Abstracts

Rationale:
Whilst group studies provide some support for the material specific model of memory function, there are considerable individual variations in memory function in people with temporal lobe epilepsy, even in those with the same underlying pathology. We examined the sensitivity and specificity of a single measure of an individual’s relative strength for the encoding of verbal or visual learning.
Method:
732 patients with unilateral hippocampal sclerosis (HS) n=314 Right; n =418 Left, completed verbal and visual encoding tasks with similar structures. A Memory Specialisation Index (MSI) was calculated by subtracting the Visual Learning Z score from the Verbal Learning Z score. A positive value on the MSI indicates a relative strength in verbal learning. A negative score indicates a relative strength in visual learning.
Results:
The sensitivity of the MSI to LHS was 0.50 with a specificity of 0.70.  The sensitivity of the MSI to RHS was 0.34 with a specificity of 0.79. In patients with LHS, the MSI was significantly correlated with age and duration of epilepsy. Older patients who had a longer duration of epilepsy were more likely to demonstrate a similar level of impairment in both verbal and visual encoding.
Conclusion:
Our Memory Specialisation Index provides a measure with high specificity for the laterality of HS. The pattern of strengths and weaknesses in visual and verbal encoding may evolve with age and duration of epilepsy and clinicians should be aware of these factors when interpreting the neuropsychological profile of presurgical patients.
Funding:
:No funding was received in support of this study