Abstracts

Rationale: Epilepsy patients often report memory deficits in the setting of normal objective testing, suggesting that available measures are insensitive or that non-mnemonic factors are involved. The Visual Paired Comparison Task (VPCT) is based on novelty preference, the tendency to fixate on novel images as opposed to previously viewed items, reflecting recognition memory for the “old” images. As novelty preference is a sensitive measure of hippocampal-dependent memory function, we predicted impaired VPCT performance in epilepsy patients compared to healthy controls.

Methods: During the VPCT, identical pictures were shown side by side ("encoding trial"). After a delay, two pictures were displayed; one was an image from a previous encoding trial, and one was a novel image ("recognition trial"). We assessed 26 healthy adult controls and 31 epilepsy patients (16 focal-onset, 13 generalized-onset, 2 unknown onset) with the VPCT using 40 image sets at delays of 2 or 30 seconds between encoding and recognition (Figure 1A-B). Fifteen healthy controls and 17 epilepsy patients (10 focal-onset, 5 generalized-onset, 2 unknown onset) completed the task at 2-, 5-, and 30-minute delays, with 24 image sets at each delay (Figure 1c). Infrared camera-based eye tracking measured fixations. A “novelty preference score” was calculated, reflecting the percentage of time a subject fixated on the novel image relative to the total fixation time ([fixation time_new/fixation time_new+old] * 100) during recognition. Using a one-sample t-test, mean novelty preference scores were compared to 50%, the value expected should there be no preference for viewing either novel or old items during recognition. Subjects also performed standard memory measures, including the Medical College of Georgia (MCG) Paragraph Test, California Verbal Learning Test Second Edition (CVLT-II), and Brief Visual Memory Test-Revised (BVMT-R).

Results: The epilepsy group was high functioning, with greater estimated IQ (p = 0.041), greater years of education (p = 0.034), and higher BVMT-R scores (p = 0.024) compared to controls. Novelty preference was intact in healthy controls at 2-second (p ≤ 0.001), 30-second (p ≤ 0.001), 2-minute (p = 0.003), and 5-minute delays (p ≤ 0.001), with a decline in performance at 30 minutes (ns). The epilepsy cohort, as well as focal- and generalized-onset subgroups, had intact novelty preference at 2- and 30-second delays (p ≤ 0.001), but were impaired at 2-, 5-, and 30-minute delays (ns; Table 1).

Conclusions: Memory for the “old” items decayed more rapidly in overall, focal-onset, and generalized-onset epilepsy groups. The VPCT detected deficits while standard memory measures were largely intact, suggesting that the VPCT may be a more sensitive measure of temporal lobe memory function than standard neuropsychological batteries.

Funding: This study was supported by Career Development Award number IK2 CX-001255-01 from the U.S. Department of Veterans Affairs Clinical Sciences R&D (CSRD) Service (BAL).