The development of biomarkers is now especially critical, as there are a number of promising disease-modifying therapies entering early phase clinical trials, with additional novel therapeutic strategies in development. It is essential to develop biomarkers that can detect a "signal of efficacy" over a relatively short time frame for use in Phase II trials. Ideally biomarkers are needed that can reliably detect the earliest brain alterations due to AD pathology, perhaps at a point when there is synaptic dysfunction but not yet widespread neuronal loss. Functional neuroimaging, in particular functional MRI (fMRI), has significant potential, having already shown promise in detecting regionally specific pharmacological effects on memory related neural activity, and as a sensitive marker of very early cognitive impairment.