The other three networks are sensory in nature, auditory, visual and somatosensory. “With the help of statistical analyses, it is easy to specify these six networks”, says Steven Laureys. “But on the other hand, it is much more difficult to analyse them”. This is exactly what the researchers of the Coma Science Group and the Massachusetts Institute of Technology, tasked themselves with.

Brain activity in the different networks fluctuates. Therefore we observe a negative correlation between the activity of the regions involved in self-awareness and that of regions involved in awareness of the external world. The connections of our brain (the wiring) are fixed, in such a way that, in a healthy individual, the regions that are interconnected communicate with each other on a permanent basis with a greater or lesser level of intensity, even when an individual is experimentally anaesthetised by means of propofol, for example, as evidenced by the work of the CRC (4). Steven Laureys uses the analogy of the brain as a motorway with vehicles that can be seen passing along it by means of fMRI technology and these vehicles are more numerous when the subject is in the waking state than when asleep.

Athena Demertzi and Georgios Antonopoulos, both of whom are researchers at the CRC, are the two first authors of the article published in Brain. With their colleagues, they studied 73 individuals suffering from consciousness problems, 51 of whom were patients cared for in Liege. By means of 10-minute recordings by fMRI in the resting state, they were able to quantify, in the six above-mentioned networks, brain activity in these brain-damaged individuals.

Can they hear? Can they see? Have they retained their sense of touch? Do they feel any emotions? Are they self-aware? Are they conscious of the external world? The answers to these questions are an ideal to be achieved. For the moment, the method is not finely-tuned enough to be able to address the nature of the abovementioned issues. Indeed, what the study measured was to determine whether a given patient was totally unconscious or whether she/he had the residual consciousness characteristic of a minimally conscious state.

In more than 90% of cases

By comparing the activity measurements for each network, the use of algorithms for statistical classification (classifiers) revealed that the auditory network was the most effective for establishing the separation between patients in a vegetative / unresponsive state and patients in a minimally conscious state. Additionally, the higher the score of the individuals on the Coma Recovery Scale-Revised, the more this this network appeared to be clearly active. “However, it is not merely made up of auditory regions but it also recruits visual and sensorimotor regions, for example. This is logical: when we hear somebody, we can easily picture their face, think of their job, etc.”, comments the head of the Coma Science Group.

This raised the question as to whether, within the auditory system, some elements were more informative than others. The classifiers demonstrated that this was indeed the case, that the activity in the connection between the auditory and visual regions of the network, therefore in the crossmodal auditory and visual interaction zone, was the best predictor of the presence or absence of consciousness in the examined patients.

(4) Boveroux, P., Vanhaudenhuyse, A., Bruno, M.-A., Noirhomme, Q., Lauwick, S., Luxen, A., Degueldre, C., Plenevaux, A., Schnakers, C., Phillips, C., Brichant, J. F., Bonhomme, V., Maquet, P., Greicius, M. D., Laureys, S., & Boly, M. (2010). Breakdown of within- and between-network resting state functional magnetic resonance imaging connectivity during propofol-induced loss of consciousness. Anesthesiology, 113, 1038-1053.