Many studies show that sleep apnea is linked with cognitive decline in late life, but this relationship remains complicated. What’s more, certain domains of cognition remain intact even in those with severe untreated sleep apnea. It is therefore important to investigate different cognitive domains to determine whether they are affected by apnea in older adults. Implicit memory (memory for things that we don’t realize we’re memorizing, like when we learn how to ride a bike) can be tested with a motor sequencing task. This task, which involves tapping fingers in response to a prompted sequence on a computer screen, forms a memory of the sequence without explicit recognition of the sequence. In other words, you learn the sequence without even realizing that there is a sequence. This type of memory has not been investigated with regard to sleep apnea.
In a recent study, 44 subjects were obtained from a sleep clinic, and these subjects had already undergone an overnight sleep study to assess the presence and severity of sleep apnea. Age was used in analysis to assess whether older subjects with sleep apnea were affected more or less than young subjects with sleep apnea. All subjects performed the motor sequencing task before bed and were then re-tested after waking. Importantly, all sleep apnea subjects had a night without treatment during this study, meaning their sleep was “natural” (i.e., full of apneas). Performance on the motor sequencing task was compared between young, old, apnea, and non-apnea groups.
Results showed that the subjects with sleep apnea improved much less on the task following a night of sleep when compared to the group without sleep apnea. Interestingly, in the sleep apnea group, there was a link between age and improvement. In other words, the older subjects with sleep apnea did worse than the younger subjects with sleep apnea.
This study had results that indicated learning impairment on an implicit memory task in those with sleep apnea. What’s more, those with sleep apnea who were of advanced age had even worse overnight improvement than the others. This is very unfortunate, given that sleep apnea increases with age even in those who are not overweight. Older individuals with any suspicion of sleep apnea should therefore be tested and immediately treated for the sake of their memory and their general well-being!
Source: Djonlagic, I., Guo, M., Matteis, P., Carusona, A., Stickgold, R., & Malhotra, A. (2014). Untreated Sleep-Disordered Breathing: Links to Aging-Related Decline in Sleep-Dependent Memory Consolidation. PloS one, 9(1), e85918.