Inclusion Criteria:

• Age, ≥ 18 years old.
• Must speak English as primary language.
• Must have an informant who can provide an independent evaluation of functioning.
• Bilingual patients and ethnic and racial minorities whose primary language is English will be eligible.
• Each new patient must present with a chief complaint of progressive impairment of speech or language and must have evidence of AOS documented by a speech-language pathologist during routine clinical evaluation.
• At study entry, all patients must have speech sufficiently intelligible for a confident diagnosis of AOS, dysarthria, and/or aphasia, and for acoustic analysis.
• Patients with aphasia will be included, as long as AOS is also present, regardless of whether the aphasia or AOS is more dominant (i.e., patients with aphasia, but without AOS, will not be eligible).
• Patients with dysarthria will be included as long as the aphasia and/or apraxia of speech is more prominent.

Exclusion Criteria:

• Any patient whose speech is not intelligible enough for confident speech-language diagnosis.
• 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 dementia).
• Patients with aphasia, but without apraxia of speech will be excluded.
• Patients with dysarthria who do not have PAOS, or whose dysarthria at study entry is more severe than PAOS, will be excluded.
• 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.
• 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).
• Patients will be excluded if they do not have an informant, or do not consent to the research.