Abstracts

Rationale: Accelerated long-term forgetting (ALF) refers to a new type of memory impairment characterised by normal learning and recall after short delays, but impaired recall at long delays. ALF has mainly been documented in patients with temporal lobe epilepsy (TLE). It has been proposed that in patients with TLE, ALF may be secondary to impaired initial learning. Studies involving patients with focal extra-temporal epilepsy (ETE) are scarce. Yet, extratemporal cortex is involved in long-term memory storage, and seems to have little role in initial learning. The current study examines the impact of initial learning and site of epilepsy focus on long-term verbal memory in patients with focal TLE and ETE. Methods: Participants included 22 patients with epilepsy (TLE = 12; ETE = 10) and 28 normal controls (NC). Patients were asked to learn a list of 12 words to criterion: a perfect recall of words on 2 consecutive trials, with a maximum of 12 trials. Recall of the list was tested at a short (30 min) and long (1 day, 7 days) delays. Results: Patients with TLE were significantly less likely to reach criterion compared to the NC participants (?2 (1) = 9.64, p = .002) and patients with ETE (?2 (1) = 4.02, p = .04) who did not differ from the NCs (?2 (1) = 0.83, p = .77). A one-way analysis of variance showed that the groups differed in the number of learning trials (F[2, 47] = 3.78, p = .03); the TLE, but not the ETE group, requiring significantly more learning trials relative to the NC group (p = .03). Greater number of learning trials was related to fewer words recalled at 1 day and 7 days (r = -.35, p = .01, and r = -.35, p = .01, respectively), but not with the number of words recalled at 30 min (r = -.13, p = .36).A Group [NC, TLE, ETE] x Delay [30-min, 1 day, 7 days] repeated measure analysis of covariance (with the number of learning trials as covariate) revealed a significant interaction (F(4, 90) = 3.03, p = .021). Post-hoc analysis showed that both epilepsy groups recalled significantly fewer words at 1 day (TLE, p = .01; ETE, p = .03) and 7 days (TLE, p = .007; ETE, p = .010), but not at 30 min, relative to controls. Hence, both TLE and ETE groups showed ALF. Conclusions: Patients with focal TLE and ETE are at risk of ALF, which is not explained by impaired initial learning. Standardised neuropsychological tests are sensitive to deficits in initial learning, but not to ALF. Changes to our standard memory testing protocols are needed to detect long-term memory deficits that currently remain undiagnosed and untreated. Funding: Not applicable