Conspicuous changes in both brain histology and behavior are hallmarks of Alzheimer's disease (AD). Microscopically, the AD brain is defined by the presence of two types of aberrant structures: extracellular amyloid plaques and intraneuronal neurofibrillary tangles, both of which are made up of extremely insoluble, densely packed filaments. Amyloid-β (Aβ) peptides for plaques and tau for tangles are the soluble building components of these formations. Amyloid-peptides are proteolytic fragments of the transmembrane amyloid precursor protein, whereas tau is a microtubule-associated protein found in the brain that is abundant in axons. The formation of plaques and tangles in the brain correlates with behavioral symptoms of Alzheimer's disease, and these symptoms are a direct result of the damage and loss of synapses that mediate memory and cognition. Synapse loss can occur when live neurons fail to retain functional axons and dendrites, or when neurons die. Over the last ten years, a growing amount of research has suggested that soluble forms of Aβ and tau function in unison.