Abstracts

Rationale: Greater prevalence of atypical language representation (≈30% patients vs. 5% controls) has been observed in right handed adults with childhood onset epilepsy and normal MRI. It is unknown whether reorganization is driven by seizure activity or due to underlying substrate. We compared the laterality index (LI) of a new onset pediatric epilepsy population to controls to determine whether atypical language is present at epilepsy onset. Methods: 17 age-matched (mean age 7.9, range 4-11), right handed patients (12 M) and controls (8 M) underwent BOLD fMRI (3T) and neuropsychological testing. Patients had a left hemisphere seizure focus with habitual seizure onset <1 year and normal structural MRI. Lifetime number of seizures ranged from 3 to daily in the first year. Subjects completed an auditory description decision task (ADDT). Task was controlled for primary auditory processing, attention, and motor responses, and selected based on subject’s developmental level. ROI analysis of IFG and Wernicke’s Area (WA) was conducted using the LI Toolbox bootstrap method. Atypical language (AL) for each area was defined as LI<0.20. Results: IQ was comparable for controls (FSIQ=109) and patients (FSIQ=104). Controls had higher IFG mean LI (0.62 vs. 0.08; p<.01). There was a trend for WA mean LI (0.63 vs. 0.35; p=0.09). 12% of controls had atypical language in IFG and WA. Patients had a higher incidence of AL for IFG (47%, p<.05) and WA (41%, p=.07). AL in controls only occurred if <6 years. AL in patients >6 years also decreased, but rates are comparable to adult literature for IFG (36%) and WA (27%). Over age 6, there was stronger lateralization for IFG and WA, with lower IFG mean LI in patients (0.80 vs. 0.24; p<.01), but differences were no longer significant for WA (Control 0.73 vs. Patient 0.54 (p=.22)). Correlation analyses revealed no significant associations between number of lifetime seizures or IQ and laterality (p>0.05). Conclusions: A greater incidence of atypical language representation is evident at onset of epilepsy suggesting that underlying substrate rather than seizure activity drives reorganization of language networks. Regional and age-related differences in mean LI and %AL suggest that frontal systems may have greater capacity for plasticity across a larger age range than posterior language systems. Atypical language is more likely in younger children regardless of epilepsy, which supports a general developmental trajectory of greater plasticity of language function until age 6.