The research focus of Arjen Slooter is on delirium and on neuropsychiatric outcome after anesthesia/surgery or critical illness. Using various methods and approaches (epidemiology, EEG, MRI), he has investigated all aspects of delirium, including its phenomenology and brain network characteristics, detection and monitoring, risk factors, prognosis, prevention and treatment. Research on neuropsychiatric outcomes includes ICU-related risk factor analyses on cognitive decline, mental illness and chronic pain after critical illness and treatment in the ICU.