Abstract
The corpus callosum (CC) plays an important role in generalization of seizure activity. We used resting-state function magnetic resonance imaging (rs-fMRI) to investigate the regional and interregional functional connectivity of CC in patients with magnetic resonance imaging (MRI)-negative and secondarily generalized seizures. We measured the multi-regional coherences of blood oxygen level-dependent (BOLD) signals via rs-fMRI, cortical thickness via high-resolution T1-weighted MRI, and white matter (WM) integrity via diffusion-tensor imaging in 16 epilepsy patients as well as in 16 age- and gender-matched healthy subjects. All patients had non-lesional MRI, medically well-controlled focal epilepsy and history of secondarily generalized convulsions. Individuals with epilepsy had significant differences in regional and interregional hypersynchronization of BOLD signals intrahemispherically and interhemispherically, but no difference in cortical thickness and WM integrity. The only area with increased regional hypersynchrony in WM was over the anterior CC, which also exhibited lower activation of neighboring resting-state networks. The present study revealed abnormal local and distant synchronization of spontaneous neural activities in epileptic patients with secondarily generalized seizures.
Highlights
When a seizure evolves into a generalized convulsion, the electro-clinical features, including bilateral stiffening, jerking of limbs, and synchronization of electroencephalography (EEG) discharges, are not very different from those of most generalized seizures in and among epilepsy patients
From a medically well-controlled patient group with a history of generalized convulsions, a localizable seizure source and without visible lesions on magnetic resonance imaging (MRI), we studied structural connectivity by measuring the white matter (WM) integrity via Diffusion-tensor imaging (DTI) and the functional connectivity via resting-state function magnetic resonance imaging (rs-fMRI)
Patients showed significantly increased regional homogeneity (ReHo) compared to healthy controls in the genu of corpus callosum (CC), right superior temporal pole, right lingual gyrus, left lobule VI of the cerebellar hemisphere, lobule III of the vermis, and left putamen
Summary
When a seizure evolves into a generalized convulsion, the electro-clinical features, including bilateral stiffening, jerking of limbs, and synchronization of electroencephalography (EEG) discharges, are not very different from those of most generalized seizures in and among epilepsy patients. Sequential involvement of different cortices and their associated neural fibers for the widespread propagation of epileptic activity is a generally accepted scenario for the development of high amplitude, bilaterally synchronous EEG discharge from a period of locally repetitive spiking [1]. The widespread cortical connection through the CC is assumed to implicate the interhemispheric transmission of epileptic electricity. Callosotomy, a surgical procedure, may Callosal Resting Functional Connectivity be conducted to disconnect the bilateral hemispheres to reduce the severity and frequency of secondary generalization in patients with pharmacoresistant focal seizures [2]. During the generalized seizure period, the limited temporal difference between the EEG spiking ridges of remote cerebral regions indicates that there is an effective process to synchronize the interhemispheric electrical activity independent of synaptic transmission, gap junctions, and ion diffusion. In addition to the synchrony disruption, callosotomy decreases the intrahemispheric temporal coupling between cortices, supporting the facilitation mechanism of the CC [3]
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