Abstracts

Rationale: In healthy adults, normal cognitive function is defined by the harmonious interaction among multiple neuropsychological ability areas including language, memory, spatial skills, executive function and processing speed. It is well recognized that epilepsy can have a profound disruptive effect on cognitive function, but it is yet unclear how epilepsy alters the interrelationship among these diverse cognitive systems. This study used graph theory to analyze the community structure of the cognitive networks in adults with temporal lobe epilepsy compared with healthy subjects. Methods: An extensive neuropsychological test-battery was administered to 82 patients with temporal lobe epilepsy and 100 age and gender matched healthy controls. The test battery assessed multiple cognitive domains including intelligence, academic skills, language, verbal and visual memory and multiple aspects of executive function and cognitive/psychomotor speed (Table 1). For each group (patients and controls), we constructed an adjacency matrix representing the pair-wise correlation coefficient adjusted for age between the raw scores obtained in each possible combination of tests. All tests were adjusted to reflect a higher score for better performance, and only positive correlation coefficients were maintained. A weighted non-directed graph was constructed from each adjacency matrix where each node corresponded to a behavioral test and each link corresponded to the correlation coefficient between the tests. Only links with a correlation coefficient greater than 0.7 were maintained, and the community structure from each graph was calculated. The spatial distribution of nodes representing their inter-relationship was plotted using a Force Atlas algorithm and modularity was qualitatively assessed. Results: The cognitive networks from patients and controls are demonstrated in Figure 1. We observed a community structure composed of fewer, larger, and more mixed modules in TLE participants characterized by three main modules representing close relationships between: 1) aspects of executive function and verbal and visual memory, 2) speed and fluency and 3) speed, executive function, perception, language, intelligence, and nonverbal memory. Conversely, controls exhibited a relative division between cognitive functions, which segregated into more numerous and smaller modules consisting of 1) verbal memory, 2) language, perception, intelligence, 3) speed and fluency, and 4) visual memory and executive function. Conclusions: Adults with temporal lobe epilepsy demonstrate a cognitive network landscape where the segregation between multiple cognitive domains is less clear and poorly structured. This panorama suggests a higher degree of interdependency across multiple cognitive domains in patients with epilepsy, possibly indicating a compensatory mechanism to overcome functional impairments.