Mental Health

Sleep Improves Memory in People with Parkinson's Disease

By Staff Reporter | Update Date: Aug 21, 2012 04:55 PM EDT

New research have shown that sleep improves memory in people with Parkinson's disease.

Researchers found that 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.

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.

People with Parkinson's disease often suffer from tremors and slow movements, and interference of the memory, including working memory.

The results were published in the journal Brain.

Researchers examined 54 study participants who had Parkinson's disease, and 10 who had dementia with Lewy bodies. Lewy bodies is 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.

The participants took a test and had to repeat a list of numbers forward and backward. The test was conducted in an escalating fashion: the list grows incrementally until someone makes a mistake. Participants took the test eight times during a 48-hour period, four during the first day and four during the second. In between, they slept.

Participants with Parkinson's who were taking dopamine-enhancing medications saw their performance on the test jump up between the fourth and fifth test. 

On average, they could remember one more number backwards. The ability to repeat numbers backward improved, even though the ability to repeat numbers forward did not.

Repeating numbers in the original order is a test of short-term memory, while repeating the numbers in reverse order is a test of working memory.

Patients needed to be taking dopamine-enhancing medications to see the most performance benefit from sleep. Patients not taking dopamine medications, even though they had generally had Parkinson's for less time, did not experience as much of a performance benefit. This may reflect a role for dopamine, an important neurotransmitter, in memory.

Researchers plan to conduct an expanded study of sleep and working memory, in healthy elderly people as well as patients with neurodegenerative diseases because many elderly people go through a decline in how much slow wave sleep they experience and this may be a significant contributor to working memory difficulties.

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.

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