Sleep-wake changes and cognition in neurodegenerative disease.

With the increasing aging population, neurodegenerative disorders will become more common in clinical practice. These disorders involve multiple pathophysiological mechanisms that differentially affect cognition, mood, and physical functions. Possibly due to the involvement of common underlying neurobiological circuits, sleep and/or circadian (sleep-wake) changes are also common in this disease group. Of significance, sleep-wake changes are often a prodromal feature and are predictive of cognitive decline, psychiatric symptoms, quality of life, need for institutional care, and caregiver burden. Unfortunately, in neurodegenerative disease, few studies have included detailed polysomnography or neuropsychological assessments although some data indicate that sleep and neurocognitive features are related. Further studies are also required to address the effects of pharmacological and nonpharmacological treatments on cognitive functioning. Such research will hopefully lead to targeted early intervention approaches for cognitive decline in older people.