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, wearable-grade optical neuroimaging. We present LUCID, a longitudinal study of 92 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 reaction time (RT) across the 2N-Back and Stroop tasks and both hemispheres (r = -0.37 to -0.53), greater activation accompanying faster responses, consistent with a capacity/recruitment account. Activation showed moderate test-retest reliability (intraclass correlation coefficient, ICC = 0.56-0.71), with between-person variance exceeding within-person fluctuation, indicating stable individual differences. Demographic and lifestyle features incrementally predicted activation, with age the strongest predictor and modest contributions from sleep and physical activity. These findings establish TD-fNIRS dlPFC activation as a longitudinally stable, behaviourally relevant functional neural marker for scalable tracking of modifiable risk.