Abstracts

Rationale: Mounting evidence continues to demonstrate abnormal functional connections in patients with temporal lobe epilepsy (TLE). Focus has largely been on the medial temporal region, as this is the typical seizure onset region and the most common site of pathology observed with the disease. However, there is increasing evidence that the medial temporal region forms a functional network with other brain regions, suggesting that other nodes in this network may be affected and function as disease markers for TLE. Here we used resting state BOLD fMRI to characterize the functional network of the medial temporal region with the inferior, medial and superior temporal neocortical regions and demonstrated abnormal connectivity that has lateralizing value with regards to seizure onset. Methods: Thirty-two patients with TLE were consecutively enrolled in a resting-state BOLD fMRI study in a 3 T scanner. Each patient had video-EEG localization of seizures. Only patients with unilateral seizure onset were included. A group of age-, gender-, and handedness matched healthy subjects (n = 32) served as controls. Regions of interest (ROIs) were defined a priori based on anatomical segmentation, and functioned as seed in a functional connectivity analysis using typical methods (e.g. Fox et al., J. Neurophysiol., 2009, 101:3270-83). Results: Neocortical temporal regions exhibited significantly altered functional connectivity in TLE compared to healthy controls. Specifically there was a significant decrease in the strength of the functional connections between homologous temporal regions in the inferior, medial and superior temporal gyri, mirroring the decoupling between medial temporal regions also seen with the disease (p<.01, post-hoc paired t-test, after cluster-level correction for multiple comparisons). Moreover, in the hemisphere ipsilateral to seizure onset, neocortical temporal regions showed increased connectivity with the ipsilateral insula and regions immediately medial to it, such as the basal ganglia (p<.01, post-hoc paired t-test, after cluster-level correction for multiple comparisons). Conclusions: TLE is associated with strong functional network changes that go beyond the medial temporal region and involve the temporal neocortex. The observed increased coupling with the insula and basal ganglia exhibited by temporal neocortex ipsilateral to the seizure focus is of particular interest, and may be a correlate of a seizure propagation pathway or speculatively reflect an increased propensity of the network to generate and/or propagate seizures. The laterality it provides may have a clinical role in seizure localization and presurgical planning.