Abstracts

Reduced volume of cerebral white matter has been reported in temporal lobe epilepsy (TLE). A core neurobehavioral consequence of white matter abnormality reported in other clinical populations (eg., multiple sclerosis, closed head injury) is a reduction in information processing speed. The purpose of this investigation was to examine information processing speed performance in TLE and its relationship to volumetric measures of cerebral white matter and clinical seizure variables.
Subjects included 31 patients with TLE and 24 healthy controls, comparable in age, education, and gender. As expected, TLE patients had a significantly lower IQ (103 vs 93, p[lt].05). Subjects were administered the Sternberg paradigm, a well-known task that assesses the speed of information processing of items in short-term memory. Dependent variables included response accuracy, reaction time, and information processing speed defined as the latency of response as a function of increasing memory load. In addition to examining group differences, the relationship between performance and cerebral white matter volume was assessed
TLE patients exhibited significantly slower reaction time (p[lt].01) and poorer accuracy (p[lt].05) compared to controls, which becomes more evident with increased processing demands. Among TLE subjects, slower processing speed was associated with increasing duration of epilepsy (r= .47, p[lt].05) and polytherapy (r= .45, p[lt].05 ). Quantitative volumetric MRI data was available for a consecutive series of 18 control and 27 TLE subjects, including volumes of total cerebral gray and white matter. TLE subjects were dichotomized into two groups based on a median split of white matter volume and their Sternberg performance compared. TLE subjects with smaller cerebral white matter volumes exhibited significantly slower speed of information processing (steeper slope) compared to healthy controls (p[lt].01) and TLE patients with normal white matter volumes. These same patients also demonstrated poorer accuracy than the control group.
Information processing capacity is reduced in TLE. Specifically, TLE subjects demonstrated disproportionately slower processing speed performance as demands on memory load increase. In addition, there appears to be a relationship between features of information processing ability and clinical seizure features (duration of epilepsy, AED polytherapy) as well as the volume of cerebral white matter. Volumetric reduction of cerebral white matter therefore appears to have distinct neurocognitive correlates.
[Supported by: NIH grants RO1-37738 and MO1 RR03186]