Detecting emotion in individuals with disorders of consciousness: a pilot study of heart rate deceleration on affective auditory stimuli.

OBJECTIVE

To evaluate heart rate deceleration on affective auditory stimulations as an objective marker of purposeful affective behaviour, as used in the diagnosis of minimally conscious state (MCS) in brain-injured individuals with disorders of consciousness (DoC), awake but unable to communicate.

METHODS

We recorded the heart rate of participants (14 healthy controls and 10 brain injured individuals, conscious or with DoC) on repeated exposure to a random sequence of three emotional sounds of neutral, positive, and negative valence, in an unconditioned manner (experiment 1) or in a trace-conditioning procedure (experiment 2), with successful trace-conditioning assumed to indicate consciousness.

RESULTS

In experiment 1, heart rate deceleration after aversive acoustic stimulus was significantly higher in healthy subjects at the group level from the second to the seventh inter-beat interval, with limited sensitivity at the individual level. In experiment 2, there was no evidence of trace-conditioned learning in healthy subjects, precluding any extrapolation to brain-injured individuals.

CONCLUSIONS

Heart rate deceleration after aversive acoustic stimulus was significant in passive hearing but not in a trace-conditioning paradigm and was of limited sensitivity at the individual level.

SIGNIFICANCE: Heart rate deceleration may constitute an objective marker of purposeful affective behaviour triggered by emotional sounds. The question of whether this response is a reflex or a marker of conscious access needs further study.