Default mode network abnormalities in idiopathic generalized epilepsy.
ABSTRACT Idiopathic generalized epilepsy (IGE) is associated with widespread cortical network abnormalities on electroencephalography. Resting state functional connectivity (RSFC), based on fMRI, can assess the brain's global functional organization and its disruption in clinical conditions. We compared RSFC associated with the 'default mode network' (DMN) between people with IGE and healthy controls. Strength of functional connectivity within the DMN associated with seeds in the posterior cingulate cortex (PCC) and medial prefrontal cortices (MPFC) was compared between people with IGE and healthy controls and was correlated with seizure duration, age of seizure onset and age at scan. Those with IGE showed markedly reduced functional network connectivity between anterior and posterior cortical seed regions. Seizure duration positively correlates with RSFC between parahippocampal gyri and the PCC but negatively correlates with connectivity between the PCC and frontal lobe. The observed pattern of disruption provides evidence for integration- and segregation-type network abnormalities and supports aberrant network organization among people with IGE.
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ABSTRACT: Working memory is a critical building block for almost all cognitive tasks, and impairment can cause significant disruption to daily life routines. We investigated the functional connectivity (FC) of the visuo-spatial working memory network in temporal lobe epilepsy and its relationship to the underlying white matter tracts emanating from the hippocampus. Fifty-two patients with unilateral hippocampal sclerosis (HS) (30 left) and 30 healthy controls underwent working memory functional MRI (fMRI) and Diffusion Tensor Imaging (DTI). Six seed regions were identified for FC analysis; 4 within a task-positive network (left and right middle frontal gyri and superior parietal lobes), and 2 within a task-negative network (left and right hippocampi). FC maps were created by extracting the time-series of the fMRI signal in each region in each subject and were used as regressors of interest for additional GLM fMRI analyses. Structural connectivity (SC) corresponding to areas to which the left and right hippocampi were connected was determined using tractography, and a mean FA for each hippocampal SC map was calculated. Both left and right HS groups showed atypical FC between task-positive and task-negative networks compared to controls. This was characterised by co-activation of the task-positive superior parietal lobe ipsilateral to the typically task-negative sclerosed hippocampus. Correlational analysis revealed stronger FC between superior parietal lobe and ipsilateral hippocampus, was associated with worse performance in each patient group. The SC of the hippocampus was associated with the intra-hemispheric FC of the superior parietal lobe, in that greater SC was associated with weaker parieto-frontal FC. The findings suggest that the segregation of the task-positive and task-negative FC networks supporting working memory in TLE is disrupted, and is associated with abnormal structural connectivity of the sclerosed hippocampus. Co-activation of parieto-temporal regions was associated with poorer working memory and this may be associated with working memory dysfunction in TLE.NeuroImage : clinical. 01/2013; 2:273-81.
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ABSTRACT: Previous studies using voxel-based morphometry (VBM) provided emerging evidence of structural changes of the thalamus in idiopathic generalized epilepsy (IGE). However, the location of atrophy within the thalamus in IGE has been somewhat inconsistent across the studies. We, therefore, examined the location of thalamic atrophy and its relationship with clinical factors in IGE, using multiple analytic methods. Fifty IGE patients and 50 controls were scanned on a 3T MRI. Structural evaluation consisted of automated thalamic volumetry, VBM, and thalamic shape analysis. Group comparison between patients and controls was made to assess thalamic atrophy. Within-group correlations between thalamic atrophy and clinical variables were further performed in patients. Both thalamic volumes were reduced in IGE patients, and were negatively correlated with disease duration. The VBM showed a significant regional grey matter volume reduction in bilateral anterior-medial thalami in patients compared to controls. Voxel values extracted from the anterior-medial thalamic cluster were negatively correlated with disease duration. Vertex-based shape analysis revealed regional atrophy on the anterior-medial and posterior-dorsal aspects of thalamus bilaterally in patients compared to controls. Correlation analysis showed that anterior-medial and posterior-dorsal aspects of bilateral thalami were negatively correlated with disease duration. Combining multiple analyses, we demonstrated regional atrophy of anterior-medial and posterior-dorsal thalamus in patients with IGE. Given the anatomical connection of these thalamic regions with the frontal lobe, our finding of greater thalamic atrophy in relation to increasing disease duration further supports the pathophysiological concept of thalamo-frontal network abnormality underlying IGE, and may implicate frontal cognitive dysfunctions and disease progression.Journal of Neurology 03/2013; · 3.58 Impact Factor
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ABSTRACT: We aimed to study the effect of a potential default mode network (DMN) dysfunction on language performance in epilepsy. Language dysfunction in focal epilepsy has previously been connected to brain damage in language-associated cortical areas. In this work, we studied generalized epilepsy (GE) without focal brain damage to see if the language function was impaired. We used functional magnetic resonance imaging (fMRI) to investigate if the DMN was involved. Eleven persons with GE and 28 healthy controls were examined with fMRI during a sentence-reading task. We demonstrated impaired language function, reduced suppression of DMN, and, specifically, an inadequate suppression of activation in the left anterior temporal lobe and the posterior cingulate cortex, as well as an aberrant activation in the right hippocampal formation. Our results highlight the presence of language decline in people with epilepsy of not only focal but also generalized origin.Epilepsy & Behavior 05/2013; 28(1):26-35. · 1.84 Impact Factor