Heart rate variability changes induced by auditory stimulation in persistent vegetative state

Previous studies, using neuroimaging and electrophysiology, have identified the presence of cerebral responses to auditory stimulation in clinically unresponsive persistent vegetative state (PVS) patients. In normal individuals, it has been shown that stimulation with emotional content has a strong influence on autonomic cardiovascular regulation tested by heart rate variability (HRV). In this paper, we assessed responses to auditory stimulation with emotional content in PVS and minimally conscious (MCS) cases by HRV. We found a pattern of changes induced by auditory stimulation in three of our patients (decreased heart rate, increased HRV, decrease power in the low and increased power in high frequencies) consistent with increased cardiovagal stimulation. Both time and frequency domain changes were more pronounced during affective than during non-affective auditory stimulation, suggesting that PVS patients are able to discriminate between stimuli of different content and are more reactive to emotional than non-emotional stimulation. Our results demonstrate (is a conclusion, should be in present) that auditory stimulation can induce recordable changes in HRV in some PVS cases, providing evidence that these patients retain some preserved cognitive function examined by cardiovascular correlates. The use of HRV to study residual cognitive functions could have practical implications for the management of PVS and MCS.