## 4 Discussion  
This exploratory study aimed to assess whether EEG could be a useful tool to evaluate consumers' emotions during the real-time topical application of a cosmetic product on the skin. Such an objective measure of emotions would be of major importance to the industry because it is well known that the emotional component of such products has a significant impact on consumer satisfaction [34]. We compared two cosmetics creams that have been used previously in hedonic studies. We noted differences of valence that were visualized in real-time in the form of moving particles. The cosmetic product 2 was the most appreciated by participants and was also the one with the most positive valence, as measured by EEG. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of Emotion** & **Product 1 (\%)** & **Product 2 (\%)** & **Significance (\(p\) Value)** \\ \hline High positive emotion & 19.7 & 37.7 & 0.04 \\ Low positive emotion & 21.3 & 28.7 & 0.31 \\ High negative emotion & 32.6 & 18.5 & 0.07 \\ Low negative emotion & 26.5 & 15.2 & 0.07 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Percentage of high positive, low positive, low negative, and high negative emotions detected with EEG during the application of the 2 products in 12 participants. Figure 4: Example of artistic representation of emotions felt by one subject while applying CP1 (left) and CP2 (right) and detected in real-time by EEG. Left: the direction of the particles in real-time indicates that the subject feels a negative emotion (negative valence) of high intensity (high arousal) when applying CP1. Right: particles are moving to the right, indicating positive emotions when applying CP2. See the sample videos to see particles moving during the application of each cream. The capacity of EEG to detect differences of valence is new in the application of a cosmetic product, but not in certain other domains, such as viewing movies [35] or listening to music [36]. The detection of such emotions during the application was not unexpected because it has been suggested that different tactile textures evoke highly selective activity in the secondary somatosensory cortex [37], which in turn is known to provide input to the insula [38]. The insula is associated with basic emotions such as anger, fear, disgust, joy, or sadness. Effects from the insula project onto other brain areas such as the anterior cingulate [39] and prefrontal cortices [40]. Activity in the right and left prefrontal areas can then be measured with EEG and analyzed to detect the corresponding emotion. The recorded alpha prefrontal asymmetry reflected functional differences between positive and negative emotions (see as reviews [18, 41, 42, 43, 44]). Because alpha power is assumed to reflect a decrease in metabolic activity [45, 46], reduced alpha activity at the right prefrontal electrodes is associated with negative emotions. Compared with valence, the EEG measures of arousal alone were not sufficient to discriminate between the two cosmetic products. However, we were able to detect that the two products differed in terms of positive high-arousal emotional responses, corresponding to emotions such as excitement, happiness, and delight, according to the circumplex model of emotions [30]. Participants were more excited and happy during the application of CP2 than during the application of CP1. The results we obtained using the dimensional valence-arousal model of emotions further validated the notion that the application of a cosmetic product has effects on the brain. Other researchers have investigated the neural consequences of the application of a cosmetic product, but on other aspects than emotions. One study used functional magnetic resonance imaging--a technique that produces images with high spatial resolution--to compare the response of sensory areas during a passive touch, either after application of a cosmetic product on the skin or when the skin alone was touched [10].