Insulin resistance, hyper-insulinemia and products associated to insulin metabolism can affect the amyloid cascade and promote the onset of Alzheimer`s disease or aggravate the condition, in early or old age regardless of the development of type 2 diabetes. The changes described in pathological studies and molecular research, classify two types of mechanism involved with cognitive impairment in these cases: one related to cerebrovascular events due the action of vascular risk factors, and the other more controversial, non-cerebrovascular mechanism involving the interaction of insulin with Aβ in the entorhinal cortex and hippocampus, as well as its synaptogenesis action that involves signaling of intracellular molecular paths in the modulating of neurotransmitters such as acetylcholine, norepinephrine and glutamate receptors. Based on a literature review, the role of insulin in the Central Nervous System is examined along with its participation in the amyloidogenesis process in progression to Alzheimer Disease.