Symptoms of stress and depression as correlates of sleep in primary insomnia

Previous studies have not evaluated the clinical correlates of the electroencephalographic spectral profile in patients with insomnia. In the preliminary study described here, we evaluated the extent to which symptoms of stress and depression are associated with subjective sleep complaints and quantitative measures of sleep in individuals with chronic insomnia.

Subjects were 14 healthy adults who met criteria for primary insomnia as specified in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders. Measures of stress, depression, and subjective sleep quality were collected before subjects participated in a two-night laboratory sleep series. We hypothesized that elevated symptoms of stress and depression would be associated with subjective sleep complaints and electroencephalographic evidence of hyperarousal during sleep. Hyperarousal during sleep was defined as decreases in delta power and elevations in alpha and beta power throughout non-rapid eye movement sleep, and symptoms of stress were defined as the tendency to experience stress-related intrusive thoughts and the interaction between intrusion tendency and the number of recent stressful events (subjective stress burden).

A stronger tendency to experience stress-related intrusive thoughts was associated with greater sleep complaints and a trend toward higher beta power, whereas increases in subjective stress burden were associated with decreases in delta power. In addition, elevations in subclinical symptoms of depression were associated with greater sleep complaints and elevations in alpha power.

Observed relationships among symptoms of stress, depression, subjective sleep complaints, and electroencephalographic power may be relevant to the discrepancy between subjective and objective measures of sleep in patients with insomnia and may be more broadly applicable to sleep complaints in association with stressful life events and major depression.