This study is designed to learn more about overall tau burden in the brain of patients with Primary Progressive Aphasia (PPA) and Frontotemporal Dementia.

Primary progressive aphasia (PPA) is an umbrella term that encompasses a group of neurodegenerative syndromes characterized by varying combinations of progressive speech and language problems. Three clinical variants of PPA have been described and are well recognized: the agrammatic variant characterized by grammatical errors in speech and writing and typically associated with phonetic errors in speech; the semantic variant characterized by poor naming from loss of knowledge about the meaning of words; and the logopenic variant characterized by word retrieval problems and poor sentence repetition from impairment of working memory and phonemic errors. Pathological studies of PPA patients that died with postmortem examination of their brains have demonstrated that PPA is associated with a number of different abnormal cellular proteins that do not have perfect associations with the three PPA variants. One such protein is the microtubule associated protein, tau, which is the most common abnormal protein found in the brains of patients with PPA. Tau is an important protein that has been linked to the neurodegenerative process in many diseases. No neuroimaging studies have investigated tau deposition in PPA and hence the binding characteristics of AV-1451 (the Tau binding drug used in this study) in PPA are unknown. Understanding the binding characteristics of AV-1451 is crucial to help determine whether it can serve as a biomarker for tau deposition in the brains of patients with PPA.

FTD or Frontotemporal Dementias, including bvFTD, will also be included in this study.

Inclusion Criteria:

• Must be over the age of 18
• Must speak English as your primary language
• Must have an informant who can provide independent evaluation of functioning
• Must present with a chief complaint of progressive impairment of speech/language or changes in behavior
• Must fulfill diagnostic criteria for Primary Progressive Aphasia or Frontotemporal Dementia

Exclusion Criteria:

• Any subject who is mute or whose speech is unintelligible will be excluded
• All subjects with concurrent illnesses that could account for speech and language deficits, such as traumatic brain injury, strokes or developmental syndromes, and subjects meeting criteria for another neurodegenerative disease, such as amnestic Alzheimer's type dementia, dementia with Lewy bodies, progressive supranuclear palsy, and corticobasal syndrome will be excluded
• All pregnant, post-partum and breast-feeding women will be excluded
• Subjects will also be excluded if MRI is contraindicated (metal in head, cardiac pace maker, etc.), if there is severe claustrophobia, if there are conditions that may confound brain imaging studies (e.g. structural abnormalities, including subdural hematoma or intracranial neoplasm), or if they are medically unstable or are on medications that might affect brain structure or metabolism,(e.g. chemotherapy).
• Subjects who meet criteria for PPA and have mild behavioral changes, eye movement abnormalities or mild limb apraxia but who do not meet diagnostic criteria for, progressive supranuclear palsy or corticobasal syndrome respectively, will also be excluded.
• Subjects will be excluded from the study if they have any of the following genetic conditions which can increase the chance of cancer: Cowden disease, Lynch syndrome, hypogammaglobulinemia, Wiskott-Aldrich syndrome, and Down's syndrome.