Neuropsychological Aspects of Epilepsy Surgery

Abstract

Only a small number of patients with epilepsy undergo a neurosurgical operation in which the area from which epileptic neurons generate seizures is removed. From a neuropsychological perspective several different assessments and outcomes are being looked at. Chapter 2 deals with research on the Wada test. In this test, the language-dominant hemisphere can be assessed and can be predicted which individuals are at risk for post-surgical global amnesia. The Wada test is thought to be sensitive to bilateral dysfunction of the critical memory function in the temporomesial area. We tried to do the reverse. If the Wada test showed a lower memory score in one hemisphere, could this be related to the side of focus? We applied logistic regression in which we included four variables: both memory scores after injection, memory of a story told before injection, and an attention score. With this set of variables the side of a focus can be classified in 85% of the patients. Additionally, false prediction results in a slightly lowered chance of becoming seizure free. The neurosurgeon has the option of operating under local anaesthesia in which the operation can be carried out without damaging the language areas. In chapter 3 we looked at cognitive differences between both procedures six months after surgery. We found a relationship between the extent of the removed brain tissue in the superior temporal gyrus under general anaesthesia and a lowered verbal IQ and verbal comprehension. In chapter 4 we described a study on differences in auditory rhythm perception in both cerebral hemispheres. It is known that longer visual rhythms are better (holistically) processed by the right hemisphere. We used a rhythm test which consisted of 30 pairs of rhythms varying in length. We expected that the removal of brain tissue in right-sided resections should lead to a diminished recognition of longer rhythms. This appeared to be the case. Chapter 5 deals with the effects of an operation on intelligence. It is known from literature that half a year after left temporal lobe surgery verbal intelligence shows a slight decrease and performal intelligence shows less increase after right surgery than after left temporal lobe surgery. We followed now patients 6 years after surgery (with assessments after six months, two years and six years). This study showed that the decrease of verbal IQ after left temporal lobe surgeries is undone after two years. From two to up to six years this IQ shows an increase of up to normal values. Chapter 6 is devoted to long term follow-up of verbal memory. This function is purported to be a risk function in left temporal lobe surgery. The study revealed a specific group at risk. This group consists of patients with mesiotemporal sclerosis with an atrophic hippocampus. Verbal acquisition and consolidation in general shows an ongoing decrease up to two years after surgery, but the verbal memory of patients with a diagnosis of mesiotemporal sclerosis shows an ongoing decrease up to six years after surgery.