Cognitive impairments in chronic temporal lobe epilepsy patients: an event-related potential study of prospective memory

Abstract

Introduction: Cognitive impairments are common in patients with temporal lobe epilepsy (TLE), and impairment of prospective memory (PM) can seriously affect their daily independence. PM has several cognitive components related to working memory, inhibition, and other executive functions. This study aimed to delineate the PM impairment in patients with TLE. Method: A total of 68 subjects were recruited including 23 refractory TLE patients, 19 well-controlled TLE patients, and 26 healthy controls. They were assessed with neuropsychological tests including the digit span test, verbal fluency test, and Symbol Digit Modalities Test. An event-related potential task was used to explore the neural correlates of the PM. A PM paradigm combined with sub-tasks, including an oddball task and a go/ no go task, were performed to delineate which cognitive component was more impaired. Results: TLE patients scored worse than healthy controls in the three neuropsychological tests. Reduction of the P300 amplitudes in the oddball task revealed impaired novel detection in the central-parietal sites in the well-controlled TLE patients. Decreased P3 amplitudes over the frontal-central sites in refractory TLE patients indicated impaired inhibition. Reductions in amplitudes of the prospective positivity component over the frontal, central, and parietal sites in refractory TLE patients suggested PM impairment. Conclusion: Adverse effects of TLE on PM may be caused by complicated mechanisms involving frontal and central sites and are partly attributed to impairment of inhibition function.