Abstracts

We have previously raised a question whether the well-known hemispheric difference in memory function might be process-specific as well as material-specific^1,2; i.e., related to both novelty vs. familiarity and verbal vs. nonverbal material. To test this question using neuroimaging, recognition memory must be used; our prior results with patients used recall. We have developed a single recognition memory protocol to be used in both clinical and neuroimaging research. We use 4 types of stimulus dichotomized along verbal/nonverbal and novel/familiarity dimensions (abstract words, nonsense words, drawings of objects and abstract designs). For each stimulus type, the task consists of two learning/recognition trials and a delayed recognition trial. The fMRI task differs from that used in clinical research primarily in that it uses a block design for item presentation (alternating blocks of stimuli and baseline items), includes a simple perceptual decision task (is item primarily [ldquo]straight[rdquo] or [ldquo]curvy[rdquo]) to ensure fixation during encoding, and does not use an interference task between learning and delayed recognition. Comparability of the two versions was assessed with groups of matched neurologically healthy participants (fMRI vs. clinical version; N=35 and N=18, respectively). A small sample of individuals with either primarily left- or right-sided temporal lobe (TL) epilepsy was tested using the clinical version. Our results show that healthy individuals demonstrate significant learning over the two first trials, with little-to-no forgetting following a delay. ANOVAs revealed: 1) no effect of version; 2) main effect of novelty (familiar [gt] novel); 3) main effect of material ([ldquo]nonverbal[rdquo] [gt] verbal); 4) main effect of trial. Significant interactions showed poor initial learning of novel material (with bigger improvements on Trial 2), and better overall recognition of drawings of objects. Preliminary results with a small sample of patients suggests that those with a left TL focus improve much more on learning novel than familiar material, whereas those with a right TL focus show little change over trials. We have developed a simple yes-no recognition memory protocol allowing study of material- and process-specific learning/retention using an almost identical paradigm in fMRI or clinical testing. The clinical and fMRI versions of the task appear directly comparable with respect to memory performance. To our knowledge, this represents the first learning/memory protocol using an identical paradigm, potentially yielding complementary information about brain regions active during memory compared with the result of focal lesions. The novelty/familiarity dimension yielded a large effect, confirming the importance of this factor in learning, and may be particularly salient in elucidating laterality effects in temporal-lobe epilepsy.
¹Majdan et al. [italic]JCEN[/italic] (1996)[underline];[/underline]18[underline]:[/underline]416-30
²Jones-Gotman et al. [italic]Neuropsychologia[/italic] (1997);35:963-73 (Supported by Canadian Institutes of Health Research.)