Early life stress explains reduced positive memory biases in remitted depression.

BACKGROUND: There is contradictory evidence regarding negative memory biases in major depressive disorder (MDD) and whether these persist into remission, which would suggest their role as vulnerability traits rather than correlates of mood state. Early life stress (ELS), common in patients with psychiatric disorders, has independently been associated with memory biases, and confounds MDD versus control group comparisons. Furthermore, in most studies negative biases could have resulted from executive impairments rather than memory difficulties per se. METHODS: To investigate whether memory biases are relevant to MDD vulnerability and how they are influenced by ELS, we developed an associative recognition memory task for temporo-spatial contexts of social actions with low executive demands, which were matched across conditions (self-blame, other-blame, self-praise, other-praise). We included fifty-three medication-free remitted MDD (25 with ELS, 28 without) and 24 healthy control (HC) participants without ELS. RESULTS: Only MDD patients with ELS showed a reduced bias (accuracy/speed ratio) towards memory for positive vs. negative materials when compared with MDD without ELS and with HC participants; attenuated positive biases correlated with number of past major depressive episodes, but not current symptoms. There were no biases towards self-blaming or self-praising memories. CONCLUSIONS: This demonstrates that reduced positive biases in associative memory were specific to MDD patients with ELS rather than a general feature of MDD, and were associated with lifetime recurrence risk which may reflect a scarring effect. If replicated, our results would call for stratifying MDD patients by history of ELS when assessing and treating emotional memories.

A novel resting-state functional magnetic resonance imaging signature of resilience to recurrent depression.

BACKGROUND: A high proportion of patients with remitted major depressive disorder (MDD) will experience recurring episodes, whilst some develop resilience and remain in recovery. The neural basis of resilience to recurrence is elusive. Abnormal resting-state connectivity of the subgenual cingulate cortex (sgACC) was previously found in cross-sectional studies of MDD, suggesting its potential pathophysiological importance. The current study aimed to investigate whether resting-state connectivity to a left sgACC seed region distinguishes resilient patients from those developing recurring episodes. METHOD: A total of 47 medication-free remitted MDD patients and 38 healthy controls underwent resting-state functional magnetic resonance imaging (fMRI) at baseline. Over 14 months, 30 patients remained resilient whilst 17 experienced a recurring episode. RESULTS: Attenuated interhemispheric left-to-right sgACC connectivity distinguished the resilient from the recurring-episode and control groups and was not correlated with residual depressive symptoms. CONCLUSIONS: The current study revealed a neural signature of resilience to recurrence in MDD and thereby elucidates the role of compensatory adaptation in sgACC networks.

Negative emotions towards others are diminished in remitted major depression.

BACKGROUND: One influential view is that vulnerability to major depressive disorder (MDD) is associated with a proneness to experience negative emotions in general. In contrast, blame attribution theories emphasise the importance of blaming oneself rather than others for negative events. Our previous exploratory study provided support for the attributional hypothesis that patients with remitted MDD show no overall bias towards negative emotions, but a selective bias towards emotions entailing self-blame relative to emotions that entail blaming others. More specifically, we found a decreased proneness for contempt/disgust towards others relative to oneself (i.e. self-contempt bias). Here, we report a definitive test of the competing general negative versus specific attributional bias theories of MDD. METHODS: We compared a medication-free remitted MDD (n=101) and a control group (n=70) with no family or personal history of MDD on a previously validated experimental test of moral emotions. The task measures proneness to specific emotions associated with different types of self-blame (guilt, shame, self-contempt/disgust, self-indignation/anger) and blame of others (other-indignation/anger, other-contempt/disgust) whilst controlling for the intensity of unpleasantness. RESULTS: We confirmed the hypothesis that patients with MDD exhibit an increased self-contempt bias with a reduction in contempt/disgust towards others. Furthermore, they also showed a decreased proneness for indignation/anger towards others. CONCLUSIONS: This corroborates the prediction that vulnerability to MDD is associated with an imbalance of specific self- and other-blaming emotions rather than a general increase in negative emotions. This has important implications for neurocognitive models and calls for novel focussed interventions to rebalance blame in MDD.

Lack of behavioural effects after acute tyrosine depletion in healthy volunteers.

Acute dietary tyrosine depletion has previously been shown to reduce dopamine neurotransmission in both animals and humans. In this study, we investigated the effects of brain dopamine depletion, through acute tyrosine and phenylalanine depletion, on plasma prolactin, mood and neuropsychological function in 12 normal subjects. In a randomized, double-blind, cross-over design, subjects received two amino-acid drinks separated by a week, a nutritionally balanced mixture (Bal) and on the other occasion a tyrosine and phenylalanine deficient mixture (TP-). The plasma ratio of tyrosine and phenylalanine to the other large neutral amino acids decreased significantly on the TP- occasion (-78.7%, p < 0.0001) and there was an increase in plasma prolactin concentration relative to the balanced drink in the seven subjects for whom results were available for both occasions (p < 0.02). Acute tyrosine depletion did not alter mood as measured by visual analogue scale ratings, and measures of memory, attention and behavioural inhibition were also unaffected. Our results are consistent with acute dietary tyrosine depletion causing a reduction in brain dopamine neurotransmission but raise questions about how robust or consistent the effects are on psychological function.