The study is aimed to carry out an epidemiology study investigating the prevalence of obstructive sleep apnea (OSA) and the association with cognitive impairment.

Inclusion Criteria:

• Have stability of at least 4 weeks on permitted medications (i.e. medications known not to affect sleep architecture or circadian rhythms).

Exclusion Criteria:

• Suspected dementia or a score of <24 on the mini-mental state examination
• A diagnosis of neurological disorders (e.g. Parkinson's Disease, Epilepsy, Multiple Sclerosis)
• Psychiatric disorders including current major depression; bipolar disorder; schizophrenia
• Other known clinically significant sleep disorders (e.g. narcolepsy)
• Been currently receiving CPAP or bi-level pressure for OSA

Consecutive subjects are recruited from the Brain Health Longitudinal Study which was launched in July 2019. Up to 5000 subjects aged 40-74 years without a confirmed brain disorder. Participants will be assigned to undergo a portable at-home sleep study which records the airflow, heart rate, body position and oxygen saturation.