Lee SJ, Beam DE, Schjetnan AGP, et al. - It demonstrates that impaired memory is a common comorbidity of refractory temporal lobe epilepsy (TLE) and is often perceived by patients as more problematic than the seizures themselves. This study was undertaken to investigate what the association of these behavioral impairments is to the underlying pathophysiology, as there are currently no treatments for these deficits, and it remains unknown what circuits are affected. Single neurons were recorded in the medial temporal lobes (MTLs) of 62 patients (37 with refractory TLE) who performed a visual recognition memory task to characterize the relationship between behavior, tuning, and anatomical location of memory selective and visually selective neurons. The data illustrate that single-cell responses can be applied to evaluate the causal effects of local circuit disruption by a seizure onset zone in the MTL and construct a neural correlate of cognitive impairment due to epilepsy that can be applied as a biomarker to evaluate the effectiveness of novel treatments.