Investigations into the cognitive functioning of subjects with epilepsy in relation to anticonvulsant medication.
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The literature on epilepsy is vast. The first review in this thesis presented a short introduction to the nature of the disease and its relationship to cognitive functioning. The pharmacological treatment of epilepsy by three major anticonvulsant drugs (carbamazepine, sodium valproate and phenytoin) and the possibility of effects of this treatment on cognitive functioning is presented in the second review. This review identified certain areas of cognitive functioning, for example memory, that warrant further investigation. A third review discussed those relevant areas of cognitive functioning, including both theory and suitable methodologies for investigating working memory and attentional resources. The three review chapters provided theoretical and practical frameworks to carry out investigations of the effects of anticonvulsant medication on cognitive functioning. Four experimental studies are presented. The design of the first study was a between-groups comparison, in which four groups of subjects with epilepsy (three on monotherapy and a polytherapy group) and a control group were compared on a battery of memory tests. The only significant group difference was the impaired performance of the polytherapy group compared to the control group. The second study was a between-groups comparison of the performance of four groups with epilepsy (three on monotherapy and one untreated group) and one control group, on a new battery of tests measuring working memory and attentional resources. The sodium valproate group was significantly impaired on two of the working memory tasks compared to the control group. No other group differences were found and increasing task complexity did not significantly affect the drug groups compared to the control group. Of interest in both study one and two was the consistent pattern of results across the test batteries, which did not produce significant differences between the groups. Both studies revealed large variance in the clinical subject groups, such that a number of the subjects with epilepsy, particularly on sodium valproate and phenytoin were performing very poorly compared to control group performance. No obvious reasons were identified for the poor performance. Study three investigated the effects on cognitive functioning of a new anticonvulsant drug (Lamotrogine). The clinical subject group was very impaired compared to a control group, and a small amount of further impairment was present after the subjects began taking Lamotrogine. The fourth study piloted tests designed to measure aspects of perceptual and motor functioning. The only significant result obtained was that the polytherapy group performed significantly worse compared to the control and the monotherapy groups on simple reaction time tasks. The focus of the discussion chapter was a summary of the important aspects of the studies in the thesis with comparisons made to other studies in the published literature.
Thesis, PhD Doctor of Philosophy
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