Sophie Achard
Tuesday 23rd June 2015
Time: 11.00am
Basement Seminar Room
Alexandra House, 17 Queen Square, London, WC1N 3AR
Hubs of brain functional networks are radically reorganized in comatose patients
In this talk, I will present a method to analyse functional magnetic resonance
imaging (fMRI) or magnetoencephalographic (MEG) data, in order to characterize
the network of connections in the brain.
I will show how to measure the network connections in the brain at different frequency bands, using a wavelet correlation measure.
Then, significant correlations are marked as effective connections, this
allows us to construct a graph. Finally, topological parameters of these graphs, such as efficiency, are extracted, and comparisons between populations are conducted.
This suggests that correlated, low-frequency oscillations in human fMRI data
have a small-world architecture that probably reflects underlying anatomical
connectivity of the cortex. Because the major hubs of this network are
critical for cognition, its slow dynamics could provide a physiological
substrate for segregated and distributed information processing.
I will also illustrate this method on a recent fMRI data set with resting state functional MRI data acquired from 17 patients with severely impaired consciousness and 20 healthy volunteers (Achard et al. PNAS 2012). We found that many global network properties were conserved in comatose patients. Specifically, there was no significant abnormality of global efficiency, clustering, small-worldness, modularity, or degree distribution in the patient group. However, in every patient we found evidence for a radical reorganization of high degree or highly efficient ``hub’’ nodes. Cortical regions that were hubs of healthy brain networks had typically become non-hubs of comatose brain networks and vice versa. These results indicate that global topological properties of complex brain networks may be homeostatically conserved under extremely different clinical conditions and that consciousness likely depends on the anatomical location of hub nodes in human brain networks.