To test whether exogenous NRG1 improves congnitive function in AD post-symptomatically, control lentiviruses (LV-control) and lentiviruses expressing full-length rat β1α NRG1 type I (LV-NRG1/I) or type III (LV-NRG1/III) under the CMV promoter were generated and stereotaxically injected into the hippocampus of 7-month old female line 41 transgenic mice expressing a mutated human APP (APP-Tg)25 and female non-TG control littermates. Here, APP is linked to Alzheimer disease.