Objectively measured cognitive function in insomnia patients with and without comorbid depression treated with...

Insomnia and depression are common, comorbid conditions with cognitive consequences. Cognitive behavioral therapy for insomnia (CBT-I) improves subjective cognition, but effects on objective performance are unclear. This study aims to examine cognitive differences in insomnia with and without comorbid depression, and changes in cognition following CBT-I.

This study examined cognitive outcomes in 170 (124 for longitudinal analyses) participants from two randomized clinical trials of internet-delivered 9 or 12 weeks CBT-I for patients with insomnia (n = 78) or comorbid insomnia and depression (n = 92). Cognitive performance was assessed pre- and post-treatment using selected computerized cognitive tests from the CANTAB battery. Linear regression and mixed-effects models were used for evaluation.

Following CBT-I, improvements were statistically significant on seven out of 17 outcomes across patients with and without comorbid depression: the Rapid Visual Processing task (correct hits, p < .001, misses, p < .001, latency, p = .040), Stockings of Cambridge (problems solved on first choice, p = .042), and Affective Go/No gGo (commissions, p = .005; omissions, p = .022; affective bias, p = .020). Comorbid depression was not statistically significantly associated with cognitive performance on most tasks. However, on the Spatial Span task, comorbid depression was associated with lower span length (p = .038), fewer attempts (p = .021), and longer latency (p = .030), suggesting impaired spatial working memory in depressed individuals. No statistically significant associations were found between changes in insomnia or depression severity and changes in cognitive performance after treatment.

Differences in cognitive performance between patients with insomnia and patients with both insomnia and depression seem very small. CBT-I may be associated with improvements in objective cognitive performance across some domains, including attention, working memory, executive function, and emotional processing. Future research should employ better control for e.g. practice effects, and explore any long-term cognitive effects of CBT-I.

The present study reports follow-up analyses based on data from two previously conducted and preregistered clinical trials (ClinicalTrials.gov Identifier: NCT01663844, study registry date 2012-08-03). The current analyses explore additional outcomes not included in the primary endpoints.