Emotion Study/Substudy: Flexible Brain Study

Inclusion Criteria: Young adults * aged 18-35 years of age * native English speaker * at least 8th grade education * generally physically and neurologically healthy as determined by the Health Demographics Screener * eligible for MRI as determined by the MRI Eligibility Interview (including not being pregnant) * scores within normal limits on a cognitive screener (MoCA) * no indication of serious psychiatric disturbance including major depression (based on Mental Health Screener) * willing and able to give informed consent Inclusion Criteria: Older adults * age 55-100 years of age * native English speaker * at least 8th grade education * generally physically and neurologically healthy as determined by the Health Demographics Screener * eligible for MRI as determined by the MRI Eligibility Interview * no indication of dementia based on score of 30 or above on the Telephone Interview for Cognitive Status and nonimpaired score on the Montreal Cognitive Assessment (MoCA -- score of 22 and above) * no indication of serious psychiatric disturbance including current major depression (based on Mental Health Screener) * willing and able to give informed consent Inclusion Criteria: Parkinson patients * must meet criteria for diagnosis of idiopathic Parkinson disease according the UK Brain Bank by a movement trained neurologist. * age 55-100 years of age * native English speaker * at least 8th grade education * generally physically and neurologically healthy other than Parkinson disease * eligible for MRI as determined by the MRI Eligibility Interview * no indication of dementia based on cognitive screening measures (TICS -- score of 30 or above, and MoCa -- score of 22 and above) * no indication of serious psychiatric disturbance including current major depression * willing and able to give informed consent Inclusion Criteria: Individuals with SCD and a family history of dementia or Alzheimer's disease * age 55-100 years of age * native English speaker * at least 8th grade education * generally physically and neurologically healthy as determined by the Health Demographics Screener * eligible for MRI as determined by the MRI Eligibility Interview * no indication of dementia based on score of 30 or above on the Telephone Interview for Cognitive Status and nonimpaired score on the Montreal Cognitive Assessment (MoCA -- score of 22 and above) * no indication of serious psychiatric disturbance including current major depression (based on Mental Health Screener) * willing and able to give informed consent * community-dwelling with subjective report of cognitive complaints with scores \>16 on the Cognitive Change Index (CCI-20) * no evidence of dementia or mild cognitive impairment based on cognitive screening using the MoCA; scores must fall within normal limits for age, education, and sex * no psychometric evidence of neuropsychological impairment on a modified Neuropsychological Battery from the NACC Unified Data Set, version 3 * score of 0 on the Global Clinic Dementia Rating (CDR) scale * normal functional behavior in terms of daily activities, based on the Functional Activities Scale (FAQ) * availability of an informant (over the phone) who can provide information about the participant's complaints using the informant version of the CCI-20, and corroborate normal activities of daily living on the FAQ and the CDR scale. Exclusion Criteria: * Pregnant or possibly pregnant * Claustrophobia * Large pieces of metal in the body, particularly in the face and neck. * Piercings or metal implants that cannot be removed from the body * Surgery on the brain or any prior serious brain damage or disease * Dementia or severe cognitive disorders * use of antipsychotics, sedatives, or other medications with significant anticholinergic properties (due to potential influence on memory) * use of prescribed 'memory enhancing' medications such as Aricept or Namenda.