Abstracts

Many studies have shown that memory for words is sensitive to resection from the left temporal lobe. The Abstract Word List learning test (AWL) and the Rey Auditory Verbal Learning Test (RAVLT) are currently used in the Montreal Neurological Institute as measures of verbal learning and memory. In addition, learning and memory for the content of a short prose passage are evaluated with a Story Learning test. These measures allow us to better differentiate patient groups. However, we have noted that some patients showed an unexpected pattern: they demonstrated a good retention for abstract and concrete words but a deficit in memory for the story. The aim of the present study was to determine which group(s) of patients exhibits this particular memory deficit. A further aim was to determine the specific validity of these three tests in patients with epilepsy before and after surgery.
We studied patients who were admitted in the last ten years in our institute with either unilateral or bilateral epilepsy of either the temporal or frontal lobe. All were administered the AWL, RAVLT and Story Learning tests before or/and after surgery. Selection criteria were: age between 16 and 56 years old, IQ of 75 or above, right-handed with left hemisphere speech dominance. Variables of interest were the side of epileptic focus (EEG) and lesion (MRI), the site of eventual resection, and pre vs follow-up performance. The RAVLT measure was the delayed-recall score 30 min after 5 learning trials. The AWL measure was the delayed recall score 24 hr after four learning trials. The Story Learning retention measure was the 24-hr delayed recall of a short prose passage that had been learned to a strict criterion.
Data analyzed to date show that left temporal (LT) patients perform significantly worse than right temporal (RT) patients on recall of concrete and abstract words in preoperative and follow-up assessment. Moreover, before and after surgery, the AWL is clearly the more sensitive and specific measure. Patients with frontal-lobe focus showed no retention deficits at either time, except a few left frontal cases with mild difficulty retaining abstract words. Interestingly, in this sample, we found no significant difference between LT and RT patients on story recall preoperatively but a clear difference after surgery. Further, a cluster analysis showed that the unexpected pattern (good recall for abstract and concrete words but deficit in story recall) appeared only in some patients with clear right temporal focus. The reason for this surprising result will be explored.
We have uncovered a specific deficit in certain RT patients of forgetting a story (while showing the expected good memory for word lists). We also demonstrate that the AWL is a more sensitive measure than RAVLT in LT epilepsy. Our results underline the importance of examining different aspects of verbal learning and memory with specific tools to increase the discriminative power of memory tests.
[Supported by: Canadian Institutes of Health Research]