Australian researchers found that patients suffering from sleep apnea find it hard to recall specific details of memories taken from their own experiences. Furthermore, the inability to remember important parts of their lives could cause them to develop depression.
Obstructive sleep apnea is a sleeping disorder wherein the person experiences difficulties breathing during sleep. Around 936 million people around the world suffer from this severe disorder.
Patients with obstructive sleep apnea experience problems with their memory. They also appear to be much more vulnerable to depression. However, earlier studies did not uncover much information on the connection between sleep apnea and the other two issues.
In the new study, researchers from RMIT University looked at the effects of sleep apnea on autobiographical memory. Lead researcher Dr. Melinda Jackson explained that she drew from the identified connections between depression and memory. She and her team discovered that patients who did not undergo treatment for their sleep apnea experienced issues remembering particular details from their lives.
“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,” Jackson stated. “Our study suggests sleep apnea 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.”
Examining the link between sleep apnea, autobiographical memory, and depression
Obstructive sleep apnea is growing more common in Australia and other parts of the world. It appears in 30 percent of older adults. In Australia, it affects one out of every four men above the age of 30. It is also considered an essential factor in the risk of depression.
Jackson wanted to identify the neurobiological connection between sleep apnea and depression. She believed the information will help researchers do something for millions of people who suffer mental problems due to sleeping disorders.
The cohort of her team’s experiment consisted of adult participants with untreated obstructive sleep apnea and healthy counterparts who served as the control group. These volunteers went through memory tests, where they tried to remember various types of autobiographical memories about their childhood, early adulthood, and recent experiences.
Furthermore, the study also investigated the recall of semantic and episodic memories. Semantic memory covered facts and ideas from the history of a person – for example, the names of people met during high school. Episodic memory, on the other hand, dealt with episodes or events.
Sleep apnea affects semantic memory, which increases the risk of depression
The RMIT researchers discovered that patients with obstructive sleep apnea showed much more generalized memories. Slightly more than half of them suffered from this issue.
Furthermore, patients maintained their episodic memory, but experienced problems with their semantic memory. It appeared to stem from disrupted sleeping patterns – other studies indicated that sleep plays an integral part in storing semantic autobiographical memory.
Also, the older the participant, the larger the number of very general autobiographical memories. This finding applied to both sleep apnea patients and healthy people alike.
Finally, poor semantic memory appeared to lead to higher chances of depression. Jackson stressed the need to further understand the role of untreated sleep apnea on how the brain processes memories.
“Brain scans of people with sleep apnea 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 apnea?”