Can acute tryptophan depletion modulate brain function in absence of behavioural effects?

Modulation of neural response to happy and sad faces by acute tryptophan depletion

“…Overall, our findings are consistent with previous reports that the accuracy of gender discrimination is unaffected by ATD in healthy volunteers , although an effect is seen in depression-prone individuals (Bouhuys et al 1999;Suslow et al 2001;Watkins et al 2000). A major concern in the literature of ATD is the difficulty to interpret the effects of 5HT manipulation on brain activation of healthy subjects in the absence of mood and performance effects (Fusar-Poli et al 2006a). However, we argue that task performance is a relatively crude index of effects on brain function, and the absence of a performance effect does not necessarily mean that ATD has no effect on brain function.…”

“…Healthy subjects may be able to compensate for physiological effects by employing other cognitive strategies that maintain performance but alter brain activation. Thus, studies employing tasks at varying levels of demand could be useful to address whether behavioural effects appear when these are very high, with physiological effects at all levels but increasingly evident as demand increased (Fusar-Poli et al 2006a). Another interesting approach may be to examine the ATD effects on healthy subjects taking into account genetic factors.…”

Effects of acute tryptophan depletion on neural processing of facial expressions of emotion in humans

“…For example, it may be that impairments of disgust recognition as measured using explicit behavioral tasks require a greater lowering of 5-HT levels than those which modulate the neural response to incidentally viewing the faces. There may be cognitive compensation to ATD that preserves performance but not brain activation (Fusar-Poli et al 2007a). This question could be addressed in future studies by measuring disgust recognition and brain activity in conjunction with parametric variation of the level of ATD.…”