Effects of acute tryptophan depletion on memory, attention and executive functions: A systematic review

Converging evidence for central 5-HT effects in acute tryptophan depletion

“…ATD can be administered in liquid form, which is highly unpleasant, or in capsule form, which is less unpleasant; these different procedures produced similar effects on fear recognition. 8 We also note that dietary depletion of other amino acids, such as tyrosine and phenylalanine, has effects on cognition, distinct from those of ATD. 9 Furthermore, most of the proposed alternative mechanisms would likely predict broad attentional and executive impairments following ATD, but these have not been reported; 8 rather, ATD produces highly selective effects on emotional processing and episodic memory.…”

“…8 We also note that dietary depletion of other amino acids, such as tyrosine and phenylalanine, has effects on cognition, distinct from those of ATD. 9 Furthermore, most of the proposed alternative mechanisms would likely predict broad attentional and executive impairments following ATD, but these have not been reported; 8 rather, ATD produces highly selective effects on emotional processing and episodic memory. 5,8 Second, van Donkelaar et al 2 claim there is insufficient proof that ATD alters 5-HT release, citing two microdialysis studies that report no effects of ATD on basal 5-HT efflux in the medial prefrontal cortex or raphé nuclei.…”

Influence of reward motivation on human declarative memory

“…In human experiments, central serotonin depletion impairs the encoding, delayed but not immediate recall, as well as delayed recall of source episodic memory in a verbal learning task. However, it does not impair spatial memory nor does it affect spatial episodic or general declarative memory (Mendelsohn et al, 2009). In sum, while serotonin does not appear to play a clear role in reward memory formation, and because noradrenaline mainly enhances sensory processing and general invigoration (Section 2.1), we consider that the type of reward-induced modulation of declarative memory discussed in the remaining part of the review is primarily caused by dopamine release.…”

Self-regulatory depletion in dogs: Insulin release is not necessary for the replenishment of persistence

“…The afferent connections of the vagus nerve provide direct projections to many of the modulatory regions of the brain that have been implicated in executive control and motivation (Ruffoli et al, 2012) and electronic vagal nerve stimulation affects the release of norepinephrine and serotonin in rats (Dorr and Debonnel, 2006). Thus, further investigation into noradrenergic and serotonergic mechanisms is warranted and may ultimately lead to a more comprehensive Fructose and Persistence 15 understanding of self-regulatory depletion and cognitive fatigue, the latter of which has already been strongly linked to serotonergic depletion by researchers who have studied the effects of tryptophan depletion (the amino acid precursor to serotonin) on cognitive fatigue (Mendelsohn et al, 2009). …”