The Neurobiology of Two Distinct Types of Progressive Apraxia of Speech

Inclusion Criteria: 1. All enrolled patients must be over the age of 18, speak English as their primary language, and have an informant who can provide an independent evaluation of functioning. 2. Each new patient must present with a chief complaint of progressive impairment of speech and must have evidence of AOS documented by a speech-language pathologist during routine clinical evaluation. 3. At study entry, all patients must have speech sufficiently intelligible for a confident diagnosis of AOS, dysarthria, and/or aphasia, and for acoustic analysis. Exclusion Criteria: 1. Any patient whose speech is not intelligible enough for confident speech-language diagnosis will be excluded from the study. 2. All patients with concurrent illnesses that could account for speech deficits (e.g., traumatic brain injury, strokes, developmental syndromes), and patients meeting criteria for another neurodegenerative disease (e.g., Alzheimer's type dementia57), will be excluded. 3. Patients with aphasia or dysarthria who do not have PAOS, or whose aphasia or dysarthria at study entry is more severe than PAOS, will be excluded. 4. All women who are pregnant, or post-partum and breast-feeding, will be excluded as they are unable to undergo the required imaging. All women who can become pregnant must have a pregnancy test no more than 48 hours before the DaTscan. 5. Patients will also be excluded if MRI is contraindicated (e.g., metal in head, cardiac pace maker), 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). 6. Patients will be excluded if they do not have an informant, or do not consent to the research.