The Impact of Availability of Monoaminergic Precursors on Human Cognition
Monoamines are a group of biogenic amines which contain an amino group connected to an aromatic ring and serve as neurotransmitters or neuromodulators in the human central nervous system (CNS). Molecules included in this group are dopamine, epinephrine, and norepinephrine (catecholamines); serotonin and melatonin (indolamines); and histamine (imidazolamine). As neurotransmitters, they form monoaminergic systems, which play a major role in the CNS signalling, including functions such as mood regulation, executive function, certain types of memory or learning. Consequently, they are crucial in the pathogenesis of many neuropsychiatric or neurodegenerative disorders, and are a target for several drug treatments. They are synthesized from their respective amino acid precursors, whose availability can be experimentally manipulated by a targeted short-term dietary depletion or loading. The aim of this systematic review is to critically evaluate the role of availability of the precursors of monoaminergic neurotransmitters. It includes published empirical studies that employ manipulation of availability of precursor molecules from which monoaminergic neurotransmitters are synthesized, and also investigate their impact on human cognition or neural processing. Although this particular area has been researched for several years, there is very little consensus about specific effects
of manipulation of monoaminergic systems. For example, many experiments use different tasks to measure the same concepts (e.g. both Continuous Performance Test and Stop Signal task are thought to measure response inhibition), or employ slightly varying methodological approaches. Reasons such as these might explain some of the seemingly conflicting results, and systematic review can therefore provide unique insight into this research area. With a better understanding of these crucial systems lies the possibility to create new drug treatments, improve diagnostic tools, and further our knowledge about both normal and pathological states.
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