completed two sessions of fMRI scanning, separated by a one-week washout period. A single dose of the selective serotonin reuptake inhibitor, escitalopram (20mg) was administered to participants using a double-blind, randomized, placebo-controlled crossover design. When participants were administered escitalopram (relative to a placebo) and asked to reappraise negative emotional stimuli, left amygdala activation was decreased and right inferior frontal gyrus (R IFG) activation was increased. Also observed was a greater negative left amygdala-R IFG functional connectivity when participants were administered escitalopram relative to placebo, and this change in connectivity was associated with reductions in subjective ratings of valence and arousal of negative stimuli. Further analysis revealed connectivity modulation across multiple frontal regions. Results suggest that the acute effect of a commonly prescribed antidepressant may include facilitating the regulation of negative emotional stimuli, providing new important leads for models of antidepressant action.

Single-dose serotonergic stimulation shows widespread effects on functional brain connectivity

The serotonergic system is widely distributed throughout the central nervous system. It is well known as a mood regulating system, although it also contributes to many other functions. With resting state functional magnetic resonance imaging (RS-fMRI) it is possible to investigate whole brain functional connectivity. We used this non-invasive neuroimaging technique to measure acute pharmacological effects of the selective serotonin reuptake inhibitor sertraline (75 mg) in 12 healthy volunteers. In this randomized, double blind, placebo-controlled, crossover study, RS-fMRI scans were repeatedly acquired during both visits (at baseline and 3, 5, 7 and 9h after administering sertraline or placebo). Within-group comparisons of voxelwise functional connectivity with ten functional networks were examined (p<0.005, corrected) using a mixed effects model with cerebrospinal fluid, white matter, motion parameters, heart rate and respiration as covariates. Sertraline induced widespread effects on functional connectivity with multiple networks; the default mode network, the executive control network, visual networks, the sensorimotor network and the auditory network. A common factor among these networks was the involvement of the precuneus and posterior cingulate cortex. Cognitive and subjective measures were taken as well, but yielded no significant treatment effects, emphasizing the sensitivity of RS-fMRI to pharmacological challenges. The results are consistent with the existence of an extensive serotonergic system relating to multiple brain functions with a possible key role for the precuneus and cingulate.

Local and Global Resting State Activity in the Noradrenergic and Dopaminergic Pathway Modulated by Reboxetine and Amisulpride in Healthy Subjects

BACKGROUND

Various psychiatric populations are currently investigated with resting state fMRI, with the aim of individualizing diagnostics and treatment options and improving treatment outcomes. Many of these studies are conducted in large naturalistic samples, providing rich insights regarding disease-related neural alterations, but with the common psychopharmacological medication limiting interpretations of the results. We therefore investigated the effects of common noradrenergic and anti-dopaminergic medications on local and global resting state activity (rs-activity) in healthy volunteers to further the understanding of the respective effects independent from disease-related alterations.

METHODS

Within a randomized, double-blind, placebo-controlled crossover design, we investigated 19 healthy male subjects by resting state fMRI after the intake of reboxetine (4 mg/d), amisulpride (200mg/d), and placebo for 7 days each. Treatment-related differences in local and global rs-activity were measured by the fractional amplitude of low frequency fluctuations (fALFF) and resting state functional connectivity (rs-FC).

RESULTS

fALFF revealed alterations of local rs-activity within regions of the core noradrenergic pathway, including the locus coeruleus under reboxetine, correlated with its plasma levels. Moreover, reboxetine led to increased rs-FC between regions within this pathway, i.e. the locus coeruleus, tectum, thalamus, and amygdala. Amisulpride modulated local rs-activity of regions within the dopaminergic pathway, with the altered signal in the putamen correlating with amisulpride plasma levels. Correspondingly, amisulpride increased rs-FC between regions of the dopaminergic pathway comprising the substantia nigra and putamen.

CONCLUSION

Our data provide evidence of how psychopharmacological agents alter local and global rs-activity within the respective neuroanatomical pathways in healthy subjects, which may help with interpreting data in psychiatric populations.

Allelic variation in 5-HTTLPR and the effects of citalopram on the emotional neural network

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs), such as citalopram, which selectively block serotonin transporter (5-HTT) activity, are widely used in the treatment of depression and anxiety disorders. Numerous neuroimaging studies have examined the effects of SSRIs on emotional processes. However, there are considerable inter-individual differences in SSRI effect, and a recent meta-analysis further revealed discrepant effects of acute SSRI administration on neural responses to negative emotions in healthy adults.

AIMS

We examined how a variant of the serotonin-transporter polymorphism (5-HTTLPR), which affects the expression and function of 5-HTT, influenced the acute effects of an SSRI (citalopram) on emotion-related brain activity in healthy adults.

METHOD

Combining genetic neuroimaging, pharmacological technique and a psychological paradigm of emotion recognition, we scanned the short/short (s/s) and long/long (l/l) variants of 5-HTTLPR during perception of fearful, happy and neutral facial expressions after the acute administration of an SSRI (i.e. 30 mg citalopram administered orally) or placebo administration.

RESULTS

We found that 5-HTTLPR modulated the acute effects of citalopram on neural responses to negative emotions. Specifically, relative to placebo, citalopram increased amygdala and insula activity in l/l but not s/s homozygotes during perception of fearful faces. Similar analyses of brain activity in response to happy faces did not show any significant effects.

CONCLUSIONS

Our combined pharmacogenetic and functional imaging results provide a neurogenetic mechanism for discrepant acute effects of SSRIs.

The electrophysiological effects of the serotonin 1A receptor agonist buspirone in emotional face processing

Emotional face processing is critically modulated by the serotonergic system, and serotonin (5-HT) receptor agonists impair emotional face processing. However, the specific contribution of the 5-HT1A receptor remains poorly understood. Here we investigated the spatiotemporal brain mechanisms underpinning the modulation of emotional face processing induced by buspirone, a partial 5-HT1A receptor agonist. In a psychophysical discrimination of emotional faces task, we observed that the discrimination fearful versus neutral faces were reduced, but not happy versus neutral faces. Electrical neuroimaging analyses were applied to visual evoked potentials elicited by emotional face images, after placebo and buspirone administration. Buspirone modulated response strength (i.e., global field power) in the interval 230-248ms after stimulus onset. Distributed source estimation over this time interval revealed that buspirone decreased the neural activity in the right dorsolateral prefrontal cortex that was evoked by fearful faces. These results indicate temporal and valence-specific effects of buspirone on the neuronal correlates of emotional face processing. Furthermore, the reduced neural activity in the dorsolateral prefrontal cortex in response to fearful faces suggests a reduced attention to fearful faces. Collectively, these findings provide new insights into the role of 5-HT1A receptors in emotional face processing and have implications for affective disorders that are characterized by an increased attention to negative stimuli.

Affective prosody perception in symptomatically remitted patients with schizophrenia and bipolar disorder

Affect perception has frequently been shown to be impaired in patients suffering from schizophrenia or bipolar disorder (BD), but it remains unclear whether these impairments exist during symptomatic remission and whether the two disorders differ from each other in this regard. Most previous studies have investigated facial affect recognition, but not the ability to decode mental states from emotional tone of voice, i.e. affective prosody perception (APP). Accordingly, the present study directly compared APP in symptomatically remitted patients with schizophrenia or BD and healthy control subjects and investigated its relationship with residual symptomatology in patients. Patients with schizophrenia and BD showed comparable APP impairments despite being symptomatically remitted. In comparison to healthy control subjects, overall APP deficits were found in BD but not in schizophrenia patients. Both patient groups were particularly impaired in the identification of anger and confounded it with neutral prosody. In addition, schizophrenia patients frequently confused sadness with happiness, anger, or fright. There was an inverse association between the degree of residual positive symptoms and the ability to correctly recognize happiness in schizophrenia patients. Overall, these data indicate that impairments in APP represent an enduring deficit and a trait marker of both schizophrenia and BD and that the level of impairment is comparable between disorders.

Dissociation of explicit and implicit measures of the behavioral inhibition and activation system in borderline personality disorder

Patients with borderline personality disorder (BPD) suffer from various impairments in emotional functioning such as affective instability, inappropriate anger and unstable relationships. These deficits may influence two fundamental motivational systems, the behavioral inhibition system (BIS) and behavioral activation system (BAS). To investigate behavioral intentions and possible impairments in BPD we applied an implicit joystick task to measure implicit behavioral tendencies in response to facial expressions (happiness, sadness, anger, fear and neutral) in 25 patients with BPD and matched 25 healthy controls (HC). Additionally, we evaluated explicit approach and avoidance reactions to these social stimuli, emotion recognition abilities and subjective behavioral ratings. Our data analysis suggests that, although BPD patients accurately identified facial emotional expressions and reacted to them similarly as HC in the joystick task, they had significantly stronger avoidance tendencies in the rating task, especially for happiness and fear. On top of this they exhibited increased BIS sensitivity and decreased BAS sensitivity in the self-report measures. Possible influences are maladaptive cognitive schemas, high negative affect, insecure attachment style and a negative evaluation bias. The observed dysfunctional avoidance ratings may influence the appraisal of socially relevant stimuli and therefore adds further knowledge on social interaction problems in BPD.

Impact of acute administration of escitalopram on the processing of emotional and neutral images: a randomized crossover fMRI study of healthy women

BACKGROUND

Acute neural effects of antidepressant medication on emotion processing biases may provide the foundation on which clinical outcomes are based. Along with effects on positive and negative stimuli, acute effects on neutral stimuli may also relate to antidepressant efficacy, yet these effects are still to be investigated. The present study therefore examined the impact of a single dose of the selective serotonin reuptake inhibitor escitalopram (20 mg) on positive, negative and neutral stimuli using pharmaco-fMRI.

METHODS

Within a double-blind, randomized, placebo-controlled crossover design, healthy women completed 2 sessions of treatment administration and fMRI scanning separated by a 1-week washout period.

RESULTS

We enrolled 36 women in our study. When participants were administered escitalopram relative to placebo, left amygdala activity was increased and right inferior frontal gyrus (IFG) activity was decreased during presentation of positive pictures (potentiation of positive emotion processing). In contrast, escitalopram was associated with decreased left amygdala and increased right IFG activity during presentation of negative pictures (attenuation of negative emotion processing). In addition, escitalopram decreased right IFG activity during the processing of neutral stimuli, akin to the effects on positive stimuli (decrease in negative appraisal).

LIMITATIONS

Although we used a women-only sample to reduce heterogeneity, our results may not generalize to men. Potential unblinding, which was related to the subjective occurrence of side effects, occurred in the study; however, manipulation check analyses demonstrated that results were not impacted.

CONCLUSION

These novel findings demonstrate that a single dose of the commonly prescribed escitalopram facilitates a positive information processing bias. These findings provide an important lead for better understanding effects of antidepressant medication.

Healthy individuals treated with clomipramine: an fMRI study of brain activity during autobiographical recall of emotions

Various functional magnetic resonance imaging studies addressed the effects of antidepressant drugs on brain functioning in healthy subjects; however, none specifically investigated positive mood changes to antidepressant drug. Sixteen subjects with no personal or family history of psychiatric disorders were selected from an ongoing 4-week open trial of small doses of clomipramine. Follow-up interviews documented clear positive treatment effects in six subjects, with reduced irritability and tension in social interactions, improved decision making, higher self-confidence and brighter mood. These subjects were then included in a placebo-controlled confirmatory trial and were scanned immediately after 4 weeks of clomipramine use and again 4 weeks after the last dose of clomipramine. The functional magnetic resonance imaging (fMRI) scans were run during emotion-eliciting stimuli. Repeated-measures analysis of variance of brain activity patterns showed significant interactions between group and treatment status during induced irritability (P<0.005 cluster-based) but not during happiness. Individuals displaying a positive subjective response do clomipramine had higher frontoparietal cortex activity during irritability than during happiness and neutral emotion, and higher temporo-parieto-occipital cortex activity during irritability than during happiness. We conclude that antidepressants not only induce positive mood responses but also act upon autobiographical recall of negative emotions.

Imaging the pathophysiology of major depressive disorder - from localist models to circuit-based analysis

The neuroimaging literature of Major Depressive Disorder (MDD) has grown substantially over the last several decades, facilitating great advances in the identification of specific brain regions, neurotransmitter systems and networks associated with depressive illness. Despite this progress, fundamental questions remain about the pathophysiology and etiology of MDD. More importantly, this body of work has yet to directly influence clinical practice. It has long been a goal for the fields of clinical psychology and psychiatry to have a means of making objective diagnoses of mental disorders. Frustratingly little movement has been achieved on this front, however, and the 'gold-standard’ of diagnostic validity and reliability remains expert consensus. In light of this challenge, the focus of the current review is to provide a critical summary of key findings from different neuroimaging approaches in MDD research, including structural, functional and neurochemical imaging studies. Following this summary, we discuss some of the current conceptual obstacles to better understanding the pathophysiology of depression, and conclude with recommendations for future neuroimaging research.

Neural correlates of dysfunctional emotion regulation in major depressive disorder. A systematic review of neuroimaging studies

Abnormal emotion processing is a core feature of major depressive disorder (MDD). Since the emergence of functional neuroimaging techniques, many studies have been conducted in MDD subjects to elucidate the underlying abnormalities in the neural systems involved in emotion regulation. In this systematic review, we discuss this research in the context of the neural model of emotion regulation previously described by Phillips et al. (2008). This model differentiates between automatic and voluntary emotion regulation subprocesses. Automatic regulation subprocesses were shown to involve predominantly medial prefrontal cortical structures, in addition to the hippocampus and parahippocampus, while voluntary regulation processes additionally recruited lateral prefrontal cortical regions. In conclusion, although the available data is limited, findings suggest that MDD subjects demonstrate abnormally reduced activity in lateral prefrontal cortices during explicit voluntary control of emotional experience. During early, automatic stages of emotion regulation, on the other hand, MDD subjects appear to achieve successful emotion regulation by recruiting additional lateral prefrontal neural regions, that may be mediated by medial prefrontal, especially rostral/dorsal anterior cingulate gyrus (ACG) functioning. Dysfunctional automatic regulation may impair successful voluntary emotion regulation, and may present a target for novel therapeutic approaches in MDD.

Antidepressant treatment and emotional processing: can we dissociate the roles of serotonin and noradrenaline?

The ability to match individual patients to tailored treatments has the potential to greatly improve outcomes for individuals suffering from major depression. In particular, while the vast majority of antidepressant treatments affect either serotonin or noradrenaline or a combination of these two neurotransmitters, it is not known whether there are particular patients or symptom profiles which respond preferentially to the potentiation of serotonin over noradrenaline or vice versa. Experimental medicine models suggest that the primary mode of action of these treatments may be to remediate negative biases in emotional processing. Such models may provide a useful framework for interrogating the specific actions of antidepressants. Here, we therefore review evidence from studies examining the effects of drugs which potentiate serotonin, noradrenaline or a combination of both neurotransmitters on emotional processing. These results suggest that antidepressants targeting serotonin and noradrenaline may have some specific actions on emotion and reward processing which could be used to improve tailoring of treatment or to understand the effects of dual-reuptake inhibition. Specifically, serotonin may be particularly important in alleviating distress symptoms, while noradrenaline may be especially relevant to anhedonia. The data reviewed here also suggest that noradrenergic-based treatments may have earlier effects on emotional memory that those which affect serotonin.

Acute neural effects of selective serotonin reuptake inhibitors versus noradrenaline reuptake inhibitors on emotion processing: Implications for differential treatment efficacy

Clinical research has demonstrated differential efficacy of selective serotonin reuptake inhibitors (SSRIs) and norepinephrine reuptake inhibitors (NRIs), which may relate to differential acute effects these medications have on emotional brain processes. Here we present findings from a Multi-Level Kernel Density Analysis meta-analysis that integrates and contrasts activations from disparate fMRI studies in order to examine whether single dose SSRIs and NRIs have different effects on emotion processing tasks in healthy participants. Seven SSRI and four NRI studies were eligible for inclusion. SSRIs decreased amygdala responses, suggesting reduced emotional reactivity to emotional stimuli, whereas NRIs increased frontal and medial activation, suggesting increased emotion regulation. As hypothesised, an interaction of antidepressant and task type was found, such that SSRIs modulated amygdaloid-hippocampal, medial and frontal activity during both the presentation of faces and pictures, whereas NRIs only modulated the activation in medial and frontal regions during the presentation of pictures. Findings are interpreted within a novel model of the differential effects of SSRIs and NRIs on emotion processing.

Prone to excitement: adolescent females with Non-suicidal self-injury (NSSI) show altered cortical pattern to emotional and NSS-related material

Emotion-regulation difficulties have been identified as one of the core components in Non-suicidal self-injury (NSSI), a behaviour often beginning in adolescence. This pilot study evaluated differences in emotion processing between 18 female adolescents with and without NSSI by using verbal responses and functional magnetic resonance imaging (fMRI). Responses to pictures taken from the International Affective Picture System and slides with reference to NSSI were recorded both by verbal rating of valence and arousal and by fMRI. The NSSI group rated pictures with self-injurious reference as significantly more arousing than controls. For emotional pictures, the NSSI group showed a significantly stronger brain response in the amygdala, hippocampus and anterior cingulate cortex bilaterally. Depression explained differences between groups in the limbic area. Furthermore, the NSSI group also showed increased activity in the middle orbitofrontal cortex, and inferior and middle frontal cortex when viewing NSSI picture material. Participants with NSSI showed decreased activity in correlation to arousal in the occipital cortex and to valence in inferior frontal cortex when watching emotional pictures. The fMRI data support the notion that individuals with NSSI show an altered neural pattern for emotional and NSSI pictures. Behavioural data highlight proneness to excitement regarding NSSI topics. This fMRI study provides evidence for emotion-regulation deficits in the developing brain of adolescents with NSSI.