Elemental spatial and temporal association formation in left temporal lobe epilepsy

PLoS One. 2014 Jun 30;9(6):e100891. doi: 10.1371/journal.pone.0100891. eCollection 2014.

Abstract

The mesial temporal lobe (MTL) is typically understood as a memory structure in clinical settings, with the sine qua non of MTL damage in epilepsy being memory impairment. Recent models, however, understand memory as one of a number of higher cognitive functions that recruit the MTL through their reliance on more fundamental processes, such as "self-projection" or "association formation". We examined how damage to the left MTL influences these fundamental processes through the encoding of elemental spatial and temporal associations. We used a novel fMRI task to image the encoding of simple visual stimuli, either rich or impoverished, in spatial or spatial plus temporal information. Participants included 14 typical adults (36.4 years, sd. 10.5 years) and 14 patients with left mesial temporal lobe damage as evidenced by a clinical diagnosis of left temporal lobe epilepsy (TLE) and left MTL impairment on imaging (34.3 years, sd. 6.6 years). In-scanner behavioral performance was equivalent across groups. In the typical group whole-brain analysis revealed highly significant bilateral parahippocampal activation (right > left) during spatial associative processing and left hippocampal/parahippocampal deactivation in joint spatial-temporal associative processing. In the left TLE group identical analyses indicated patients used MTL structures contralateral to the seizure focus differently and relied on extra-MTL regions to a greater extent. These results are consistent with the notion that epileptogenic MTL damage is followed by reorganization of networks underlying elemental associative processes. In addition, they provide further evidence that task-related fMRI deactivation can meaningfully index brain function. The implications of these findings for clinical and cognitive neuropsychological models of MTL function in TLE are discussed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Brain Mapping
  • Epilepsy, Temporal Lobe / pathology
  • Epilepsy, Temporal Lobe / physiopathology*
  • Female
  • Hippocampus / pathology
  • Hippocampus / physiopathology*
  • Humans
  • Magnetic Resonance Imaging
  • Male
  • Middle Aged
  • Neuropsychological Tests
  • Pattern Recognition, Visual*
  • Space Perception
  • Task Performance and Analysis
  • Temporal Lobe / pathology
  • Temporal Lobe / physiopathology*
  • Time Perception

Grants and funding

This research was supported by NH&MRC Program Grant 400121 and in part by a National Academy of Neuropsychology Clinical Research Grant (PI: Benjamin). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.