Cardiac responses to auditory irregularities reveal hierarchical information processing during sleep

Our ability to process environmental stimuli varies during sleep. Although much research focused on neural processing, emerging evidence shows that bodily signals may play a key role in understanding the variations of high-level sensory processing. Here, we investigated the cardiac responses to the local-global paradigm, a typical oddball task probing the processing of simple (local) and complex (global) sensory irregularities across unresponsive conscious states. To do so, we analyzed electrocardiography signals in response to auditory deviants obtained during wakefulness and sleep in a total of 56 participants. Our findings revealed that cardiac activity slowed down after global deviants during Rapid-Eye Movement (REM) sleep, especially in tonic REM sleep, i.e., in absence of rapid eye movements and further uncovered that cardiac acceleration effects could also be present in non-REM sleep, restricted to light NREM sleep stage, i.e, in absence of slow-wave activity. Overall, our findings show that cardiac responses to auditory irregularities can inform the variations of hierarchical information processing across sleep states. They also highlight the embodiment of sleep functions and the value of cardiac signals to study the bodily correlates of sensory processing during sleep.