Tyrosine supplementation mitigates working memory decrements during cold exposure

Abstract

In rats, dietary supplementation with the amino acid tyrosine (TYR) prevents depletion of central catecholamines observed during acute environmental stress. Concomitant changes in the animals' behavioral responses to stress suggest that TYR might have similar effects on central catecholamines and cognition in humans exposed to environmental stress. This study aimed to determine if severe cold exposure impairs human cognition and if dietary supplementation with TYR would ameliorate such deficits. Volunteers (N = 19) completed three test sessions on different days (35°C control/placebo, ∼10°C/placebo, ∼10°C/TYR) using a double-blind, within subjects design. During each session, volunteers completed two 90-minute water immersions and consumed a food bar (150 mg/kg TYR or placebo) before each immersion (total TYR 300 mg/kg). Cognitive performance, mood, and salivary cortisol were assessed. Cortisol was elevated in the cold (p b .01). Volunteers made fewer correct responses on a Matchto-Sample memory measure (p b .05) and reaction time (RT) and errors increased on a choice RT test (p b .01) in the cold. Self-reported tension (p b .01), depression (p b .05) and confusion (p b .01) also increased in the cold. When volunteers consumed TYR, correct responses increased on a Match-to-Sample memory measure (p b .05) and study time for the sample was shorter (p b .05), indicative of more rapid and accurate information processing. Finally, RT on the memory measure revealed a similar pattern across immersions for TYR and thermoneutral conditions, but not cold/placebo (p b .05). This study demonstrates cold exposure degrades cognitive performance and supplementation with TYR alleviates working memory decrements.

Chronic intermittent cold stress and serotonin depletion induce deficits of reversal learning in an attentional set-shifting test in rats

“…Acute cold exposure during cognitive testing degraded performance, including vigilance, reaction time, reasoning skills and short-term memory (e.g., see Coleshaw et al 1983;Mahoney et al 2007;Patil et al 1995;Shurtleff et al 1993). In addition to decrements in performance on a 4-choice reaction task and impairment in delayed match-to-sample tasks, cold-stressed individuals also reported higher levels of tension, confusion and depression on the subscale of the Profile of Mood States questionnaire, and had significantly higher "total mood disturbance" scores (Mahoney et al 2007). Taken together, these results indicate that cold stress can impair cognitive performance and evoke adverse changes in both behavior and mood.…”

Mood and selective attention in the cold: the effect of interval versus continuous exercise

“…In particular, beta-endorphins (Harber and Sutton 1984), thyroxine (Reed et al 2001), and the tyrosine-catecholamine cascade (Mahoney et al 2007) are all affected by both cold and exercise. Although the POMS is commonly used in environmental physiology research, the SCWT was designed to measure severe cognitive impairments and may not be sensitive enough to detect small differences.…”

Oral tyrosine supplementation improves exercise capacity in the heat

“…Acute tyrosine consumption in humans does improve measures of mood, and dopamine dependant cognition, psychomotor performance, and behaviour, across a variety of dissimilar stressors which are theorised to increase brain catecholamine activity (Dollins et al 1995;Banderet and Lieberman 1989;Mahoney et al 2007;Neri et al 1995;O'Brien et al 2007). One study has measured a net brain uptake of tyrosine during prolonged exercise (Nybo et al 2003); however, acute tyrosine supplementation did not improve either prolonged exercise capacity (Strüder et al 1998) or performance (Chinevere et al 2002) in temperate conditions.…”