Inter-individual differences in sleep homeostasis and circadian rythmicity on cognition in older people

Who wouldn’t agree that healthy aging goes hand in hand with a preserved mind? However, “many older people experience decrements in cognitive performance, which may result from age-related sleep alterations,” says Prof. Pierre Maquet. These alterations are caused by a reduction in both drives for sleep: homeostatic and circadian. The interplay of these processes is complex and can vary between individuals. For example, the gene PER3 exists in different versions (called “alleles”) amongst the population. The longer version makes people sleepier (i.e., increases their “sleep pressure”) and reduces their cognitive performance after sleep loss. Maquet is studying how the circadian phase, homeostatic sleep pressure and their interaction influence cognitive function (i.e., mind function) in older people.
Maquet’s project involves volunteers between 55 and 75 years of age: 20 volunteers with the short PER3 allele and 20 volunteers with the long PER3 allele are participating in two separate visits. Each visit consists of two sessions of cognitive tasks under brain imaging: one before sleep time and the other after wake time. During one visit, the participants sleep at the laboratory between the two sessions, and during the other visit, the participants stay awake.
The great novelty in this project lies in the monitoring of both the circadian and the homeostatic factors. Circadian rhythms are measured through melatonin (the sleep hormone) content in samples of saliva taken each hour (except when people are sleeping). The homeostatic factor is monitored using two brain imaging techniques. One of these allows a direct probe of the local sleep pressure in the brain, which is very innovative.
Maquet’s project aims at a better understanding of the mechanisms involved in changes in sleep and cognitive function. The effect of genetics on all the factors measured could provide a major contribution in terms of the practical application of chronobiology to changes in circadian and sleep control in older individuals. The results could be directly translated into health-promoting practices to increase sleep and cognitive performance in older people.