Memory impairment following right hemisphere stroke: a comparative meta-analytic and narrative review.

We examined the evidence for widely held clinical beliefs about memory impairment following right hemisphere stroke (RHS), conducting both narrative and meta-analytic reviews of the literature [MEDLINE (1966-January 2003), PsycINFO (1974-January 2003), and CINAHL (1982-December 2002)]. We sought to determine whether RHS patients experience more problems with non-verbal memory than non-stroke controls (NSCs) and left hemisphere stroke (LHS) patients. Secondarily, we sought to determine whether RHS patients experience more problems with verbal memory than NSCs and fewer verbal memory problems than LHS patients. We also examined the effect of type of memory assessment (recall versus recognition) on reported findings. As regards non-verbal memory, narrative and meta-analytic reviews found that RHS patients had deficits relative to NSCs, on tests of both recall and recognition. The evidence for RHS non-verbal memory deficits relative to LHS was mixed in the narrative review, whereas the meta-analysis found RHS deficits on non-verbal recognition tests, but no difference between RHS and LHS patients on non-verbal recall tests. Deficits on recognition tests imply problems with early encoding of material or possibly its storage. Regarding verbal memory, the narrative review found that RHS patients performed more poorly than NSCs in about half of all studies. The meta-analytic review confirmed poorer RHS performance on tests of verbal recall, but none of the studies that compared RHS and NSCs on verbal recognition could be included in this type of review. The narrative review found mixed evidence as regards the performance of RHS and LHS patients on verbal memory tests, but the meta-analysis pointed to RHS superiority for both verbal recall and recognition. The relative strengths of both types of review are discussed.