Early Onset Alzheimer Disease (EOAD) and Late Onset Alzheimer Disease (LOAD) share the same pathological features and are considered the same disorder affecting people at different ages, under 65years for EOAD, over 65years for LOAD. Whether the different pathological burden could influence also synaptic plasticity mechanisms has never been addressed yet. The aim of our study is to investigate the neurophysiological characteristics of these patients through transcranial magnetic stimulation protocols, comparing with two control groups, respectively old healthy and young healthy age-matched subjects. To verify this hypothesis we evaluated a group of 22 sporadic EOAD and 33 LOAD for plasticity induction of LTP/LTD-like effects using respectively intermittent TBS (iTBS) or continuous TBS (cTBS). Central cholinergic activity was evaluated by means of short afferent inhibition (SAI) protocol. Patients, both EOAD and LOAD, showed an impairment of LTP mechanisms while healthy controls, showed a normal profile of cortical plasticity. SAI protocol results show a positive correlation between SAI dysfunction and aging, reflecting acetylcholine role in aging. The central cholinergic pathway seems to be affected more by age than by the disease process itself. LTP mechanisms are altered in AD patients despite the age, thus representing a reliable marker of disease.