Enhancement of prefrontal functional connectivity under the influence of concurrent physical load during mental tasks

Cheng, Shan; Cong, Lin; Hui, Duoduo; Teng, Chaolin; Li, Wenbin; Ma, Jin · 2024 · Crossref

DOI: 10.3389/fnhum.2024.1500470

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Summary

This study investigates how concurrent physical load (PL) influences prefrontal cortex (PFC) functional connectivity (FC) during cognitive tasks, addressing a gap in understanding how non-cognitive factors affect mental workload (MWL) assessment. While functional near-infrared spectroscopy (fNIRS) is widely used to evaluate MWL, its sensitivity to simultaneous physical exertion remains unclear. The authors aimed to determine if physical activity alters hemodynamic features and FC in the PFC, which is critical for real-time MWL monitoring in complex operational environments like aviation or driving. The researchers recruited 33 healthy male subjects who performed n-back working memory tasks at three difficulty levels (1-back, 2-back, 3-back) to induce varying cognitive loads. Concurrently, subjects performed isotonic contraction exercises with their left upper limb at three physical load levels: none (0 kg), medium (3 kg), and high (5 kg). fNIRS signals were recorded from eight channels covering the bilateral dorsolateral PFC, ventrolateral PFC, and orbital frontal cortex. FC was quantified using Pearson’s correlation coefficient (CORR), coherence value (COH), and phase-locking value (PLV). Subjective workload was assessed via the NASA-TLX scale, and task performance was measured by reaction times and accuracy rates. Results indicated that concurrent physical activity significantly increased subjective NASA-TLX scores and decreased task performance compared to cognitive tasks alone. Crucially, cognitive and physical loads exhibited significant interaction effects on CORR, COH, and PLV metrics, although their main effects were not significant. Specifically, FC between the right dorsolateral PFC and the bilateral orbital frontal cortex was significantly enhanced under combined high physical and high cognitive loads. For instance, CORR values for specific channel pairs increased significantly under high physical load during 2-back and 3-back tasks compared to no physical load. These findings demonstrate that physical exertion modulates PFC connectivity patterns during cognitive processing. The study concludes that physical factors measurably impact operators’ mental load as reflected in prefrontal functional connectivity. This suggests that MWL assessment models must account for concurrent physical demands to avoid misinterpretation of neural signals. The results provide a reference for developing more accurate, real-time MWL monitoring systems using fNIRS in naturalistic, multi-demand environments where cognitive and physical loads co-occur.

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• neuro workload indices
• workload measurement

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• Empirical Findings: physiological data