The use of saliva markers in psychobiology: mechanisms and methods

In the social sciences, the use of saliva parameters has greatly expanded in recent years from the measurement of steroid hormones, like cortisol, and now includes a wide range of biochemical parameters. These salivary constituents can be broadly classified into two groups: (1) constituents that enter saliva from plasma (e.g. hormones, inflammatory markers, drug chemicals) and (2) constituents that are produced locally by the saliva glands (e.g. α-amylase, secretory IgA). Reliable measurement of blood-borne constituents assumes a constant saliva/plasma ratio (SPR), which implies that the concentration in saliva truthfully follows intra- and interindividual variations in plasma. The first part of this review discusses the main determinants of the SPR: the mechanism by which plasma constituents enter saliva (i.e. passive diffusion, active transport, ultrafiltration, leakage) and associated physiochemical factors. The second part of this review provides an overview of central and peripheral neural mechanisms that regulate saliva gland function and the release of glandular proteins. This section provides a neurobiological underpinning for a section, which addresses methodological implications for the assessment of glandular secretions. Salivary psychophysiology is a fast-growing field and the time seems ripe for more rigorous methodological studies that may help this discipline to reach its full potential.