The Influence of Aromas Essential Oils on Cognitive Processes in Individuals with Different Level of Extraversion and Neuroticism

Proceedings of the 9th International Multidisciplinary Conference «Stress and Behavior» Saint-Petersburg, Russia, 16–19 May 2005.Essential Oils (EO) as olfactory stimuli are widely used to affect functional state of the CNS, especially to reduce anxiety and for relaxation. Nevertheless, the data on concrete ЕО effects on cognitive and neurodynamic brain processes are inconsistent, possibly due to individual differences in extraversion (E) and neuroticism (N) — traits strongly connected with brain activation and activity of the septo-hippocampal system (where numerous projections from olfactory bulbs go). The aim of our study was to analyze influence of a lemon and a lavender EO on sensomotor and cognitive performance in persons with a different E and N. The choice of these EO is due to their properties: a lemon EO is believed to be stimulating, and EO lavenders mainly causing sedation.Methods. 140 healthy students (19–23 years) were distributed in 3 groups. In group I (control, n = 30), testing was carried out at absence of any odorants, in the group II (n = 102) lemon EO was used, and the group III (n = 70) was exposed to lavender EO. In all subjects, reaction times (RT) (simple, choice reaction); duration of central delay (CD); factor of strength of nervous system (FS); functional mobility of nervous processes (FMNP); parameters of accuracy of short-term memory (STM) on letters, numbers and figures, were registered. E and N levels were measured by Eysenk personality questionnaire. After this, the general group was divided into 4 subgroups as follows: Sanguine (+E – N, n = 23), choleric (+E + N, n = 47), melancholic (–E + N, n = 21) and phlegmatic (–E – N, n =10).Results and discussion. Lemon EO reduced RT of choice reaction, duration of CD, FS nervous system, and raised FMNP, proving stimulating influence of this EO on brain functioning. Moreover, error rate in STM tests significantly decreased, showing positive action of Lemon EO on concentration of attention and accuracy of STM. Lavender ЕО did not alter neurodynamic functions in the general group, although increasing the number of errors in STM tests (figures) by 7 %, possibly reflecting its slight relaxing effect. We saw no differences in neurodynamic and memory parameters between groups with different E and N levels in the control group. In contrast, under odor conditions, marked differences in FMNP and accuracy of STM were found. Lavender EO increased FMNP by 12 % in introverts (I) whereas decreased by 7 % in E. It is possible to explain such influence of lavender EO on FMNP by unequal initial arousal levels in E and N during complex task performance. In the controls, in E the level of activation grows, and N develop «over-excitation», thus resulting in approximately equal arousal. Under sedative EO, performance of a task will not cause over-excitation in N (that is why FMNP rose), and in E activation was insufficient, that was reflected in reduced FMNP. Under lavender EO, antagonistic changes in FMNP typically occurred in subjects with different level of N, reducing by 12 % in emotionally stable subjects, and rising by 8 % in neurotics. It is possible to assume that relaxing influence of this EO in neurotics was suppressed through high activity septohippocampal system. In general, FMNP reflecting speed of processing of the information in the CNS, appeared to be the most sensitive to smell-evoked interpersonal differences. From 4 subgroups, altered responses to EO were observed only in sanguine persons (emotionally stable extraverts): FMNP grew after lemon EO and declined after sedative action of lavender. Comparison of groups with different levels of N, we found opposite changes of STM accuracy on figures under lemon EO. Persons with low N showed more errors (+31 %) whereas emotionally unstable subjects showed fewer errors (–17 %). It is known that persons with high levels of N also have higher anxiety and greater motivation in task performance (probably explaining the reduction of mistakes in lemon ЕО conditions observed in this group).Conclusion. Reaction on olfactory stimuli depends on personal characteristics, such as the levels of extraversion and neuroticism, reflected by altered FMNP and accuracy of STM. Sanguine subjects — emotionally stable extraverts — were the most responsive to EO odors