Study Of Brain Network In Epilepsy Using Functional MRI

Epilepsy is characterized by transient behavioral and electrophysiological disturbances,which may or may not be associated with detectable structural lesions. At intervals of epilepsy,a variety of foci within a single neuron may become paroxysmal depolarization shift(Paroxysmal depolarization shift,PDS) electricity situation,Which may be shown as sharp waves or slow the emergence of spine in the electroencephalogram This kind of epiletiform discharge,which can be transformed into high-frequency ictal ones,are more often effect human brain's function at the intervals on the slow onset form in the long-term,such as causing memory,language,cognitive and other damage.Functional magnetic resonance imaging(functional MRI,fMRI) as an imaging method of blood oxygenation level-dependent(BOLD) caused by brain neuron activity but not harmful to human body,is more and more used in the study of epileptic pathogenesy,brain functional evaluation localization of epileptic foci.With the study of human brain function and the development of physical test equipment and technology,various new methods are putting forward,among which EEG-fMRI is one of the main method,as it is combined the advantage of high temporal resolution and high spatial resolution.In recent years,the resting fMRI study of brain networks have become more and more interest to the scientist,and become one of the hot spots in the field of neuroscience,particularly the further study on the DMN which finds out to be important in the cognition,attention and episodic memory.The relevant EEG-fMRI study also found that default mode network of brain areas of the patients with epilepsy are abnormally activative or negatvely active on which there are still a lot of controversies.While EEG-fMRI,as a method of model-driven rely on the hypothesis testing to study the network of brain function,has certain limitations.The resting functional connectivity(RFC) will measure the distance between different brain regions of the synchronization signal with the different degree of oscillation.RFC is not sensitive to the extent of brain activation,but very sensitive to the temporal and spatial oscillation of the signal.These brain regions with synchronized oscillations can be thought to be one network.Therefore,it it more helpful in studying the brain network.So far,RFC has become to be the most sophisticated and widely used method to study the network of brain function connection.In addition,as this method is simple,completely non-harmful on the human body,it can be applied to a variety of brain disorders and normal study groups.In this study,we use the RFcMRI technology to assess the total focal epilepsy and temporal lobe epilepsy resting function of the network with comparison between normal control and epileptic patient with the aim to explore the changes of default mode and the abnormal epileptic propagation.Here,we will discuss this study in two parts as follows.Parti Disturbances of default mode in focal epilepsy,a functional connectivity MRI studyObjective to evaluate the changes of functional connectivity in the default mode network(DMN) of patients with focal epilepsy.Methods 33 patients with focal epilepsy and 33 normal controls matched with gender/age were enrolled in this study.The patients were divided to two groups according to relationships between the focal location and default mode network.10 patients belonged to the first group that the epileptogenic focus located in the region of default mode,while 23 patients belonged to the second group that the epileptogenic focus located in the region of extrinsic system.Functional connectivity was calculated with the seed point of the epileptogenic focus.The relationship of connectivity between the epileptogenic focus and default network was studied in comparison with the control.Results Of the patients in the first group,7 patients showed reversed negative correlation between the focus and default mode.1 patient showed negative correlation with part of default mode.Meanwhile,of the patients in the second group,18 patients showed negative correlation between focus and default mode with the lower connectivity in contrast with controls.Conclusion The default mode network was disturbed by the epileptic activity in the patient with focal epilepsy,which suggests the changes of default mode are generally existed in the focal epilepsy in addition to the generalized epilepsy.Part 2 Altered functional connectivity of the hippocampus in temporal lobe epileps-afMRI studyObjectives:In comparison with the control,to study the change of functional connectivity of temporal epilepsy with right hippocampus sclerosis(HS)Methods:The authors studied 23 patients with mesial temporal lobe epilepsy (mTLE)and right(HS),and 25 normal control subjects.All subjects underwent a resting functional connectivity MR scan.The right hippocampus connectivity and default mode networks were mapped using the functional connectivity analysis with the seed points in the right hippocampusRsults:functional connectivity between the right hippocampus and DMN areas during rest was markedly different;whereas controls showed a firm connectivity between the seed area and the DMN areas,patients showed connectivity only with a few areas, particularly the seed area itself.This difference was significant in the direct comparison of patients and control connectivity maps.We also found decreased functional connectivity in the extrinsic system in mTLE,these regions are bilateral dorsolateral prefrontal cortex(DLPFC),bilateral intraparietal sulcus(IPS),primary motor and sensory cortices(PMSC).Increased functional connectivity were found between bilateral hippocampus inferior frontal cortex(IFC),superior temporal gyrus and PMSC.Conclusion:we suggest that this reduced connectivity in right temporal lobe epilepsy may reflect a disturbance of the extrinsic system and DMN during resting state.while the right hippocampus together with IFC,STG form a epileptic discharge network.