Abstracts

Rationale: The default mode network (DMN) of the brain is involved in consciousness and is disrupted in several neurologic diseases. Epilepsy is associated with cognitive deficits and the effects of epilepsy on the DMN have not been elucidated. We evaluated the DMN in temporal lobe epilepsy (TLE) using resting state functional MRI (fMRI) connectivity analysis, a technique that analyzes hemodynamic coherence of a seed area and non-invasively maps the underlying associated network. Methods: Seeds 6 mm in diameter were defined in the retrosplenium/ precuneus region in 5 subjects with right TLE (R-TLE), 5 with left TLE (L-TLE), and 6 control subjects during the resting state. The DMN associated with this seed was compared between the groups using whole-brain independent t-tests conducted for each group pair (cluster corrected, z > 2.0, p < 0.05). Analyses were done using the FEAT component of FSL (FMRIB s software library, Oxford University, UK). Results: A DMN was demonstrable in all 3 subject groups. Compared to control subjects, the DMN observed in L-TLE was significantly larger than controls and the DMN observed in R-TLE was significantly smaller. Other comparisons did not yield significant results (see table and images). Conclusions: The DMN observed by coherence to the retrosplenium/ precuneus was found to be smaller in R-TLE and larger in L-TLE. The effect of TLE on the DMN is expected considering that the retrosplenium is heavily interconnected with the medial temporal lobe, which provides 40% of its extrinsic input (1). Involvement of the DMN may be relevant to the cognitive change differences between R-TLE and L-TLE and is possibly part of the mechanism of cognitive impairment during seizures for R-TLE and L-TLE. Ref: 1. Kobayashi & Amaral 2003