Impaired spatial pattern separation performance in temporal lobe epilepsy is associated with visuospatial memory deficits and hippocampal volume loss.

Individuals with chronic temporal lobe epilepsy (TLE) experience episodic memory deficits that may be progressive in nature. These memory decrements have been shown to increase with the extent of hippocampal damage, a hallmark feature of TLE. Pattern separation, a neural computational mechanism thought to play a role in episodic memory formation, has been shown to be negatively affected by aging and in individuals with known hippocampal dysfunction. Despite the link between poor pattern separation performance and episodic memory deficits, behavioral pattern separation has not been examined in patients with TLE. We examined pattern separation performance in a group of 22 patients with medically-refractory TLE and 20 healthy adults, using a task hypothesized to measure spatial pattern separation with graded levels of spatial interference. We found that individuals with TLE showed less efficient spatial pattern separation performance relative to healthy adults. Poorer spatial pattern separation performance in TLE was associated with poorer visuospatial memory, but only under high interference conditions. In addition, left hippocampal atrophy was associated with poor performance in the high interference condition in TLE. These data suggest that episodic memory impairments in patients with chronic, refractory TLE may be partially due to less efficient pattern separation, which likely reflects their underlying hippocampal dysfunction.