Of the 50 million people worldwide affected by epilepsy, roughly a third do not respond to medication.1 In such cases, surgical intervention is often recommended. A critical step before operating on these patients is accurately localizing the seizure onset zone (SOZ) - i.e., the region of the brain where seizures originate.

Many seizures arise in the temporal lobes, involving the hippocampus - a region important for learning and memory. Structural magnetic resonance imaging (MRI) may show hippocampal atrophy on the affected side. Functional imaging (fMRI) can also indicate hippocampal dysfunction. Indeed, decreased ipsilateral hippocampal functional connectivity to the brain's default mode network (DMN) has been found in temporal lobe epilepsy (TLE) using resting-state fMRI (rs-fMRI).2

We hypothesized that asymmetrically decreased hippocampal connectivity to the DMN or the brain as whole measured with rs-fMRI might provide a means to lateralize the SOZ in individual TLE patients using non-invasive imaging alone.