Quantifying objective sleep measures and their associations with memory in older adults with depression

Abstract

Disturbed sleep is a key symptom of depression in older adults and is a risk factor for the recurrence of depressive episodes and neurodegeneration. In older adults with depression, the nature of the objective sleep alterations and the links with memory are not well characterised. Further, biases in emotional memory are believed to contribute to the worsening of depressive symptoms. The thesis aimed to characterise objectively measured abnormalities in sleep macro- and micro-architecture observed in older adults with depression and to explore the relationships between sleep, emotional and episodic memory, and brain integrity.

Using systematic methods, we showed that compared to controls, older adults with depression also had poor sleep continuity (greater stage 1 and less stage 2 sleep) and shorter REM onset latency.

In older adults with and without depression, the associations between sleep and episodic memory, and measures of brain integrity (MRI) were explored. In those with depression, less time spent in slow-wave sleep (SWS) was associated with poorer memory.

Associations between arousal during sleep, measured using high-density EEG, and overnight emotional memory was measured in older adults with and without depression. The depression group demonstrated specific overnight perception changes in response to negative information relative controls. The study found a global loss of EEG delta power during (non-REM) NREM sleep in the depression group. No relationships between EEG outcomes and emotional memory were found.

Older people with depression have objective EEG changes which are above and beyond the changes seen in healthy older people. The global deficits in delta power suggests that the sleep homeostatic process may be disrupted in older adults with depression. While the link between SWS and memory in older adults with depression was emphasised. This work underscores the potentially utility of interventions targeted at enhancing SWS.