Detecting emotion in individuals with disorders of consciousness: a pilot study of heart rate deceleration on affective auditory stimuli
Hugo Ardaillon1, Anne Dubois2, Kate-Mary Ndocko3
1Department of Neuro-Rehabilitation, Hospices Civils de Lyon, Université Claude Bernard Lyon 1, Lyon, France; Université Claude Bernard Lyon 1, Université de Lyon, 43 boulevard du 11 Novembre, 191869622 Villeurbanne cedex, France; Centre de recherche en neuroscience de Lyon (CRNL), équipe TRAJECTOIRES, Inserm U1028, France.
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.
