Objective1.To investigate characteristics of EEG Approximate Entropy(ApEn) in healthy older volunteers under different physiological states.2. To examine differences of cognitive impairment measured by EEG ApEn between patients with Parkinson’s disease (PD) and healthy older people in order to identify the validity and sensitivity of EEG ApEn as a cognitive assessment tool for patients with PD.MethodsA cross-sectional survey was carried out among 31 patients with PD and 31 healthy older people, using the Mini-mental state examination (MMSE), the Montreal Cognitive Assessment Scale (MoCA), Eevent-related potential (ERP) ,,P300 peak latency (P3PL) and EEG ApEn. The EEG was recorded under three states : eyes closed, eyes opened, and mental arithmetic with eyes closed . The EEG ApEn was calculated and compared with different states.Results1. The EEG ApEn in eye-opened state was significantly higher that in eye-closed state among healthy older people. The EEG ApEn in mental arithmetic with eyes closed, particularly in FP1、FP2、F3、C3、P3、P4、O1、O2、T3、T5, was siginificantly higher than that in eye-closed state among healthy older people.2. Compared with healthy older people, patients with PD had significant lower scores in MMSE and MoCA and more prolonged P3PL.3. There were significant differences in EEG ApEn between healthy older people and paitents with PD in terms of FP1、FP2、F4、O2、F8、T3、T4、T5、T6 for the eye-closed state, FP1、F3、F4、C3、P3、O1、T3、T5、T6for mental arithmetic with eyes closed, and all records for the eye-opened state except C4.4. There were significant differences in the variation of EEG ApEn between healthy older people and paitents with PD in terms of F3、C3、P3、O1.5. There was a significant correlation among the scores of EEG ApEn, MMSE, MoCA and P3PL.ConclusionsEEG ApEn could be used as a tool to assess cognitive impairment in patients with PD.