Maria Keil

Differentiating unipolar and bipolar depression by alterations in large-scale brain networks.

Misdiagnosing bipolar depression can lead to very deleterious consequences of mistreatment. Although depressive symptoms may be similarly expressed in unipolar and bipolar disorder, changes in specific brain networks could be very distinct, being therefore informative markers for the differential diagnosis. We aimed to characterize specific alterations in candidate large‐scale networks (frontoparietal, cingulo‐opercular, and default mode) in symptomatic unipolar and bipolar patients using resting state fMRI, a cognitively low demanding paradigm ideal to investigate patients.

Disturbed anterior prefrontal control of the mesolimbic reward system and increased impulsivity in bipolar disorder.

Bipolar disorder (BD) is characterized by recurrent mood episodes ranging from severe depression to acute full-blown mania. Both states of this severe psychiatric disorder have been associated with alterations of reward processing in the brain. Here, we present results of a functional magnetic resonance imaging (fMRI) study on the neural correlates and functional interactions underlying reward gain processing and reward dismissal in favor of a long-term goal in bipolar patients. Sixteen medicated patients diagnosed with bipolar I disorder, euthymic to mildly depressed, and sixteen matched healthy controls performed the ‘desire-reason dilemma’ (DRD) paradigm demanding rejection of priorly conditioned reward stimuli to successfully pursue a superordinate goal. Both groups exhibited significant activations in reward-related brain regions, particularly in the mesolimbic reward system. However, bipolar patients showed reduced neural responses of the ventral striatum (vStr) when exploiting a reward stimulus, and exhibited a decreased suppression of the reward-related activation of the mesolimbic reward system while having to reject immediate reward in favor of the long-term goal. Further, functional interaction between the anteroventral prefrontal cortex and the vStr in the ‘DRD’ was significantly impaired in the bipolar group. These findings provide evidence for a reduced responsivity of the vStr to reward stimuli in BD, possibly related to clinical features like anhedonia. The disturbed top-down control of mesolimbic reward signals by prefrontal brain regions in BD can be interpreted in terms of a disease-related enhanced impulsivity, a trait marker of BD.

Dissociating pathomechanisms of depression with fMRI: bottom- up or top-down dysfunctions of the reward system

Depression is a debilitating psychiatric disorder characterized among other aspects by the inability to properly experience or respond to reward. However, it remains unclear whether patients with depression present impaired reward system due to abnormal modulatory mechanisms. We investigated the activation of the nucleus accumbens (NAcc), a crucial region involved in reward processing, with functional magnetic resonance imaging using the desire-reason-dilemma paradigm. This task allows tracking the activity of the NAcc during the acceptance or the rejection of previously conditioned reward stimuli. Patients were assigned into subgroups of lower (LA) or higher (HA) NAcc activation according to beta weights. LA patients presented significant hypoactivation in the ventral tegmental area in addition to bilateral ventral striatum, confirming impairments in the bottom-up input to the NAcc. Conversely, HA patients presented significant hyperactivation in prefrontal areas such as the rostral anterior cingulate cortex and the anterior ventral prefrontal cortex in addition to bilateral ventral striatum, suggesting disturbances in the top-down regulation of the NAcc. Demographic and clinical differences explaining the abnormal co-activations of midbrain and prefrontal regions were not identified. Therefore, we provide evidence for dysfunctional bottom-up processing in one potential neurobiological subtype of depression (LA) and dysfunctional top-down modulation in another subtype (HA). We suggest that the midbrain and prefrontal regions are more specific pathophysiological substrates for each depression subtype. Above all, our results encourage the segregation of patients by similar dysfunctional mechanisms of the dopaminergic system, which would finally contribute to disentangle more specific pathogeneses and guide the development of more personalized targets for future therapies.

Gender Differences in Verbal and Visuospatial Working Memory Performance and Networks

Background: Working memory (WM) has been a matter of intensive basic and clinical research for some decades now. The investigation of WM function and dysfunction may facilitate the understanding of both physiological and pathological processes in the human brain. Though WM paradigms are widely used in neuroscientific and psychiatric research, conclusive knowledge about potential moderating variables such as gender is still missing. Methods: We used functional magnetic resonance imaging to investigate the effects of gender on verbal and visuospatial WM maintenance tasks in a large and homogeneous sample of young healthy subjects. Results: We found significant gender effects on both the behavioral and neurofunctional level. Females exhibited disadvantages with a small effect size in both WM domains accompanied by stronger activations in a set of brain regions (including bilateral substantia nigra/ventral tegmental area and right Brocas area) independent of WM modality. As load and task difficulty effects have been shown for some of these regions, the stronger activations may reflect a slightly lower capacity of both WM domains in females. Males showed stronger bilateral intraparietal activations next to the precuneus which were specific for the visuospatial WM task. Activity in this specific region may be associated with visuospatial short-term memory capacity. Conclusion: These findings provide evidence for a slightly lower capacity in both WM modalities in females.

CREB1 Genotype Modulates Adaptive Reward-Based Decisions in Humans

Cyclic AMP response element-binding protein (CREB) contributes to adaptation of mesocorticolimbic networks by modulating activity-regulated transcription and plasticity in neurons. Activity or expression changes of CREB in the nucleus accumbens (NAc) and orbital frontal cortex (OFC) interact with behavioral changes during reward-motivated learning. However, these findings from animal models have not been evaluated in humans. We tested whether CREB1 genotypes affect reward-motivated decisions and related brain activation, using BOLD fMRI in 224 young and healthy participants. More specifically, participants needed to adapt their decision to either pursue or resist immediate rewards to optimize the reward outcome. We found significant CREB1 genotype effects on choices to pursue increases of the reward outcome and on BOLD signal in the NAc, OFC, insula cortex, cingulate gyrus, hippocampus, amygdala, and precuneus during these decisions in comparison with those decisions avoiding total reward loss. Our results suggest that CREB1 genotype effects in these regions could contribute to individual differences in reward- and associative memory-based decision-making.

Reactivity of the Reward System in Artists During Acceptance and Rejection of Monetary Rewards

Humans possess an invaluable ability of self-expression that extends into visual, literary, musical, and many other fields of creation. More than any other profession, artists are in close contact with this subdomain of creativity. Probably one of the most intriguing aspects of creativity is its negative correlation with the availability of monetary reward. The aim of this study was to investigate the reactivity of the dopaminergic reward system in artists and nonartist controls using the desire-reason-dilemma (DRD) paradigm, which allows separate evaluation of reactivity to the acceptance and rejection of rewards. Using fMRI, blood-oxygen-level-dependent (BOLD) responses were measured in key regions of the reward system, namely the ventral striatum (VS), the ventral tegmental area (VTA), and the anterior ventral prefrontal cortex (AVPFC). In contrast to controls, artists presented significantly weaker VS activation in reward acceptance. Additionally, they showed stronger suppression of the VS by the AVPFC in reward rejection. No other differences in demographic or behavioral data were evidenced. These results support the existence of characteristic neural traits in artists, who display reduced reactions to monetary reward acceptance and increased reactions to monetary reward rejection.

Investigating the Impact of a Genome-Wide Supported Bipolar Risk Variant of MAD1L1 on the Human Reward System

Recent genome-wide association studies have identified MAD1L1 (mitotic arrest deficient-like 1) as a susceptibility gene for bipolar disorder and schizophrenia. The minor allele of the single-nucleotide polymorphism (SNP) rs11764590 in MAD1L1 was associated with bipolar disorder. Both diseases, bipolar disorder and schizophrenia, are linked to functional alterations in the reward system. We aimed at investigating possible effects of the MAD1L1 rs11764590 risk allele on reward systems functioning in healthy adults. A large homogenous sample of 224 young (aged 18–31 years) participants was genotyped and underwent functional magnetic resonance imaging (fMRI). All participants performed the ‘Desire-Reason Dilemma’ paradigm investigating the neural correlates that underlie reward processing and active reward dismissal in favor of a long-term goal. We found significant hypoactivations of the ventral tegmental area (VTA), the bilateral striatum and bilateral frontal and parietal cortices in response to conditioned reward stimuli in the risk allele carriers compared with major allele carriers. In the dilemma situation, functional connectivity between prefrontal brain regions and the ventral striatum was significantly diminished in the risk allele carriers. Healthy risk allele carriers showed a significant deficit of their bottom-up response to conditioned reward stimuli in the bilateral VTA and striatum. Furthermore, functional connectivity between the ventral striatum and prefrontal areas exerting top-down control on the mesolimbic reward system was reduced in this group. Similar alterations in reward processing and disturbances of prefrontal control mechanisms on mesolimbic brain circuits have also been reported in bipolar disorder and schizophrenia. Together, these findings suggest the existence of an intermediate phenotype associated with MAD1L1.