Long-Term Stability of EEG Spectral Asymmetry Index – Preliminary Study

The purpose of this preliminary study was to assess the long-term stability of the electroencephalography (EEG) based spectral asymmetry index (SASI) previously proposed as an objective measure for evaluation of depression. Due to high variability between individuals, a long-term study is required to examine how SASI changes over longer period of time for an individual subject. One healthy adult was surveyed over the period of 15 months. The eyes closed resting state EEG was analyzed over 15 sessions, on average once a month. The SASI was calculated from EEG power spectrum density as a relative difference in powers of higher and lower band of the EEG spectrum maximum. The long-term stability of SASI for an individual was compared to inter-individual variability of the measure within the group of healthy subjects in our previous study. The results demonstrated that the individual long-term variability of SASI is less than inter-individual variability within a group, supporting the possibility of application of SASI for evaluation of depression symptoms for an individual. In future, the investigations should be extended on larger number of subjects to study the individual properties of SASI.