Slow-wave sleep may be an important modulator of dopamine-related improvement in working memory among patients with PD.

To investigate whether sleep parameters are associated with improvement in working memory among patients with Parkinson disease (PD) or dementia with Lewy bodies (DLB), researchers conducted overnight polysomnography for 2 nights, followed by cognitive testing, in 53 patients with PD (most without dementia) and 10 patients with DLB. After each night of polysomnography, participants performed digit-span testing four times, beginning 2 hours after awakening and repeated every 2 to 3 hours. The digit-span forward task tested short-term memory, and the digit-span backward task tested working memory.

Sleep parameters did not differ among PD patients who were or were not taking dopaminergic medication and DLB patients. Based on the mean difference in digit-span scores from day 1 and day 2, the PD patients who were taking dopaminergic medications improved significantly on the digit-span backward task; the PD group not taking dopaminergic medications and the DLB patients did not show improvement. On the digit-span forward test, the PD patients did not improve significantly and the DLB patients’ scores declined significantly. In PD patients taking dopaminergic medication, improvement in digit-span backward performance correlated positively with the percentage of sleep that was slow-wave sleep and correlated negatively with duration of time with an oxygen saturation level <90%.

The authors concluded that (1) improvements in working memory based on digit-span backward performance can be seen in PD patients, particularly in those taking dopaminergic medications; (2) slow-wave sleep may be important for these improvements; and (3) nocturnal oxygen desaturation may impede these improvements.

Comment: These findings offer insight into the potential for cognitive improvement in patients with Parkinson disease, particularly those who do not have dementia and who are taking dopaminergic medications. Slow-wave sleep may be an important modulator of this improvement. Increasing slow-wave sleep may improve working memory in people with PD, although the clinical utility of using dopaminergic medications specifically to enhance cognition requires further investigation. Future research should examine the exact mechanisms by which dopamine may enhance working memory, determine whether dopaminergic medications increase slow-wave sleep, and clarify how nocturnal oxygen desaturation can impede this cognitive process.

Source: Journal Watch Neurology