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Sleep loss has detrimental effects on neurogenesis and long-term potentiation in animals; sleep loss in humans worsens neurocognitive performance and consolidation of hippocampus-dependent memories. These authors used MRIs to measure brain structure in eight patients with self-reported chronic sleep loss due to primary insomnia. As controls, eight good sleepers were carefully matched by age, gender, educational status, and body-mass index.
All participants were healthy and had no current or lifetime history of a psychiatric disorder. Patients were medication-free for at least 2 weeks before the study. Manual morphometry was used to examine MRI volumes of the dorsolateral prefrontal cortex, orbitofrontal cortex, anterior cingulate, amygdala, and hippocampus.
As expected, the patients subjectively reported greater sleep latency, less total sleep time, and worse sleep efficiency than the controls. Patients had significantly smaller hippocampal volumes bilaterally. Other regions of interest did not differ between the two groups.
Riemann D et al. Chronic insomnia and MRI-measured hippocampal volumes: A pilot study. Sleep 2007 Aug 1; 30:955.
Comment
This is a small and preliminary study, and diagnoses of primary insomnia were based on self-report, rather than on polysomnography or sleep diaries. Nonetheless, the findings are intriguing and consistent with prior findings of impaired consolidation of hippocampus-dependent memories with sleep loss. Chronic insomnia may contribute to or explain similar findings of reduced hippocampal volumes in patients with depression, post-traumatic stress disorder, and borderline personality disorder. Chronic primary insomnia may either cause altered hippocampal structure or stem from it. For clinicians, even the possibility of altered brain structure with sleep deprivation adds yet more impetus for treating insomnia aggressively.