Prefrontal oxygenation during verbal fluency in severe obesity

Obesity is a highly prevalent chronic disease with major medical, psychosocial, and economic consequences worldwide. Beyond its association with metabolic and cardiovascular comorbidities, obesity is increasingly linked to impairments in executive functioning and alterations in prefrontal control networks. Neuropsychological and neuroimaging studies consistently indicate deficits in inhibition, cognitive flexibility, and executive control in overweight and obese individuals, accompanied by context-dependent changes in prefrontal activation under cognitive load. These findings underscore the relevance of investigating task-related prefrontal functioning in obesity using established executive paradigms. In this study, 40 healthy normal-weight controls (HC) and 43 patients with severe obesity (OB) were included, and task-related prefrontal activation was assessed with functional near-infrared spectroscopy (fNIRS) during performance of the verbal fluency task (VFT). On the behavioral level, patients with severe obesity showed reduced performance in the Stroop task assessing interference control and lower phonemic (letter) verbal fluency, with only a non-significant trend toward lower semantic (category) fluency during the VFT. On the neural level, these behavioral deficits were accompanied by reduced activation in prefrontal and frontotemporal regions, with attenuated left-lateralized oxygenation responses observed in patients across VFT conditions, and a reduced frontotemporal response most evident in the letter condition. Overall, the results highlight a close link between executive dysfunction and altered prefrontal activation patterns in severe obesity under cognitively demanding conditions.