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People with sleep apnoea struggle to remember their memories, potentially making them vulnerable to depression, new research has shown.

Obstructive sleep apnoea is estimated to affect more than 936 million people worldwide.

People with OSA are known to suffer memory problems and also have higher rates of depression but it is not well understood how these issues are connected with the development of the disease.

The new study led by RMIT University in Victoria examined how the condition affected autobiographical memory and found people with untreated OSA had problems recalling specific details about their lives.

Lead investigator Dr Melinda Jackson said the research built on the known links between depression and memory.

“We know that overly general autobiographical memories, where people don’t remember many specific details of life events, are associated with the development of persistent depression,” Dr Jackson said.

“Our study suggests sleep apnoea may impair the brain’s capacity to either encode or consolidate certain types of life memories, which makes it hard for people to recall details from the past.

“OSA is increasingly common, affecting up to 30% of elderly people and around one in four Australian men aged over 30.

“Sleep apnoea is also a significant risk factor for depression so if we can better understand the neurobiological mechanisms at work, we can have a chance to improve the mental health of millions of people.”

The study also looked at recall of semantic memory such as facts and concepts from your personal history and names of your school teachers. The research also reviewed episodic memory including events or episodes, such as first day of high school.

While people with OSA struggled with semantic memory, their episodic memory was preserved. This is likely related to their fragmented sleeping patterns, as research has shown that good sleep is essential for the consolidation of semantic autobiographical memory.

Across both groups, being older was associated with having a higher number of over general autobiographical memories while higher depression was linked to having worse semantic memory.

Dr Jackson, said the results showed the need for further studies to better understand the role of untreated OSA on memory processing.

“Brain scans of people with sleep apnoea show they have a significant loss of grey matter from regions that overlap with the autobiographic memory network,” she said.

“We need to look at whether there’s a shared neurobiological mechanism at work – that is, does the dysfunction of that network lead to both depression and memory problems in people with sleep apnoea?”

Dr Jackson said the use of CPAP machines to treat OSA had been shown to improve some of the cognitive impairments related to the condition.

“An important next step will be to determine whether successful treatment of sleep apnoea can also help counter some of these memory issues or even restore the memories that have been lost.”

The study – conducted with collaborators from the Institute for Breathing and Sleep, Florey Institute of Neuroscience and Mental Health, and University of Melbourne – was published in Journal of the International Neuropsychology Society.