In a randomized controlled trial of 56 adults with insomnia disorder and 20 good sleepers, CBT for insomnia (CBTi) significantly improved self-reported cognitive functioning and sleep quality at both three months and one-year follow-up — but produced no measurable changes in working memory performance, fMRI task-based brain activity, or resting-state functional connectivity. Notably, even at baseline, people with insomnia showed no objective memory deficits or neural differences versus good sleepers, despite reporting greater cognitive impairment and rating sleep-related imagery as more emotionally negative.
This finding lands in a long-running debate: insomnia's cognitive toll may be more perceptual than neurological. The disconnect between subjective suffering and objective performance is well-documented in insomnia research — a phenomenon sometimes called paradoxical insomnia or sleep-state misperception extended to cognition. CBTi's well-established efficacy for sleep symptoms is here extended to subjective cognitive concerns, which matter enormously for quality of life. However, the absence of objective brain changes raises an important question: is CBTi correcting a real neurological deficit, or recalibrating inaccurate self-appraisal? The sample is relatively small (56 treated participants), limiting statistical power to detect subtle neuroimaging effects. This is a preprint posted on medRxiv and has not yet been peer-reviewed, so conclusions warrant caution. If confirmed, the finding suggests adults troubled by insomnia-related cognitive worries have strong evidence to seek CBTi, even if the mechanism is primarily psychological reassurance rather than neural restoration.