Assessing the usability of aromatic mouthwashes in alleviating physiological stress responses.

Background: Mouthwashes play a pivotal role in oral care, and their efficacy has been explored extensively across various dimensions. As a contribution to the development of novel oral care products, this study aims to investigate the psychophysiological effects of aromatic mouthwashes during the resilience period from a short-term cognitive stressor utilizing biological signals and subjective evaluations. Methods: A within-participant experimental design with 22 healthy females was conducted with four mouthwashes; peppermint (Mint), peppermint + bergamot (MB), peppermint + sweet orange (MO), and peppermint + lavender (ML), and water as the control (Ctl), after a 20-min calculation task. Subjective evaluations and physiological responses including skin conductance level and electrocardiogram were recorded throughout the experiment. Results: Citrus mouthwashes (MO and MB) showed a greater decrease in heart rate and a significant increase in the high-frequency component of heart rate variability. The participants indicated a significant effect in terms of "flavor preference" and "refreshing sensation" for mouthwash use compared to the Ctl. Conclusion: The results suggest that rinsing with citrus-flavored mouthwashes has a positive impact in alleviating the physiological stress response (in terms of cardiac activity). These findings may have implications for the development of innovative, novel oral care products that promote stress reduction and improve oral health.

Alleviation of acute stress response by black pepper aroma administration.

BACKGROUND: Black pepper is one of the most popular spices globally. As black pepper essential oil has not yet been used in the context of aromatherapy, this study examined the effect of black pepper aroma on cardiac and peripheral autonomic nervous system (ANS) activity under stressful conditions using an olfactometer to administer aroma in a precise and controlled manner to ensure reproducibility. METHODS: A within-participant design experiment was conducted with 20 male university students who performed a 30-min calculation task as a short-term stressor under three aroma conditions: black pepper, ginger, and dipropylene glycol (DPG) (scentless air as a control). Each aroma was sporadically delivered (first 20 s of each 1-min interval) with the olfactometer during the task. Electrocardiograms and skin conductance level (SCL) were measured to evaluate ANS's physiological acute stress response. Subjective evaluations for the given stressful task and impressions on the types of aromas were assessed. RESULTS: The physiological acute stress response induced by the short-term stressor, which is characterized by the enhancement of the heart rate (HR) and SCL and decreases in the heart rate variability (HRV), was suppressed with black pepper: the increase in HR and reduction in HRV from the baseline were 38.9% (p = 0.048 when compared with DPG) and 32.9% smaller (p = 0.002 for multiple comparisons) than those in DPG, respectively, and the increase of SCL was 15.5% smaller (p = 0.005 for multiple comparisons) than that in ginger. However, there was no significant difference in subjective scores among the conditions. CONCLUSION: Although black pepper is a stimulative agent, the study findings showed that black pepper aroma alleviated the physiological acute stress response, which can be beneficial in aromatherapy under stressful conditions.

Time-course changes in fingernail cortisol levels during pregnancy and postpartum.

The cortisol level in fingernails can reflect the cumulative hormones produced in the body several months prior. However, previous studies have only demonstrated the cross-sectional associations of fingernail cortisol with salivary or hair cortisol, and not longitudinal changes in fingernail cortisol in situations where cortisol levels in the body could be expected to change. Therefore, this study focused on pregnancy as a model for changes in cortisol levels over a prolonged period of time, and investigating the time courses of fingernail cortisol during pregnancy and the postpartum period. We collected nail samples from 30 healthy women during pregnancy and 12 months postpartum to measure the cortisol levels in the nail. Results showed that cortisol levels in fingernail clippings increased from 1 month before childbirth to 4 months postpartum, with the levels peaking at 2 months postpartum. Additionally, we found higher cortisol levels in fingernail clippings in primiparas than in those of multiparas. The time course of fingernail cortisol levels could replicate the longitudinal changes in cortisol in the body, and differences between multiparas and primiparas seemed to be biologically plausible, which could support the concept of fingernail cortisol as a retrospective index of hormone production.

An illusion of disownership over one's own limb is associated with pain perception.

Viewing one's body and even a fake/virtual body experienced as one's own has been suggested to modulate pain perception. However, what happens to pain perception when one's own body part is felt as not belonging to one? We designed a paradigm to induce an illusory feeling of disownership regarding one's limb, investigating whether the feeling affects pain threshold. Participants observed right-side images of their bodies from a third-person perspective via a head-mounted display in real-time. Following instructions, they moved their left hand while keeping their left elbow behind the upper body, so that the connection of their arm to the torso was not visible (test condition), or in front of it, so they could see the arm being part of them (control condition). Then, pain threshold was tested with a thermal stimulator. We found a significantly higher strength of disownership in the test condition than in the control condition. While there was no pain modulation within and between conditions, disownership ratings negatively correlated with pain-threshold changes, where the participants reporting explicit disownership showed lower pain-threshold changes than the others. The finding suggests that while multisensory disintegration had no modulatory effect, the individual sense of disownership was associated with pain perception.

A validation study on fingernail cortisol: correlations with one-month cortisol levels estimated by hair and saliva samples.

Several studies have focused on the cortisol levels in fingernail samples as a possible index of cumulative hormone production; however, the biological validity of fingernail cortisol has not been fully established. We investigated the association between cortisol levels in fingernail samples and other biological specimens, including hair and saliva samples, in healthy young adults to determine whether fingernail cortisol was associated with past cumulative hormone production. Participants were 23 adults (14 men and 9 women; mean age = 22.7 ± 2.8 years). Saliva samples were collected three times per day for 30 days, and hair samples (1 cm) from participants' scalps were obtained. Fingernail samples were repeatedly collected for 8 months, considering growth rate of fingernail and time lag for fingernails to fully extend from the nail matrix. Cortisol levels in hair samples were significantly associated with the levels in fingernail samples that were obtained 3 months after hair collection (r = .48, p < .05). The 30-day integrated area under the curve, based on salivary cortisol levels at awakening and bedtime, were significantly associated with cortisol levels in fingernail samples that were collected 2-5 months after saliva collection. This finding was especially significant after adjusting for the awakening time when the saliva was collected. This study provided evidence that fingernail cortisol was associated with cumulative hormone levels measured several months before but not those in the present. The samples may be useful for endocrinological evaluation in the investigation of chronic stress, cortisol levels, and health; moreover, the use of fingernail samples would permit larger-scale studies.

Association between hair cortisol and diurnal basal cortisol levels: A 30-day validation study.

This study aimed to validate the association between hair cortisol and 30-day integrated salivary cortisol levels. Additionally, the intra-individual stability of the hair cortisol and the association between hair cortisol and salivary cortisol in several time domains were systematically explored. Twenty-four adults (15 men and 9 women, mean age: 22.7 ± 2.8 years) were asked to collect three saliva samples per day for 30 days, immediately after awakening (time 1), 30 min after awakening (time 2), and at bedtime (time 3). The hair sample was taken from the posterior vertex as close as possible to the scalp at the end of the 30-day study period. The area under the curve based on times 1 and 3 showed that cortisol levels in the 1 cm hair segment closest to the scalp were moderately correlated with the 30-day salivary cortisol levels (r = 0.41, p = 0.047). However, this correlation was not observed for the cortisol awakening response, diurnal slope, or other metrics in different time domains. The mean salivary cortisol at time 3 was significantly correlated with hair cortisol (r = 0.42, p = 0.041). Intra-individual stability of the hair cortisol was maintained for at least 4 months. Hair cortisol may reflect basal cortisol levels more substantially over longer periods (longer than 1 month and for at least 4 month), thus reflecting longitudinal cortisol production, rather than the day-to-day temporal cortisol response. Salivary cortisol is an ideal metric for short-term or day-to-day stress response. Researchers should select suitable metrics, such as hair cortisol for basal level (or trait) or salivary cortisol for response (or state), depending on the study objective.

Neural basis of individual differences in the response to mental stress: a magnetoencephalography study.

Stress is a risk factor for the onset of mental disorders. Although stress response varies across individuals, the mechanism of individual differences remains unclear. Here, we investigated the neural basis of individual differences in response to mental stress using magnetoencephalography (MEG). Twenty healthy male volunteers completed the Temperament and Character Inventory (TCI). The experiment included two types of tasks: a non-stress-inducing task and a stress-inducing task. During these tasks, participants passively viewed non-stress-inducing images and stress-inducing images, respectively, and MEG was recorded. Before and after each task, MEG and electrocardiography were recorded and subjective ratings were obtained. We grouped participants according to Novelty seeking (NS) - tendency to be exploratory, and Harm avoidance (HA) - tendency to be cautious. Participants with high NS and low HA (n = 10) assessed by TCI had a different neural response to stress than those with low NS and high HA (n = 10). Event-related desynchronization (ERD) in the beta frequency band was observed only in participants with high NS and low HA in the brain region extending from Brodmann's area 31 (including the posterior cingulate cortex and precuneus) from 200 to 350 ms after the onset of picture presentation in the stress-inducing task. Individual variation in personality traits (NS and HA) was associated with the neural response to mental stress. These findings increase our understanding of the psychological and neural basis of individual differences in the stress response, and will contribute to development of the psychotherapeutic approaches to stress-related disorders.