Exercise-Induced Fatigue and Caffeine Supplementation Affect Psychomotor Performance but Not Covert Visuo-Spatial Attention

Fatigue resulting from strenuous exercise can impair cognition and oculomotor control. These impairments can be prevented by administering psychostimulants such as caffeine. This study used two experiments to explore the influence of caffeine administered at rest and during fatiguing physical exercise on spatial attention—a cognitive function that is crucial for task-based visually guided behavior. In independent placebo-controlled studies, cohorts of 12 healthy participants consumed caffeine and rested or completed 180 min of stationary cycling. Covert attentional orienting was measured in both experiments using a spatial cueing paradigm. We observed no alterations in attentional facilitation toward spatial cues suggesting that covert attentional orienting is not influenced by exercise fatigue or caffeine supplementation. Response times were increased (impaired) after exercise and this deterioration was prevented by caffeine supplementation. In the resting experiment, response times across all conditions and cues were decreased (improved) with caffeine. Covert spatial attention was not influenced by caffeine. Together, the results of these experiments suggest that covert attentional orienting is robust to the effects of fatiguing exercise and not influenced by caffeine. However, exercise fatigue impairs response times, which can be prevented by caffeine, suggesting that pre-motor planning and execution of the motor responses required for performance of the cueing task are sensitive to central nervous system fatigue. Caffeine improves response time in both fatigued and fresh conditions, most likely through action on networks controlling motor function.剧烈运动引发的疲劳可损害认知功能与动眼控制（oculomotor control）能力，此类功能损伤可通过摄入咖啡因等精神兴奋剂（psychostimulants）进行预防。本研究通过两项实验，探究了静息状态下与疲劳性运动过程中摄入咖啡因，对空间注意（spatial attention）——这一对基于任务的视觉引导行为至关重要的认知功能——的影响。在两项独立的安慰剂对照（placebo-controlled）研究中，每组各纳入12名健康受试者，受试者分别摄入咖啡因后，或保持静息，或完成180分钟的固定式骑行运动。两项实验均采用空间线索范式（spatial cueing paradigm），对内隐注意定向（covert attentional orienting）进行量化评估。研究未观察到空间线索相关的注意易化（attentional facilitation）出现显著变化，这表明内隐注意定向不受运动疲劳或咖啡因补充的影响。运动后受试者的反应时（response times）显著延长（功能受损），而咖啡因补充可阻止这一性能恶化。在静息实验中，所有实验条件与线索下的反应时均因咖啡因摄入而缩短（性能提升）。咖啡因并未对内隐空间注意产生影响。综合两项实验结果可知，内隐注意定向对疲劳性运动的影响具有耐受性，且不受咖啡因的干预。然而，运动疲劳会损害反应时，而咖啡因可预防此类损伤，这表明完成线索任务所需的运动前规划（pre-motor planning）与运动反应执行过程，对中枢神经系统（central nervous system）疲劳较为敏感。咖啡因可在疲劳与非疲劳两种状态下缩短反应时，其作用机制大概率是通过调控控制运动功能的神经网络实现。