Abstracts

Rationale: Frontal lobe epilepsy (FLE) is the second most common type of focal epilepsy. These patients often experience motor deficits during daily activities including impaired coordination, decreased dexterity, and poor impulse control (Exner et al. 2002, Seizure 11:20-32). Previous studies have associated behavioural impairments in patients with epilepsy with changes in resting-state connectivity (Waites et al. 2006, Ann Neurol 59:335-343; Doucet et al. 2012, Hum Brain Map 00:00-00), a technique that examines temporally correlated brain regions at rest using modalities such as functional magnetic resonance imaging (fMRI). However, it is not known whether patients with FLE have altered motor networks, and if such alterations could contribute to functional motor deficits. We therefore examined resting-state motor networks in participants with FLE using fMRI.Methods: Thirteen participants with epilepsy (seven with right lateralized FLE and six with left lateralized FLE) and ten healthy controls between the ages of 16 and 65 were studied. FMRI was performed at 3T and participants underwent a five-minute scan during which they were asked to focus on a projected fixation cross. FMRI data were pre-processed and analyzed using FSL. The left and right sensorimotor cortices were identified as regions of interest (ROI) using the Harvard-Oxford cortical atlas (Desikan et al. 2006, NeuroImage 31:968-980), and the average BOLD signal from voxels contained within the ROI was compared to every voxel in the brain in order to assess the temporal correlation between BOLD signals. Mean parametric maps were generated for each group (right FLE, left FLE, controls) and compared to determine voxels exhibiting significant differences (Z>2.3 with a corrected cluster significance of p=0.05). Laterality indices were calculated from each participant s connectivity map and correlated with the number of years since epilepsy diagnosis, number of lifetime seizures (total/GTC seizures only), number of seizures in past year (total/GTC seizures only) and number of months since the last experienced seizure, in order to determine significant relationships. Results: Both the right and left FLE groups demonstrated significantly decreased connectivity between the left and right sensorimotor cortices when compared to controls (Z>2.3; Fig. 1). Laterality indices were significantly correlated to the total number of lifetime seizures in both FLE groups (left FLE: rs=0.89, right FLE: rs=1.00; Fig. 2). Specifically, these correlations showed that the sensorimotor cortex in the healthy hemisphere became less functionally connected to the sensorimotor cortex in the epileptic hemisphere as participants experienced a greater number of lifetime seizures.Conclusions: Resting-state motor networks are altered in participants with FLE when compared to controls. These differences became more pronounced when participants experienced a greater number of lifetime seizures. These results may have important implications for understanding the mechanisms behind daily motor deficits experienced by patients with FLE.