In this study, we assessed the utility of two EEG metrics measuring brain arousal (a dimension of functional brain states comprising different levels of wakefulness and sleep) including the newly developed Arousal-Index (AI) (developed by Andreas Müller and researchers at the Brain and Trauma Stiftung) and the meanwhile established VIGALL-index in depressive patients and healthy controls.

Resting-state EEG of 64 patients and 46 healthy controls obtained in the eye-closed condition was analyzed by both AI and VIGALL. Additionally, the correlation between the two measures was calculated. It was found that: (i) patients with depression disorder showed a significantly higher AI level when compared to healthy controls. Concerning this finding,  our results extend the knowledge that depression has a significant correlation with brain arousal and that generally depressed patients demonstrate a higher level of arousal. (ii) depressed patients demonstrated a significantly decreased mean VIGALL as assessed by VIGALL compared to healthy controls; (iii) there was a significant negative correlation between AI and the VIGALL metric in both groups; (iv) the AI metric obtained for both hemispheres were highly correlated for both groups suggesting a strong bilateral involvement of arousal control, and (v) using the AI, we were able to distinguish two subgroups of depressive patients, one with low AI and one with high AI measures. the treatment of a depressed patient with high arousal would be very different than a patient with low arousal.

Vigall and Arousal Index show a high correlation (0.8)

In conclusion, our results provided unique evidence for the sensitivity of the AI score as a potential diagnostic tool for arousal measurement in depression disorder. Also, the results showed that depressive patients can be separated in subgroups based on the EEG marker and their medication history. This highlights the need for AI as an accurate diagnostic tool for arousal measurement in depression disorder. The depression and arousal project is currently being going under some for final editions by the authors and it will be sent for publication reviews afterwards.