Human vagal heart rate responses in warned reaction time tasks: a cross-validation with simulated vagus-sino-atrial...

This study examines the hypothesis that human heart rate responses in reaction time (RT) tasks are mediated by changes in vagal nerve activity. Experimental results were compared to simulated heart rate (HR) responses. An animal model of vagus-cardiac sino-atrial node interactions reconstructed the cardiac beats. Hypothetical human, vagal excitation patterns were presented to the model. Simulated and human phase-dependent cardiac responses were highly similar. Three human heart rate responses were examined: anticipatory HR deceleration, stimulus evoked HR deceleration, and response related HR acceleration. Fast motor responses were associated with fast vagal withdrawal. Inhibition of a motor response was associated with delayed onset of vagal withdrawal. However, the nature of the motor conditions did not affect the slope of vagal withdrawal. Preceding stimulus-related vagal excitation may be partly masked in the HR response, when a fast motor response and early vagal withdrawal follow. In RT tasks, a timekeeping response to the repeatedly presented and temporally regular RT signals is assumed which is under functional control of higher brain centers. Anticipatory vagal excitation that starts some time before the RT signal and continues till the RT signal, may be related to this timekeeping response.