Abstracts

Patients with chronic seizure disorder are at increased risk for academic achievement deficits; however, the relation of neurophysiological abnormality to these deficits is not well known. We used magnetoencephalography (MEG) to examine the functional status of brain mechanisms for language in patients with chronic epilepsy and reading achievement deficits, and the manner in which seizure variables affect this status. MEG data was collected while 83 patients (IQ [gt] 69; age 9 - 56 yrs.) performed a continuous recognition memory task for concrete nouns presented auditorily. Patients raised either the right or left index finger (counterbalanced across patients) for a repeated stimulus. Sources of late (post N1m resolution) MEG activity were modeled as equivalent current dipoles at 4 ms intervals; MEG scans were co-registered with structural MRI scans using fiducial markers. An index of interhemispheric asymmetry of activation in perisylvian language areas in the left hemisphere and homologous areas of the right hemisphere was formed as: r - l / l + r. All patients underwent pre-surgical evaluation, including 24-hour VEEG, MRI, and neuropsychological testing. Patients were identified as reading deficient if the reading score on the Wide Range Achievement Test was [lt] 25% ile. Among patients with left hemisphere seizure onset (n = 58) those with reading achevement deficits (n = 18) exhibited a greater degree of bilateral activation during the MEG task than the non-impaired group, F(3,54) = 11, p [lt] .002, (see Fig. 1). Results were unchanged when Full Scale IQ was used as a covariate to control for global intellectual disability.[figure1]Within the left hemisphere group with seziures of cryptogenic etiology (n = 33) the degree of atypical (bilateral) language representation was independently related to age at onset (partial r = .50, p [lt] .003) and age at MEG scan (partial r = .53, p [lt] .002), with earlier onset and increasing age associated with a greater degree of right hemisphere engagement during the MEG language task. Reading achievement deficit in chronic epilepsy of left hemipshere origin is associated with abnormal activation of left hemipshere areas during a task previously shown to be valid for localizing language cortex. In a subgroup of these patients with cryptogenic etiology this abnormality is greater with earlier onset and longer duration of the disorder. (Supported by NINDS grant NS37941 to A.C. Papanicolaou.)