Midbrain volume predicts fMRI and ERP measures of reward reactivity

Neurocognitive reward processes measured via event-related potentials are associated with binge-eating disorder diagnosis and ecologically-assessed behavior

Altered reward processing has been implicated in the onset and maintenance of binge-eating disorder (BED). However, it is unclear which precise neurocognitive reward processes may contribute to BED. In the present study, 40 individuals with BED and 40 age-, sex-, and BMI-matched controls completed a reward (incentive delay) task while their neural activity was recorded using electroencephalography (EEG). Individuals with BED also completed a 10-day ecological momentary assessment (EMA) protocol assessing binge-eating behavior in the natural environment. Event-related potential (ERP) analysis of the EEG indicated that individuals with BED had stronger anticipatory (CNV) and outcome-related (RewP) neural reward activity to food and monetary rewards, compared to controls. However, within the BED group, greater frequency of binge eating during the EMA protocol was associated with stronger anticipatory (CNV) but weaker outcome-related (RewP) neural reward activity. These associations within the BED group were unique to food, and not monetary, rewards. Although preliminary, these results suggest that both anticipatory ("wanting") and outcome ("liking") reward processes may be generally amplified in BED. However, they also suggest that among individuals with BED, disorder severity may be associated with increased anticipatory reward processes ("wanting"), but relatively decreased reward-outcome processing ("liking"), of food rewards specifically.

Abnormal neurophysiological sensitivity to rewards in depression is moderated by sex and age in middle adulthood

A candidate pathophysiological process in major depressive disorder is diminished neural reactivity to reward delivery, which is theorized to give rise to anhedonia. Reduced amplitude in the reward positivity (RewP), which captures initial reward evaluation, has been linked to current symptoms of depression among child, adolescent, and young adult samples. However, the developmental trajectory of this association is incomplete, with relatively few studies in middle and older adulthood. Further, emerging evidence in the literature also suggests that this association may be linked to female sex-specific processes, but no studies to date have directly contrasted the effect of sex on the depression-RewP association. The current study sought to address these gaps by testing how sex and age may moderate the depression-RewP association within a mature adult community sample. Symptoms of depression were evaluated using a survey and a clinical interview, and the RewP was elicited using a simple guessing task. There was a three-way interaction between depression symptom severity, age, and sex in predicting RewP amplitude. This was driven by younger (late 30's to early 40's) female-sexed people such that for this group, elevated symptoms of depression were associated with blunting of the RewP. This association tapered around age 50. This effect was specific to clinician-rated rather than self-reported depressive symptom severity. This pattern of effects suggests that among female-sexed people, developmental processes continue to shape the association between reward responsiveness and depression throughout middle adulthood.

The potential application of event-related potentials to enhance research on reward processes in eating disorders

OBJECTIVE

Reward-related processes have been posited as key mechanisms underlying the onset and persistence of eating disorders, prompting a growing body of research in this area. Existing studies have primarily utilized self-report, behavioral, and functional magnetic resonance imaging measures to interrogate reward among individuals with eating disorders. However, limitations inherent in each of these methods (e.g., poor temporal resolution) may obscure distinct neurocognitive reward processes, potentially contributing to underdeveloped models of reward dysfunction within eating disorders. The temporal precision of event-related potentials (ERPs), derived from electroencephalography, may thus offer a powerful complementary tool for elucidating the neurocognitive underpinnings of reward. Indeed, a considerable amount of research in other domains of psychopathology (e.g., depression, substance use disorders), as well as studies investigating food reward among non-clinical samples, highlights the utility of ERPs for probing reward processes. However, no study to date has utilized ERPs to directly examine reward functioning in eating disorders.

METHODS

In this paper, we review evidence underscoring the clinical utility of ERP measures of reward, as well as a variety of reward-related tasks that can be used to elicit specific ERP components with demonstrated relevance to reward processing. We then consider the ways in which these tasks/components may be used to help answer a variety of open questions within the eating disorders literature on reward.

RESULTS/DISCUSSION

Given the promise of ERP measures of reward to the field of eating disorders, we ultimately hope to spur and guide research in this currently neglected area.

PUBLIC SIGNIFICANCE

Abnormalities in reward functioning appear to contribute to eating disorders. Event-related potentials (ERPs) offer temporally precise measures of neurocognitive reward processing and thus may be important tools for understanding the relationship between reward and disordered eating. However, research in this area is currently lacking. This paper attempts to facilitate the use of ERPs to study reward among individuals with eating disorders by reviewing the relevant theories and methods.

Manipulating Reward Sensitivity Using Reward Circuit-Targeted Transcranial Magnetic Stimulation

BACKGROUND

The reward circuit is important for motivation and learning, and dysregulations of the reward circuit are prominent in anhedonic depression. Noninvasive interventions that can selectively target the reward circuit may hold promise for the treatment of anhedonia.

METHODS

We tested a novel transcranial magnetic stimulation intervention for modulating the reward circuit. A total of 35 healthy individuals participated in a crossover controlled study targeting the reward circuit or a control site with intermittent theta burst stimulation (iTBS), an excitatory form of transcranial magnetic stimulation. Individual reward circuit targets were defined based upon functional magnetic resonance imaging functional connectivity with the ventral striatum, yielding targets in the rostromedial prefrontal cortex (rmPFC). Reward circuit function was assessed at baseline using functional magnetic resonance imaging, and reward circuit modulation was assessed using an event-related potential referred to as the reward positivity, which has been shown to reliably track reward sensitivity, as well as individual differences in depression and risk for depression.

RESULTS

Relative to control iTBS, rmPFC iTBS enhanced the reward positivity. This effect was moderated by reward function, suggesting greater enhancements in individuals with lower reward function. This effect was also moderated by rmPFC-ventral striatum connectivity insofar as iTBS reached the rmPFC, suggesting that efficacy relies jointly on the strength of the rmPFC-ventral striatum pathway and ability of transcranial magnetic stimulation to target the rmPFC.

CONCLUSIONS

These data suggest that the reward circuit can be modulated by rmPFC iTBS, and amenability to such modulations is related to measures of reward circuit function. This provides the first step toward a novel noninvasive treatment of disorders of the reward circuit.

Win, lose, or draw: Examining salience, reward memory, and depression with the reward positivity

The reward positivity (RewP) is a putative biomarker of depression. Careful control of stimulus properties and manipulation of both stimulus valence and salience could facilitate interpretation of the RewP. RewP interpretation could further be improved by investigating functional outcomes of a blunted RewP in depression, such as reduced memory for rewarding outcomes. This study sought to advance RewP interpretation first by advancing task design through use of neutral (i.e., draw) control trials and counterbalanced feedback stimuli. Second, we examined the RewP's association with memory and the impact of depression. Undergraduates completed self-report measures of depression and anhedonia prior to a modified doors task in which words were displayed in colored fonts that indicated win, loss, or draw feedback. Memory of the feedback associated with each word (i.e., source memory) was tested. Results showed that RewP response to wins was more positive than to losses, which was more positive than to draws. The RewP was not associated with depression or anhedonia. The low depression group showed a source memory advantage for win words, but the high depression group did not. Source memory showed small relations to the RewP, but these did not survive Bonferroni correction. Results suggest the RewP is sensitive to salience and highlight challenges in detecting an association between the RewP and depression in modified doors tasks. Findings indicate that depression is related to dysfunctional source memory for reward but not loss and that future research should probe the possible associations between the RewP and memory in depression.

Sequential gains and losses during gambling feedback: Differential effects in time-frequency delta and theta measures

One critical aspect of reward-feedback is the impact of local outcome history-how past experiences with choices and outcomes influences current behavior and neural activity. Yet, prior event-related potential work in this area has been contentious. This study contributes to this field by using time-frequency measures to better isolate constituent processes. Specifically, we identify how theta and delta are differentially sensitive to local outcome history. Participants completed a binary monetary choice task while we collected EEG data. Unbeknownst to them, trial outcomes were manipulated into pre-determined sequences, ranging from one to eight gains or losses in a row. Analyses were arranged by sequence establishment (first 2 trials of a sequence) and continuation (prolonged sequences of 3-8 trials). During the establishment of a sequence, delta activity to gains and losses were virtually identical on the first (change) trial, demonstrating marked divergence only on the second trial. This difference grew throughout the continuation period, as delta activity was sustained with accruing gains but declined with multiple losses. Theta activity, conversely, demonstrated a maximal loss-gain difference on the change trial but was insensitive to the establishment of a new sequence. Differential theta activity between outcomes decreased as sequences continued, with theta activity increasing over accruing gains and remaining stable over losses. Results indicate that delta-gain and theta-loss signals are relatively stable across sequential outcomes. Furthermore, theta is most sensitive to loss-gain differences on the initial change trial, while delta is more sensitive to gain-loss differences with the continuation of a sequence.

A systematic review of event-related potentials as outcome measures of attention bias modification

Attention bias modification (ABM) was initially developed with the goal of reducing attentional bias to threat-and subsequently anxious symptoms-in individuals with heightened anxiety. Although controversial, ABM appears to be generally effective in achieving this goal. Yet, the primary outcome measure of ABM (i.e., the reaction time-based differences score) has poor reliability and temporal resolution, which limits the inferences that can be drawn. In contrast, event-related potentials (ERPs) have superior reliability as well as temporal resolution and may therefore be better outcome measures of ABM. In this review, I systematically assess the research using ERPs as outcome measures in ABM protocols. I focus on the extent to which the ERPs modified by ABM represent earlier or later stages of information processing. In addition, I explore the extent to which ABM produces near and/or far transfer of learning effects on ERP measures. The reviewed literature suggests that ERPs are promising outcome measures of ABM. ABM modulates the effects of affective stimuli on posterior visually evoked ERPs (i.e., P1) as well as ERPs at anterior electrodes (i.e., P2, N2, and ERN). Based on the state of the field, several directions for future research are identified.

The effect of perceived effort and perceived control on reward valuation: Using the reward positivity to test a dissonance theory prediction

Past psychological theory and research suggest two opposing relationships between effort and reward valuation. Cognitive dissonance theory and research suggest that increased effort is associated with increased reward valuation, whereas theory and research on effort discounting suggest that increased effort is associated with decreased reward valuation. The present study was designed to test these two opposing perspectives, by examining a potential moderator of the relationship between effort and reward valuation - the belief that the effort was necessary to obtain the reward. Results (n = 44) suggested that increased perceptions of effort following a task were associated with larger neural responses to rewards (as assessed by the event-related potential referred to as the reward positivity) when individuals believed that their effort led to the reward but not when they believed that their effort did not lead to the reward. Discussion considers the implications of these results.

The Effect of Perceived Effort on Reward Valuation: Taking the Reward Positivity (RewP) to Dissonance Theory

The present research was designed to test whether the subjective experience of more effort related to more reward valuation as measured by a neural response. This prediction was derived from the theory of cognitive dissonance and its effort justification paradigm. Young adult participants (n = 82) engaged in multiple trails of a low or high effort task that resulted in a loss or reward on each trial. Neural responses to the reward (loss) cue were measured using EEG so that the event-related potential known as the Reward Positivity (RewP) could be assessed. Results revealed no significant differences between low and high effort conditions on the RewP. However, within the high effort condition, a more subjective experience of effort was associated with a larger RewP. This research extends past research on the effort justification paradigm of cognitive dissonance theory by suggesting that effort justification is associated with an implicit measure of reward valuation. It, therefore, challenges recent perspectives on dissonance processes that posit that these evaluative changes should only occur on explicit but not implicit measures.

The role of avoidance motivation in the relationship between reward sensitivity and depression symptoms in adolescents: An ERP study

Blunted neural responses to reward in an EEG paradigm (RewP) are associated with vulnerability to depression, but the pathways linking this biomarker to depressive symptoms are unclear. We examined whether the relationship between reward response (RewP mean amplitude and latency) and depression was in part explained by approach-motivated behaviors in adolescents with varying levels of depression. EEG was collected during a game rigged to provide win/loss trials. Longer RewP latency was associated with depression symptoms only when scores on a measure of avoidance motivation were included. These results suggest that treatments targeting avoidance may decrease vulnerability to depressive episodes.

No Money, No Problem: Enhanced Reward Positivity in the Absence of Monetary Reward

The reward-related positivity (RewP) is an event-related potential (ERP) with a positive amplitude occurring approximately 250–350 ms post-feedback at frontocentral electroencephalogram (EEG) electrode sites. The RewP is typically elicited in monetary gambling tasks and has a relatively larger amplitude for positive vs. negative outcomes. However, the extent to which RewP amplitude is modulated by non-monetary feedback is less clear. To address this issue, EEG was used to record reward-related electrocortical activity during a simple non-monetary gambling task. We hypothesized that the RewP would be enhanced for non-monetary wins relative to losses, which was supported by the results. In our supplementary material, we provide additional analyses suggesting that this effect was not observed for the P3. In sum, RewP amplitudes were larger for positive (nonmonetary) feedback relative to negative feedback at frontocentral electrode sites—suggesting that monetary reward is not necessary to elicit the RewP.

Time-frequency approaches to investigating changes in feedback processing during childhood and adolescence

Processing feedback from the environment is an essential function during development to adapt behavior in advantageous ways. One measure of feedback processing, the feedback negativity (FN), is an ERP observed following the presentation of feedback. Findings detailing developmental changes in the FN have been mixed, possibly due to limitations in traditional ERP measurement methods. Recent work shows that both theta and delta frequency activity contribute to the FN; utilizing time-frequency methods to measure change in power and phase in these frequency bands may provide more accurate representation of feedback processing development in childhood and adolescence. We employ time-frequency power and intertrial phase synchrony measures, in addition to conventional time-domain ERP methods, to examine the development of feedback processing in the theta (4-7 Hz) and delta (.1-3 Hz) bands throughout adolescence. A sample of 54 female participants (8-17 years old) completed a gambling task while EEG was recorded. As expected, time-domain ERP amplitudes showed no association with age. In contrast, significant effects were observed for the time-frequency measures, with theta power decreasing with age and delta power increasing with age. For intertrial phase synchrony, delta synchrony increased with age, while age-related changes in theta synchrony differed for gains and losses. Collectively, these findings highlight the importance of considering time-frequency dynamics when exploring how the processing of feedback develops through late childhood and adolescence. In particular, the role of delta band activity and theta synchrony appear central to understanding age-related changes in the neural response to feedback.

The sweetness of successful goal pursuit: Approach-motivated pregoal states enhance the reward positivity during goal pursuit

Traditionally, the reward positivity (RewP) is thought to index a binary performance monitoring system sensitive to approach motivation. However, recent theoretical models have argued that feedback processing extends beyond simple "good" vs. "bad" associations, such that performance monitoring incorporates the complex, multi-step sequence of behaviors often necessary to attain rewards. The present study sought to go beyond simple stimulus-response paradigms to examine how approach-motivated states occurring in multi-step goal pursuit impacts the RewP. Additionally, outcome frequency was varied to examine how the P3, a neural marker of expectancy, influences the RewP. Using a modified monetary incentive delay paradigm, participants played a reaction time game where multiple correct responses were required to attain a reward. Additionally, each trial had the potential for a reward (approach-motivated state) or no reward (neutral state). Results revealed that RewP amplitudes were larger after reward trial win feedback than after reward trial no-win feedback across multiple stages of goal pursuit. Additionally, after for controlling outcome frequency via the P3, RewP amplitudes were larger in reward trials than in neutral trials across incremental stages of goal pursuit. The RewP appears to be sensitive to feedback indicating successfully completing sub-goals during pursuit of a goal, even when no immediate reward is given. Approach motivation enhances performance monitoring when multiple steps are needed to attain a desired outcome, which may increase the likelihood of goal acquisition and attainment.

Neural responses to social and monetary reward in early adolescence and emerging adulthood

Reward processing is often considered to be a monolithic construct, with different incentive types eliciting equivalent neural and behavioral responses. The majority of the literature on reward processing has used monetary incentives to elicit reward-related activity, yet social incentives may be particularly important due to their powerful ability to shape behavior. Findings from studies comparing social and monetary rewards have identified both overlapping and distinct responses. In order to explore whether reward processing is domain general or category specific (i.e., the same or different across reward types), the present study recorded ERPs from early adolescents (ages 12-13) and emerging adults (ages 18-25) while they completed social and monetary reward tasks. Temporospatial principal components analysis revealed morphologically similar reward positivities (RewPs) in the social and monetary reward tasks in each age group. In early adolescents, no significant difference was found between the magnitude of the RewP to social and monetary rewards. In emerging adults, however, the RewP to monetary rewards was significantly larger than the RewP to social rewards. Additionally, responses to feedback between the two tasks were not significantly correlated in either age group. These results suggest that both domain-general and category-specific processes underlie neural responses to rewards and that the relative incentive value of different types of rewards may change across development. Findings from this study have important implications for understanding the role that neural response to rewards plays in the development of psychopathology during adolescence.

Gender differences in reward and punishment for monetary and social feedback in children: An ERP study

Gender differences in feedback processing have been observed among adolescents and adults through event-related potentials. However, information on whether and how this feedback processing is affected by feedback valence, feedback type, and individual sensitivity in reward/punishment among children remains minimal. In this study, we used a guessing game task coupled with electroencephalography to investigate gender differences in feedback processing, in which feedback to reward and punishment was presented in the context of monetary and social conditions. Results showed that boys were less likely to switch their response after punishment, had generally less feedback-related negativity (FRN) amplitude, and longer FRN latency in monetary and punishment conditions than girls. Moreover, FRN for monetary punishment, which is related to individual difference in reward sensitivity, was observed only in girls. The study provides gender-specific evidence for the neural processing of feedback, which may offer educational guidance for appropriate feedback for girls and boys.

Reward Dependent Invigoration Relates to Theta Oscillations and Is Predicted by Dopaminergic Midbrain Integrity in Healthy Elderly

Motivation can have invigorating effects on behavior via dopaminergic neuromodulation. While this relationship has mainly been established in theoretical models and studies in younger subjects, the impact of structural declines of the dopaminergic system during healthy aging remains unclear. To investigate this issue, we used electroencephalography (EEG) in healthy young and elderly humans in a reward-learning paradigm. Specifically, scene images were initially encoded by combining them with cues predicting monetary reward (high vs. low reward). Subsequently, recognition memory for the scenes was tested. As a main finding, we can show that response times (RTs) during encoding were faster for high reward predicting images in the young but not elderly participants. This pattern was resembled in power changes in the theta-band (4–7 Hz). Importantly, analyses of structural MRI data revealed that individual reward-related differences in the elderlies’ response time could be predicted by the structural integrity of the dopaminergic substantia nigra (SN; as measured by magnetization transfer (MT)). These findings suggest a close relationship between reward-based invigoration, theta oscillations and age-dependent changes of the dopaminergic system.

Alterations in the brainstem volume of patients with major depressive disorder and their relationship with antidepressant treatment

BACKGROUND

Morphologic changes of the brainstem in major depressive disorder (MDD) have rarely been reported in neuroimaging studies, even though, monoaminergic neurotransmitters are synthesized in several brainstem regions. We aimed to investigate volume changes in each region of the brainstem and their association with antidepressant use or the remission status of MDD.

METHODS

A total of 126 patients with MDD and 101 healthy controls underwent T1-weighted structural magnetic resonance imaging. We analyzed volumes of each brainstem region, including the medulla oblongata, pons, midbrain, and superior cerebellar peduncle, and the volume of the whole brainstem using the FreeSurfer.

RESULTS

The patients with MDD had significantly greater midbrain volumes (P=0.013) compared to healthy controls. In particular, drug-naïve patients with MDD had significantly greater brainstem volumes compared to healthy controls (P=0.007), while no significant findings were observed between the antidepressant treatment group and healthy controls. The remitted patient group had reduced pons (P=0.002) and midbrain (P=0.005) volumes compared to healthy controls, while the non-remitted MDD patient group had significantly greater midbrain volumes compared to the healthy controls (P=0.017).

LIMITATIONS

We could not distinguish gray versus white matter volumes changes in our analysis.

CONCLUSIONS

We observed that the midbrain is enlarged in patients with a current depressive episode, who are not undergoing antidepressant treatment. This volume then returns to normal after antidepressant treatment, and is even reduced, when the patient is in remission. Further studies are needed to confirm our observations.

Perceived control increases the reward positivity and stimulus preceding negativity

The reward positivity (RewP) and the stimulus preceding negativity (SPN), two ERPs associated with reward delivery and reward anticipation, are modulated by motivational intensity. Motivational intensity is the effort organisms would make to exert behaviors, and it varies with the difficulty of exerting that behavior. If a task is perceived as impossible, which means that one does not have control over own outcomes, motivational intensity is low. In the current study, we tested the prediction that perceiving control over one's outcomes increases both the RewP to feedback and the SPN prior to feedback compared to perceiving no control. We also examined whether P300 and LPP amplitudes to reward and nonreward images were similarly modulated. Twenty-five female participants completed a gambling task in which correct choices were followed by pictures of attractive men and incorrect choices were followed by pictures of rocks. To manipulate perceived control, participants were told that, in one block of trials, they could learn a mouse-click rule in order to see only pictures of men (high perceived control condition), while in the other block, the pictures would appear randomly (low perceived control condition). However, in both conditions, feedback appeared randomly. Although the RewP was elicited in both blocks, the RewP and SPN were higher in the high perceived control condition (i.e., when participants thought that they could influence their outcomes). Perceived control did not modulate the P300 and LPP to pictures. The results suggest that approach motivation and its intensity modulate the processing of performance feedback.

Attentional Bias Predicts Increased Reward Salience and Risk Taking in Bipolar Disorder

BACKGROUND

There is amassing evidence that risky decision-making in bipolar disorder is related to reward-based differences in frontostriatal regions. However, the roles of early attentional and later cognitive processes remain unclear, limiting theoretical understanding and development of targeted interventions.

METHODS

Twenty euthymic bipolar disorder and 19 matched control participants played a Roulette task in which they won and lost money. Event-related potentials and source analysis were used to quantify predominantly sensory-attentional (N1), motivational salience (feedback-related negativities [FRN]), and cognitive appraisal (P300) stages of processing. We predicted that the bipolar disorder group would show increased N1, consistent with increased attentional orienting, and reduced FRN, consistent with a bias to perceive outcomes more favorably.

RESULTS

As predicted, the bipolar disorder group showed increased N1 and reduced FRN but no differences in P300. N1 amplitude was additionally associated with real-life risk taking, and N1 source activity was reduced in visual cortex but increased activity in precuneus, frontopolar, and premotor cortex, compared to those of controls.

CONCLUSIONS

These findings demonstrate an early attentional bias to reward that potentially drives risk taking by priming approach behavior and elevating reward salience in the frontostriatal pathway. Although later cognitive appraisals of these inputs may be relatively intact in remission, interventions targeting attention orienting may also be effective in long-term reduction of relapse.

Using fMRI to study reward processing in humans: past, present, and future

Functional magnetic resonance imaging (fMRI) is a noninvasive tool used to probe cognitive and affective processes. Although fMRI provides indirect measures of neural activity, the advent of fMRI has allowed for1) the corroboration of significant animal findings in the human brain, and2) the expansion of models to include more common human attributes that inform behavior. In this review, we briefly consider the neural basis of the blood oxygenation level dependent signal to set up a discussion of how fMRI studies have applied it in examining cognitive models in humans and the promise of using fMRI to advance such models. Specifically, we illustrate the contribution that fMRI has made to the study of reward processing, focusing on the role of the striatum in encoding reward-related learning signals that drive anticipatory and consummatory behaviors. For instance, we discuss how fMRI can be used to link neural signals (e.g., striatal responses to rewards) to individual differences in behavior and traits. While this functional segregation approach has been constructive to our understanding of reward-related functions, many fMRI studies have also benefitted from a functional integration approach that takes into account how interconnected regions (e.g., corticostriatal circuits) contribute to reward processing. We contend that future work using fMRI will profit from using a multimodal approach, such as combining fMRI with noninvasive brain stimulation tools (e.g., transcranial electrical stimulation), that can identify causal mechanisms underlying reward processing. Consequently, advancements in implementing fMRI will promise new translational opportunities to inform our understanding of psychopathologies.

Gender moderates the association between dorsal medial prefrontal cortex volume and depressive symptoms in a subclinical sample

Major depressive disorder is associated with lower medial prefrontal cortex volumes. The role that gender might play in moderating this relationship and what particular medial prefrontal cortex subregion(s) might be implicated is unclear. Magnetic resonance imaging was used to assess dorsal, ventral, and anterior cingulate regions of the medial prefrontal cortex in a normative sample of male and female adults. The Depression, Anxiety, and Stress Scale (DASS) was used to measure these three variables. Voxel-based morphometry was used to test for correlations between medial prefrontal gray matter volume and depressive traits. The dorsal medial frontal cortex was correlated with greater levels of depression, but not anxiety and stress. Gender moderates this effect: in males greater levels of depression were associated with lower dorsal medial prefrontal volumes, but in females no relationship was observed. The results indicate that even within a non-clinical sample, male participants with higher levels of depressive traits tend to have lower levels of gray matter volume in the dorsal medial prefrontal cortex. Our finding is consistent with low dorsal medial prefrontal volume contributing to the development of depression in males. Future longitudinal work is needed to substantiate this possibility.

Blunted neural response to rewards as a vulnerability factor for depression: Results from a family study

Depressive disorders are associated with significant economic and public health burdens as well as increased morbidity. Yet, perhaps due to the heterogeneous nature of the disease, prevention and intervention efforts are only moderately efficacious. A better understanding of core mechanisms of depressive disorders might aid in the development of more targeted intervention, and perhaps help identify individuals at risk. One mechanism that may be particularly important to depressive phenotypes is reward insensitivity. Examination of neurobiological correlates of reward-processing, which should relate more directly to the neuropathology of depression, may be helpful in identifying liability for the disorder. To that end, we used a family study design to examine whether a neural response to rewards is a familial risk factor for depression in a sample of probands with a wide range of internalizing psychopathology, as well as their biological siblings. Event-related potentials were recorded during a simple forced-choice gambling paradigm, in which participants could either win or lose small amounts of money. Lower levels of positive affect in probands predicted a reduced neural response to rewards in siblings, even over and above the sibling's own level of positive and negative affect. Additionally, the neural response to rewards was familial (i.e., correlated among siblings). Combined, these analyses suggest that a blunted neural response to rewards may be useful in identifying individuals vulnerable to depressive illnesses.

Anterior cingulate activity to monetary loss and basal ganglia activity to monetary gain uniquely contribute to the feedback negativity

OBJECTIVE

The feedback negativity (FN) is an event-related potential that differentiates unfavorable versus favorable outcomes. Although thought to reflect error-related activity within the anterior cingulate cortex, recent work indicates the FN may also reflect reward-related activity that has been linked to the basal ganglia. To date, it remains unclear how to reconcile these conflicting perspectives.

METHODS

We decomposed the FN by applying time-frequency analysis to isolate activity unique to monetary losses and gains. The FN was recorded from 84 individuals during a laboratory gambling task.

RESULTS

Two signals contributed to the FN elicited by unpredictable outcomes: theta activity (4-7Hz) was increased following monetary loss, and delta activity (<3Hz) was increased following monetary gain. Predictable outcomes elicited delta but not theta activity. Source analysis revealed distinct generators, with loss-related theta localized to the anterior cingulate cortex and gain-related delta to a possible source in the striatum. Symptoms of depression, anxiety, and stress reactivity were specifically associated with blunted gain-related delta.

CONCLUSIONS

The FN may be a composite of loss- and gain-related neural activity, reflecting distinct facets of reward processing.

SIGNIFICANCE

Gain-related delta activity may provide unique information about reward dysfunction in major depression and other internalizing psychopathology.

Reward dysfunction in major depression: multimodal neuroimaging evidence for refining the melancholic phenotype

Reward dysfunction is thought to play a core role in the pathophysiology of major depressive disorder (MDD). Event-related potential (ERP) and functional magnetic resonance imaging (fMRI) studies have identified reward processing deficits in MDD, but these methods have yet to be applied together in a single MDD sample. We utilized multimodal neuroimaging evidence to examine reward dysfunction in MDD. Further, we explored how neurobiological reward dysfunction would map onto subtypes of MDD. The feedback negativity (FN), an ERP index of reward evaluation, was recorded in 34 unmedicated depressed individuals and 42 never-depressed controls during a laboratory gambling task. Ventral striatal (VS) activation to reward was recorded in a separate fMRI session, using an identical task, among a subgroup of 24 depressed individuals and a comparison group of 18 non-depressed controls. FN amplitude was blunted in MDD. This effect was driven by a MDD subgroup characterized by impaired mood reactivity to positive events, a core feature of melancholic MDD. A similar pattern was observed for VS activation, which was also blunted among the MDD subgroup with impaired mood reactivity. Neither FN amplitude nor VS activation was related to the full, DSM-defined melancholic or atypical MDD subtypes. Across the MDD sample, FN amplitude and VS activation were correlated, indicating convergence across methods. These results indicate that not all MDD is characterized by reward dysfunction, and that there is meaningful heterogeneity in reward processing within MDD. The current study offers neurobiological evidence that impaired mood reactivity is a key phenotypic distinction for subtyping MDD, and further suggests that the existing melancholic phenotype may require further refinement.