In recent times, there has been a growing interest in mental health, leading to increased research on various approaches to promote relaxation and recovery. For example, practices such as meditation and sauna provide healing and vitality to our mind and body.

Therefore, we have decided to focus on "music" as a more accessible means to achieve equivalent relaxation effects. This is because the impact of music on human emotions and cognition has been studied extensively over the years. It has been revealed that music not only promotes relaxation but also induces significant changes in brain activity.

 

Music and Brainwaves: A New Endeavor to Replicate the "Totonou" State

 

Recognizing the potential of "music," we attempted to replicate the equivalent relaxation effects experienced after a sauna by taking an innovative approach of listening to music incorporating auditory stimuli proven by neuroscience. Previous research has shown that auditory stimuli in the form of low-frequency waves, such as theta waves, may help suppress anxiety and enhance a sense of well-being. However, these auditory stimuli, if too monotonous, can potentially cause discomfort or distract attention. Therefore, by integrating them into regular music, we hypothesized that we could provide stimulation to specific brain activity patterns, creating a sense of pleasantness similar to the "Totonou" state.

 

Comparison between Sauna and Music Sessions: Consistent Increase in Theta Waves

 

First, we conducted an experiment to measure the brain activity during the "Totonou" state. In this study, participants experienced three sets of sauna, cold water exposure, and rest. Measurements of brain activity and subjective evaluation surveys were conducted before and after each sauna session and during the rest period. Through this, we aimed to reveal the brain activity and mood changes during the "Totonou" state.

As a result, it was found that the activity of theta waves and alpha waves increased after both the sauna session and the rest period (Figure 1). Furthermore, during the auditory oddball task conducted before and after the sauna session (measuring reaction time to target stimuli), a significant decrease in P300 and a substantial increase in MMN (Mismatch Negativity) were observed after the sauna (Figure 2). The response time to target stimuli also showed a significant decrease (Figure 3). These results suggest that the brain has reached an efficient state. Additionally, the survey revealed significant changes, with mental relaxation being the most prominent effect after the sauna session (Table 1).

Next, we conducted a study where participants listened to music incorporating monaural beats. We started by creating pleasant music, analyzing its frequency spectrum, and incorporating monaural beats to stimulate the activity of alpha and theta waves. Subsequently, we compared the brain activity during the listening of this specially generated music with that during listening to regular music and in a silent condition.

As a result, during the auditory oddball task conducted after listening to the music session, there was a significant increase in MMN when participants listened to the special music (Figure 4). Additionally, the activity of theta waves showed a substantial increase while participants were listening to the special music (Figure 5). The survey results showed a significant increase in the average score for the perception of relaxation only when participants listened to the special music.

Comparing the results of this study with sauna sessions, the significant increase in MMN indicates a notable improvement in sensitivity to auditory stimuli, similar to the results obtained from the sauna sessions. Additionally, the substantial increase in theta waves, observed in both the special music session and sauna session, is strongly associated with relaxation. When considering the survey results, it suggests that when individuals are able to detach themselves from the external environment and self, the brain enters a theta state, potentially enhancing creative thinking.

Regarding alpha waves, there was no amplification observed similar to sauna sessions. This could be attributed to the fact that the peaks of the envelope (volume changes) in the special music were around 7Hz, within the theta wave range, suggesting that only theta waves were stimulated. On the other hand, the peak of the envelope in regular music was around 13Hz, theoretically allowing for the amplification of alpha waves; however, in this study, a decrease in alpha waves was observed. Considering existing research showing a decrease in alpha wave activity as individuals transition from an awake state to a sleep state, this result may suggest that participants were gradually transitioning into a sleep state.

In the survey, only items that showed significant interaction in the sauna session were selected. The results indicated that there were no changes in the items "Heartbeat is faster than usual" and "Back feels stiff," while similar changes were observed in the subsequent items, similar to the sauna session (Table 2). These two items are likely related to the alternating hot and cold effects experienced during the sauna session, which may be less reproducible by simply listening to music.

Reproducing the Sauna Effect through Music: Exploring New Avenues for Relaxation

 

Overall, despite the different trends in alpha wave activity changes between sauna and music sessions, there was consistency in the significant increase in theta waves and MMN amplitude. This suggests the potential success in creating a state closely resembling the "Totonou" state by listening to music incorporating monaural beats. Music, which does not require a special environment like a sauna, may provide a more accessible way to achieve relaxation, and in the future, it could be tailored to individual preferences. Further research, including individual differences and comparisons with other relaxation methods, is needed, but this study is likely to make a significant contribution to improving mental health and happiness.

Chang, M., Tanaka, K., Naruse, Y., Imamura, Y., & Fujii, S. (2023). Influence of Monaural Auditory Stimulation Combined with Music on Brain Activity. bioRxiv, 2023-10.

※引用元は、こちら