Vagal involvement in sinus arrhythmia attenuation under mental load.

Experimental data document the slight increase of heart rate found during mildly stressing mental load as not being sufficient to explain concomitant sinus arrhythmia attenuation by pure sympathetic reaction. A general outlook on autonomic regulation and more specific direct and indirect arguments show heart rate response to mental load as underlain by a higher level balance of sympathetic and vagal drives. Their competition results mostly in slight increase yet sometimes in preservation or decrease of mean HR, while the consistency of sinus arrhythmia attenuation remains to reflect vagal increase specifically connected to cortex activation.