Behavioural Improvement in Minimally Conscious State After Caloric Vestibular Stimulation: Evidence from two single case studies.

Objective: To investigate whether caloric vestibular stimulation, a non-invasive form of neuro-modulation, alters level of awareness in people residing in minimally conscious state.

Design: Single-case (n=2), prospective, controlled (ABAB) efficacy study.

Setting: Tertiary, neuro-rehabilitation in-patient ward within a university hospital

Participants: Two individuals in minimally conscious state

Intervention: Left ear caloric vestibular stimulation was performed in two four/five-week blocks interleaved with two four/five-week blocks of sham stimulation. Session duration and frequency gradually increased within each block from once per day for 10 minutes (week 1) to once per day for 20 minutes (week 2) to 20 minutes twice per day in the remaining weeks.

Measures: Wessex Head Injury Matrix, JFK Coma Recovery Scale – Revised.

Results: Both participants’ Wessex Head Injury Matrix scores indicated a transition from involuntary (i.e. mechanical vocalization) to voluntary (i.e. gesture making, selective responses to family members) behaviour that was time-locked to the onset of active stimulation. In one participant, this improvement persisted for at least 4 weeks after active stimulation while in the other it diminished 2 weeks after stimulation. Allied, although less dramatic, changes were seen on the arousal and auditory subscales of the JFK Coma Recovery Scale – Revised.

Conclusion: The data provide the first evidence that vestibular stimulation may help improve outcome in low awareness state although further studies are needed to replicate effect and determine longer-term benefit.