Authors :
Presenting Author: Aaron Struck, MD – University of Wisconsin School of Medicine and Public Health
Camille Garcia-Ramos, PhD – Neurology – University of Wisconsin School of Medicine and Public Health; Kevin Dabbs, MS – Neurology – University of Wisconsin School of Medicine and Public Health; Veena Nair, PhD – Radiology – University of Wisconsin School of Medicine and Public Health; Vivek Prabhakaran, MD, PhD – Radiology – University of Wisconsin School of Medicine and Public Health; David Loring, PhD – Emory University; Conant Lisa, PhD – Neurology – Medical College of Wisconsin; Binder Jeffrey, MD – Medical College of Wisconsin; Marybeth Meyerand, PhD – Medical Physics – University of Wisconsin School of Medicine and Public Health; Bruce Hermann, PhD – Neurology – University of Wisconsin School of Medicine and Public Health
Rationale:
Administration of IQ tests to children and adults with epilepsy is a longstanding tradition in the neuropsychology of epilepsy. With few exceptions, these tests were not constructed on the basis of conceptual models of “intelligence.” While advances in the field of individual differences occurred over decades, epilepsy research remained agnostic to the use of a meaningful biological or conceptual characterization of general cognitive ability, instead relying on existing measures purporting to assess “intelligence.” Spearman noted the intercorrelation among diverse measures of cognitive ability (“positive manifold”) and demonstrated that a general ability factor (g) represented the major underlying dimension of cognitive performance. Research has shown that g can be identified in global cognitive datasets, has long-term predictive significance for important life outcomes, with demonstrated heritability and underlying neuroimaging signatures. Yet to date, we are unaware of any investigation of g in epilepsy despite its long history in the general field of individual differences and extended history of IQ research in epilepsy.
Methods:
Participants included 114 patients with TLE and 83 controls between the ages of 19 -60. Traditional psychometric tests and subtests from the NIH ToolBox Cognition Battery were used to assessing language, visuoperception, memory, executive function, and psychomotor and processing speed. Factor analysis identified the primary underlying factor g. We then: 1) contrasted g in TLE vs controls, 2) correlated g with clinical seizure features and sociodemographics, 3) examined the explanatory power of g compared to specific cognitive domains in TLE vs control comparisons, and 4) correlated g with brain structural and resting state network features.
Results:
Findings include: 1) significantly (p< 0.005) lower g in TLE than in controls, 2) significant associations of g with clinical seizure features (lower g with earlier age of medication onset, greater ASM number, longer duration [p’ < 0.04]) and sociodemographics (lower g with less parental education, greater deprivation [p’s < 0.012]), 3) comparing TLE to control participants on cognitive measures independent of the construction of g, and using g as a covariate, only processing speed discriminated groups, and 4) among TLE participants, g was linked to total adjusted intracranial volume (ICV) (p= .019), age and ICV adjusted total tissue volume (p= 0.019), age and ICV adjusted total corpus callosum volume (p= 0.012) - particularly posterior, mid-posterior and anterior (p’s < 0.022) regions. FreeSurfer vertex analyses revealed increasing g with greater local gyrification in the bilateral medial orbitofrontal regions. Network analysis of resting state data with focus on the participation coefficient showed g to be positively associated with the superior parietal network.