Lack of sleep can make anyone moody. Fatigue can create a feeling of mental sluggishness and cause people to have difficulty completing simple cognitive tasks. But do unrested people with depression have sharper declines in cognitive functioning than those without depression? That was the question that Christine Sutter of the University of Zurich in Switzerland sought to answer in a recent study. Sleep problems have been shown to contribute to many psychological and physical ailments. As people age, they tend to experience more difficulties with sleep. Likewise, cognitive functioning declines with age. Although these relationships have been studied in depth, few studies have examined how depression moderates the effect of sleep disturbance on executive functions such as memory, cognitive speed, and processing in older adults.
Sutter focused on adults over the age of 61. She enlisted 107 adults with and without depression and assessed their sleep patterns using the Pittsburgh Sleep Quality Index. The participants completed a series of tasks that gauged their executive function processing, speed, and memory recall. Sutter found that the participants with more significant depressive symptoms and sleep problems had more difficulty with the cognitive tasks than those with fewer depressive symptoms and more moderate sleep problems. Although many executive function domains were impacted by depression and sleep disturbances, memory recall pertaining to specific episodes was not. This suggests that sleep deprivation weakens higher-order executive functions, especially in people who have depression.
Sleep problems can cause problems with mood regulation. Therefore, the depressive symptoms in this sample of participants could be exacerbated by lack of sleep. Future work should examine the nuances of the sleep/mood relationship more closely. Additionally, even though psychological medicine was accounted for in this study, other medications that could influence the outcome were not. This is yet another area that must be fully explored to better understand the association between sleep disturbances, mood, and cognitive performance. Sutter notes that overall, the findings of this study demonstrate a clear link between sleep impairment and executive processing in older individuals. “However, it also seems important to consider low levels of depressive symptomatology together with sleep quality, as they appear to be interrelated,” she said.
Sutter, C., Zöllig, J., Allemand, M., Martin, M. (2012). Sleep quality and cognitive function in healthy old age: The moderating role of subclinical depression. Neuropsychology. Advance online publication. doi: 10.1037/a0030033
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