The effects of laughter on attention focusing and psychological stress in healthy older adults: a single-blind, randomized controlled trial using a comic video intervention

doi:10.21203/rs.3.rs-4598246/v1

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Research Article

The effects of laughter on attention focusing and psychological stress in healthy older adults: a single-blind, randomized controlled trial using a comic video intervention

https://doi.org/10.21203/rs.3.rs-4598246/v1

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Background

Disorders associated with mental health significantly impact disability-adjusted life year values and represent a social problem in stressed societies. Worsening mental health also affects cognitive functions and quality of life. To address these issues, increasing attention is attracted to preventive measures vis-à-vis mental and brain health in daily life. Therefore, growing interest in care using laughter has recently been noted. This study was designed to assess the effects of a short-term laughter-based intervention on the mental health and cognitive functions of middle-aged and older adults.

Methods

The study applied a single-blind, crossover-controlled trial design. Cognitive tasks were performed after participants viewed a video clip of approximately four minutes (humor or control video) and the resulting scores were treated as the primary endpoint. Secondary endpoints included cerebral blood flow in the dorsolateral prefrontal cortex, heart rate variability, subjective mood state assessment, and salivary stress biomarkers.

Results

The study was conducted on 25 healthy Japanese-speaking adults aged 40 to 65 years. Results revealed a significant increase in digit vigilance scores and in comparison to viewing the control video, participants evinced a trend toward an increase in serial 7 subtraction scores after viewing the humor video. No significant differences were found in scores on other cognitive tasks. The cerebral blood flow was also significantly higher in the dorsolateral prefrontal cortex during cognitive tasks performed after participants viewed the humor video compared to the control video. The outcomes of heart rate variability, subjective mood state assessment, and salivary stress markers also suggested that the humor video intervention could subsequently contribute to the activation of parasympathetic activity and reduce psychological stress levels induced by the cognitive tasks.

Conclusions

The study outcomes indicated that interventions using short humor videos can improve attention focus and may help to reduce psychological stress levels. These results support the clinical benefits of humor, which could be utilized as a simple and non-invasive approach to promoting the health of middle-aged and older adults.

Trial registration

The study was registered at the University Hospital Medical Information Network (UMIN) database (Registration No. UMIN000043332||http://www.umin.ac.jp/ctr/) on 15/02/2021.

Laughter

Humor

Focusing attention

Cerebral blood flow

Psychological stress levels

Parasympathetic activity

Mental health

Well-being

Intense competition, along with high-pressured lifestyles and social conditions adversely impact individuals living in present-day societies, causing stress and poor quality of life, which are becoming urgent social problems [1, 2]. Mental health exerts a significant impact on disability-adjusted life year values [3]. The deterioration of mental health is also associated with cognitive decline and significantly impacts labor productivity [4, 5]. Chronic mental health difficulties can trigger mood disorders such as anxiety and depression; hence, preventive care is essential for the resolution of problems before they become severe. Given this context, a growing interest in care using laughter has been observed in recent years [6]. Laughter therapy does not require specialized equipment and high costs and has thus already been introduced in the medical domain as a treatment program without side effects [7, 8]. An observational study conducted on 14,233 individuals demonstrated an association between infrequent laughter and a higher risk of developing a functional disability [9].

Laughter also contributes to psychosocial and physical health aspects and several studies [10, 11, 12, 13, 14, 15] have shown that it can effectively alleviate negative emotions such as anxiety and depression. Physiologically, laughter reduces stress hormones [6, 14] and increases T lymphocytes by activating natural killer cells, which causes an upsurge in white blood cells and immunoglobulin (Ig) levels, thus increasing a body’s immunity [15, 16, 17]. Laughter also lowers blood pressure: it reduces vasoconstriction through a decrease in the breakdown of nitric oxide, a vasorelaxant substance, and raises blood glucose levels by reducing cortisol [14, 18, 19]. Laughter therapy is non-invasive, non-pharmacological, and relatively easy to implement; it is thus considered an effective complementary treatment that can reduce the intensity of many diseases [20] and is also expected to ameliorate the health of middle-aged and older adults [21]. The effects of laughter have been demonstrated on a range of psychosocial and physical health outcomes as noted above; however, the extant research has not comprehensively tested how positive psychological states achieved from short-term laughter influence cognitive functioning and stress responses. Previous studies [22] have shown that humor video interventions improve short-term memory in healthy older people, suggesting that such means could improve cognitive functions. However, the effects of humor video interventions on other cognitive functions (such as attention focusing and working memory) or on changes in the biological responses of middle-aged people remain unclear. The present study designed an intervention trial with middle-aged and older adults to assess the effects of a brief laughter-based intervention on their autonomic nervous systems and stress responses and to determine the effects of autonomic improvement on cognitive functions, primarily attention. We hypothesized that laughter interventions would be associated with improved cognitive functions and increased regional cerebral blood flow (rCBF) in the dorsolateral prefrontal cortex (DLPFC) during the performance of cognitive tasks. We used near-infrared spectroscopy (NIRS) to measure rCBF during the intervention. The DLPFC region of the prefrontal cortex enacts an essential role in the executive functions of working cognition flexibility [23], planning [24], memory, inhibition, and reasoning; it is also crucial for the executive functions of cognitive process management [25]. In addition, we measured changes in salivary stress biomarkers [26, 27, 28, 29, 20, 31, 32] (cortisol, α-amylase, s-IgA, and β-endorphin) at every given event and calculated the autonomic nervous system activity using heart rate variability (HRV) [33] as biometric information associated with mood state.

Ethics and registration

This study was conducted following the Declaration of Helsinki and Ethical Guidelines for Medical and Health Research Involving Human Subjects and was approved by the ethics committee of Kirin Holdings Company. All participants provided written informed consent. Before enrolling participants, the study was registered at the University Hospital Medical Information Network (UMIN) database (Registration No. UMIN000043332||http://www.umin.ac.jp/ctr/; Registration title. Effects of watching videos on brain function: A single-blind, crossover comparative study) on 15/02/2021.

Participants

We recruited 25 healthy middle-aged and older Japanese-speaking adults aged between 40 and 65 years. In a previous study[22], the effect of humor on short-term memory were reported in 20 healthy older adults. Based on this report, an equivalent sample size was established in this study. The following exclusion criteria were established:

(i) Suffering from hearing or visual impairment that interfered with daily life

(ii)Wearing a device that interfered with heart rate measurement (e.g., pacemaker)

(iii) Having developed symptoms of arrhythmia in the past 12 months

Intervention

Experimental intervention

The experimental intervention required participants to view a sufficiently funny comic dialog video (humor video) of approximately four minutes. The audiovisual clip was provided by Yoshimoto Kogyo Holdings Company (Tokyo, Japan).

Control intervention

The control intervention made participants view a less funny, approximately four-minute-long comic dialog video clip (control video) provided by Yoshimoto Kogyo Holdings Company (Tokyo, Japan).

After viewing the video clips, the participants rated them on a questionnaire comprising seven items: funniness, frequency of laughter, understanding, sympathy, exciting language, enjoyable movement, and tempo.

Procedure

A randomized, single-blind, crossover comparative design was applied for the trial. Registered participants were alternately allocated to two sequences (1 and 2) in the order of their registration to exclude the order effect reflective of the experiment’s experience. Participants designated to sequence 1 viewed the humor video as the experimental intervention in Phase 1 and the control video as the control intervention in Phase 2. The order was reversed for participants assigned to sequence 2.

The interval between Phase 1 and Phase 2 was > 15 minutes. Figure 1 presents the examination flow on the study day.

The study sequence allocator was not involved in assessing eligibility, data collection, or analysis. The research staff and outcome assessors were blinded to sequence allocations until data analysis. On the trial day, the participants were instructed to avoid caffeine-containing foods and beverages, excessive exercise, alcohol consumption, and smoking.

The participants were also instructed not to eat or drink anything except water for two hours before the intervention. The data were collected in April 2020 at Hamamatsu City in Shizuoka prefecture in Japan. This study was conducted by Kirin Holdings Company (Tokyo, Japan).

Primary outcomes

The primary outcome comprised the scores of the cognitive tasks performed by the participants.

Participants took a five-minute rest after viewing the humor or control video as previously described. They subsequently performed the cognitive tasks comprising digit vigilance, serial 7 subtraction, alphabetic working memory, and n-back (Fig. 1). The participants were granted a 20-second rest period for each task. The digit vigilance, serial 7 subtraction, and alphabetic working memory tasks were presented using the Computerized Mental Performance Assessment System (COMPASS, Northumbria University, Newcastle upon Tyne, UK), a purpose-designed software application for the flexible delivery of randomly generated parallel versions of standard and novel cognitive assessment tasks. This assessment system has also been previously utilized to measure the effectiveness of nutritional interventions [35, 36].

Fixed numbers were displayed on the right side of the screen for the digit vigilance task, and numbers changing at the rate of 150 per minute were presented one after another on the left side of the screen. Participants were required to respond when the number on the left matched the number on the right. The task lasted for 1.5 minutes and the participants were scored for accuracy (%), reaction times for correct responses (ms), and false alarms (number).

A random number between 800 and 999 was presented on the screen for the serial 7 subtraction task and participants were required to continually subtract seven from the presented number as quickly as possible. The starting number was cleared on the entry of the first answer, and asterisks indicated the next three digits. This task was scored for the number of responses (number), the number of correct responses (number), and false alarms (number).

The alphabetic working memory task displayed a series of five letters on the screen, one letter at a time, and participants memorized the displayed letters. Thirty letters were then displayed on the screen one by one and participants were required to press computer keyboard keys corresponding to YES or NO as quickly as possible to answer whether the letter belonged to the original series. The task was scored for accuracy (%) and reaction times for correct responses (ms).

The n-back task was presented on a touchpad using brain training apps (Kirin Holdings Company, Japan). The n-back task required participants to memorize the colors and shapes of trains displayed one after the other. Subsequently, participants were asked to tap the train whose color and shape corresponded to the one displayed three trains before. This task was scored for accuracy (%), the number of correct responses (number), and false alarms (number).

Secondary outcomes

Measurements of cerebral blood flow

The rCBF was measured during the intervention using a 2CH NIRS system (HOT-2000, NeU Corporation, Tokyo, Japan) with a single wavelength of 810 nm, and the concentration change in total hemoglobin (total Hb) was calculated as demonstrated in a previous report [37] (Fig. 1).

Two dual-source detectors were placed in the left and right DLPFC. This area corresponds to the Fp1-Fp2 region as defined by the international 10–20 system used in electroencephalography [38, 39]. Total Hb was defined as the mean value of Hb in the left and right DLPFC. The pre-task baseline was defined as the mean value of total Hb in the 60 seconds before beginning the cognitive tasks. The mean values of total Hb during the task period minus the baseline were compared.

Measurement of HRV

ECG was measured using a Silmee Bar type Lite (TDK Corporation, Tokyo, Japan) at a time resolution of 1000 Hz [40]. The participants were asked to apply the device to the anterior chest with a gel pad. ECG measurements were taken from before the start of the intervention until after the end of the cognitive tasks (Fig. 1). The RR interval was calculated from the ECG data by the Slimee measurement and analysis system, and HRV analysis was then performed using Kubios HRV analysis software ver 3.4.1. A threshold-based artifact correction algorithm was employed to correct artifacts and ectopic beats in the RR interval data HRV parameters in the frequency domain, specifically LF (0.04–0.15 Hz), HF (0.15–0.4 Hz), the ratio between LF and HF band powers (LF/HF), and total power (TP, 0–0.4 Hz) were analyzed using FFT. HF was used as the indicator of parasympathetic activity [41], LF/HF as the marker for sympathetic activity [42], and TP as the sign of the overall autonomic nervous system activity [41].

Assessment of the subjective mood state of participants

The visual analog scale (VAS) and TDMS-ST [43] were used to assess the mood states of participants. The VAS evaluated fatigue, stress, motivation, depression, concentration, and drowsiness of participants, who rated their current mood state on 100-mm VAS before and after the video intervention and after performing the cognitive tasks (Fig. 1). The VAS scores were converted to z-scores for each participant to reduce the influence of subjective rating scales and to ensure appropriate comparisons. The z-scores were calculated using the mean and standard deviation changes in the VAS scores of every participant. Consequently, the mean and the standard deviation were adjusted to a z-score of 0 and 1 for each participant.

The TDMS-ST comprises eight mood descriptors: energetic, lively, lethargic, relaxed, calm, irritable, and nervous. The participants reported their current mood by rating each item on a six-point Likert-like scale before and after the video intervention, and after completing the cognitive tasks (Fig. 1). Vitality, stability, pleasure, and arousal scores were then calculated according to the established protocol.

Salivary biomarkers

Salivary cortisol, α-amylase, s-IgA, and β-endorphin were measured as stress biomarkers, and salivary oxytocin was calculated as the indicator of psychological fulfillment. Participants were instructed to collect drooling saliva using a saliva collection aid (SalivaBio Corporation, Carlsbad, CA, United States) before and after the video intervention and after accomplishing the cognitive tasks (Fig. 1). The collected saliva samples were measured at the Yanaihara Institute Inc. (Shizuoka, Japan).

Statistical analysis

Data were expressed as mean ± standard deviation. Comparisons between the experimental and control phases were accomplished using paired t-tests. The Sidak test was applied to compare temporal changes during the same phase. Statistical comparisons were performed using BellCurve for Excel (Social Survey Research Information, Tokyo, Japan) and Microsoft Excel 2016 (Microsoft, Redmond, WA, USA). Statistical significance was set at p < 0.05.

Missing values for each outcome were defined as meeting the following criteria.

Score for cognitive tasks; Data from participants who self-reported that they gave up performing the task.

Measurements of cerebral blood flow; Data from subjects who self-reported that they gave up performing the task.

Measurement of HRV; Data evincing a data loss rate of more than 50% due to poor ground contact between the sensor and skin.

Assessment of the subjective mood state of participants; Non-response data.

Salivary biomarkers; Data below detection limit.

Baseline characteristics of the study sequences

Figure 2 presents the study flowchart. We recruited 25 participants (male/female = 12/13). Registered participants were alternately allocated as previously mentioned: Sequence 1 comprised 13 participants and sequence 2 encompassed 12 participants. Alternate assignments were made in each sequence for male and female participants to avoid gender bias. All participants completed the study; therefore, the total analyzed data included all 25 participants, whose characteristics are displayed in Table 1. There were no significant between-sequences differences in baseline characteristics. No serious adverse effects were observed.

Table 1

Subject characteristics at baseline
Characteristics	Sequence1 (n = 13)	Sequence2 (n = 12)	p-value
Age	49.5 ± 6.7	52.8 ± 6.9	0.25
Male / Female	6 / 7	6 / 6	0.74

Data were presented as means standard deviations (SD); p-value of the age was calculated using unpaired t-tests. The sex ratio was analyzed using the χ2 tests.

Evaluation of video clips

Table 2 shows the participant ratings reported for each video after it was viewed. The humor video was rated significantly higher than the control video on all assessment items (funniness, frequency of laughter, understanding, sympathy, exciting language, enjoyable movement, and tempo) (p < 0.001, all assessment items). This result confirmed that the humor video was appropriately funny in comparison to the control video.

Table 2

Evaluation of video clips
Evaluation item	Humor video	Control video	n	p-value
Funniness	5.9 ± 0.3	2.2 ± 0.2	25	p < 0.001
Frequency of laughter	4.0 ± 0.2	1.6 ± 0.1	25	p < 0.001
Understanding	6.5 ± 0.2	3.4 ± 0.4	25	p < 0.001
Sympathy	5.8 ± 0.3	2.6 ± 0.3	25	p < 0.001
Exciting language	6.2 ± 0.2	2.7 ± 0.4	25	p < 0.001
Enjoyable movement	5.3 ± 0.3	2.4 ± 0.2	25	p < 0.001
Tempo	6.5 ± 0.1	3.6 ± 0.4	25	p < 0.001

Data were presented as means standard error (SE); p-value was calculated using paired t-tests

Primary outcomes

Scores for cognitive tasks

Table 3 records the scores for the cognitive tasks performed after the viewing of each video (humor and control). Response speeds for the digit vigilance tasks accomplished after viewing each video were significantly faster for the humor video than for the control video (p = 0.039). Similarly, the number of correct responses for the serial 7 subtraction tasks undertaken after participants viewed each video tended to be higher for the humor video (p = 0.079). No significant differences were found in the other scores. However, participants performed better on many scores after viewing the humor video than after viewing the control video.

Table 3

Score for the cognitive tasks
Cognitive task		Humor video	Control video	n	p-value
Digit vigilance	Accuracy (%)	97.39 ± 0.69	97.54 ± 0.67	23	0.87
	Reaction times for correct responses (ms)	462.78 ± 6.81	473.00 ± 6.64	23	0.039
	False alarms (number)	0.74 ± 0.20	0.83 ± 0.21	23	0.70
Serial 7 subtraction	The number of responses (number)	21.24 ± 1.63	20.33 ± 1.42	21	0.26
	The number of correct responses (number)	19.10 ± 1.51	17.57 ± 1.42	21	0.079
	False alarms (number).	2.14 ± 0.42	2.76 ± 0.44	21	0.30
Alphabetic working memory	Accuracy (%)	94.49 ± 1.25	94.30 ± 1.25	23	0.88
Alphabetic working memory	Reaction times for correct responses (ms)	984.96 ± 30.88	983.18 ± 32.40	23	0.94
N-back	Accuracy (%)	87.87 ± 2.6	87.19 ± 2.48	21	0.79
	The number of correct responses (number)	12.30 ± 0.36	12.21 ± 0.35	21	0.79
	False alarms (number)	1.70 ± 0.36	1.79 ± 0.35	21	0.79
Data were presented as means standard error (SE); p-value of the age was calculated using paired t-tests.

Table 3. Score for the cognitive tasks

Secondary outcomes

Measurements of cerebral blood flow

We measured the changes from the pre-task baseline in total Hb concentration during the cognitive tasks. These results are presented in Tables 4 and 5. There was no significant difference at baseline before the intervention. Compared to the pre-task baseline, the total Hb concentration of participants increased significantly during the serial 7 subtraction, the alphabetic working memory, and the n-back tasks performed after viewing the humor video (p < 0.001, p = 0.0014, p < 0.001, respectively). In contrast, no significant change was detected compared to the pre-task baseline when these tasks were performed after viewing the control video. Further, the changes in total Hb concentrations while undertaking the cognitive tasks were significantly greater than the pre-task baselines after participants had viewed the humor video compared to after they had viewed the control video. (p = 0.022; Fig. 3 and Table 5)

Table 4

The changes from the pre-task baseline in total Hb concentration
	Cognitive task	Hb concentration	n	p-value
After viewing the humor video	Digit vigilance	0.08 ± 0.04	23	0.73
	Serial 7 subtraction	0.28 ± 0.06	23	p < 0.001
	Alphabetic working memory	0.18 ± 0.05	23	0.0014
	N-back	0.23 ± 0.07	23	p < 0.001
	During all tasks	0.18 ± 0.05	23	p < 0.001
After viewing the control video	Digit vigilance	0.03 ± 0.06	23	1.00
	Serial 7 subtraction	0.11 ± 0.06	23	0.064
	Alphabetic working memory	0.06 ± 0.05	23	0.87
	N-back	0.08 ± 0.05	23	0.39
	During all tasks	0.07 ± 0.05	23	0.74

Data were presented as means standard error (SE); p-value was calculated using sidak test.

Table 5

Comparison of the changes from the pre-task baseline in total Hb concentration
	After viewing the humor video	After viewing the control video	n	p-value
Digit vigilance	0.08 ± 0.04	0.03 ± 0.06	23	0.25
Serial 7 subtraction	0.28 ± 0.06	0.11 ± 0.06	23	0.014
Alphabetic working memory	0.18 ± 0.05	0.06 ± 0.05	23	0.031
N-back	0.23 ± 0.07	0.08 ± 0.05	23	0.023
During all tasks	0.23 ± 0.07	0.07 ± 0.05	23	0.022

Data were presented as means standard error (SE); p-value was calculated using paired t-tests.

Measurement of HRV

Supplementary Tables 1 and 2 show the time series changes in the actual measured HRV values. LF/HF was significantly higher when the humor video was viewed compared to when participants viewed the control video (p = 0.012). Conversely, the LF/HF measured during the cognitive tasks was lower after viewing the humor video compared to after participants viewed the control video. A statistically significant difference was noted during the performance of the last task (N-back). (p = 0.002) (Fig. 4). Time series changes in HF exhibited an inverse change to the changes noted in LF/HF. No significant changes were observed in TP (Supplementary Tables 1 and 2).

Subjective mood state assessment by participants

VAS z-scores for fatigue, stress, motivation, depression, and concentration were significantly higher (p = 0.0012, p < 0.001, p < 0.001, p = 0.0031, p = 0.0032, respectively; Table 6) after viewing the humor video compared to after the control video was viewed. Further, the scores allotted by participants for stress, motivation, and depression after completing the cognitive tasks were significantly higher after viewing the humor video compared to after they had viewed the control video (p = 0.0027, p = 0.0021, p = 0.0083 respectively; Table 6). However, no significant differences were observed in the drowsiness scores. No mood state was significantly different at baseline before the intervention. The actual scores of vitality, stability, and pleasure were significantly higher in TDMS-ST after participants had viewed the humor video compared to after they had viewed the control video (p = 0.0017, p = 0.013; Supplementary Table 3). No significant differences were observed in arousal scores.

Table 6

Score for VAS
Mood states		Humor video	Control video	n	p-value
Fatigue	Before the video intervention	-0.04 ± 0.17	-0.02 ± 0.10	24	0.78
	After the video intervention	0.79 ± 0.12	-0.05 ± 0.17	24	0.0012
	After performing the cognitive tasks	-0.49 ± 0.19	-0.87 ± 0.16	24	0.15
Stress	Before the video intervention	-0.03 ± 0.15	-0.08 ± 0.12	24	0.093
	After the video intervention	0.86 ± 0.11	0.03 ± 0.15	24	p < 0.001
	After performing the cognitive tasks	-0.42 ± 0.15	-1.13 ± 0.14	24	0.0027
Motivation	Before the video intervention	0.02 ± 0.16	-0.15 ± 0.17	24	0.75
	After the video intervention	0.64 ± 0.12	-0.25 ± 0.16	24	p < 0.001
	After performing the cognitive tasks	0.12 ± 0.17	-0.95 ± 0.16	24	0.0021
Depression	Before the video intervention	0.04 ± 0.16	0.03 ± 0.17	24	0.093
	After the video intervention	0.65 ± 0.14	-0.01 ± 0.15	24	0.0031
	After performing the cognitive tasks	-0.32 ± 0.13	-0.95 ± 0.16	24	0.0083
Concentration	Before the video intervention	0.26 ± 0.13	-0.13 ± 0.19	24	0.18
	After the video intervention	0.38 ± 0.15	-0.38 ± 0.16	24	0.0032
	After performing the cognitive tasks	0.13 ± 0.17	-0.43 ± 0.25	24	0.058
Drowsiness	Before the video intervention	0.12 ± 0.15	0.00 ± 0.22	24	0.75
	After the video intervention	0.17 ± 0.17	-0.20 ± 0.14	242	0.14
	After performing the cognitive tasks	0.06 ± 0.19	-0.42 ± 0.20	24	0.069
Data were presented as means standard error (SE); p-value of the age was calculated using paired t-tests.

Table 6. Score for VAS

Salivary biomarkers

Supplementary Table 4 displays the salivary cortisol, α-amylase, s-IgA, β-endorphin, and oxytocin measurements before and after participants had viewed each video, and after the cognitive tasks, respectively. No significant differences were observed between the experimental and control interventions. The changes in α-Amylase from before viewing the video to after the cognitive tasks tended to be higher after viewing the control video compared to after viewing the humor video (p = 0.060; Supplementary Table 4). No differences between the two interventions were noted in the changes in cortisol, s-IgA, β-endorphin, and oxytocin.

This single-blind, crossover, and comparative study recruited 25 healthy adults aged between 40 and 65 to investigate how a short humor video intervention affected cognitive functions and mood states. The study utilized the digit vigilance task to assess focusing attention [44, 45] and employed the serial 7 subtraction, alphabetic working memory, and n-back tasks to assess working memory [46, 47, 48]. The results revealed that the digit vigilance scores improved significantly and that the serial 7 subtraction scores tended to increase after the humor video intervention compared to after the control video was shown. It is therefore suggested that viewing short humor videos could enhance attention focus. A previous study [22] found that viewing humor videos improved short-term memory in healthy older people, but the current result is the first report on attention focusing. In addition, the present study evidenced the effects of video-based interventions on middle-aged and older adults (40–65 years), whereas previous investigations [22] have targeted people aged 65 and older. Noteworthily, while previous studies [22, 49] have used 20-minute humor videos, the current study confirmed the constructive effects of viewing even shorter funny video clips of only four minutes. A further feature of this study involved the real-time measurement of the biometric impact of the short humor video intervention using a NIRS[40, 50]. The rCBF in the DLPFC region was significantly higher during the cognitive tasks after participants had viewed the humor video compared to after they had viewed the control video. The DLPFC region of the prefrontal cortex enacts an essential role in the executive functions of cognitive process management [25]. Extant research has shown that damage to the DLPFC impairs attention focusing [51]. DLPFC dysfunction has also been associated with decreased attention focus, increased mental health problems [52], and reduced rCBF in the DLPFC. The outcomes of this study suggest that the viewing of short humor videos promotes DLPFC activity during cognitive tasks and is associated with improvements in DLPFC-related cognitive functions such as attention focusing and may also exert constructive effects vis-à-vis problems related to mental health.

The VAS and TDMS-ST scores were used to assess subjective mood states and were significantly higher for all categories except sleepiness and arousal after participants had viewed the humor video compared to after they had viewed the control video. As previous studies have described [12, 13], laughter was found to effect temporary improvements in mood state. LF/HF is an indicator of sympathetic activity, and HF is an indicator of parasympathetic activity [33, 53, 54]. LF/HF rose transiently while watching the humor video and then quickly declined. HF was significantly higher during the last cognitive task after participants had viewed the humor video compared to after they had viewed the control video. Laughter may have stimulated a transient activation of sympathetic activity, which may have increased subsequent parasympathetic activity under the influence of homeostasis. Parasympathetic activity has been reported to be associated with reduced psychological stress[54], suggesting that laughter reduces psychological stress. At the same time, the changes in VAS scores registered after the cognitive tasks for stress, depressed mood, and motivation were significantly higher after participants had viewed the humor video compared to after they had viewed the control video. These results suggest that the humor video intervention could have contributed subsequently to the activation of parasympathetic nerve and reduced the psychological stress levels induced by the cognitive task.

Further, changes in α-amylase activity from before the videos were viewed to after the cognitive tasks were accomplished tended to be higher after participants had viewed the control video compared to after they had viewed the humor video. The α-amylase activity is a known indicator of physical and mental stress [55] and is known to respond on a relatively fast timescale. The results of this study suggested that the humor video intervention may have diminished the increase in stress levels during the tests. Unlike previous studies [6, 14, 18], the current investigation observed no changes in cortisol concentrations. This result could be attributed to the relative brevity of the humor video, which was only around four minutes and may not have allowed enough response time for these indicators to change.

These results support the contention that the viewing of short humor videos by middle-aged and older adults could promote DLPFC activity and thus enhance cognitive functions such as attention focus and reduce psychological stress levels through the subsequent activation of parasympathetic activity.

The study must acknowledge several limitations. First, the sample size was small. The study’s sample had adequate power as confirmed by the results of previous studies; however, a larger sample size would have allowed a better assessment of the middle-aged and older adults population as a whole. Second, we did not measure the effects of repeated interventions using the humor video. Third, we only measured the immediate post-intervention effects of the humor video and therefore did not evaluate how long the effects of laughter would last. Future initiatives would need to demonstrate the effectiveness of repeated interventions and the persistence of the effects for laughter to be routinely and continuously utilized as a tool for the amelioration of cognitive functions and the alleviation of stress levels in the daily lives of individuals.

This study aimed to determine the impact of a short humor video intervention on the cognitive functions, mood states, and associated biometric information of the participants. The study outcomes indicated that the conducted intervention using a short humor video clip increased rCBF during the cognitive tasks and may have improved attention focus. The results of the study also suggested that interventions involving short humor videos could be associated with reduced psychological stress levels. These enjoyable interventions can represent continuous and practicable approaches to difficulties of daily living and could contribute to improvements in the cognitive functions and stress levels of middle-aged and older adults.

rCBF regional cerebral blood flow

DLPFC The dorsolateral prefrontal cortex

NIRS near-infrared spectroscopy

HRV heart rate variability

UMIN university hospital medical information network

COMPASS computerized mental performance assessment system

VAS visual analog scale

Ethics approval and consent to participate

This study was conducted following the Declaration of Helsinki and Ethical Guidelines for Medical and Health Research Involving Human Subjects and approved by the ethics committee of Kirin Holdings Company. All participants provided written informed consent. The study was registered at the UMIN database before subject enrollment (Registration No. UMIN000043332||http://www.umin.ac.jp/ctr/; Registration title. Effects of viewing videos on brain function: A single-blind, crossover comparative study) on 15/02/2021.

Consent for publication

Not applicable.

Availability of data and materials

The data presented in this study are available from the corresponding author upon reasonable request

Competing interests

This research was conducted with the support of a research fund from Kirin Holdings Company, Ltd.

Funding

This study was funded by Kirin Holdings Company, Ltd.

Authors’ contributions

T.Y., Y.A., and A.K. designed the study, posited the principal conceptual ideas, and wrote the draft outline. T.Y., Y.A., and T.F. collected the data. A.K. and R.S. contributed to the interpretation of the results. Y.T. wrote the manuscript with support from Y.A. All authors have read and approved the final manuscript.

Acknowledgements

We appreciate Mr. Kuniaki Obara for his assistance in managing this clinical project.

We acknowledge the Hamamatsu City Hall officers involved in this study and thank the citizens of Hamamatsu for participating in our study. We are also grateful to Yoshimoto Kogyo Holdings Company for providing us with the intervention videos.

Author information

¹Kirin Central Institute, Kirin Holdings Company, Limited, 2-26-1, Muraoka-higashi, Fujisawa-shi, Kanagawa, 251-8555, Japan.

²Department of Psychosomatic Medicine, Kindai University Faculty of Medicine, Osakasayama, Osaka, Japan

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No competing interests reported.

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The effects of laughter on attention focusing and psychological stress in healthy older adults: a single-blind, randomized controlled trial using a comic video intervention

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Abstract

Background

Methods

Results

Conclusions

Trial registration

Figures

Background

Methods

Ethics and registration

Participants

Intervention

Experimental intervention

Control intervention

Procedure

Primary outcomes

Secondary outcomes

Measurements of cerebral blood flow

Measurement of HRV

Assessment of the subjective mood state of participants

Salivary biomarkers

Statistical analysis

Results

Baseline characteristics of the study sequences

Evaluation of video clips

Primary outcomes

Scores for cognitive tasks

Secondary outcomes

Measurements of cerebral blood flow

Measurement of HRV

Subjective mood state assessment by participants

Salivary biomarkers

Discussion

Conclusions

List Of Abbreviations

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References

Additional Declarations

Supplementary Files

Status:

Version 1