Prefrontal activation predicts response latency and is shaped by age and lifestyle

Neurological and neuropsychiatric conditions affect 43% of the global population, many shaped by modifiable lifestyle exposures, yet their relationship to cortical haemodynamics is poorly characterised. The dorsolateral prefrontal cortex (dlPFC) is a particularly tractable target: it underpins executive function, is disrupted across neuropsychiatric and age-related conditions, and lies on the cortical surface, within reach of scalable optical neuroimaging. We present LUCID, a longitudinal study of 98 healthy adults combining consumer wearable sleep and physical activity metrics with task-evoked dlPFC haemodynamics, measured by time-domain functional near-infrared spectroscopy (TD-fNIRS). Log-transformed peak dlPFC activation was negatively associated with response latency during the Switching Stroop task in both hemispheres (r = -0.32 to -0.38), with stronger associations for the maximum response gradient (r = -0.46 to -0.48), such that greater haemodynamic responses accompanied faster responses. Peak activation showed moderate test-retest reliability (intraclass correlation coefficient, ICC = 0.57-0.69), with between-person variance exceeding within-person fluctuation. Activation was lower in older age groups and higher in females across both tasks. In a subset of 36 participants with complete wearable data, exploratory models combining demographic, lifestyle and scan-quality features predicted bilateral activation under participant-grouped cross-validation (R-squared = 0.29-0.37), more consistently than task performance, with sex, recent change in REM sleep and age among the strongest participant-level contributors. Together, these findings identify task-evoked dlPFC haemodynamics as a repeatable, behaviourally relevant candidate functional marker, with potential for longitudinal investigation of lifestyle-associated variation in brain function.