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Major depressive disorder (MDD) has been associated with abnormalities in speech and behavioural mimicry. These abnormalities may contribute to the impairments in interpersonal functioning that are often seen in MDD patients. MDD has also been associated with disturbances in the brain serotonin system, but the extent to which serotonin regulates speech and behavioural mimicry remains unclear. In a randomized, double-blind, crossover study, we induced acute tryptophan depletion (ATD) in individuals with or without a family history of MDD. Five hours afterwards, participants engaged in two behavioural-mimicry experiments in which speech and behaviour were recorded. ATD reduced the time participants waited before speaking, which might indicate increased impulsivity. However, ATD did not significantly alter speech otherwise, nor did it affect mimicry. This suggests that a brief lowering of brain serotonin has limited effects on verbal and non-verbal social behaviour. The null findings may be due to low test sensitivity, but they otherwise suggest that low serotonin has little effect on social interaction quality in never-depressed individuals. It remains possible that recovered MDD patients are more strongly affected., (© The Author(s) 2016.)

Rationale: Major depressive disorder (MDD) has been associated with disturbances in social functioning and in the brain serotonin system. Reduced levels of serotonin may negatively influence social functioning, for example by impairing the recognition of facial emotion expressions., Objectives: The present study investigated the effect of acute tryptophan depletion (ATD), which reduces brain serotonin, on a related component of social functioning, empathic accuracy (EA), and oxytocin levels., Methods: Individuals with (FH+) and without (FH−) a family history of MDD participated in a randomized, double-blind, crossover study. On two separate test days, participants ingested tryptophan-deficient and nutritionally balanced amino acid mixtures. Six hours later, they performed an EA task, which involved watching videos of people recounting autobiographical emotional events. While watching, participants continuously rated how these people felt during the recounting. Mood state was repeatedly assessed using the Positive Affect and Negative Affect Schedule and a series of visual analogue scales. Blood samples obtained at baseline and 5 h after mixture ingestion were assessed for tryptophan and oxytocin levels., Results: ATD decreased circulating levels of tryptophan and oxytocin. Nevertheless, there were no significant effects of ATD on EA or mood in either FH group., Conclusions: While previous studies have shown that acute reductions in brain serotonin alter the recognition of facial emotion expressions in never-depressed individuals, the present study suggests that empathic abilities may remain unaffected.

Background: Individuals with a family history of depression show subtle abnormalities in the processing of social stimuli. This could negatively affect their interpersonal functioning and contribute to their depression risk. Repeated administration of the serotonin precursor tryptophan has previously been shown to increase agreeable behavior and reduce quarrelsome behavior in irritable people, who are also considered at risk for depression., Methods: To examine the effects of tryptophan on social functioning in individuals with a family history of depression, 40 men and women with at least one first-degree relative with depression received tryptophan (1g three times a day) and placebo for 14 days each in a double-blind crossover design and recorded their social behavior and mood during everyday interpersonal encounters. Participants also provided daily ratings of their positive and negative cognitions concerning their social functioning., Results: Tryptophan improved mood. Unexpectedly, tryptophan increased quarrelsome behavior and reduced agreeable behavior, specifically during interactions at home. The behavioral effects of tryptophan were not moderated by mood or by the interaction partner. Negative social cognitions were lower when tryptophan was given second and lower during placebo when placebo was given second., Conclusion: Overall, tryptophan may not alter social behavior in individuals with a family history of depression as it does in irritable people. However, the behavioral effects of tryptophan at home might be seen as a way for individuals with a family history of depression to achieve more control. Over time, this may positively influence the way they feel and think about themselves in a social context., (© The Author 2015. Published by Oxford University Press on behalf of CINP.)

In healthy never-depressed individuals, acute tryptophan depletion (ATD) may selectively decrease the accurate recognition of fearful facial expressions. Here we investigated the perception of facial emotions after ATD in more detail. We also investigated whether bright light, which can reverse ATD's mood-lowering effect, can also reverse its effect on the perception of facial emotions. On two separate test days, spent in a room that was either bright (n = 14) or dim (n = 16), healthy never-depressed women completed a facial emotion perception task six hours after ingesting tryptophan-deficient and balanced amino acid mixtures. Treatments were administered double blind and in randomized order using a crossover design. In dim light ATD decreased recognition accuracy of anger, disgust, and surprise. The labeling of fear and sadness was not affected. In bright light no effects of ATD were seen. Bright light was identified as a potential confounding factor in task performance. The effects of ATD on facial emotion perception may be less emotion-specific than thought previously, and occurred in a direction opposite to what might be expected based on theories of mood-congruent bias.

We investigated the influence of bright light exposure on the mood-lowering effect of acute tryptophan depletion (ATD). Mildly seasonal healthy young women without a personal or family history of psychiatric disorders remained in either dim or bright light during two test days. Tryptophan-deficient and nutritionally balanced amino acid mixtures were administered in counterbalanced order. Mood state was assessed using the Profile of Mood States (POMS) and Visual Analogue Scales (VAS). In dim light, ATD decreased POMS scores across most subscales, indicating a worsening of mood. In bright light, mood was unaffected by ATD. Thus, bright light blocked the worsening of mood caused by ATD. This was also observed on the positive mood VAS. These results indicate a direct, immediate interaction between bright light and serotonin function. Bright light might help protect against ATD-induced mood change by increasing serotonin above the threshold level below which there is a lowering of mood.

Objective: We hypothesized that increasing brain serotonin in healthy individuals with high scores on 2 self-report measures of trait quarrelsomeness would reduce quarrelsome behaviours and enhance agreeable behaviours when measured ecologically using an event-contingent recording method., Methods: We conducted a double-blind crossover study, in which participants took tryptophan (3 g/d) and placebo for 15 days each and recorded how they behaved, felt and perceived others during everyday social interactions., Results: Tryptophan significantly decreased quarrelsome behaviours and increased agreeable behaviours and perceptions of agreeableness. Men also behaved less dominantly, whereas both men and women perceived others as more dominant., Conclusion: Tryptophan's effects on behaviours and perceptions, while more marked in the men, were generally positive and accompanied by improved affect. Increasing serotonin in quarrelsome people may not only reduce behaviours associated with a predisposition to various mental and physical disorders but also enhance socially constructive behaviours and improve social perceptions.

Background: Individuals with a family history of depression show subtle abnormalities in the processing of social stimuli. This could negatively affect their interpersonal functioning and contribute to their depression risk. Repeated administration of the serotonin precursor tryptophan has previously been shown to increase agreeable behavior and reduce quarrelsome behavior in irritable people, who are also considered at risk for depression. Methods: To examine the effects of tryptophan on social functioning in individuals with a family history of depression, 40 men and women with at least one first-degree relative with depression received tryptophan (1g three times a day) and placebo for 14 days each in a double-blind crossover design and recorded their social behavior and mood during everyday interpersonal encounters. Participants also provided daily ratings of their positive and negative cognitions concerning their social functioning. Results: Tryptophan improved mood. Unexpectedly, tryptophan increased quarrelsome behavior and reduced agreeable behavior, specifically during interactions at home. The behavioral effects of tryptophan were not moderated by mood or by the interaction partner. Negative social cognitions were lower when tryptophan was given second and lower during placebo when placebo was given second. Conclusion: Overall, tryptophan may not alter social behavior in individuals with a family history of depression as it does in irritable people. However, the behavioral effects of tryptophan at home might be seen as a way for individuals with a family history of depression to achieve more control. Over time, this may positively influence the way they feel and think about themselves in a social context. [ABSTRACT FROM AUTHOR]

Abstract.: In humans there is an association between low serotonin levels and aggressive behavior, and drugs that increase serotonin function have been used to treat aggression. In monkey alterations in serotonin function seem to influence behavior along the agonistic–affiliative axis, with increases in serotonin function not only decreasing aggression but also increasing the grooming of other animals. Measurement of human social behavior in everyday life has advanced to the stage where it is possible to measure behavior along the agreeable–quarrelsome axis. Therefore we performed two double-blind cross-over studies to compare the effects of tryptophan, the serotonin precursor, with placebo on the social behavior of healthy people. In the first study tryptophan decreased quarrelsome behaviors. In the second study on irritable people tryptophan not only decreased quarrelsome behaviors but also increased agreeable behaviors and improved mood. Our studies suggest that increasing serotonin synthesis with tryptophan moves behavior along the axis that encompasses aggressive, quarrelsome, and agreeable behaviors towards more positive social behavior in healthy people in everyday life. Irritability is a risk factor for various mental and physical disorders. It remains to be seen whether increasing serotonin function in irritable people improves their mental and physical health. [Copyright &y& Elsevier]

Abstract: Increased serotonergic activity is often described as increasing the inhibition of behaviors. This study examined the more general hypothesis that increased serotonergic activity produces greater control over social behavior. Participants were drawn from two samples, individuals elevated on irritability and individuals unselected on personality characteristics. Individuals participated in a double blind cross-over design, providing event contingent records about their behavior during two 9-day periods which involved taking tryptophan or placebo. When taking tryptophan (which increases serotonergic activity), within-person variability among social behaviors across events (i.e., interpersonal spin) was reduced for irritable individuals, particularly those low on trait Agreeableness. These results suggest that higher levels of serotonergic activity enhance greater control and consistency in social behavior among irritable–disagreeable individuals. [Copyright &y& Elsevier]