I just read a report that in a study involving fruit flies, Belgian investigators have discovered that the normal function of the amyloid precursor protein (APP) is to stimulate the growth of nerve paths in the brain. This may aid in recovery after brain injury. From Reuters Health:
The researchers found that human APP and its fruit fly counterpart, APPL, promoted nerve cell branching in the brains of mature fruit flies. Brain injury in the fruit fly stimulated APPL in nerve cells – and fruit flies genetically engineered to lack APPL showed increased mortality after traumatic brain injury.