Abstracts

RATIONALE: Although there is evidence to support the potential usefulness of face memory tests in the assessment of right hemisphere function, the clinical utility of current tests has been questioned. The aim of this study was to investigate the sensitivity of a new face learning and memory test to right temporal lobe function. As a first step in determining the clinical utility of this test we wanted to show that it was sensitive to the integrity of the right temporal lobe structures. Therefore, we tested patients with resection from a temporal lobe because the areas of brain lesion are clearly delineated in operated subjects. As healthy subjects can remember faces well after a single exposure, the Twins Test uses foil faces that are only slightly different from their respective targets, thereby increasing the difficulty of the task. This allowed examination of learning across more than one trial.
METHODS: Seventy-two subjects participated in this study (19 Left Temporal resection [LT], 17 Right Temporal resection [RT], 36 Healthy subjects [NC]). Twelve faces were shown four times, for learning. Recognition trials occurred after the first presentation (single exposure recognition: SER), after the fourth presentation (4ER) to examine learning, and after a 24hr delay. Each recognition trial contained the 12 target faces and 12 foil faces that were only slightly different from the target items. Scores were number of correctly identified plus correctly rejected faces (max. score = 24 per trial).
RESULTS: The RT group performed significantly worse than the NC (p=0.007) and LT groups (p=0.007). There was no difference between the LT and NC groups (p=0.06). All groups performed significantly better on the FER trial than on the SER trial (p[lt]0.001), and than on the 24hr delay(p[lt]0.01). Performance after 24hr delay was significantly better than on the SER trial (p[lt]0.001). The ability of the test to correctly classify individual patients to the side of temporal lobe resection was examined. Optimal test sensitivity and specificity ratings were obtained using a combined averaged score from the 4ER and 24hr delay trials and a cut-off score of 18. The test correctly classified 82% of RT patients (sensitivity), and correctly rejected 79% of LT patients (specificity).
CONCLUSIONS: These results are in concordance with earlier findings supporting a dominant role of the right temporal lobe in face processing. In addition, the Twins Test is sensitive to right temporal lobe function within individuals, and should therefore prove useful in clinical practice. We are currently studying the sensitivity and specificity of this test in unoperated epilepsy patients whose temporal lobe status is known from EEG and volumetric MRI. Preliminary data from these patients will be discussed.
Support: Research supported by Grant MT144991 from the Canadian Institute of Health Research to M. Jones-Gotman.