Activity-Based Prospective Memory and Motor Sleep Inertia in Insomnia

The aim of this study is to shed light on activity-based prospective memory upon the awakening and its association with motor sleep inertia in different phenotypes of insomnia disorder.

To this end, 67 patients with insomnia and 51 healthy controls took part in the study. After enrollment, previously proposed actigraphic quantitative criteria were adopted, and the following phenotypes of insomnia disorder were observed in the patient sample: sleep onset (n = 12), maintenance (n = 19), mixed (n = 17), and negative misperception (n = 19). Each participant had used the Micro Motionlogger Watch (Ambulatory Monitoring, Inc., Ardsley, NY, USA) actigraph for one week. Actigraphic recording allowed for a description of both the activity-based prospective memory performance upon the awakening-by computing the time interval between sleep end and the time participants actually remembered to push the event-marker button of the actigraph-and the motor sleep inertia, i.e., the mean motor activity, minute-by-minute, in the first 60 min after sleep end in the morning.

Compared to healthy controls, a longer time interval was observed between sleep end and activity-based prospective memory performance in patients with mixed and maintenance insomnia. Moreover, a significant association was highlighted between motor sleep inertia and the activity-based prospective memory performance: higher levels of motor activity in those who remembered to perform the memory task early after sleep end, that spread over a longer time interval in maintenance and mixed insomnia.

Overall, the present results seem to highlight a more marked cognitive inertia in patients with mixed and maintenance insomnia as well as a significant association between motor and cognitive inertia that spreads over a different time interval according to the phenotype of insomnia.