Alzheimer's disease (AD) is an age-related, progressive degenerative disorder that is characterized by synapse and neuron loss in the brain and the accumulation of protein-containing deposits (referred to as 'senile plaques') and neurofibrillary tangles. Insoluble amyloid [beta]-peptide (A[beta]) fibrillar aggregates found in extracellular plaques have long been thought to cause the neurodegenerative cascades of AD. However, accumulating evidence suggests that prefibrillar soluble A[beta] oligomers induce AD-related synaptic dysfunction. The size of A[beta] oligomers is distributed over a wide molecular weight range (from < 10 kDa to > 100 kDa), with structural polymorphism in A[beta] oligomers of similar sizes. Recent studies have demonstrated that A[beta] can accumulate in living cells, ...