The impact of right temporal lobe epilepsy on nonverbal memory: meta-regression of stimulus- and task-related moderators

Nonverbal memory tests have great potential value for detecting the impact of lateralized pathology and predicting the risk of memory loss following right temporal lobe resection (TLR) for temporal lobe epilepsy (TLE) patients, but this potential has not been realized. Previous reviews suggest that stimulus type moderates the capacity of nonverbal memory tests to detect right-lateralized pathology (i.e., faces > designs), but the roles of other task-related factors have not been systematically explored. We address these limitations using mixed model meta-regression (k = 158) of right-lateralization effects (right worse than left TLE) testing the moderating effects of: 1) stimulus type (designs, faces, spatial), 2) learning format (single trial, repeated trials), 3) testing delay (immediate or long delay), and 4) testing format (recall, recognition) for three patient scenarios: 1) presurgical, 2) postsurgical, and 3) postsurgical change. For presurgical patients the size of the right-lateralization effect was significantly moderated by stimulus type (faces > designs), testing format (recall > recognition) and its interaction with the learning format (repeated trials more affected by format effect than single trials) of the nonverbal memory tests. For postsurgical patients and presurgical-postsurgical change, test format moderated the size of the right-lateralization effect (recognition > recall) and this explained and overshadowed effects of stimulus type (i.e., faces > designs). This comprehensive review reveals the value of recognition testing in gauging the risk of nonverbal memory decline.