The goal of this study is to examine olfactory function in preclinical subjects or individuals with neurological diseases such as Probable Alzheimer's Disease (PRAD), Frontotemporal Dementias (FTD), Dementia with Lewy Bodies (DLB), Traumatic Brain Injury (TBI), and Amyotrophic Lateral Sclerosis (ALS).

The goal of this study is to examine olfactory function in preclinical subjects [n = 150] or individuals with neurological diseases such as Probable Alzheimer's Disease (PRAD) [n = 50], Mild Cognitive Impairment [n = 50], Frontotemporal Dementias (FTD) [n = 50], and Dementia with Lewy Bodies (DLB) [n = 50] that are part of the Longitudinal Research Cohort of the Massachusetts Alzheimer's Disease Research Center (IRB Protocol #: 1999P003693), are being treated by neurologists in the Memory Disorders or Movements Disorders Clinics at MGH, or are part of the community. The investigators will also examine individuals with Amyotrophic Lateral Sclerosis (ALS) [n = 50], ALS probands [n = 50], and ALS family controls [n = 50] that are part of the Neurological Clinical Research Institute (NCRI) protocols "NeuroBANK" (2013P001670), "Repository" (2006P000982), and "Longitudinal CSF" (2011P000785). Olfactory data will be correlated with existing data collected under the above-mentioned IRB protocols. The investigators will also be studying olfactory function in patients with mild TBI [n=50], and moderate and severe TBI [n=50], that are patients of Spaulding Rehabilitation Network. Specifically, the investigators will assess odor discrimination, odor identification, and episodic olfactory memory, using the OLFACT olfactometer run by a laptop or through a wireless iPad interface (Osmic Enterprises). Olfactory data collected from patients and age-matched control subjects [n = 100] will be correlated with existing structural MRI, functional MRI, and PET imaging data and with existing neuropsychological data collected under IRB protocols 1999P003693 and 2007P002107 ("Neurological Disease Registry"), NeuroBANK™ IRB protocol 2013P001670, Repository IRB protocol 2006P000982, and Longitudinal CSF IRB protocol 2011P000785.

Inclusion Criteria:

• Diagnosis of Probable Alzheimer's Disease, prodromal Alzheimer's Disease, Frontotemporal Dementia, Mild Cognitive Impairment, or Dementia with Lewy Bodies or mild and moderate/severe TBI.
• Diagnosis of familial or sporadic ALS per El Escorial Criteria or individuals with known gene mutations associated with ALS (regardless of clinical phenotype).
• Age-matched controls
• Males and females with a minimum age of enrollment of 18 years. There is no maximum age of enrollment.

Exclusion Criteria:

• Primary pulmonary disease such as severe emphysema or asthma not under good medical control.
• Current sinusitis or common cold or upper respiratory infection, nasal polyps, or sinusitis.
• Traumatic or congenital anosmia
• Current or recent (past 6 months) alcohol or substance dependence. A prior history of alcohol or substance abuse will not be grounds for exclusion.
• Pregnancy
• Severe cognitive dysfunction
• Pneumocephalus
• Basilar skull fracture
• Known CSF leak
• Facial fractures to include Lefort I, II or III

1. Diagnosis of Probable Alzheimer's Disease, prodromal Alzheimer's Disease, Frontotemporal Dementia, Mild Cognitive Impairment, or Dementia with Lewy Bodies or mild and moderate/severe TBI.
2. Diagnosis of familial or sporadic ALS per El Escorial Criteria or individuals with known gene mutations associated with ALS (regardless of clinical phenotype).
3. Age-matched controls
4. Males and females with a minimum age of enrollment of 18 years. There is no maximum age of enrollment.