Implicit and explicit memory retrieval within and across the disconnected cerebral hemispheres

The authors report that the divided right and left cerebral hemispheres are both adept at priming, a type of implicit memory, and that subcortical routes can mediate implicit memory retrieval across the hemispheres. Two individuals with complete section of all forebrain commissures, L.B. and N.G., were given tests of recall and recognition (explicit memory) and stem-completion priming (implicit memory). The right and left hemispheres of N.G. and the left hemisphere of L.B. exhibited significant intrahemispheric priming. Interhemispheric priming was similar in extent to intrahemispheric priming. Under several intra- and interhemispheric conditions, significant implicit retrieval occurred in the face of abnormal explicit retrieval, Because all forebrain commissures had been severed in L.B. and N.G., interhemispheric priming was necessarily supported by subcortical structures. The observed dissociation between explicit and implicit memory performance indicates that the routes of interhemispheric transfer vary with type of memory retrieval.