Neural correlates of (non-)behavioural signs of consciousness – what can we learn from resting state neuroimaging?

Background and aims: Unresponsive patients at the
bedside may present covert consciousness. This
retrospective cross-sectional study aimed to determine brain
regions needed to demonstrate behavioural signs of
consciousness.
Methods: We looked at the 18fluorodesoxyglucose Positron
Emission Tomography (FDG-PET-scan) of 96 patients with
disorders of consciousness (see table 1). All patients were
assessed 5 times with the Coma Recovery Scale-Revised.
The diagnosis of MCS* was based on the FDG-PET relative
preservation of global brain metabolism as assessed by 3
experts. We compared brain metabolism of patients in
MCS* to UWS and MCS and performed seed-based
connectivity analyses. MRI and EEG data were also
analysed. Prognosis was collected using the Glasgow
Outcome Scale Extended.
Results: Out of the 35 behavioural UWS, 22 presented a
partial preservation of brain metabolism (i.e., patients in
MCS*), specifically in the fronto-parietal networks (Fig 1
– left). Patients in MCS* had more hypometabolism in the
right posterior regions (Fig 1 – right). We found a higher
correlation between the right superior temporal gyrus (seed)
and motor cortices, somato-sensory associative areas,
prefrontal area, and the thalami in MCS compared to
MCS*(Fig 2), as well as a higher connectivity (EEG) in the
theta band in the left hemisphere. Finally, MCS* patients
had a 50% chance to recover signs of consciousness (MCS)
at follow-up, while no patient in UWS improved.
Conclusion: Many patients clinically unresponsive may
present covert consciousness. The integrity of the
connectivity between the superior temporal gyrus and
sensori-motor regions, prefrontal cortex and thalami is
crucial to clinically demonstrate signs of consciousness.