Editors' ChoiceEpilepsy

Broken connections

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Science Translational Medicine  27 Feb 2019:
Vol. 11, Issue 481, eaaw5333
DOI: 10.1126/scitranslmed.aaw5333

Abstract

Interictal discharges affect functional connectivity in patients with temporal lobe epilepsy.

In epilepsy, the most salient symptom is the occurrence of spontaneous seizures, and treatment is aimed at reducing their frequency and intensity. Yet epilepsy is commonly accompanied by cognitive, behavioral, and psychiatric challenges. These comorbidities have been shown to be independent of seizure control or medication use. Instead, they seem to be a fundamental part of epilepsy itself, leading to the notion of seizures as a marker for a more complex disorder of brain function.

Most patients with epilepsy have interictal epileptiform discharges (IEDs), brief spikes of electrical activity that occur between seizures and are clinically asymptomatic. However, IEDs transiently interrupt normal brain activity, suggesting that they could play a role in the cognitive and psychiatric features of epilepsy.

In this study, Tong et al. examined simultaneously obtained electroencephalographic (EEG) and functional magnetic resonance imaging (fMRI) data from 21 patients with temporal lobe epilepsy (TLE) to understand the immediate effects of IEDs on functional connectivity. The authors assessed networks involving the hippocampus and amygdala, noting connectivity alterations in the 10-s period immediately following an IED. Interestingly, the nature of these alterations depended on the side of IED origin. Left-sided IEDs attenuated ipsilateral hippocampal-based networks, including the default-mode network, prefrontal-limbic, and visual systems. In contrast, right-sided IEDs amplified amygdala-dependent pathways, including the reward-emotion network.

The 21 individuals who participated in this study varied with respect to age of epilepsy onset, MRI findings, degree of seizure control, and use of anti-seizure medications—factors that all have the potential to influence IED frequency and functional connectivity in unpredictable ways. The extent to which this study's results will be validated in larger cohorts of patients with other forms of epilepsy remains to be seen. Moreover, the relationship between transient alterations in functional connectivity and chronic neuropsychiatric challenges has not been established. However, the authors add to a growing body of evidence that for patients with epilepsy, seizures may not be the whole story.

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