Whole-brain functional connectivity increases with extended duration of focal epileptiform activity

Madhavan, Deepak; Heinrichs‐Graham, Elizabeth; Wilson, Tony W.

doi:10.1016/j.neulet.2013.02.052

Cited by 10 publications

(12 citation statements)

References 15 publications

(20 reference statements)

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“…Furthermore, using graph theory analysis, Haneef et al noted global decreases in resting fMRI connectivity in MTLE, along with a progressive reduction in connectivity diversity over time. Several other investigations have also demonstrated positive relationships between disease severity and/or duration with intrinsic connectivity aberrations in various networks of both MTLE and FNE patients. Although directionality cannot be definitively established from these correlational studies, the progressive nature of connectivity alterations seen in focal epilepsy suggests that brain network perturbations likely develop over time with recurrent seizures, and are less likely to represent inherent network properties that predispose the brain to developing epilepsy.…”

Section: Global Connectivity Alterationsmentioning

confidence: 77%

Regional and global connectivity disturbances in focal epilepsy, related neurocognitive sequelae, and potential mechanistic underpinnings

2016

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Epilepsy is among the most common brain network disorders, and it is associated with substantial morbidity and increased mortality. While focal epilepsy was traditionally thought of as a regional brain disorder, growing evidence has demonstrated widespread network alterations in this disorder which extend beyond the epileptogenic zone from which seizures originate. The goal of this review is to summarize recent investigations examining functional and structural connectivity alterations in focal epilepsy, including neuroimaging and electrophysiology studies utilizing model-based or data-driven analysis methods. A significant subset of studies in both mesial temporal lobe epilepsy and focal neocortical epilepsy have demonstrated patterns of increased connectivity related to the epileptogenic zone, coupled with decreased connectivity in widespread distal networks. Connectivity patterns appear to be related to the duration and severity of disease, suggesting progressive connectivity reorganization in the setting of recurrent seizures over time. Global resting-state connectivity disturbances in focal epilepsy have been linked to neurocognitive problems, including memory and language disturbances. While it is possible that increased connectivity in a particular brain region may enhance the propensity for seizure generation, it is not clear if global reductions in connectivity represent the damaging consequences of recurrent seizures, or an adaptive mechanism to prevent seizure propagation away from the epileptogenic zone. Overall, studying the connectome in focal epilepsy is a critical endeavor which may lead to improved strategies for epileptogenic zone localization, surgical outcome prediction, and a better understanding of the neuropsychological implications of recurrent seizures.

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Section: Global Connectivity Alterationsmentioning

confidence: 77%

Regional and global connectivity disturbances in focal epilepsy, related neurocognitive sequelae, and potential mechanistic underpinnings

2016

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“…Without the contamination of interictal spike activities, increased functional connectivity in TLE patients was found in the right MT region at delta band and in the bilateral ACC regions at theta band. An increased level of functional connectivity during a resting-state condition was reported in various types of epilepsy in the EEG [ 54 , 55 ], MEG [ 56 ], and fMRI studies [ 57 – 64 ]. These evidences are in line with the consistent morphological changes involved in distinct brain regions in TLE patients [ 65 ], or between and within hemispheres in epilepsy [ 66 ], which was attributed to an altered configuration of grey matter regions and interconnecting white matter tracts in TLE [ 23 ].…”

Section: Discussionmentioning

confidence: 99%

“…These evidences are in line with the consistent morphological changes involved in distinct brain regions in TLE patients [ 65 ], or between and within hemispheres in epilepsy [ 66 ], which was attributed to an altered configuration of grey matter regions and interconnecting white matter tracts in TLE [ 23 ]. Moreover, it has been suggested that an enhanced connection may be the consequence of functional reorganization or plasticity [ 57 , 60 , 64 ] and cortical inhibitory mechanisms [ 56 ] in epilepsy. Apart from an enhanced connectivity, the association between disruption of cortical connections in the DMN and cognitive impairment of epilepsy patients was noted in previous fMRI studies [ 23 , 57 , 62 , 66 , 67 ].…”

Section: Discussionmentioning

confidence: 99%

Increased Intrinsic Connectivity of the Default Mode Network in Temporal Lobe Epilepsy: Evidence from Resting-State MEG Recordings

Hsiao

Chen

et al. 2015

PLoS ONE

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The electrophysiological signature of resting state oscillatory functional connectivity within the default mode network (DMN) during spike-free periods in temporal lobe epilepsy (TLE) remains unclear. Using magnetoencephalographic (MEG) recordings, this study investigated how the connectivity within the DMN was altered in TLE, and we examined the effect of lateralized TLE on functional connectivity. Sixteen medically intractable TLE patients and 22 controls participated in this study. Whole-scalp 306-channel MEG epochs without interictal spikes generated from both MEG and EEG data were analyzed using a minimum norm estimate (MNE) and source-based imaginary coherence analysis. With this processing, we obtained the cortical activation and functional connectivity within the DMN. The functional connectivity was increased between DMN and the right medial temporal (MT) region at the delta band and between DMN and the bilateral anterior cingulate cortex (ACC) regions at the theta band. The functional change was associated with the lateralization of TLE. The right TLE showed enhanced DMN connectivity with the right MT while the left TLE demonstrated increased DMN connectivity with the bilateral MT. There was no lateralization effect of TLE upon the DMN connectivity with ACC. These findings suggest that the resting-state functional connectivity within the DMN is reinforced in temporal lobe epilepsy during spike-free periods. Future studies are needed to examine if the altered functional connectivity can be used as a biomarker for treatment responses, cognitive dysfunction and prognosis in patients with TLE.

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“…There are several EEG studies of FC that measured an increase in EEG-based FC in epileptogenic regions (for example, Refs. [24][25][26]). The apparent discrepancy between FC measured using EEG versus rsfMRI [3].…”

Section: Discussion and Future Directionsmentioning

confidence: 99%

Characterization of Seizure Generating and Propagating Regions in Human Focal Epilepsy with Resting State Functional Connectivity MRI

Karkar¹,

Lie²,

Szabó³

et al. 2013

J Neurosci Neuroengng

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Focal seizures represent aberrant electrical rhythms that originate in a specific cortical region, the seizure onset zone (SOZ), and propagate in a network of anatomically connected regions. MRI has emerged as a leading diagnostic methodology in the field of epilepsy over the last 20 years and has significantly impacted the surgical evaluation of patients with medically refractory focal epilepsy. However, thus far clinical MRI has largely been used as a structural tool, and there is an interest in developing MRI-based measures of seizure propagation and interregional connectivity. Resting state functional connectivity MRI (rsfMRI) allows identification of macroscopic brain networks based on functional connectivity, or co-activation, within regions (nodes) comprising the network. Functional connectivity (FC) describes the temporal correlation between spatially remote neurophysiologic events, and has been measured using different modalities including rsfMRI. Given the network characteristics of epilepsy, there has been an interest in applying rsfMRI to examine the seizure-generating regions of the brain and their functional interactions with other parts of the brain. In this review, we have focused on focal epilepsy, one of the two subtypes of epilepsy by physiology. Most studies of focal epilepsy, with notable exceptions, reported reduced functional connectivity of epilepsy producing and propagating regions, as well as associated reduction in functional connectivity of networks performing cognitive functions including memory, attention and language. We also reviewed reports of early applications of rsfMRI to lateralize/localize epileptic activity. Overall, resting state functional connectivity MRI (rsfMRI) has already contributed to a better understanding of epilepsy-related networks and promises to add to the non-invasive evaluation of patients with a non-lesional clinical MRI.

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Whole-brain functional connectivity increases with extended duration of focal epileptiform activity

Cited by 10 publications

References 15 publications

Regional and global connectivity disturbances in focal epilepsy, related neurocognitive sequelae, and potential mechanistic underpinnings

Regional and global connectivity disturbances in focal epilepsy, related neurocognitive sequelae, and potential mechanistic underpinnings

Increased Intrinsic Connectivity of the Default Mode Network in Temporal Lobe Epilepsy: Evidence from Resting-State MEG Recordings

Characterization of Seizure Generating and Propagating Regions in Human Focal Epilepsy with Resting State Functional Connectivity MRI

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