Major depressive disorder (MDD) and bipolar disorder are associated with alterations in multiple domains, including interpersonal and social functioning.1–4
Recent studies have examined the nature of social impairment in patients with mood disorders through the lens of social cognition, involving the ability to understand and respond to the thoughts and feelings of others and thought central to successful social interactions.5,6
The goal of the present review was to examine the findings of neuroimaging studies concerning social cognitive processing in patients with MDD and bipolar disorder. Here, we focus on studies investigating 2 different but overlapping aspects of social cognition — emotion comprehension and theory of mind (ToM) — that have recently been investigated in patients with mood disorders. Emotion recognition refers to an individual’s ability to infer the emotional state of another from observable information, such as prosody and facial expression. By contrast, ToM has been defined as the ability to ascribe mental states, such as beliefs, desires and intentions, to oneself and others.7
Taken together, these theoretical definitions reveal substantial overlap and distinct processes involved in these key components of social cognition. For example, theoretical models propose that the ability to recognize another’s emotion is critical to ToM,8
with empirical evidence supporting this view.9–15
Hence, we included these 2 domains of social cognition in our review to provide a broad understanding of the neural correlates of social cognition in patients with mood disorders. Other domains of social cognition, including empathy and moral reasoning, remain unexplored in these patients.
In healthy individuals, the neural basis of social cognition consists of a complex network of brain areas involved in cognitive and affective processes (for a recent review, see Adolphs16
). Key regions that contribute to this network include prefrontal regions, such as the ventromedial prefrontal cortex, an area involved in the regulation of emotion and reward evaluation,17
and the dorsolateral prefrontal cortex (DLPFC), an area implicated in higher-order cognitive processes, such as cognitive control and executive functioning.18,19
The anterior cingulate cortex, involved in conflict monitoring and integration of information to motivate behaviour, has also been implicated.16
The amygdala, which is critical to processing and evaluation of emotional stimuli, and the ventral striatum, which is involved in emotional and motivational aspects of behaviour, also constitute important nodes in the social cognition network.5
Finally, temporal regions, such as the temporoparietal junction, which is involved in a sense of agency as well as perspective-taking, and the temporal poles, which are implicated in diverse memory functions, have been shown to be recruited across various social cognitive tasks, including ToM, empathy and facial emotion processing.20–22
Critically, many of the same neural regions thought to mediate the cognitive (e.g., memory, executive functioning) and affective (e.g., emotion evaluation) processes necessary for social cognitive responding have been implicated in patients with bipolar disorder and MDD, showing altered metabolic functioning and/or structural abnormalities (for a recent review see Price and Drevets23
). Coupled with growing evidence of cognitive and affective processing impairments among patients with MDD and bipolar disorder,20,24–28
we expected our review to reveal that patients with mood disorders show alterations in neuronal functioning during social cognitive processing. Specifically, we expected that individuals with MDD and bipolar disorder would show lowered activation in prefrontal areas involved in emotion regulation and higher-order cognitive processes and increased activity in subcortical and limbic regions implicated in emotion appraisal and generation, indicating a lack of inhibition of higher-order cognitive centres on limbic and emotion-related structures.
Here, the neural basis of each of these social cognitive domains is briefly reviewed and is followed by a synopsis of relevant behavioural studies of patients with mood disorders. The neuroimaging literature concerning social cognition in patients with mood disorders is then summarized. Where possible, neuroimaging findings involving patients with mood disorders are contextualized based on several key variables, including illness burden (e.g., number of affective episodes), illness state (e.g., active v. remitted), medication status, age, cognitive load and comorbidity, thought to moderate cognitive performance in patients with mood disorders.29
Depending on data availability, results for patients with MDD and bipolar disorder are presented separately and are subsequently compared. We conclude the review by discussing future research directions and the clinical implications of alterations in the neural circuitry underlying social cognition with respect to improving treatment interventions and preventing relapse in patients with mood disorders.
On balance, patients with mood disorders experience substantial disruptions in interpersonal function,30–34
and deficits in social cognition may underlie these difficulties. An enhanced understanding of the neural correlates of social cognition may help improve diagnostic accuracy and early intervention among patients with these disorders. This is particularly pertinent to the study of bipolar disorder, given that patients with this illness experience depression more than hypomania or mania,35,36
which may result in the mis-diagnosis of bipolar depression as MDD,37,38
suboptimal treatment and poor outcome.39,40
Elucidating the neural correlates of social cognition may also assist in identifying the neuroanatomical basis of vulnerability to these disorders. Improved knowledge of the underlying neural mechanisms and nature of social cognitive deficits in patients with mood disorders may also assist in clarifying the nature of social dysfunction in patients with MDD and bipolar disorder and may aid in the development of psychologic interventions aimed at improving social perception and adjustment in these patient populations.