Delayed Reaction Time in Patients with Temporal Lobe Epilepsy.

Abstract

Purpose: Many reports have indicated that patients with temporal lobe epilepsy display a variety of cognitive impairments. The delay of reaction time is one of these impairments. However, it has been suggested that most of the tests used to measure cognitive function, such as reaction time, are influenced by motor speed. To clarify this ques‐ tion, we measured reaction times and carried out a Finger Tapping Test (FTT) in patients and controls, and differences in reaction time between these groups were analyzed after the motor speed component was removed. To avoid the influence of difference in stimulation and test difficulty, we measured 3 different reaction times. In addition, we investigated relationships between performance on these tasks and clinical characteristics to clarify factors related to these impairments. Methods: The subjects were 21 patients with temporal lobe epilepsy (mean age 31.8 years: mean duration of illness 14.5 years) and 11 normal controls (mean age 31.2years). All patients had received AEDs. All subjects were examined by auditory simple reaction time, visual simple reaction time, visual choice reaction time, and FTT. Student's t test was applied to each variable across the 2 groups. Analysis of covariance was then applied, by which the variance in reaction times between the 2 groups that could be attributed to the most simple measure of motor speed (FTT) was factored out. Spearman's correlation analysis was applied to investigate relationships between performance on these tasks and clinical characteristics Resulrs: Performance on all 3 reaction times, including auditory simple reaction time (p<0.05), visual simple reaction time (p<O.O1), and visual choice reaction time (p<0.05), were longer in patients than controls. FTT yielded a significant (p<O.O1) inter‐group difference. When the variance in reaction times attributable to a simple measure of motor speed were factored out, differences in performance on visual simple reaction time (F=5.51, p<0.05) and in performance on visual choice reaction time (F=3.88, p<O.I) persisted. There was a significant positive correlation between performance on the FTT and seizure frequency (rs=O.48, p<0.05), as well as dosage of AEDs (rs= 0.65, p<O.Ol). Conclusions: Our results suggest that the delayed reaction time in patients with temporal lobe epilepsy was not only due to reduction of motor speed but also due to impairment of other cognitive processes. It is generally accepted that many patients have some kind of cognitive impairments and many factors such as seizure, epileptic discharge, AEDs, and others may influence cognitive function. In present study it is indicated that delayed reaction time is due to several cognitive processes. Impairments of motor speed may have a relation to seizure frequency and dosage of AEDs. Several prior reports have indicated that some AEDs affect motor function. Our findings may reflect such a relationship.