Researchers found people with Parkinson's disease performed markedly better on a test of working memory after a night's sleep, and sleep disorders can interfere with that benefit.
While the classic symptoms of Parkinson's disease include tremors and slow movements, Parkinson's can also affect someone's memory, including "working memory."
Working memory is defined as the ability to temporarily store and manipulate information, rather than simply repeat it. The use of working memory is important in planning, problem solving and independent living.
The findings underline the importance of addressing sleep disorders in the care of patients with Parkinson's, and indicate that working memory capacity in patients with Parkinson's potentially can be improved with training.
"It was known already that sleep is beneficial for memory, but here, we've been able to analyse what aspects of sleep are required for the improvements in working memory performance," said postdoctoral fellow Michael Scullin, who is the first author of the paper.
The performance boost from sleep was linked with the amount of slow wave sleep, or the deepest stage of sleep. Several research groups have reported that slow wave sleep is important for synaptic plasticity, the ability of brain cells to reorganize and make new connections.
Sleep apnea, the disruption of sleep caused by obstruction of the airway, interfered with sleep's effects on memory. Study participants who showed signs of sleep apnea, if it was severe enough to lower their blood oxygen levels for more than five minutes, did not see a working memory test boost.
54 study participants had Parkinson's disease, and 10 had dementia with Lewy bodies: a more advanced condition, where patients may have hallucinations or fluctuating cognition as well as motor symptoms. Those who had dementia with Lewy bodies saw no working memory boost from the night's rest.
As expected, their baseline level of performance was lower than the Parkinson's group.
Participants with Parkinson's who were taking dopamine-enhancing medications saw their performance on the digit span test jump up between the fourth and fifth test.
The results were published this week in the journal Brain.
