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Identifying Corticothalamic Network Epicenters in Patients with Idiopathic Generalized Epilepsy - AJNR News Digest
January-February 2017
Functional

Identifying Corticothalamic Network Epicenters in Patients with Idiopathic Generalized Epilepsy

Liao pic

Wei Liao

Lu pic

Guangming Lu

Idiopathic generalized epilepsy (IGE) is a common subtype of epilepsy. The quality of life of patients with IGE could be dramatically affected by generalized spike-wave discharges (GSWDs), which manifest as abnormal EEG signals rapidly spreading to the bilateral hemispheres. For patients who are resistant to medical treatment, we still lack potentially effective therapy. Uncovering the mechanism underlying IGE may accelerate the development of new therapies.

GSWDs occur spontaneously without the presence of obviously predisposing factors. Based on this clinical feature, we predicted that abnormal spontaneous brain activity occurred in the patients. But what is the neural basis of this functional abnormality? Some theories have emphasized the role of corticothalamic circuits in the generation of GSWDs.1 However, we did not know whether all the corticothalamic nodes are involved or just a few of them. To address this issue, we investigated the intrinsic functional connectivity of patients with IGE by using resting-state functional imaging (rs-fMRI).

rs-fMRI is a very convenient clinical paradigm compared with task fMRI.2 There is no particular requirement for participants other than lying in the scanner quietly. Thus, it is especially suitable for clinical studies. More importantly, its robustness has been tested, and several methods have been developed for characterizing the spontaneous brain activity or intrinsic functional connectivity in the past 10 years.3 In the current study, we adopted functional connectivity strength (FCS) to identify the epicenters within five corticothalamic networks.4

Four of the five networks indicated excessive FCS; epicenters included the supplementary motor area (SMA), premotor cortex, inferior parietal lobule (IPL), and middle temporal gyrus. These findings suggest an increased intrinsic functional connectivity in patients with IGE at rest. The identification of epicenters provided spatial information for novel therapies, such as repetitive transcranial magnetic stimulation (rTMS). As rTMS can only affect superficial cortex, we suggest the SMA and IPL as potential targets for treatment. To decrease spontaneous brain activity, future studies may select inhibitory protocols such as 1 Hz or continuous theta burst stimulation rTMS.

The development of neuroimaging approaches enabled us to detect pathophysiological changes precisely. However, how this explosive information could benefit patients is still an open question. In the future, we would like to make an effort to bridge neuroimaging findings with clinical practice.

References

  1. Blumenfeld H. From molecules to networks: cortical/subcortical interactions in the pathophysiology of idiopathic generalized epilepsy. Epilepsia 2003;44:7–15, 10.1046/j.1528-1157.44.s.2.2.x
  2. Lee MH, Smyser CD, Shimony JS. Resting-state fMRI: a review of methods and clinical applications. AJNR Am J Neuroradiol 2013;34:1866–72, 10.3174/ajnr.A3263
  3. Poldrack RA, Farah MJ. Progress and challenges in probing the human brain. Nature 2015;526:371–79, 10.1038/nature15692
  4. Zhang D, Snyder AZ, Shimony JS, et al. Noninvasive functional and structural connectivity mapping of the human thalamocortical system. Cereb Cortex 2010;20:1187–94, 10.1093/cercor/bhp182

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