Aliva testing also has specific uses in clinical and experimental psychological settings. Due to its ability to provide insight into human behavior, emotions, and development, it has been used to investigate psychological phenomenon such as anxiety, depression, PTSD, and other behavioral disorders.[9] Its primary purpose is to test cortisol and alpha amylase levels, which are indicative of stress levels.
Salivary cortisol is a good stress index, with increased levels of cortisol correlating positively with increased levels of stress. Cortisol levels rise slowly over time and take a while to return to base level, indicating that cortisol is more associated with chronic stress levels.[10] Alpha amylase, on the other hand, spikes quickly when confronted with a stressor and returns to baseline soon after the stress has passed, making salivary amylase measurement a powerful tool for psychological research studying acute stress responses.[10] Samples are usually collected from participants by having them drool through a straw into a collection tube while experiencing a stimulus, with samples taken every few minutes to record the gradual change in stress hormone levels. Because the collection of saliva samples is non-invasive, it has the advantage of not introducing further stress on the participant that may otherwise distort results.[11]
In more specific studies looking at the link between cortisol levels and psychological phenomena, it has been found that chronic stressors such as life-threatening situations(example: diseases), depression, and social or economic hardship correlate with significantly higher cortisol levels.[11] In situations where a subject undergoes induced anxiety, high cortisol levels correspond with experiencing more physiological symptoms of nervousness, such as increased heart rate, sweating, and skin conductance.[12] Additionally, a negative correlation was discovered between baseline levels of cortisol and aggression. [13] Salivary cortisol levels can thus provide insight into a number of other psychological processes.
Alpha amylase levels in saliva provide a non-invasive way to examine sympathoadrenal medullary(SAM) activity, which can otherwise be measured with electrophysiological equipment or blood plasma readings. Salivary alpha amylase levels have been found to correlate with heightened autonomic nervous system activity levels, reacting in similar ways to the hormone norepinephrine.[14] Subsequent findings reveal a relationship between a-amylase and competition. Results showed that alpha amylase levels changed when reacting to competition, but not when anticipating it. Furthermore, by testing alpha amylase levels, scientists noticed a difference in reactivity behavior among individuals with previous experience in a similar situation. [15]
While saliva testing has the promise of becoming a valuable and more widely used tool in psychological research in the future, there are also some disadvantages to the method that must be kept in mind, including the cost of collecting and processing the samples and the reliability of the measure itself. There is a substantial amount of both within-person and between-person variability in cortisol levels that must be taken into account when drawing conclusions from studies.[16]
Many studies have been performed to further examine the variables that contribute to these within-person and between-person variances. Analyses of the variables that affect cortisol levels has yielded an extensive list of confounding variables.
Diurnal variation is a major factor for within-person variance because baseline cortisol levels have been known to differ based on the time of day. For normally developing individuals who follow a typical day–night schedule, cortisol production peaks during the last few hours of sleep. This peak is thought to aid in preparing the body for action and stimulate the appetite upon waking.[17] Diurnal variation is also affected by psychological conditions. For example, Early morning cortisol levels have been found to be elevated in shy children and late night levels elevated in depressed adolescents, particularly the between the hours of two and four PM.[17] This might be important for understanding emotions and depressive symptoms.