Compelling preclinical and clinical evidence supports a pathophysiological connection between
Alzheimer’s disease (AD) and diabetes. Altered metabolism, inflammation, and insulin resistance are
key pathological features of both diseases. For many years, it was generally considered that the brain
was insensitive to insulin, but it is now accepted that this hormone has central neuromodulatory func-
tions, including roles in learning and memory, that are impaired in AD. However, until recently, the
molecular mechanisms accounting for brain insulin resistance in AD have remained elusive. Here, we
review recent evidence that sheds light on how brain insulin dysfunction is initiated at a molecular
level and why abnormal insulin signaling culminates in synaptic failure and memory decline. We
also discuss the cellular basis underlying the beneficial effects of stimulation of brain insulin
signaling on cognition. Discoveries summarized here provide pathophysiological background
for identification o