# A Novel Approach for Acute Mental Stress Mitigation Through Adapted Binaural Beats: A Pilot Study
## 4 Discussion
### Limitations and Future Directions  
Despite the promising results of this pilot study, it is not free of limitations. Altogether, we identify five main aspects that should be taken into account in future research:  
* Number of participants and their mental health condition: The small number of participants limits the trustworthiness of our approach. For this reason, it is necessary to consider a wider sample and structure the experiments to account for multiple factors influencing cortisol levels [17]. However, additional consideration should be given. Despite the interesting results of this study, the effects of this stimulation are modest, especially in the HR and RMSSD changes (see Figure 7). We believe this result is largely attributable to the fact that our participants were healthy individuals. Accordingly, we anticipate that a more pronounced effect might be observed in individuals experiencing chronic stress, as they may have greater potential for improvement.
* Task: Given the intrinsic variability in the subject's response to stress [52, 53, 54], recreating a stressful event for all the participants is still a challenge [17]. In this regard, technologies like virtual and augmented reality can be utilized to design laboratory experiments that replicate the stress levels encountered in real-world situations [55].
* Sensors: For this pilot study, a commercial chest strap (PolarH10) was used to collect the ECG. This device does not ensure that the signal quality meets medical standards. Therefore, future studies could consider using higher-quality sensors while simultaneously ensuring user comfort, such as integrating electrodes into clothes [56]. In our work, we decided to minimize the number of sensors, but future experiments could consider the acquisition of additional signals like electrodermal activity, which is well established for stress detection [57, 58], and the EEG, which could permit a better understanding of the physiological and neural response of the participants during the stimulation. However, it should be pointed out that increasing the number of sensors can significantly increase the complexity of the system and discomfort on the part of the user, which could also impact stress perception.
* Algorithm for \(f_{BB}\) modulation: The proposed algorithm can certainly be optimized. For instance, it does not currently include a \"reset\" to restart the search for the optimal stimulation frequency (e.g., from the initial one at 6.0 Hz). Implementing this feature would enhance adaptability, allowing the algorithm to better accommodate variations in the subject's optimal stimulation frequency throughout the task or under stressful conditions.
* Loudness of the BBs: In this study, we chose to focus solely on the frequency of the BBs, keeping their loudness constant. Indeed, our choice was to work on one degree of freedom at a time, leaving the combination of more stimulation parameters (e.g., beat frequency and amplitude) for future works, to assess if better results than the ones presented here can be obtained.  
All the above justify the need for additional research to investigate the efficacy of this novel stimulating approach. Once validated, an important application could involve this technology, either alone or in combination with others like vagus nerve stimulation, to alleviate the effects of psychological disorders.