The effects of Roman chamomile, spike lavender, petitgrain, and rosemary essential oils on psychological, physiological, and psychophysiological processes
Creators: name: Montgomery, K
Publisher: name: University Of Tasmania
Year: 2023

description: The overriding aim of this series of studies was to investigate the psychological, physiological, and psychophysiological effects of exposure to odours of purportedly sedative (petitgrain and Roman chamomile) and stimulant (rosemary and spike lavender) essential oils. More specifically, the purpose of these studies was to determine whether inhalation of essential oils produces reliable changes in mood, behavioural responding, physiological functioning, psychological functioning, and cognitive processing, as well as whether these changes are consistent with the supposed therapeutic effects of these oils as cited in aromatherapy literature. Furthermore, these studies aimed to extend the current knowledge regarding the mechanisms via which the inhalation of essential oils may produce changes in human functioning. In particular, the aim of the studies was to investigate the direct versus indirect action of essential oils on nervous system functioning by removing, controlling, or specifically assessing the effects of variables that are hypothesised to mediate an individual's response to an odour. These mediating variables include hedonic ratings of odour pleasantness, expectations regarding the purported therapeutic effects of the odours, and semantic associations arising from previous experiences with the odours. Consequently, all participants (n=17, females) were screened for knowledge of the experimental odours and were required to rate each odour according to its pleasantness and to identify whether exposure to each odour elicited particular memories. Study One measured changes in self-report ratings of 10 mood dimensions following odour exposure. Study Two assessed the effects of exposure to the odours of the experimental oils on accuracy and reaction time on a visual three-stimulus odd-ball task. In Study Three, changes in physiological parameters such as heart rate, respiration rate and respiratory sinus arrhythmia were assessed in response to odour exposure. Study Four investigated the effects of odour exposure on electroencephalographic responses in the alpha, beta, and theta frequencies. Finally, Study Five assessed the effects of exposure to the experimental odours on the Ni, N2, P2, P3a and P3b components of event-related potentials. In each of these studies, the overall effects of odour exposure on each of the experimental parameters was assessed, as well as the contributing effects of ratings of odour pleasantness and the presence or absence of semantic associations. Overall, the results revealed that there is a complex relationship between experimental parameters, odour type, hedonic ratings, and semantic associations. There are inconsistent results across studies for each of the experimental odours, and the effects of ratings of odour pleasantness or the existence of semantic associations on each experimental parameter varied between essential oil odour types. The fact that the variability in the results was not fully accounted for by the effects of the hedonic and semantic variables alone suggests that there may be other factors that contribute to the action of essential oils on humans.