Disrupted Practice Effects and Altered Prefrontal Activation in Mild Cognitive Impairment: An fNIRS Study Using the Stroop Task

Introduction: Executive dysfunction, particularly inhibitory control, is an early core symptom of mild cognitive impairment (MCI) and is often associated with altered prefrontal cortical activity. Repeated engagement in cognitive tasks may offer a means of assessing and potentially enhancing neural adaptability in these regions. Objective: This study examined how repeated Stroop task performance modulates executive function and prefrontal cortical activation in older adults with MCI, compared to cognitively healthy controls (HC), using functional near-infrared spectroscopy (fNIRS). Methods: A total of 37 older adults (17: MCI, 20: HC) completed three consecutive sessions of a computerized color–word Stroop task. Behavioral performance (reaction time) and hemodynamic responses (oxyhemoglobin, HbO) were recorded across predefined prefrontal regions of interest, including the ventrolateral prefrontal cortex (VLPFC), dorsolateral prefrontal cortex, orbitofrontal cortex, and frontopolar cortex. Results: The results demonstrated a significant improvement in response time and reduced HbO activation in the VLPFC across sessions in the HC group, suggesting enhanced cognitive efficiency and selective inhibition. By contrast, the MCI group demonstrated delayed and limited adaptation, with meaningful changes occurring only in the final session. Conclusion: Healthy aging is associated with rapid neurofunctional adaptation to cognitive challenges, whereas individuals with MCI exhibit impaired plasticity in executive control circuits. fNIRS sensitively detects early executive deficits, supporting its potential for early diagnosis of cognitive impairment.