Salivary alpha-amylase levels and hyperbolic discounting in male humans.

OBJECTIVE: Little is known regarding the role of the sympathetic-adrenal-medullary (SAM) system in self-control and impulsivity in intertemporal choice (delay discounting), although the roles of dopaminergic and serotonergic systems have been extensively examined. This study was aimed to examine the relationships between salivary alpha-amylase (sAA, a non-invasive biological marker of adrenergic/SAM activities) levels and hyperbolic discounting, which is of interest in psychoneuroendocrinology and neuroeconomics.

METHODS: We assessed degrees to which delayed monetary gains were discounted (hyperbolic discount rates) in healthy male students. Participants' sAA were also assessed.

RESULTS: We observed negative relationships between sAA and hyperbolic discounting of small, medium, and large monetary gains.

CONCLUSIONS: The results indicate that subjects with low sAA are impulsive in intertemporal choice. Implications for the roles of adrenergic and SAM systems in self-control in intertemporal choice are discussed.