Abstracts

RATIONALE: The association between verbal memory impairment and left hippocampal sclerosis is well known. In this study, we sought to determine whether there might be parallel or independent relationships between lateral temporal lobe gliosis and verbal cognitive abilities in patients with left temporal lobe epilepsy.
METHODS: Lateral and mesial temporal lobe tissue from 50 patients who underwent standard left temporal lobectomy was examined to determine hippocampal pathology grade (Wyler criteria) and the degree of intracortical gliosis (avg. number of GFAP reactive astrocytes per 400X field) in the anterior middle temporal gyrus. These pathology measures were examined in relation to preoperative neuropsychological test performance. All subjects were left hemisphere dominant for language and had no MRI scan evidence of structural lesion other than hippocampal sclerosis.
RESULTS: The degree of left temporal lobe intracortical gliosis correlated significantly (and inversely) with performance on measures of verbal learning (CVLT Total Words Learned, r=-.38) and immediate memory for semantically structured verbal information (WMS Logical Memory immediate, r=-.33; Paired Associate Learning of easy items, r=-.52; Serial Clustering ratio, r=.49). These relationships were significant after controlling for grade of hippocampal pathology. Hippocampal sclerosis grade correlated significantly with measures of learning and immediate memory (CVLT Total Words, r= -.31; Logical Memory Immediate, r= -.27; unrelated Paired Associates, r=-.37) and retention of this information after a 20-30 minute delay (CVLT Long Delay Free Recall, r=-.44; Delayed Logical Memory, r=-.42), but not with Serial Clustering Ratio (r=-.20, ns). Temporal lobe intracortical gliosis did not correlate significantly with any of the delayed recall measures, although there was a trend (p=.08) for lower recall of the semantically related (r=-.27), but not the unrelated, paired verbal associates.
CONCLUSIONS: These findings suggest a partial dissociation between components of verbal memory that may be referable to the mesial and lateral temporal lobe. Lateral temporal lobe pathology is associated with reduced immediate recall, especially for semantically related or meaningful information. Retention of newly learned information after a short delay interval is more dependent on the hippocampus.
Support: Epilepsy Foundation Junior Investigator Research Grant.