The effects of tryptophan depletion on cognitive and affective processing in healthy volunteers

Abstract

The present data indicate that serotonergic factors may be more involved in the disrupted inhibitory and emotional processing characteristic of depression than in other aspects of executive function, such as planning ability. These findings support the recent proposal that serotonergic manipulation may have greater effects on tasks mediated by frontal circuitry that includes the orbitofrontal cortex than by dorsolateral prefrontal cortex circuitry.

Acute Tryptophan Depletion in Healthy Volunteers Enhances Punishment Prediction but Does not Affect Reward Prediction

“…This is consistent with the finding that effects of systemic serotonergic manipulations in human volunteers are not specific to the reversal stage of discrimination learning tasks, but extend to simple and compound discrimination learning stages of such tasks (Park et al, 1994;Rogers et al, 1999;Murphy et al, 2002;Chamberlain et al, 2006). In keeping with these findings, ATD enhanced the BOLD response to punishment in a probabilistic reversal-learning paradigm regardless of whether punishment led to switching (Evers et al, 2005).…”

“…Studies with healthy human volunteers have demonstrated potentiated processing of punishment-related signals after dietary depletion of the 5-HT precursor tryptophan (TRP; acute tryptophan depletion, ATD), particularly in vulnerable individuals. For example, ATD enhanced the amygdala response to fearful faces (Cools et al, 2005b; Van der Veen et al, 2007), decreased the impact of positively valenced words (Murphy et al, 2002), and increased the impact of negatively valenced emotional words in Stroop-like tasks (Evers et al, 2006a). In addition, ATD potentiated neural activity during negative feedback in a probabilistic reversal-learning task (Evers et al, 2005), which was also sensitive to acute administration of the selective serotonin reuptake inhibitor citalopram (Chamberlain et al, 2006).…”

Tryptophan Depletion Disrupts the Motivational Guidance of Goal-Directed Behavior as a Function of Trait Impulsivity

“…Indeed, Rogers et al (2003) recently reported that ATD impaired the ability to discriminate between large and small rewards. Diminished behavioral sensitivity to cues signaling reward and enhanced behavioral sensitivity to cues signaling punishment may parallel previous findings, indicating that depression, associated with diminished 5-HT function, is characterized by under-sensitivity to reward (Henriques et al, 1994) and over-sensitivity to negative feedback (Elliott et al, 1996(Elliott et al, , 1997Murphy et al, 2002Murphy et al, , 2003. ATD did not affect SSRT, a measure of prepotent response inhibition.…”

“…In keeping with the hypothesis that 5-HT is critically involved in the processing of incentive signals, studies in humans have shown that depletion of central 5-HT impairs decision-making in gambling tasks, visual discrimination, and reversal learning, possibly due to deficits in (re)acquiring associations between stimulus and reward values (Park et al, 1994;Rogers et al, 1999Rogers et al, , 2003Murphy et al, 2002). A recent study revealed that 5-HT depletion in healthy volunteers impaired the ability to discriminate between large and small rewards (Rogers et al, 2003).…”

The Effect of Acute Tryptophan Depletion on the Neural Correlates of Emotional Processing in Healthy Volunteers

“…Nevertheless, many studies have reported that ATD impairs performance on neuropsychological tasks that have an emotional component in healthy humans. For example, it has been reported that ATD impaired decision-making on gambling games , attenuated motivation on a reinforced speeded reaction-time task (Cools et al, 2005a;Roiser et al, 2006), impaired recognition of emotional expressions (Harmer et al, 2003), and resulted in a negative bias on an emotional inhibitory control paradigm, the affective go/no-go test (AGNG) (Murphy et al, 2002). Interestingly, such a negative bias on the AGNG has also been found in depressed patients studied under basal conditions (ie without manipulation of serotonergic function: Erickson et al, 2005;Murphy et al, 1999).…”