The impact of insomnia on prefrontal activation during a verbal fluency task in patients with major depressive disorder: A preliminary fNIRS study

Background: Insomnia often co-occurs with major depressive disorder (MDD) and significantly affects patient recovery and prognosis. However, how insomnia affects prefrontal cortex activation in MDD patients and its association with both subjective and objective sleep quality remains unclear. This study combined functional near-infrared spectroscopy (fNIRS) with polysomnography (PSG) to investigate differences in prefrontal activation during a verbal fluency task (VFT) in patients with MDD, with and without insomnia. Methods: Seventy-eight patients with MDD and 42 healthy controls underwent polysomnography and sleep and mood assessments including the Pittsburgh Sleep Quality Index (PSQI) and Self-Rating Depression Scale (SDS). Prefrontal activation was measured using fNIRS during the VFT. Results: Patients with MDD and insomnia had higher PSQI scores than patients with MDD without insomnia. fNIRS revealed increased left prefrontal cortex activation in these patients, which was negatively correlated with the total sleep time and sleep efficiency and positively correlated with the PSQI score. Conclusion: This study combined fNIRS and PSG to demonstrate that MDD patients with insomnia showed increased levels of prefrontal cortex activation, associated with both subjective and objective sleep quality.