The Effects of Acute Tryptophan Depletion on Neuropsychological Function

Abstract

Serotonin (5-HT, 5-hydroxytryptamine) may have an important role in the maintenance of normal neuropsychological functioning. The method of acute tryptophan depletion (ATD) provides a pharmacological challenge by which central 5-HT levels can be temporarily decreased and effects on learning, memory and mood examined. Twenty healthy male volunteers were recruited to take part in this within-subject, double-blind, crossover study. Neuropsychological function was evaluated 4-6 h after ingestion of a control or 52 g tryptophan (TRP) depleting amino-acid drink. ATD significantly lowered levels of plasma total and free TRP (p < 0.001), but this did not affect mood or performance on tests of verbal and visuo-spatial learning and memory, attention or executive function. These results contradict previous findings; however, the degree of disruption of central 5-HT levels resulting from the use of the 52 g amino-acid protocol may be an important factor in explaining the lack of effect. By utilizing more specific probes of individual 5-HT receptor subtypes, future studies can fully explore the role of 5-HT in neuropsychological functioning and may elucidate the factors determining vulnerability to the effects of serotonergic dysfunction.

Rapid Tryptophan Depletion Improves Decision-Making Cognition in Healthy Humans without Affecting Reversal Learning or Set Shifting

“…For reversal learning, while we failed to duplicate the adverse effects of RTD previously described, our negative finding is similar to that of Hughes et al (2003). While variability in the neuromodulatory effects of RTD may have contributed to differences between studies, different task versions used may also have contributed.…”

“…In addition, the improvement in quality of decision making is consistent with several other studies demonstrating improvement in cognitive function associated with PFC. In particular, RTD has improved performance on Stroop-like interference tasks in the majority of (Coull et al, 1995;Rowley et al, 1997;Schmitt et al, 2000), but not all (Hughes et al, 2003;Sobczak et al, 2002), studies that have investigated this. The association of Stroop performance and decision-making cognition with dorsal ACC function may suggest a relatively strong neuromodulatory effect of RTD on this region in these studies.…”

“…Impairment in decision making secondary to RTD has not been replicated using the same decision making/gambling task, and at least one study has failed to find impaired reversal learning (Murphy et al, 2002). With set shifting, some studies have found no impairment Hughes et al, 2003), while others have found impaired performance only on the ED shift (Park et al, 1994) or the ID shift (Rogers et al, 1999a). Therefore, this study aimed to independently replicate the effects of RTD on decision making, reversal learning and set shifting in healthy humans, using the same decision making/gambling task reported by Rogers et al (1999b), and the ID/ED task from the computerized Cambridge Neuropsychological Test Automated Battery (CANTAB).…”

Mood is indirectly related to serotonin, norepinephrine and dopamine levels in humans: a meta-analysis of monoamine depletion studies

“…40,51,76,85,86 Especially for the POMS and the VAS the direction of a decrease of mood in subjects was not always clearly reported. 52,68,77,85 In our meta-analysis no differential effect of the applied mood-scale was observed (Q res = 3.89, df = 2, P > 0.05; data not shown).…”

Consumo de suplementos proteicos e expressão da raiva em praticantes de musculação

“…A deficiência de triptofano ou o aumento dos aminoácidos que competem com ele para cruzar a barreira hematoencefálica parecemser um fator crucial para a queda dos níveis de serotonina cerebral. Dietas hiperproteicas parecem reduzir a serotonina cerebral, o que pode desencadear depressão e comportamentos impulsivoagressivos (SCHMECK et al, 2002;YOUNG et al, 2002;HUGHES et al, 2003).…”