Cognitive processing effects on auditory event-related potentials and the evoked cardiac response

The phasic evoked cardiac response (ECR) produced by innocuous stimuli requiring cognitive processing may be described as the sum of two independent response components. An initial heart rate (HR) deceleration (ECR1), and a slightly later HR acceleration (ECR2), have been hypothesised to reflect stimulus registration and cognitive processing load, respectively. This study investigated the effects of processing load in the ECR and the event-related potential, in an attempt to find similarities between measures found important in the autonomic orienting reflex context and ERP literature. We examined the effects of cognitive load within-subjects, using a long inter-stimulus interval (ISI) ANS-style paradigm. Subjects (N = 40) were presented with 30–35 80 dB, 1000 Hz tones with a variable long ISI (7–9 s), and required to silently count, or allowed to ignore, the tone in two counterbalanced stimulus blocks. The ECR showed a significant effect of counting, allowing separation of the two ECR components by subtracting the NoCount from the Count condition. The auditory ERP showed the expected obligatory processing effects in the N1, and substantial effects of cognitive load in the late positive complex (LPC). These data offer support for ANS–CNS connections worth pursuing further in future work.