Effect of interictal epileptiform discharges on EEG-based functional connectivity networks

Abstract

Objective: Functional connectivity networks (FCNs) based on interictal electroencephalography (EEG) can identify pathological brain networks associated with epilepsy. FCNs are altered by interictal epileptiform discharges (IEDs), but it is unknown whether this is due to the morphology of the IED or the underlying pathological activity. Therefore, we characterized the impact of IEDs on the FCN through simulations and EEG analysis. Methods:We introduced simulated IEDs to sleep EEG recordings of eight healthy controls and analyzed the effect of IED amplitude and rate on the FCN. We then generated FCNs based on epochs with and without IEDs and compared them to the analogous FCNs from eight subjects with infantile spasms (IS), based on 1,340 visually marked IEDs. Differences in network structure and strength were assessed.Results: IEDs in IS subjects caused increased connectivity strength but no change in network structure. In controls, simulated IEDs with physiological amplitudes and rates did not alter network strength or structure. Conclusions:Increases in connectivity strength in IS subjects are not artifacts caused by the interictal spike waveform and may be related to the underlying pathophysiology of IS.Significance: Dynamic changes in EEG-based FCNs during IEDs may be valuable for identification of pathological networks associated with epilepsy.Epilepsy, infantile spasms, electroencephalography, functional connectivity, interictal epileptiform discharges, brain mapping Hu 3 Highlights:• Infantile spasms subjects exhibit broadly increased connectivity strength during interictal spikes • Functional connectivity network structure is unaltered by interictal spikes in infantile spasms • Simulated spikes in healthy control EEG did not alter network strength or structure

Electroencephalography–functional magnetic resonance imaging of epileptiform discharges: Noninvasive investigation of the whole brain

“…A study on hypsarrhythmia using source analysis revealed an association with delta activity in the occipital cortex, parietal cortex, putamen, caudate nucleus, and brainstem 130 . Patients with infantile spasms exhibited a broad increase in connectivity strength during IEDs 129 . Those studies support the involvement of ascending brainstem pathways that project widely to basal ganglia and cerebral cortex in the generation of hypsarrhythmia.…”

“…There have been several EEG‐fMRI studies on epileptic encephalopathy (e.g., West syndrome, Lennox–Gastaut syndrome [LGS]), that observed the regions involved in these syndromes. A study on the BOLD signals in hypsarrhythmia showed that multifocal spikes are associated with cerebral cortex (especially occipital areas) activation, whereas slow waves are associated with responses in the brainstem, thalamus, and putamen 128,129 . A study on hypsarrhythmia using source analysis revealed an association with delta activity in the occipital cortex, parietal cortex, putamen, caudate nucleus, and brainstem 130 .…”

Removal of Interictal MEG-Derived Network Hubs Is Associated With Postoperative Seizure Freedom

“…Although interictal spikes may be randomly present in any chosen epoch, their influence on functional connectivity is limited if they are present in only a minority of time windows. This influence is limited because our approach captures stationary aspects of the reconstructed network rather than the transient spikes (40,56). However, we acknowledge that in circumstances where the majority of the recording contains spikes their influence on functional connectivity may be stronger.…”