Letter to the Editor
Prospective memory in narcolepsy type 1 patients

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Introduction

Narcolepsy type 1 (NT1) is a central disorder of hypersomnolence distinguished by excessive daytime sleepiness, onset of sleep presenting a quick appearance of rapid eye movements sleep, cataplexy and loss of hypothalamic neurons that produce hypocretin [1].

Narcolepsy patients habitually report an unsatisfactory functioning of memory [2]. Only one study explored the prospective memory (PM) performance in narcolepsy, through an interview, documenting difficulties in this specific memory domain [3]. However, the investigation of PM is extremely important because, being the ability to remember to perform an action in the future, is essential in every-day life, as for example when people are required to assume a drug at a specific time of day.

We chose to compare the PM performance of NT1 patients to that of healthy controls (HC) through actigraphy, adopting a naturalistic procedure earlier used in primary insomnia patients [4]. PM performance was defined by number of times participants correctly remembered to press the event-marker button on the top of the actigraph to signal the bedtime and get-up time.

Since NT1 patients present an impaired sleep [e.g., 5], they were expected to perform the naturalistic PM task worse than HC, mainly at the get-up time.

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Method

We analysed the actigraphic recordings of two separate databases. Actigraphic recordings of NT1 patients came from the database of Centre du Sommeil et de la Vigilance, Hôtel-Dieu de Paris (France),1 while those of HC were extracted, matching age and gender, from the database of Laboratory of Applied Chronopsychology of the University of Bologna (Italy).

Thirteen NT1 patients (mean age:

Results

Overall 699 nights were analysed, of whom 423 in NT1 patients and 276 in HC.

The ANOVA showed a significant effect of group (F1,24 = 23.52; p < .001), with NT1 patients (62.6%) performing worse than HC (89.5%). Moment of day (F1,24 = 0.09; p = .77) (bedtime = 76.4%; get-up time = 75.7%) and the interaction between factors (F1,24 = 0.01; p = .93) (Fig. 1) did not reach significance.

Discussion

The performance in naturalistic PM task was lower in NT1 patients in comparison to HC at both moments of day. Although this is the first time that naturalistic PM is assessed in NT1 patients, with the resulting lack of a shared benchmark, two possible explanations can be put forward. The first is related to the effects of a sort of chronic sleep deprivation, which would affect not only the get-up time but also the bedtime. An alternative explanation sees such impaired PM performance as not

Declaration of interest

Damien Leger reports grants from Fondations Maladies Rares, during the conduct of the study; he also reports grants from Philips (Netherlands), Vanda (USA), Sanofi, Vitalaire International, Merck, JANSSEN, RHYTHM and JAZZ, outside the submitted work. Lorenzo Tonetti, Vincenzo Natale, Caroline Gauriau, Brice Faraut and Pierre Philip declare no conflict of interest.

Acknowledgments

The original survey has been granted by the Fondation Maladies Rares, France: Somnopro Project 2017.

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