Several different dementias, including FTD, are characterized by the presence of neurofibrillary tangles (NFTs) in the brain. Tangles are composed of abnormal clumps of a normally soluble protein called tau. It is not clear what changes tau from its normal form to its abnormal form in the brain of patients with FTD, but preventing this from happening is likely to stop brain cells from dying. This approach is called aggregation inhibition and it is the basis of a recent clinical trial that received world-wide press coverage this year. Commercially available dyes called cyanine dyes have been shown to dissolve artificial tau fibrils in a number of studies, and one of these dyes is already in clinical use as an imaging agent so this type of drug has potential to be used in people. We propose to assess whether one of the dyes can dissolve or prevent the formation of abnormal tau fibrils formed in living brain tissue from a mouse with FTD. This one year study will demonstrate the conditions under which a lead compound improves FTD in brain tissue which would support the future development of better cyanine dye drugs, and support the idea that aggregation inhibition is a worthwhile therapeutic approach that would benefit from identification of other lead compounds.