Restorative sleep is vital for optimal physical, mental and emotional health. Sleep disorders are one of the most disabling non-motor symptoms of Parkinson’s disease (PD), affecting more than 75 percent of people with PD.
A recently published study in the Journal of Parkinson’s disease, “Slow Wave Sleep and EEG Delta Spectral Power are Associated with Cognitive Function in Parkinson's Disease” (Wood et al., 2021), investigated the relationship between sleep and cognition.
There are four stages of sleep: one for rapid eye movement (REM) and three others for non-REM (NREM) sleep. Stage three, or slow wave sleep (SWS), is one of the three non-REM sleep stages, and is considered to be the deepest and the most restorative of the four stages of sleep. During SWS, the brain produces slow, deep waves, called delta waves, and can be measured using an electroencephalogram (EEG) in a medical office during a sleep study.
Cognitive issues affect about 30% of all people with PD. These symptoms can negatively impact everything from thinking and memory to problem-solving. People with PD may experience:
- Mild cognitive impairment: feelings of distraction or disorganization, along with finding it difficult to plan and accomplish tasks.
- Significant cognitive impairment: inability to perform common tasks such as making coffee, comprehending complex sentences and problems telling apart non-familiar faces. Often associated with caregiver distress, worse day-to-day function, diminished quality of life, poorer treatment outcomes, greater medical costs and increased mortality.
In this observational study, 32 people with PD were enrolled; 16 had high levels of deep sleep (more than 15.8% in SWS) and 16 had low levels (less than 15.8% in SWS). There were no significant differences between the groups in terms of age, disease duration, stage or medications taken known to affect sleep — although more women had high levels of deep sleep than men. All were evaluated with polysomnography (a type of sleep study that monitors sleep stages and cycles to identify if or when sleep patterns are disrupted). Sleep was measured in all participants with an actigraph (a wearable wristwatch-like device that records total sleep time, how long it takes to fully fall asleep, wakefulness after sleep onset, nocturnal awakening and quality of sleep).
To obtain a Composite Cognitive Score (CCS) — the measurement used in this study — the researchers analyzed a wide variety of neurocognitive tests, such as Attention/Working Memory Domain (letter-number sequencing), Hopkins Verbal Learning Test (total immediate recall and delayed recall), Spatial Recall Test (immediate and delayed), Processing Speed and Language. Additional tests were also used to measure estimated intellectual function and overall cognitive function.
Participants with high amounts of slow wave sleep performed better in the following areas:
- Global cognition: the main measurement of overall cognitive function
- Executive function: brain functions that include attention or concentration, needed to multitask and solve problems
- Language: analyzes cognition decline through a neuropsychological test that asks participants to name as many similar items (such as animals) as possible in a minute
- Processing speed: helps show how the brain processes information. Participants are asked to name a color that is written using a different color
What do these results mean?
Sleep dysfunction is common in people with PD. While it is well-known that poor sleep worsens motor symptoms, this study demonstrates a significant relationship between slow wave sleep (SWS) and cognitive function: Those with higher SWS had better cognition than those with lower SWS. These findings have far-reaching quality-of-life implications.
As suggested by the study authors: the percentage of SWS is potentially a modifiable protective factor. For example, there are prescription medications (such as sodium oxybate) that increase SWS in Parkinson’s, as well as non-pharmacologic interventions, such as exercise, which have been shown to increase SWS in both non-PD populations. Thus, it is imperative that sleep quality issues in the PD population garner more attention, including, but not limited to, a more robust exploration of possible interventions, and an improvement in disseminating currently known sleep improvement information.
The Parkinson’s Foundation believes in empowering the Parkinson’s community through education. Learn more about sleep by visiting the Parkinson’s Foundation resources below, or by calling our free Helpline at 1-800-4PD-INFO (473-4636) for answers to all your Parkinson’s questions.