Mental fatigue is a psychobiological state caused by prolonged periods of demanding cognitive activity which results in slower reaction times and attention deficits.
It affects the ability to focus and impacts the capacity to make optimal decisions during a given task.
Mental fatigue is often responsible for accidents in traffic or the workplace and can lead to poor study efficiency.
We know that mindfulness has been shown to have a positive effect on stress-coping and cognitive performance.
There is also cumulating evidence suggesting that listening to binaural beats may increase sustained attention. Binaural beats is an auditory illusion which has been framed as a class of cognitive and neural entrainment (Kirk et al., 2019).
Even though there are different tones of different frequency (165Hz in the left and 179 Hz in the right) presented in each ear the participant will hear one tone, which is the amalgamated difference between the two tones (beta range of 14 Hz).
TIn a new study, Johanne L. Axelsen (SDU), Ulrich Kirk (SDU) and Walter Staiano (University of Valencia) tests the efficacy of binaural beats compared to mindfulness as a cognitive recovery strategy to counteract the negative effect of mental fatigue on sustained attention.
The study also tests whether the mindfulness interventions will show an effect for the on-the-spot novice group or for the experienced mindfulness group, who have practiced mindfulness for 4 weeks in an online-based mindfulness program through the app Headspace.
There were five phases of the study, in the initial phase the participants’ mood were assessed (BRUMS) and they completed a sustained attention task to measure their mind wandering (SART).
The second phase consisted of the mental fatigue treatment for 90 minutes (AX-CPT). Immediately afterwards, the participants’ mood was assessed again, and the two on-the-spot interventions followed: either listening to a guided mindfulness meditation track for 12 min. or an audio track (with binaural beats) for 12 min.
The control group was asked to relax for 12 min. After this the effects of the interventions were tested using the sustained attention task.
The results showed that there was indeed an effect of on-the-spot binaural beats on sustained attention while in a state of experimentally induced mental fatigue. Interestingly, the experienced mindfulness group performed significantly better than the rest of the groups on the sustained attention task already before the mental fatigue was induced.
Furthermore, the group’s performance was better than that of the novice mindfulness group and the control group after the mental fatigue was induced.
The results, and results from previous work by Kirk et al. (2019), indicate that binaural beats may help suppress mind-wandering and sharpening of attentional focus, which in turn reduces the negative effect of mental fatigue. The individual might feel more relaxed and less affected by mental fatigue after listening to the music.
The results showed that there was indeed an effect of on-the-spot binaural beats on sustained attention while in a state of experimentally induced mental fatigue. The image is in the public domain.
The same goes for the experienced mindfulness group, their mindfulness training already showed on the first task where they performed better than the rest of the groups.
This could indicate that practicing mindfulness helps you focus on the task at hand and is effective in offering strategies to handling stressful situations and economizing of mental energy.
Therefore, the study demonstrates that just 12 minutes of binaural beats and 4 weeks of mindfulness training were effective recovery strategies to counteract the negative effects of mental fatigue on sustained attention.
The researchers are currently investigating whether listening to binaural beats for a longer period or practicing mindfulness will improve stressed individuals’ heart rate variability (HRV) and if this has an effect on performance in specific cognitive tasks.
Sleep has a great impact on our health and is an important factor in determining the quality of life (Walker, 2008; Zhang et al., 2015; Weber and Dan, 2016; Lee et al., 2018). However, many researchers have reported that 25% of people feel that their sleep quality is not good (Soldatos et al., 2005; Lee M. et al., 2019).
Since insufficient sleep is a common problem that leads to considerable health, social, and economic impacts (Hublin et al., 2001), a variety of methods have been developed to improve sleep quality (Besedovsky et al., 2017; Lee and Kim, 2017). Inducing sleep quickly is one way to improve the quality of sleep.
Previous studies have applied transcranial direct current stimulation (D’Atri et al., 2016), transcranial magnetic stimulation (Massimini et al., 2007), and pharmacological approaches (Walsh et al., 2008; Feld et al., 2013) as methods for inducing sleep. However, these methods are impractical to users in real-life and occasionally have adverse effects (Bellesi et al., 2014; Santostasi et al., 2016).
It has been suggested that the application of sensory stimuli, especially an auditory stimulus, provides a superior method for improving sleep quality compared to other means (Harmat et al., 2008; Chan et al., 2010; Bellesi et al., 2014; Besedovsky et al., 2017).
Electroencephalography (EEG) is a high resolution and low-cost tool that can measure very practical brain states (Lee et al., 2015, 2016; Kwak et al., 2017). Therefore, this tool is widely used to measure to observe the changed brain states for improving sleep quality.
Brainwave entrainment is the use of an external rhythmic stimulus to generate frequency-dependent EEG responses that match the frequency of the stimuli (Huang and Charyton, 2008; Seifi Ala et al., 2018). Synchronized pulsing stimuli can induce a dominant EEG frequency that appears during a given cognitive state (Tang et al., 2015; da Silva Junior et al., 2019).
One method for producing brainwave entrainment is the use of an auditory stimulus, called a binaural beat (Huang and Charyton, 2008). The binaural beat is an auditory illusion that is observed when oscillatory stimuli are delivered at two adjacent frequencies to each ear at the same time (Perez et al., 2019).
The brain can recognize the frequency difference between the two sounds (Oster, 1973). This stimulus entrained steady-state auditory responses in the brain cortex at the beat frequency (Perez et al., 2019). Initially, the superior olivary complex in the brainstem receives a separate audible input from each ear. This beat is then recognized by neurons in the inferior colliculus (Schwarz and Taylor, 2005).
The phase-locked neural activity of brainstem auditory pathways becomes consistent with the frequency-following response (Hink et al., 1980). The auditory evoked responses produced by the binaural beat can be recorded using EEG (Ozdamar et al., 2011).
This method has recently been used to induce meditation and has correlated with thoughtful processes (Lavallee et al., 2011). A 3 Hz binaural beat was shown to induce delta activity and increase the duration of non-rapid eye movement (NREM) in sleep stage 3 (Jirakittayakorn and Wongsawat, 2018).
In addition, a 6 Hz binaural beat produced meditative effects by inducing theta activity in the frontal and parietal-central regions (Jirakittayakorn and Wongsawat, 2017). The binaural beat at 15 Hz improved working memory by inducing beta activity in the brain (Beauchene et al., 2017).
It was also possible to reduce the difficulty in initiating and maintaining sleep in patients with chronic insomnia by providing an audio-visual stimulus that gradually decreases from 8 to 1 Hz (Tang et al., 2015).
However, it has also been reported that the repetitive and unnatural sound of the binaural beat could make people feel uncomfortable (Crespo et al., 2013). Some studies even claimed that the binaural beat could annoy people without inducing the desired mental states (Jirakittayakorn and Wongsawat, 2017).
Exposure to binaural beats, which do not take into account the user’s current state, can even cause dizziness, as well as discomfort (Noor et al., 2013). This is probably related to the amygdala, a central structure associated with emotional processing. This area is connected to most sensory cortical areas and plays an important role in emotional modulation in the early stages of sensory information processing (Surakka et al., 1998).
In addition, binaural beats seem to feel uncomfortable, in the sense that repeated auditory stimuli cause anxiety and depression (Watkins, 2008). This discomfort could, therefore, make some people reluctant to use binaural beats in the context of real-life.
However, the relationship between binaural beats and subjective emotions is still not well studied, including the auditory pathway to binaural beats (Munro and Searchfield, 2019; Perez et al., 2019). Thus, further research regarding psychological effects related to binaural beats is needed.
To resolve the problems associated with the use of binaural beats, recent research has investigated the possibility of combining it with other sounds, such as piano music (Wiwatwongwana et al., 2016; Gantt et al., 2017).
The binaural beat combined with music could provide relief for the cardiovascular stress response seen in military service members with post-deployment stress (Gantt et al., 2017). They also reported feeling less stressed and showed decreased low-frequency heart rate variability. Moreover, the anxiolytic effect of binaural beat music was investigated compared to plain music under general anesthesia (Wiwatwongwana et al., 2016).
They also showed a significant reduction in heart rate and decreased operative anxiety in the patients who listened to the binaural beat combined with music. These beats are made more enjoyable for users to listen to stimuli if they incorporate natural sounds (Munro and Searchfield, 2019).
Although the combined stimulation is effective for humans to compensate for the shortcomings of binaural beats, research on the various parameters (e.g., decibel, exposure duration, and frequency) is needed to optimize the combination of the two auditory stimuli (Chaieb and Fell, 2017). So far, few groups have applied combined stimuli (CS) in the context of sleep induction.
Autonomous sensory meridian response (ASMR) refers to sensory experiences such as psychological stability or pleasure in response to visual, auditory, tactile, olfactory, or cognitive stimuli (Barratt and Davis, 2015).
Recently, many studies have reported that ASMR is an efficient way to relax people’s minds in academic and social circles (Cash et al., 2018; Smith et al., 2019b). In fact, many people use ASMR to relax their negative moods to lead to sleep, which is accompanied by a feeling of calmness and rest (Barratt et al., 2017). It also correlates with emotional and physiological states (Poerio et al., 2018; Smith et al., 2019a).
Previous studies have reported that ASMR helps lead to sleep by relaxing mental states and reducing anxiety (Barratt and Davis, 2015; Lochte et al., 2018). However, these results are simple feelings based on subjective questionnaires. According to functional magnetic resonance imaging results, ASMR reduces salience and visual networks (Smith et al., 2019b) but increased activities related to sensation, motion, and attention (Smith et al., 2019a).
Also, in EEG, alpha power decreased in the left frontal regions when listening to positive music but decreased in the right frontal regions when listening to negative music, respectively (Balasubramanian et al., 2018).
In other words, the asymmetry of alpha activity in the prefrontal and frontal regions changes with emotion (Geethanjali et al., 2018; Bo et al., 2019). However, there is still a lack of objective evidence to support subjective emotions associated with ASMR based on neuroimaging studies.
In this study, we proposed a novel stimulus for inducing sleep, where we combined the binaural beat to entrain brainwaves at 6 Hz with ASMR. We hypothesized that only theta power increased with the binaural beats and combined stimulus. We also expected that optimal combination stimulus causes 6 Hz brainwaves due to binaural beats and makes a user comfortable and relaxed when using ASMR.
Our hypothesis was also supported in that the dynamic natural sound had a higher spontaneous acceptance rate than static noise (Munro and Searchfield, 2019). In particular, we noted the change in the midline concerning sleep induction. Moreover, the change in theta power over the midline region was highly relevant, since it was directly related to the transition from wakefulness to sleep (Wright et al., 1995).
There were two experimental sessions. In session 1, three auditory stimuli were presented in order to find the optimal combination ratio between the binaural beat and the ASMR trigger that initiates ASMR using natural sounds. In particular, the intensity levels of sounds are important when presenting auditory stimuli.
The average hearing thresholds for normal adults is usually 20 dB at each ear (López-Caballero and Escera, 2017; Munro and Searchfield, 2019). Also, people feel quiet at sound levels of 30 dB, and 45 dB is recommended as background noise level (Kipnis et al., 2016). Sound levels between 60 and 80 dB are regarded as noisy, and sound levels more than 80 dB are harmful (Kipnis et al., 2016).
In this regard, we have determined the ratio of combination between the two auditory stimuli. In session 2, we compared the effect of the optimally combined stimulus determined in session 1 with that of a sham condition (SHAM), binaural beats only, and ASMR triggers only. Questionnaires were conducted before and after the stimulation period to explore changes in the emotional states which sustain psychological stability.
Our results suggest that combining the stimuli could relieve the discomfort of the binaural beat and have a stabilizing effect of ASMR for inducing sleep. These findings could help induce sleep quickly as a way to improve the quality of sleep.