The age-related susceptibility to postoperative delirium quantified by bispectral electroencephalography correlates with postoperative delirium-like behavior in mice

Postoperative delirium (POD) is a severe neuropsychiatric state characterized by acute fluctuating various mental symptoms. Despite its prevalence, the underlying mechanisms of POD remain largely unknown, and effective biomarkers for its detection are lacking. We have successfully developed a novel delirium detection method, the bispectral electroencephalography (BSEEG) method, which has shown excellent performance in delirium detection and outcome prediction. From there, like the clinical situation, we hypothesize that BSEEG scores can serve as indicators of POD-like states in mice. This study investigated the correlation between POD-like behavior and BSEEG score in a mouse model following EEG head-mount implantation surgery.

First, 2-3- and 22-23-month-old male C57BL/6J mice underwent EEG head-mount implantation surgery, followed by EEG monitoring and a battery of behavioral tests, including the buried food test, the open field test, and the Y-maze, to assess POD-like behavior. We measured BSEEG scores and analyzed the correlation between these scores and the behavior measurements.

The results showed BSEEG scores correlated with attention deficit and decreases in locomotor activity in young mice, whilst BSEEG scores only correlated with a decrease in locomotor activity in aged mice. Notably, composite Z scores representing delirium severity also showed a correlation with BSEEG scores in young mice.

Our findings indicate that the BSEEG method can be an indicator of POD-like states consistent with those measured by behavior tests. This study provides a novel preclinical framework for understanding the pathophysiology of POD and underscores the potential of BSEEG as a valuable tool for delirium detection and severity assessment.