Hubs disruption in mesial temporal lobe epilepsy. A resting-state fMRI study on a language-and-memory network

Mesial temporal lobe epilepsy (mTLE) affects the brain networks at several levels
and patients suffering from mTLE experience cognitive impairment for language
and memory. Considering the importance of language and memory reorganization
in this condition, the present study explores changes of the embedded language and-
memory network (LMN) in terms of functional connectivity (FC) at rest, as
measured with functional MRI. We also evaluate the cognitive efficiency of the
reorganization, that is, whether or not the reorganizations support or allow the
maintenance of optimal cognitive functioning despite the seizure-related damage.
Data from 37 patients presenting unifocal mTLE were analyzed and compared to
48 healthy volunteers in terms of LMN-FC using two methods: pairwise correlations
(region of interest [ROI]-to-ROI) and graph theory. The cognitive efficiency
of the LMN-FC reorganization was measured using correlations between FC
parameters and language and memory scores. Our findings revealed a large perturbation
of the LMN hubs in patients. We observed a hyperconnectivity of limbic
areas near the dysfunctional hippocampus and mainly a hypoconnectivity for several
cortical regions remote from the dysfunctional hippocampus. The loss of FC
was more important in left mTLE (L-mTLE) than in right (R-mTLE) patients. The
LMN-FC reorganization may not be always compensatory and not always useful
for patients as it may be associated with lower cognitive performance. We discuss
the different connectivity patterns obtained and conclude that interpretation of
FC changes in relation to neuropsychological scores is important to determine cognitive
efficiency, suggesting the concept of “connectome” would gain to be associated
with a “cognitome” concept.