Nonverbal memory functioning following right anterior temporal lobectomy: a meta-analytic review

PURPOSE: Studies investigating nonverbal memory functioning following right anterior temporal lobectomy (RATL) in patients with intractable temporal lobe epilepsy have resulted in conflicting findings, as nonverbal memory deficits have been reported for some, but not all patients. To examine the association between nonverbal memory deficits and RATL, the present study employed meta-analytic principles in a quantitative review of the literature. METHODS: Thirteen studies, reporting pre- and postoperative nonverbal memory performance for a total of 324 RATL patients, were identified. Effect sizes were calculated to measure the extent of nonverbal memory deficit in patients following RATL. Additionally, effect sizes for primary studies comprising a common dependent variable were combined using standard meta-analytic procedures. RESULTS: Of the 22 dependent variables utilized to assess nonverbal memory, 14 indicated postoperative declines in functioning while 8 demonstrated postoperative improvements in performance. All resultant effect sizes were relatively small. Mean effect sizes calculated for dependent variables used in multiple studies identified the Warrington Recognition Memory Test for Faces as the only nonverbal memory measure which produced consistent results. CONCLUSIONS: Overall, the collective findings demonstrate the inability of the current research to provide any consistent evidence as to the nature of nonverbal memory outcome following RATL. Problems with nonverbal memory measures are discussed and suggestions for future research are proposed.