Our data show that the assessment of localisation to sound depends on what stimulus
is employed. MCS patients tend to best orient to their own name as compared to a
meaningless loud sound (i.e., ringing bell). Indeed, one’s own name is a piece
of information that we use to process in the auditory modality from infancy:
4–5 month-old infants are able to recognize the sound pattern of their own
names . In end-stage demented patients, it has also been shown that perception
of the own name deteriorates well after perception of time, place and recognition . Similarly, after general anaesthesia, the patient’s reactivity to
the own name occurs first, before reactivity to pain and noise . In MCS patients, clinical experience learns that behavioural responses
to auto-referential stimuli such as the own face are amidst the first signs
heralding further recovery of consciousness . Event-related potential studies have also shown that hearing one’s
own name, as compared to meaningless noise, leads to an increased mismatch
negativity response in patients with disorders of consciousness . In addition, functional MRI studies assessing brain activation to the
own name have reported activation of “self”-related brain regions (i.e.,
anterior cingulate and mesiofrontal cortices) depending of the level of
consciousness in patients recovering from coma [7, 13].
28% of the studied MCS patients (11/39) failed to show auditory localisation.
Neurological assessment showed that 2 of these 11 patients (18%) had absent auditory
startle, while 9 (82%) showed auditory-independent signs of consciousness. In line
with previous studies, auditory impairment probably explains this finding .
Auditory localisation seems to be related to the patient’s overall behavioural
responsivity: the more the patients are conscious, the more they tend to respond to
both auditory stimuli. Moreover, our results showed that most of the patients who
responded to the bell also responded to their own name (condition “both”
in Table 1). Three patients however showed localisation to the
bell but not to their own name. Even if they retained basic auditory processing,
these three patients might not have been able to process language, and hence
recognize their own name. Another explanation could be the presentation of the
patient's own name as last stimulus, and hence fatigue might explain orientation to
a bell in the absence of orientation to the own name.
One should note that the duration and the degree of the movement towards auditory
stimulation were not taken into account to assess auditory localisation (as
described in the CRS-R). This should nevertheless be investigated in future studies
to allow differentiating between a brief movement and a sustained fixation following
auditory stimulation. Indeed, the latter may potentially be considered as a sign of
consciousness, as it is the case for visual and tactile localisation (e.g., visual
pursuit and localisation to noxious stimulation items in the CRS-R). Such responses
may also be worth exploring further using neuroimaging techniques such as fMRI and
EEG in order to compare the behavioral responses and the underlying cerebral
networks involved when hearing the person's name being called.