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tryptophan, tyrosine & SSRI’s on cognition + reward
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tryptophan (building block to serotonin) and tyrosine dopamine precursor) are amino acids found in protein-rich food such as pork, chicken and tofu and they are ideal foods for the brain! Aside from investigative studies into the link between diet and depression, recent research reveals they may have implications in reward processing and a collection of cognitive skills including working memory, task switching, and performance [1]. Researchers at Charles Darwin University in Northern Australia also highlight that reward and cognition may be negatively impacted by some antidepressants.
antidepressant side effects on dopamine
dopamine is your reward and pleasure chemical messenger that is also associated with motivation [1]. A study published by Neuroscience revealed that SSRI drugs can reduce the speed at which dopamine is released in the brain [2]. SSRI intake in humans has been shown to decrease the motivation needed to obtain rewards [3]. This might explain the WedMD stated side effect of reduced sexual desires [4]. In animal studies, another group of antidepressants, called monamines, showed that increased dopamine concentration in the junction of neurons can lead to a condition that involves the inability to feel pleasure in everyday activities called anhedonia [1].
reduced tyrosine intake reduces motivation
dopamine has been shown to modulate reward processing in studies that decreased dopamine levels, called Acute Tyrosine Depletion. Reduced tyrosine levels have been shown to selectively impair this motivation [1] and reduce your ability to respond to stimuli that predict rewards [8]. It has also been reported that reduced tyrosine levels can affect the motivation to derive rewards that is driven by both a physiological state and learned association about a reward cue, as well as the motivation to influence future behaviour [1].
tyrosine may benefit cognition when stressed
a military study revealed that in duress, cadets that consumed tyrosine showed improvements in memory, tracking tasks, and cognitive performance [5]. Another study demonstrated that tyrosine promotes convergent (deep) thinking when multitasking creative tasks [6]. It might be helpful to know that these benefits only seem to occur when in duress. Researchers at the University of Cambridge found the reduced tyrosine levels in non-stressful circumstances had no impact on planning, decision-making, and task switching [7].
If you're looking to enhance your goal-driven behaviour, Tyrosine supplements may be an option. so far, evidence shows this has only been effective in those that carry a genetic variant to the dopamine pathways, called T/T homozygote in the DA D2 receptor gene [8]. A neurophysiological test that involved participants to predict whether a scene or face would lead to a reward or punishment, found that tyrosine enhanced the ability to think about multiple concepts simultaneously in females but not in males [9]. This may explain why women are perceived to be better at multitasking in some circumstances [10].
tryptophan may promote patience to reap larger rewards
good things come to those who wait! Scientists have revealed the brain regions where serotonin promotes patience [11] and a reduction in tryptophan has been shown to increase preference for small, immediate rewards over larger, delayed rewards [1].
tryptophan may impact decision-making
brain imaging studies showed that tryptophan depletion reduced the activity of the front part of the brain that plays a role in decision making and problem-solving during performance monitoring in a Go/No go task [12]. Overall, tryptophan in cognitively demanding tasks has been shown to have no behavioural or cognitive effect.
tryptophan V 5-HTP
tryptophan is converted into serotonin (5-HT) via the amino acid 5-HTP however, it has a number of challenges. It cannot cross the blood-brain-barrier alone, it competes poorly with other amino acids for a transporter molecule, and therefore, it is required in relatively large amounts in order to produce serotonin. Our 5-HTP (5-hydroxytryptophan) is extracted and isolated from the Griffonia seed, and it can freely enter the blood-brain barrier.
References
[1]Aquili, L. (2020) The Role of Tryptophan and Tyrosine in Executive Function and Reward Processing. International Journal of Tryptophan Research. [2]Mascio, M. & Esposito, E. (1997) The degree of inhibition of dopaminergic neurons in the ventral tegmental area induced by selective serotonin reuptake inhibitors is a function of the density-power-spectrum of the interspike interval. Neuroscience. [3]Meyniel et al. (2016) A specific role for serotonin in overcoming effort cost. Neuroscience, Computational and Systems Biology. [4]WebMd (2019) What are SSRI's? [5]Deijen, J.B., Wientjes, C.J.E., Vullinghs, H.F.M., Cloin, P.A., Langefeld, J.J., 1999. Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course. Brain Research Bulletin 48, 203–209. [6] Nutrition Reviews (2015) Food for Creativity: Tyrosine Promotes Deeper Thinking in New Study. [7]McLean et al. (2004) The effects of tyrosine depletion in normal healthy volunteers: implications for unipolar depression. Psychopharmacology. [8]Colzato et al. (2016) Effects of l-Tyrosine on working memory and inhibitory control are determined by DRD2 genotypes: A randomized controlled trial. Cortex. [9]Robinson et al. (2010) Dopamine precursor depletion improves punishment prediction during reversal learning in healthy females but not males. Psychopharmacology. [10]BBC News (2013) Women ‘better at multitasking’ than men, study finds. [11]Science News (2020) Scientists reveal regions of the brain where serotonin promotes patience.[12]Evers et al (2006) The effect of acute tryptophan depletion on the BOLD response during performance monitoring and response inhibition in healthy male volunteers. Psychopharmacology.
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