Standardized Ginkgo biloba leaf extract has been used in clinical trials for its beneficial effects on brain functions,particularly in dementia.Substantial experimental evidences indicated that Ginkgo biloba leaf extract (EGB) protected neuronal cells from a variety of insults.We investigated the effect of EGB on cognitive ability and protein kinase B (PKB) activity in hippocampal neuronal cells of dementia model rats.Rats received an intraperitoneal injection of D-galactose to induce dementia.Forty-eight Spraque-Dawley rats were randomly divided into six groups,including the control group,D-galactose group (Gal),low-dose EGB group (EGB-L),mid-dose EGB group (EGB-M),high-dose EGB group (EGB-H) and treatment group.The EGB-L,EGB-M and EGB-H groups were administered with EGB and D-galactose simultaneously.Y-maze,cresyl violet staining,TUNEL assays and immunohistochemistry staining were performed to detect learning and memory abilities,morphological changes in the hippocampus,neuronal apoptosis and the expressing level of phospho-PKB,respectively.Rats in the Gal group showed decreased abilities of learning and memory,and hippocampal pyramidal cell layer was damaged,while EGB administration improved learning and memory abilities.The Gal group exhibited many stained,condensed nuclei and micronuclei,either isolated or within the cytoplasm of cells (39.5±1.4).Apoptotic cells decreased in the groups of EGB-L (35.9±0.9),EGB-M (16.8±1.0) and EGB-H (10.1±0.8),and there were statistical significances compared with the Gal group.Immunoreactivity of phospho-PKB was localized diffusely throughout the cytosol of cells in all groups,while the immunoreactivity of the Gal group was weak.EGB significantly attenuated learning and memory impairment in a dose-dependent manner,while it could decrease the nmber of TUNEL-positive cells,and increase the activity of PKB.Our results demonstrated that EGB attenuated memory impairment and cell apoptosis in galactose-induced dementia model rats by activating PKB. Standardized Ginkgo biloba leaf extract has been used in clinical trials for its beneficial effects on brain functions, particularly in dementia. Substantial experimental evidences that Ginkgo biloba leaf extract (EGB) protected neuronal cells from a variety of insults. We investigated the effect of EGB on cognitive ability and protein kinase B (PKB) activity in hippocampal neuronal cells of dementia model rats. Rats received an intraperitoneal injection of D-galactose to induce dementia. Forty-eight Spraque-Dawley rats were differentiated into six groups, including the control group, D-galactose group (Gal), low-dose EGB group (EGB-L), mid- dose EGB group (EGB-M), high-dose EGB group , EGB-M and EGB-H groups were administered with EGB and D-galactose simultaneously. Y-maze, cresyl violet staining, TUNEL assays and immunohistochemistry were conducted to detect learning and memory abilities, morphological changes in the hippocampus, neuronal apop tosis and the expressing level of phospho-PKB, respectively. Rats in the Gal group showed decreased abilities of learning and memory, and hippocampal pyramidal cell layer was damaged, while EGB administration improved learning and memory abilities.The Gal group demonstrated many stained, condensed Apoptotic cells decreased in the groups of EGB-L (35.9 ± 0.9), EGB-M (16.8 ± 1.0) and EGB-H (10.1 ± 0.8 ), and there were statistical significances compared with the Gal group. Immunoreactivity of phospho-PKB was localized diffusely throughout the cytosol of cells in all groups, while the immunoreactivity of the Gal group was weak. EGB significantly attenuated learning and memory impairment in a dose -dependent manner, while it could decrease the nmber of TUNEL-positive cells, and increase the activity of PKB.Our results demonstrated that EGB attenuated memory impairment and cell apoptosis in galactose-induced dementia model rats byactivating PKB.