The present invention relates to devices, systems, and methods for improving memory and/or cognitive function by brain delivery of compositions of small interfering RNA or vectors containing the DNA encoding for small interfering RNA. Such compositions can be administered using devices, systems and methods for direct delivery of the compositions to the brain, or using devices, systems, methods of delivery, and compositions that deliver small interfering RNA or vectors containing the DNA encoding the small interfering RNA across the blood-brain barrier. The present invention also provides valuable small interfering RNA vectors, and methods for reduction of BACE1 levels in the hippocampus, cerebral cortex, or other regions of the brain that have beneficial effects on improving memory and/or cognitive function in a subject.