Abstracts

As part of clinical neuropsychological evaluation of patients with epilepsy, verbal and visuospatial spans are tested to assess attention in the verbal and nonverbal modalities. Our verbal task requires subjects to repeat strings of digits (digit span), while the visuospatial one requires that they repeat sequences of taps on an array of blocks (block span). The two tasks are analogs of each other and thus are identical except for modality. Patients[rsquo] scores are interpreted as indicating side of epileptogenic focus (worse performance on digit span = left side; worse performance on block span = right side), and informally they seem to yield useful clinical information about focus laterality and the effect of surgery. However, a rigorous analysis of data has not been carried out to validate this clinical impression, nor is data available on possible effects of gender or relative difficulty of the two tasks.
We tested 30 healthy subjects (15 men) on the spans tests and on verbal and nonverbal tests known to be sensitive to gender. We compared performance of men to women on the digit vs. block tasks, and on verbal fluency and a mental rotation test as control tasks. From our files, we extracted data from patients with a clearly lateralized temporal-lobe focus and grouped results according to side of epileptic abnormality based on EEG, MRI and subsequent surgery. Effects of side of focus and subsequent surgery were analyzed.
Digit spans were significantly higher than block spans in healthy subjects, but men and women did not differ (although they did differ on mental rotation). The patients showed the same superiority on the verbal task as did the healthy subjects. However, they did not differ according to side of focus, nor did their performance change after surgery.
We had predicted overall better performance on digits than on blocks and this was confirmed, suggesting that the digit task is intrinsically easier. However, within an overall superiority for digit span, we also expected an interaction in healthy subjects that would reflect a greater visuospatial facility in men; this was not borne out. This finding was particularly striking given that the same subjects showed a gender effect on a mental rotation task. The lack of laterality effect in our patients was surprising given the polarized nature of the tasks. This highlights a fundamental difference between memory and attention tasks; possible factors contributing to this result will be discussed.
[Supported by: Operating grant from Canadian Institutes of Health Research to M. Jones-Gotman and V. Sziklas]