Is there a semantic impairment following resection in temporal lobe epilepsy?
Semantic memory refers to the store of meaning that we attach to words, objects and people – and is critical in language and nonverbal activities. These include finding the names of objects and people (which is a common complaint after temporal lobe resection). A number of neurological disorders damage a brain region called the anterior temporal lobe. Studies of these patients show that this region is very important for semantic memory. This is the part of the brain that is removed in some patients who undergo resection as treatment for intractable epilepsy. There are almost no detailed studies of semantic memory in such patients whilst general clinical neuropsychological assessments are not designed to assess semantic memory.
The aims of this EA-funded project were to develop sensitive measures of semantic memory and to run these in an initial group of patients with temporal lobe resection (for the treatment of their epilepsy).
In this EA-funded project we started with assessment materials that had been developed for patients with other neurological conditions whom have known semantic impairment. From these many assessments, we selected a battery of materials designed to measure semantic memory in a careful and accurate way. These measures tested comprehension of both words and pictures, as well as using semantic memory to generate object names and also knowledge of how to use everyday objects. All tests measured the participants’ accuracy and a subset also measured the time required to complete each test.
Our patient recruitment is ongoing but we have just completed the assessment of the tenth participant. The results from this first set of people are very clear. On simple measures of semantic memory, their performance falls within the normal accuracy range. However, the timings indicate that this good accuracy is not mirrored by speed, as the patients are around 2-3 times slower than normal to complete the task. On more strenuous tests of semantic memory the patients begin to show reduced accuracy as well. This pattern is shown by every individual we have tested so far. The conclusion of the study to date is clear – semantic memory is mildly impaired in patients with resection for temporal lobe epilepsy.
Publication: Lambon Ralph MA, Ehsan S, Baker GA, Rogers TT. (2012) Semantic memory is impaired in patients with unilateral anterior temporal lobe resection for temporal lobe epilepsy. Brain. 2012 Jan;135(Pt 1):242-58.