# Using the \(\beta\)/\(\alpha\) Ratio to Enhance Odor-Induced EEG Emotion Recognition
## 4 Discussion  
This study is the first to use the inhalation of SEO or BEO as an olfactory stimulus for emotion recognition based on the EEG signals of participants. By subdividing the \(\alpha\) and \(\beta\) frequency bands, introducing new variables (\(\beta/\alpha\)), and incorporating different ROIs, new EEG spectral features were constructed, leading to the development of a high-performance emotion recognition model. In the performance test of the classification models, the introduction of the \(\beta/\alpha\) value markedly improved the performance of all models (DA, SVM, and RF). Among them, the RF model demonstrated the best performance in handling high-dimensional frequency-spatial domain EEG signal characteristics, indicating its effectiveness as a tool for analyzing odor-induced EEG emotion recognition. The subjective self-reported results showed that inhaling SEO generally induced low-arousal, high-valence emotions, while inhaling BEO generally induced high-arousal, high-valence emotions. These results align with previous studies showing that SEO has relaxing and calming properties [40]. This may be due to its main volatile component (+)-\(\alpha\)-Santalol [17]. BEO has mood-boosting and attention-focusing properties [41], and limonene may play an important role as the main volatile component of BEO [42]. Notably, the self-reported results also conveyed interesting information: in the arousal dimension, male participants were more sensitive to SEO than female participants, perceiving SEO as inducing lower arousal emotions; in the valence dimension, the ratings for BEO were highly dispersed, especially among male participants. Current EEG spectral analysis research generally recognizes that different frequency bands have different physiological meanings [33; 43]. For example, alpha rhythm synchronization is associated with enhanced calmness [44], while beta rhythms usually occur when we are alert, focused, and engaged in problem solving [45]. Furthermore, studies have shown that a higher \(\beta/\alpha\) ratio is associated with increased brain focus [13; 14; 15]. In the topographic analysis, we found that compared to RS, inhaling SEO significantly increased the PSD of the alpha1 frequency band in the frontal lobe, right temporal lobe, central area,  
Figure 6: Evaluation of test set indicators of different models. (**A**) Discriminant analysis-1 (DA-1), support vector machine-1 (SVM-1), and random forest-1 (RF-1) construct features based on traditional EEG frequency bands (\(\delta\), \(\delta\), \(\alpha\)1, \(\alpha\)2, \(\beta\)1, and \(\beta\)2). DA-2, SVM-2, and RF-2 introduce the \(\beta/\alpha\) ratio indicator when constructing features, and the other conditions are the same. Comparison of the six indicators of DA-1, SVM-1, and RF-1. The value range of these indicators is between 0 and 1. The closer to 1, the better the model performance (see Section 2.10 for details). (**B**) Receiver operating characteristic (ROC) curves of the six models. The area under the ROC curve (AUC) of each model is calculated. The dotted line represents the random guessing of the model. The value range of AUC is between 0 and 1. The closer to 1, the better the model performance. and parietal lobe, and significantly increased the PSD of the alpha2 rhythm mainly in the frontal lobe, right and central parietal lobes, and occipital lobe. Inhaling BEO significantly increased the PSD of the alpha1 rhythm in the prefrontal lobe, left temporal lobe, and a few electrodes in the central area, and significantly increased the PSD of the alpha2 rhythm mainly in the frontal lobe, right and central parietal lobes, and left occipital lobe. It is noteworthy that inhalation of SEO or BEO significantly alters the alpha1 and alpha2 rhythms in the frontal lobe, possibly due to the involvement of the orbitofrontal cortex in odor processing [46].