# A Novel Approach for Acute Mental Stress Mitigation Through Adapted Binaural Beats: A Pilot Study
## 1 Introduction  
Given the significant impact of stress in our society, especially in the professional sphere [1], innovative solutions for its detection are necessary. A consolidated and widely employed methodology for stress recognition is the analysis of cortisol levels, which requires either salivary, hair, urinary, plasma, serum, or sweat fingernail samples [2]. Nevertheless, this approach is not suited for real-time assessment [3], making the analysis of physiological signals, e.g. those, collected through wearable devices [4, 5], a more practical alternative. In this regard, a significant role is played by machine learning [6, 7] and deep learning algorithms [8, 9], which combine data from wearable sensors to detect stress effectively. Once a stressful response is detected, the secondary objective is to relieve stress. Nowadays, there are different strategies for this purpose, and one potential approach is auditory stimulation through binaural beats (BBs) [10, 11]. BBs are obtained by presenting two pure tones with different frequencies to the ears of the user (e.g., \(f_{0}\) and \(f_{0}+\delta\) Hz tothe left and right ears), resulting in a third phantom beat, named in the following as \(f_{\text{BB}}\), centred at the difference between the two frequencies. Studies in the literature investigated this stimulation both during passive listening [12; 13] and the execution of cognitive tasks [14; 15; 16], which are commonly adopted to induce acute mental stress in controlled conditions [17]. Overall, the majority of the studies involving during-task stimulation focus on assessing the enhancement of cognitive performances through BB simulations at different frequency bands: for example, beta (13.0-30.0 Hz) [18] and gamma (above 30 Hz) [18; 19]. An interesting application of this auditory stimulation is working memory enhancement, with different studies highlighting its effectiveness [14; 20; 21]. Concerning the use of BBs for stress mitigation, studies have already explored the impact of this stimulation in reducing the effects of acute mental stress [16; 22; 23], making this stimulation an alternative to meditation-relaxation techniques [24] and mindfulness-based stress reduction programs [25]. Furthermore, the findings of the systematic review in ref. [26] suggest BBs as a promising and user-friendly tool for alleviating the symptoms of anxiety and depression. Despite the fascinating outcomes mentioned above, other studies indicate either absent or inconsistent improvements in cognitive performance [27] and absent or unclear brainwave entrainment toward the frequency of stimulation [12; 28; 29], which is the concept at the basis of the BB stimulation. As suggested in ref. [30], a missed brainwave entrainment is probably due to a lack of consensus about its definition and methodological issues, which include varied frequencies used as carriers (\(f_{0}\)), different \(f_{\text{BB}}\), duration of the stimulation, and presence or absence of embedded noise to mask the beats. Given the missing consensus, the efficacy of BBs is still an open problem regardless of their application, making further research necessary to understand the effect of this stimulation better. With particular reference to the methodological issues listed above, we believe that a significant role is played by the frequency of the beats, i.e., \(f_{\text{BB}}\). In particular, almost all studies in the literature focus on a stimulation at constant frequencies, belonging to different bands of electroencephalography activity, such as theta (4.0-8.0 Hz), alpha (8.0-13.0 Hz), and beta (13.0-30.0 Hz), but not at personalized frequencies. To the best of our knowledge, only one study [31] investigated a personalized stimulation by adjusting \(f_{\text{BB}}\) for each participant in the theta and beta range based on their heart rate using the Brain-Body Coupling Theorem proposed by [PERSON] [32].