Objectives: To determine the neural responses invoked in the recognition of facial fear and disgust in euthymic bipolar patients as compared with healthy subjects.
Methods: This study examined 10 female euthymic bipolar patients, and 10 suitably matched healthy subjects using functional magnetic resonance imaging (fMRI) while subjects were engaged in an explicit facial emotion recognition task involving fear, disgust and neutral expressions. The activation paradigm involved nominating the facial expression using specified response keys. Behavioural data were collected and analysed and both within-group (Fear versus Neutral; Disgust versus Neutral) and random-effects between-group analyses were performed on fMRI data using BrainVoyager (Brain Innovations, Maastricht, the Netherlands).
Results: Patients were equally accurate in identifying facial expressions as healthy subjects but were slower to respond, especially with respect to fear and disgust. Responses to fear and disgust (within-group analyses) resulted in activation of anticipated brain regions such as amygdala and insula, respectively. However, between-group random effects analysis revealed differential responses to both disgust and fear in both healthy subjects and euthymic bipolar patients such that euthymic bipolar patients responded largely to fear and healthy subjects responded more so to disgust. This partitioning of responsiveness was reflected by differential activation involving the hippocampus and amygdala.
Conclusions: Greater responsiveness to fear with hippocampal activation in patients perhaps reflects recollection of traumatic events associated with past experiences of illness or simply the use of a more mnemonic (hippocampal) as opposed to affective (amygdala) approach when performing the task. It is possible that in bipolar disorder, prefrontal-subcortical network dysfunction that relegates neural processing to limbic regions is impaired and that clinically euthymic bipolar patients, although able to accurately and effectively identify emotions such as fear and disgust, are limited in their ability to interpret their salience. The implications of these findings are discussed.