1. women and men ages 18-80, 2. with MDD, of at least 12 weeks duration, according to Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria confirmed by the Mini International Neuropsychiatric Interview (MINI; Sheehan et al, 1998), 3. have a Montgomery-Asberg Depression Rating Scale (MADRS
•Montgomery and Asberg, 1979) score of at least 20 at screen and baseline as assessed by site clinicians, 4. meet criteria for TRD during the current major depressive episode documented in the MGH Antidepressant Treatment History Questionnaire (ATRQ) (Chandler et al., 2010), which will be defined as being non-responders (less than 50% of symptom improvement) to two or more depression treatment trials of adequate dose and duration as defined by the MGH ATRQ, 5. are currently on an antidepressant of adequate dose (as defined by the MGH ATRQ) and duration (at least 8 weeks), with the antidepressant dose being stable over the past four weeks, and with documented (in the MGH ATRQ) non-response (less than 50% improvement) to the current antidepressant. 6. Patients who have passed the MGH CTNI remote assessment, with documentation provided to sites by MGH CTNI. 1. pregnant or breastfeeding women, women of childbearing potential who are not using an accepted means of birth control, or women with a positive urine pregnancy test, 2. patients who have received treatment with rTMS, aripiprazole, electroconvulsive therapy (ECT), or venlafaxine during the current episode, 3. patients who express an objection to receiving treatment with at least one of the three treatment arms of our study, 4. patients with any history of bipolar disorder or psychosis (diagnosed by MINI), 5. patients with active alcohol or substance abuse disorders within the past 6 months (diagnosed by MINI), 6. patients with suicidal ideation of the degree that, in the opinion of the evaluating clinician, participation in the study would place them at significantly increased risk of suicide, 7. patients with unstable medical issues of such degree that, in the opinion of the evaluating clinician, participation in the study would place them at significant risk of a serious adverse event, or patients with a screening hemoglobin A1c level greater than 7.5%, or patients with epilepsy, dementia, Parkinson's disease, or Huntington's Disease, 8. patients who have received treatment with vagus nerve stimulation (VNS), 9. patients who have not responded to more than five FDA-approved antidepressant treatment trials of adequate dose and duration during the current episode, or who did not respond to ECT in previous episodes 10. patients on excluded medications, 11. patients with a positive urine screen drug test for a substance for which they do not have a valid prescription for a valid medical reason, 12. patients with currently abnormal thyroid function tests, 13. patients who have received at least one dose of a monoamine oxidase inhibitor (MAOI) four weeks or less prior, and 14. for patients on concomitant psychotropic agents (anticonvulsants, benzodiazepines, hypnotics, opiates, triiodothyronine (T3), modafinil, psychostimulants, buspirone, melatonin, omega-3 fatty acids, folate, l-methylfolate, s-adenosyl methionine, lithium) not on the same dose for at least four weeks prior to study entry or who do not agree to continue at the same dose during the acute phase of the study. 15. Patients who do not meet safety criteria for TMS: history of seizures, cardiac pacemaker, DBS or VNS, brain aneurism clips or other metallic implants in the intracranial space. 16. Also excluded is an individual who has received any administration of ketamine in the current episode for the treatment of depression.

• Current primary diagnosis of nonpsychotic major depressive disorder.
• Stable antidepressant dose of no more than one antidepressant medication for 4 weeks and no anticipated changes during the study period.
• Stable doses of all concomitant medications for over 6 weeks.
• No more than two failed antidepressant trials of adequate dose and duration, as defined by ATRQ, in the current episode.
• Psychiatric co-morbidity posing safety risk.
• Pregnant or breastfeeding or plan to become pregnant over the ensuing 2 months following study entry or are sexually active and not using adequate contraception
• Exclusionary psychiatric conditions (such as substance dependence in the last 6 months, substance abuse in the last 2 months, or lifetime history of psychotic disorders.
• Unstable or terminal general medical condition (GMC).
• Concomitant medications that interact with L-leucine (e.g. sildenafil).
• Vagus nerve stimulation, ECT, or rTMS, or other somatic antidepressant treatment during current episode
• Inadequately controlled hypothyroidism.
• Therapy that is depression specific, such as CBT or Interpersonal Psychotherapy of Depression.
• Hypersensitivity to L-leucine
• Have Maple Syrup Urine Disease.

• Youth admitted to the inpatient unit at either site for a recent suicide attempt or significant suicidal ideation with a plan or intent.
• The youth and parent are able to complete assessments in English, and the youth is able to complete therapy.
• The youth currently exhibits psychosis.
• The youth currently exhibits mania.
• The youth is currently <85% of their ideal body weight.
• The youth is intellectually incapable of completing the study, e.g. has an intelligence quotient (IQ) < 70.

• Adults aged 18 years or older
• Individuals undergoing surgery of the medial foot, medial ankle, or medial leg for which the anesthetic plan includes an adductor canal nerve block 1. Any known deficit of the ipsilateral lumbar nerve roots, ipsilateral lumbar plexus, ipsilateral femoral nerve, obturator nerve or saphenous nerve including diabetic peripheral neuropathy 2. Any local disorder of the skin or otherwise where blockade is to be performed 3. Body mass index >50 4. ASA classification greater than 3 5. Allergy to amide local anesthetic medications 6. Pregnancy 7. Incarceration 8. Inability to understand study procedures including inability to understand the English language

• Women and men ages 18-65
• Current diagnosis of Major Depressive Disorder
• Able to read, speak, and understand English
• Antidepressant use within the last 8 weeks
• Active infection or uncontrolled autoimmune disease
• Currently on oral corticosteroids or active immune suppressive therapy (methotrexate, cyclosporine, anti-cytokines medications, etc).
• Current diagnosis of uncontrolled HIV, hepatitis C or significant immunodeficiency
• Alcohol or substance use disorder
• Positive urine drug test for illicit substances or substances used out of the context of prescription
• Cognitively unable to give informed consent
• Pregnant or breastfeeding women, women of childbearing potential who are not using an accepted means of birth control, or women with a positive urine pregnancy test
• History of seizure disorder
• Previous significant adverse reaction to escitalopram or bupropion
• History of non-response to adequate doses of escitalopram or bupropion XL
• Current use of concomitant psychotropic agents (anticonvulsants, benzodiazepines, hypnotics, opiates, triiodothyronine (T3), modafinil, psychostimulants, buspirone, melatonin, folate, l-methylfolate, s-adenosyl methionine, lithium) not on the same dose for at least four weeks prior to study entry or who do not agree to continue at the same dose during the acute phase of the study.
• Lifetime history of bipolar disorder, schizophrenia, schizoaffective disorder or other psychotic disorder
• Current anorexia nervosa or bulimia nervosa
• Suicidal ideation of the degree that, in the opinion of the evaluating clinician, participation in the study would place them at significantly increased risk of suicide
• Unstable medical issues of such degree that, in the opinion of the evaluating clinician, participation in the study would place them at significant risk of a serious adverse event

1. Diagnosed with MDD 2. Ages 18-65 will be included. 3. Ability to understand and willingness to provide written informed consent. 4. Willing to provide contact information. 5. Medical clearance with protocol-defined stress testing (in accordance with American College of Sports Medicine (ACSM) guidelines) from protocol approved medical personnel. Details of guidelines and related testing protocol are provided in the study Manual of Procedures. 6. Able to comprehend and communicate in English. 1. Have a medical condition contraindicating exercise participation 2. Are currently physically active
•defined as moderate intensity physical activity on 3 or more days per week for the last month 3. Currently receiving antidepressant medication treatment 4. Currently considered a high suicide risk and/or high risk for being unable to complete the study due to the need for psychiatric hospitalization, suicide attempts or suicidality, significant self-mutilation, or other self-injurious or destructive behavior based on the judgment of the site PI, medical personnel, or designee. 5. Pregnancy. 6. Current psychotic disorder. Other comorbid psychiatric diagnosis that, in the investigator's judgment, will pose a safety issue or make it difficult for the participant to understand or complete the intervention. 7. Anticipated circumstances over the 6-month course of the trial that would render the participant unlikely to complete the study in the judgment of the PI or designee. 8. Any reason not listed herein yet, determined by the PI, medical personnel, or designee that constitutes good clinical practice and that would in the opinion of the PI, medical personnel, or designee make participation in the study hazardous. 9. Are currently enrolled in another research study, and participation in that study contraindicates participation in the current study

1. Male and female adults. 2. Diagnosis of possible or probable AD by standard NIA criteria (McKahnn et al, 1984; McKhann et all, 2011) 3. Folstein MMSE 5-26 out of 30 4. Neuropsychiatric Inventory (NPI) agitation/aggression subscale score > 4. On each subscale (frequency X severity), a score higher than 4 represents moderate to severe symptoms. 5. Female patients need to be post-menopausal 6. Availability of informant; patients without an informant will not be recruited. Patients who lack capacity must have a surrogate. 1. Medical contraindication to lithium treatment or prior history of intolerability to lithium treatment. Contraindications to lithium in this study include: resting tremor causing functional impairment, history of falls in the last month, untreated thyroid disease or any abnormal thyroid function test (T3, T4, or TSH), creatinine level greater than 1.5 mg/100ml or a glomerular filtration rate less than 44ml/min/ 1.73m2; blood pressure > 150/90 mm Hg; heart rate < 50 bpm; unstable cardiac disease based on history, physical examination, and ECG. 2. Medications, in combination with lithium, known to have adverse renal effects, including therapeutic or higher doses of diuretics, i.e. hydrochlorothiazide greater than 25mg daily or furosemide greater than 10mg daily. Whenever feasible, patients receiving concomitant antidepressants or antipsychotics will be washed off these medications for at least 24 hours before starting lithium. Patients who do not wish to discontinue antipsychotics or antidepressants, typically because of family member/caregiver objection, will be allowed to enter the trial provided there is no contraindication to concomitant lithium use with that specific psychotropic medication. During the trial, patients will be permitted to receive lorazepam as needed up to 1 mg/day for anxiety/insomnia, and non-benzodiazepine hypnotics, e.g., zolpidem. 3. Current clinical diagnosis of schizophrenia, schizoaffective disorder, other psychosis, or bipolar 1 disorder (DSM-IV TR criteria). 4. Current or recent (past 6 months) alcohol or substance dependence (DSM-IV TR criteria). 5. Current major depression or suicidality as assessed by the study psychiatrist. 6. Suicidal behavior or dangerous behavior with serious safety risk or risk of physical harm to self or others. 7. Parkinson's disease, Lewy body disease, multiple sclerosis, CNS infection, Huntington's disease, amyotrophic lateral sclerosis, other major neurological disorder. 8. Clinical stroke with residual neurological deficits. MRI findings of cerebrovascular disease (smallinfarcts, lacunes, periventricular disease) in the absence of clinical stroke with residual neurological deficits will not lead to exclusion. 9. Acute, severe, unstable medical illness. For cancer, patients with active illness or metastases will be excluded, but past history of successfully treated cancer will not lead to exclusion. 10. QTc interval > 460 ms at the time of baseline EKG is an exclusion criterion for treatment. 11. Hypernatremia as determined by serum sodium level > 150 meq/L.

Inclusion Criteria Patients will be included if they: 1. are inpatients or outpatients; 2. are voluntary and competent to consent to treatment and research procedures according to ECT/MST attending psychiatrist; 3. have a MINI International Neuropsychiatric Interview diagnosis, Version 6 (MINI-6.0) diagnosis of non-psychotic MDD 4. are 18 years of age or older 5. have a baseline HRSD-24 score > or = 21; 6. are considered to be appropriate to receive convulsive therapy as assessed by an ECT attending psychiatrist and a consultant anaesthesiologist 7. are agreeable to keeping their current antidepressant treatment constant during the intervention; 8. are likely able to adhere to the intervention schedule; 9. meet the MST safety criteria [75]; 10. If a woman of child-bearing potential: is willing to provide a negative pregnancy test and agrees not to become pregnant during trial participation. Exclusion Criteria Patients will be excluded if they: 1. have a history of MINI diagnosis of substance dependence or abuse within the past three months; 2. have a concomitant major unstable medical illness; 3. are pregnant or intend to get pregnant during the study; 4. have a MINI diagnosis of any primary psychotic disorder 5. have a MINI diagnosis of obsessive compulsive disorder, or post-traumatic stress disorder deemed to be primary and causing more functional impairment than the depressive disorder 6. have probable dementia based on study investigator assessment; 7. have any significant neurological disorder or condition likely to be associated with increased intracranial pressure or a space occupying brain lesion, e.g., cerebral aneurysm; 8. present with a medical condition, a medication, or a laboratory abnormality that could cause a major depressive episode or significant cognitive impairment in the opinion of the investigator (e.g., hypothyroidism with low TSH, rheumatoid arthritis requiring high dose prednisone, or Cushing's disease); 9. have an intracranial implant (e.g., aneurysm clips, shunts, stimulators, cochlear implants, or electrodes) or any other metal object within or near the head, excluding the mouth, that cannot be safely removed; 10. require a benzodiazepine with a dose > lorazepam 2 mg/day or equivalent or any anticonvulsant due to the potential of these medications to limit the efficacy of both MST and ECT; 11. are unable to communicate in English fluently enough to complete the neuropsychological tests; 12. have a non-correctable clinically significant sensory impairment (i.e., cannot hear or see well enough to complete the neuropsychological tests).

• Have a Major Depressive Disorder (MDD) primary diagnosis
• Have a body mass index (BMI) of 18.0 to • Be willing and able to follow the study procedures and visits as outlined in the protocol (including agreeing not to enroll in any other clinical trials)
• Have inadequate responses to antidepressant therapy (ADT) in the current Major Depressive Episode (MDE)
• Additional criteria may apply
• Has any finding that would compromise the safety of the subject or affect their ability to adhere to the protocol visit schedule or fulfill visit requirements
• Has any other significant medical condition (eg, neurological, psychiatric, or metabolic) or clinical symptom that could unduly risk the subject or affect the interpretation of study data
• Has any current primary diagnosis other than MDD, where primary diagnosis is defined as the primary source of current distress and functional impairment
• Has experienced hallucinations, delusions, or any psychotic symptoms in the current MDE
• Has been hospitalized for MDD within 3 months before screening
• Has used opioid agonists (eg, codeine, oxycodone, tramadol, morphine) or opioid antagonists (eg, naloxone, naltrexone) within 14 days prior to screening
• Has received electroconvulsive therapy treatment within the last 2 years or within the current MDE or failed a course of electroconvulsive treatment at any time
• Has a significant risk for suicide
• Has a positive breath alcohol test at screening
• Has a positive test for drugs of abuse at screening or visit 2
• Is pregnant, planning to become pregnant, or is breastfeeding during the study
• Additional criteria may apply

The participants must meet the following criteria:
• Women aged 40-62 years who are perimenopausal or early postmenopausal (within 5 years of the last menstrual period if not surgically postmenopausal), including:
• Women who have experienced changes in menstrual cycle frequency or duration, and/or physical symptoms indicative of menopausal transition, as determined by clinician
• Women who are using hormonal IUDs (i.e. brands Mirena and Skyla), with FSH level > 20 mIU/m (as menstrual periods are irregular with IUDs that utilize hormones, making irregular/absent periods difficult to assess as related to the menopausal transition).
• Women with significant menopause-related physical symptoms, indicated by any of the following criteria:
• Greene Climacteric Scale total scores > 20
• Greene Climacteric Scale sub-score for vasomotor symptoms >3
• 5 or more bothersome hot flashes per week (self-reported)
• Women meeting DSM-5 criteria for current major depressive disorder (assessed by the SCID)
• Baseline HRSD score of ≥ 18
• Subject agrees to abstain from disallowed medications for the duration of the trial The participants must not meet any of the following criteria:
• Vulnerable populations (e.g. pregnant/nursing, severe cognitive or intellectual impairment, incarcerated)
• Pregnancy (determined by urine pregnancy test), intending pregnancy or breast feeding
• Psychiatric disorder other than MDD that is acute and the primary focus of symptom burden or treatment.
• History of bipolar disorder or psychotic disorder
• Current substance use disorder
• Positive baseline urine drug screen of an illicit substance with the exception of a medication used with a prescription such as an opioid pain medication
• Current eating disorder
• Treatment resistant depression (failure of 2 adequate antidepressant trials or electroconvulsive therapy (ECT) during current episode; adequate antidepressant trials are defined as within the US FDA approved dosage for the medication and used for at least 6 weeks, with failure described by the patient as <50% improvement based on her subjective experience). )
• High risk for suicidal acts including active suicidal ideation with plan and intent or > 2 suicide attempts in lifetime or any attempt in the past 6 months
• Women who have used psychoactive or centrally acting medications within 2 weeks prior to study screening
• Use of selective estrogen-receptor modulators (SERMs), hormone replacement therapy, hormonal contraceptives (hormonal IUDs allowed), episodic sleep medications (chronic, regular, stable-dose benzodiazepines and hypnotics such as zolpiderm, Sonata (Zaleplon), and Lunesta (Eszopiclone) OR sleep-seating antihistamines such as Unisom (Doxylamine succinate) or diphenhydramine allowed), and antidepressants within 2 weeks of the baseline visit and randomization.
• Use of natural menopause and depression supplements, phytoestrogens, soy-based medications, steroids within 2 weeks of baseline visit and randomization.
• Use of selective estrogen-receptor modulators (SERMs), hormone replacement therapy, hormonal contraceptives (hormonal IUDs allowed), natural menopause supplements, episodic sleep medications (chronic, regular, stable-dose benzodiazepines allowed), antidepressants, phytoestrogens, soy-based medications, steroids within 4 weeks of randomization
• Use of any disallowed medications (specified in the Excluded Concomitant Medication section below)
• Women who have received a gonadal hormonal intervention within 1 month prior to study entry (stable thyroid medications are allowed).
• Not using a medically approved method of birth control, if sexually active and not 12 or more months since last menstrual period (IUDs, condoms, abstinence are acceptable forms of contraception in this study; due to the possible interactions with the study medication, oral contraceptive pills will be prohibited)
• Uncontrolled hypertension (>160/95mmHg)
• Active Coronary artery disease, atrial fibrillation, stroke, deep vein thrombosis, pulmonary embolism or blood clotting disorder
• Any severe, life threatening or unstable medical condition that, based on clinician-judgment, would make participation in the study unsafe or inappropriate
• Personal or first- degree family history of known hormone sensitive tumors
• History of allergic reaction or side effects with prior pregnenolone use
• Clinically significant laboratory, physical examination
• Concurrent enrollment in another clinical trial Exclusion of Concomitant Medications:
• Selective estrogen-receptor modulators (SERMs)
• Hormone replacement therapy
• Hormonal contraceptives, excluding Mirena IUD or other IUD with localized progesterone
• Natural menopause or antidepressant supplements
• Episodic sleep medications (chronic, regular, stable-dose benzodiazepines and hypnotics such as zolpidem, Sonata (Zaleplon), and Lunesta (Eszopiclone) OR sleep-sedating antihistamines such as Unisom (Doxylamine succinate) or diphenhydramine allowed)
• Antidepressants used at indicated, therapeutic, FDA-approved doses (Note: sub-therapeutic dosages of antidepressants used for other indications will be permissible with the exclusion of SSRIs, SNRIs, and Wellbutrin).
• Phytoestrogens
• Soy-based medications or supplements

• Completed study ALK5461-217
• Be willing to abide by the contraception requirements as outlined in the study protocol
• Be willing and able to follow the study procedures and visits as outlined in the protocol
• Additional criteria may apply
• Pregnant, planning to become pregnant, or breastfeeding
• A positive urine drug test for drugs of abuse
• Poses a current suicide risk
• Additional criteria may apply

Criteria for Inclusion of participants: A potential participant will be eligible for participation in this study if the following criteria are met: 1. Male and female adult or youth aged 10 and older of any race or ethnicity. 2. Ability to speak, read, and understand English. However, the parent(s) or legal guardians of minors may either speak English or Spanish as the consenting process can be conducted bilingually. 3. A lifetime or a current diagnosis of a mood disorder based upon a semi-structured diagnostic interview. 4. Adults age 18 and older must be able to provide written informed consent; for youth younger than age 18, a parent or legal guardian must provide written informed consent, and the child or teen must provide written informed assent. Eligibility for Healthy Controls For comparison purposes, potential health control participants who do NOT have a psychiatric diagnosis will be enrolled as part of the healthy control arm of this study. 1. Male and female adult or youth aged 10 and older of any race or ethnicity. 2. Ability to speak, read, and understand English. However, the parent(s) or legal guardians of minors may either speak English or Spanish as the consenting process can be conducted bilingually. 3. Adults age 18 and older must be able to provide written informed consent; for youth younger than age 18, a parent or legal guardian must provide written informed consent, and the child or teen must provide written informed assent. Criteria for Exclusion of Participants A potential participant will NOT be eligible for participation in this study if any of the following criteria are met: 1. History of schizophrenia, schizoaffective disorders or chronic psychotic disorders based upon a semi-structured diagnostic interview. 2. Diagnosis of human immunodeficiency virus (HIV) or hepatitis B or C (human immunodeficiency virus (HIV) testing is not required for this study). 3. Unable to provide a stable home address and contact information. 4. Has any condition for which, in the opinion of the investigator or designee, study participation would not be in their best interest (including but not limited to cognitive impairment, unstable general medical condition, intoxication, active psychosis) or that could prevent, limit, or confound the protocol-specified assessments. 5. Requires immediate hospitalization for psychiatric disorder or suicidal risk as assessed by a licensed study clinician. Eligibility for Healthy Controls A potential Healthy Control participant will NOT be eligible for participation in this study if any of the following criteria are met: 1. A lifetime or a current history of a mood disorder based upon a semi-structured diagnostic interview. 2. Meets any exclusion criteria as part of the main D2K study interview.

• The patient must be currently be enrolled or plan to be enrolled on a COG therapeutic study that aims to examine neuropsychological, social, emotional, and/or behavioral functioning
• The patient must have receptive and expressive language skills in English, French, or Spanish; if a patient meets these criteria but the parent/guardian speaks a language other than English, French, or Spanish, the patient may still be enrolled and tested, and the parent-report measures should be omitted
• All patients and/or their parents or legal guardians must sign a written informed consent
• All institutional, Food and Drug Administration (FDA), and National Cancer Institute (NCI) requirements for human studies must be met
• Patients with a history of moderate to profound intellectual disability (i.e. intelligence quotient [IQ] =< 55) are not eligible for enrollment; PLEASE NOTE: Children with a prior history of attention deficit hyperactivity disorder (ADHD) or a specific learning disability (e.g. dyslexia) are eligible for this study

• Child participants will be adolescents (aged 12-17.11 years) admitted to an inpatient unit for a recent suicide attempt or significant suicidal ideation with a plan or intent. We define a suicide attempt, as per the Columbia Clinical Algorithm for Suicide Assessment (C-CASA), as "self-destructive behavior with inferred or stated intent to die."
• Participants must be English-speaking.
• Participants can have unipolar or bipolar disorder, conduct or oppositional disorder, eating disorder, or alcohol or substance use or abuse or dependence.
• Child participants to be excluded will be those with current psychosis, mania, <90% of ideal body weight, or IQ<70 (based on the age-appropriate Wechsler Intelligence Scale if concerns about intellectual capabilities are evident at assessment), as these conditions may require more intensive interventions or limit comprehension of the intervention components.

• Capacity for written informed consent
• Currently (or within the last 3 weeks) admitted to inpatient hospital for symptoms of mania.
• Primary Axis I diagnosis (DSM-5) at time of admission of bipolar I (single manic episode, most recent episode manic, or most recent episode mixed) OR schizoaffective disorder, bipolar type (manic or mixed state).
• Proficient in the English language.
• Available to attend follow-up visits.
• Substance- or medically-induced symptoms of mania at time of assessment.
• HIV infection or other immunodeficiency condition (such as receiving cancer chemotherapy).
• A serious medical condition that affects brain or cognitive functioning (e.g., epilepsy, serious head injury, concussion involving loss of consciousness, brain tumor, or other neurological disorder). Note that Hepatitis-C is not an exclusion criterion unless the participant has an acute infection.
• Diagnosis of Intellectual Disability or history of severe learning disorder.
• Diagnosis of alcohol or substance use disorder (moderate/severe) according to DSM-5 criteria within the last 3 months, or has a positive drug toxicity screen proximate to the time of recruitment.
• History of IV drug use.
• Participated in any investigational drug trial in the past 30 days.
• Pregnant, breastfeeding, or planning to become pregnant during the study period.
• Documented celiac disease (as such persons should be on a gluten-free diet as this is the standard care). Of note, we are not limiting the study to individuals with elevated levels of gliadin or casein antibodies as we intend to look at these levels as a predictor of response.

• Younger than 2 years (chronological age)
• Scheduled for anaesthesia that is expected to last at least 2 hours (and/or total operating room time is scheduled to be at least 2.5 hours)
• Has a legally acceptable representative capable of understanding the informed consent document and providing consent on the participant's behalf.
• Known neurologic, chromosomal or congenital anomaly which is likely to be associated with poor neurobehavioural outcome
• Existing diagnosis of behavioural or neurodevelopmental disability
• Prematurity (defined as < 36 weeks gestational age at birth)
• Birth weight less than 2 kg.
• Congenital cardiac disease requiring surgery
• Intracranial neurosurgery and intracranial craniofacial surgery (isolated cleft lip is not an exclusion)
• Previous cumulative exposure to general anaesthesia exceeding 2 hours
• Planned future cumulative exposure to anaesthesia exceeding 2 hours before the age of 3 years.
• Any specific contra-indication to any aspect of the protocol
• Previous adverse reaction to any anaesthetic
• Circumstances likely to make long term follow-up impossible
• Living in a household where the primary language spoken at home is not a language in which we can administer the Wechsler Preschool and Primary School Intelligence Scale
• Planned postoperative sedation with any agent except opioids (e.g. benzodiazepines, dexmedetomidine, ketamine, barbiturates, propofol, clonidine, chloral hydrate, and other non-opioid sedatives). For example if such sedation is planned for post-operative ventilation

• Participants must have at least one parent who meets the criteria for diagnosis of Bipolar I disorder (BD-I) or Bipolar II disorder (BD-II), as confirmed by the Mini International Neuropsychiatric Interview (MINI) administered to the parent. MINI will be administered to parent if the history of BD is endorsed by Family Index of Risk for Mood (FIRM) or other medical information (psychiatrist, medical records). The MINI can be administered to the parent remotely through the telephone or video call if an in-person interview is not feasible due to logistical reasons. A diagnosis Bipolar Disorder Not Otherwise Specified in the parent would not qualify for eligibility
• Participants must be either drug-naive, or on stable treatment for at least 4 weeks.
• Participants (and/or their parents as applicable) must sign an Informed Consent Form (ICF) allowing data collection and source data verification in accordance with local requirements and/or sponsor policy. Adolescents (minors) who in the judgment of the investigator are capable of understanding the nature of the study can be enrolled only after obtaining consent of a legally acceptable representative. Assent must be obtained from any participating adolescents (minors), if applicable
• Participants must be willing and able to complete self-reported assessments via mobile electronic device, and to wear a wrist actigraphy device for the duration of the study
• Diagnostic and Statistical Manual of Mental Disorders (DSM) -IV Diagnosis of bipolar I or bipolar II disorder
• DSM-IV Diagnosis of schizophrenia, schizophreniform or schizoaffective disorder
• DSM-IV Diagnosis of neurodevelopmental disorders
• An intelligence quotient (IQ) score less than (<) 80 as determined by Kaufman Brief Intelligence Test (K-BIT)
• Uncorrected hypothyroidism or hyperthyroidism

• Outpatient men and women age 18-65 years old with bipolar I, II, Not Otherwise Specified (NOS) disorder, or Schizoaffective Bipolar Type
• If diagnosed with Bipolar I, Bipolar NOS w/history of mania or Schizoaffective Disorder Bipolar Type, current mood stabilizer therapy (lithium, valproic acid, lamotrigine, gabapentin) with stable dose for > 28 days prior to randomization.
• Baseline Barrett Impulsiveness Scale-11 Score of > 62 (above average impulsivity)
• Systolic BP > 100 and < 165 and Diastolic BP > 60 and < 105 with no evidence of orthostatic hypotension
• Current Diagnosis of Alcohol Use Disorder with at least moderate severity
• Alcohol use of an average of 15 drinks per 7 days in the past 28 days prior to intake for men, and an average of 8 drinks per 7 day period in the past 28 days prior to intake for women
• Current mood stabilizer therapy with stable dose for > 28 days
• Fluent in English or Spanish
• Baseline Hamilton Rating Scale for Depression (HRSD) or Young Mania Rating Scale (YMRS) scores > 35
• Mood disorders other than bipolar I, II, NOS or schizoaffective disorder bipolar type (e.g. cyclothymic disorders, schizophrenia, schizoaffective disorder depressive type, or unipolar depression based on the SCID), other disorders, e.g. anxiety disorders, will be allowed.
• Current diagnosis of amphetamine or cocaine use disorder or a cocaine or amphetamine positive baseline urine sample.
• Evidence of clinically significant alcohol withdrawal symptoms
• Current treatment with an atypical antipsychotic
• Current treatment with naltrexone, acamprosate, disulfiram, or topiramate in the last 28 days
• Prior treatment with Aripiprazole within the last year or lifetime history of intolerable side effects to Aripiprazole
• Vulnerable populations (e.g. pregnant, nursing, cognitively impaired, incarcerated.)
• Evidence of clinically significant alcohol withdrawal symptoms defined as a CIWA-Ar score of ≥ 10.
• High risk for suicide
• Aspartate Amino Transferase (AST) or Alanine Amino Transferase (ALT) > 3 times upper limit of normal
• Current use of Cytochrome P450 3A4 inducing medication (e.g. carbamazepine, rifabutin, rifampin, ritonavir).
• Use of other substances (besides cocaine/amphetamine) is allowed if the use disorder is no greater than moderate severity and alcohol is the self-identified substance of choice.
• History of neuroleptic malignant syndrome or tardive dyskinesia. More specific inclusion and exclusion criteria will be discussed with participant at baseline assessment.

• Participant is 22 years of age and older at the time of enrollment
• Participant has been diagnosed with pathogenic deletions or mutations of the SHANK3 gene
• Participant is proficient in English
• Participant provided consent

• Participants must fall into one of the following categories:
• Donor between the age of 5 and 17 who is donating to a sibling
• Parent/caregiver of study participating donor
• Recipient sibling aged 5 to 17 of study participating donor
• Any of the donor's non-donor/non-recipient siblings between 5 and 17
• Any child between 5 and 17 with a brother or sister (also between 5 and 17) receiving a transplant from an unrelated source
• Be willing and able to provide signed informed consent:
• Adults must give consent for their children's and, if applicable, their own participation
• Assent will be obtained in accordance with guidelines at the participant's transplant institution
• Be willing and able to respond to psychological assessment questions
• Must be the donor's first donation
• Recipient must consent to the CIBMTR research database
• For families with pediatric donors aged 5 to 17, at minimum, the donor child and/or one parent must consent/assent to participation. If that minimum is not met, the family will be excluded
• Donor or non-donor siblings who do not live in the same household as the recipient at lease half of the time
• Unable to consent/assent or complete a phone interview in English
• No access to a telephone

• Caregiver: Male or female, ages 18 to 70, primary asthma caregiver of the child, currently meeting criteria for Major Depressive Disorder (MDD) (based on depression symptoms for at least 2 weeks and causing clinically significant distress or impairment in social, occupational, or other important areas of functioning) based on a Structured Clinical Interview for DSM-4 (SCID) interview.
• Child: Male or female, ages 7-17 years who have a diagnosis of persistent asthma as classified by either of the following criteria:
• A. requirement for treatment with daily controller medication; or
• B. symptoms of persistent asthma in children not on a daily controller medication:
• 1. Daytime symptoms two or more days per week; or
• 2. Rescue bronchodilator use two or more times per week; or
• 3. Nocturnal symptoms two or more nights per month; or
• 4. Two or more oral steroid bursts in the last year.
• Caregiver: Severe cognitive impairment that could impair their ability to provide informed consent; member of a vulnerable population (incarcerated, pregnant or breastfeeding women); women of childbearing age who will not use acceptable methods of birth control or abstinence during the study; severe psychiatric disorder in addition to MDD that should be a primary focus of treatment (e.g. severe and disabling eating or anxiety disorders); treatment refractory depression defined as failing ≥ 3 adequate trials of antidepressants (≥ 4 weeks at a therapeutic dose); electroconvulsive therapy or repeated transcranial magnetic stimulation during the current episode; depression as part of bipolar disorder or schizophrenia or schizoaffective disorder, or current depression secondary to substances or general medical condition, or with psychotic features or accompanied by severe obsessive compulsive disorder (OCD), or high risk for suicide defined by multiple recent suicide attempts (> 2 in the past year) or any attempt in the past month, or current suicidal ideation with a well-formed plan or intent.
• Child: Severe cognitive impairment that could impair their ability to provide informed consent; high risk for suicide defined by multiple recent suicide attempts (> 2 in the past year) or any attempt in the past month, or current suicidal ideation with a well-formed plan or intent; severe or life-threatening medical illness, such as other serious cardiopulmonary conditions (e.g. congenital heart disease, cystic fibrosis, alpha-1-antitrypsin disease) or cancer, which would confound the assessment of asthma, anxiety, depression or quality of life; severe psychiatric illness, such as autism, bipolar disorder, schizophrenia or current drug/alcohol abuse/dependence. If an eligible caregiver presents with more than one child meeting inclusion criteria for the study, only one child, randomly selected, will be enrolled.

Eligibility Criteria: 1. Histologic Documentation: All patients must have histologically or cytologically documented, non-small cell carcinoma of the lung (adenocarcinoma, large cell, squamous, or mixtures of these types). 2. Extent of Disease: Stage IIIB/IV cancer by the international staging system or any Stage I-IIIA otherwise eligible patient with recurrent or progressive NSCLC after surgery or radiotherapy.
• Patients with Stage IIIB because of a malignant pleural effusion, supraclavicular node involvement, or contralateral hilar nodes are eligible (IIIB patients eligible for CALGB protocols of combined chemotherapy and chest irradiation are not eligible.
• Patients with known CNS metastases are not eligible. 3. Measurable or Non-Measurable Disease
• Measurable Disease: Lesions that can be accurately measured in at least one dimension (longest diameter to be recorded) as ≥ 20 mm with conventional techniques or as ≥ 10 mm with spiral CT scan.
• Non-measurable Disease: Only those non-measurable disease patients with ill-defined masses associated with post-obstructive changes and diffuse parenchymal malignant disease are eligible. All other lesions, including small lesions (longest diameter < 20 mm with conventional techniques or < 10 mm with spiral CT scan) and truly non-measurable lesions, are not eligible. Lesions that are considered non-measurable include the following:
• Bone lesions
• Leptomeningeal disease
• Ascites
• Pleural/pericardial effusion
• Abdominal masses that are not confirmed and followed by imaging techniques
• Cystic lesions 4. Prior Treatment:
• No prior chemotherapy.
• ≥ 2 weeks since radiation therapy.
• No antidepressant treatment (eg, selective serotonin reuptake inhibitors, tricyclics, novel antidepressants, St. John's Wort or monoamine oxidase inhibitors) currently or within the last month. 5. If the patient requires pain medication, pain must be managed with non-codeine preparations, including but not limited to: acetaminophen, any morphine based preparation (short or long acting), hydromorphone, fentanyl, levorphanol or methadone. 6. CTC Performance Status 0-1. 7. Non-pregnant and non-nursing because of significant risk to the fetus/infant. 8. Required Initial Laboratory Data:
• Granulocytes ≥ 1,500/µl
• Platelet count ≥ 100,000/µl
• Serum creatinine ≤ 1.5 mg/dl or Calculated CrCl ≥ 60 ml/min
• Bilirubin ≤ 2.0 x Upper Limit of Normal (ULN)
• Serum glutamic oxaloacetic transaminase (SGOT) ≤ 2.0 x ULN

RESTORE subjects
• Age ≤8 years and PCPC=1 at RESTORE PICU admission
• PCPC ≤3 at RESTORE hospital discharge Sibling control subjects Inclusion criteria:
• Age 4 to 17 years at time of testing
• PCPC=1
• Same biological parents as primary subject
• Lives with the primary subject RESTORE subjects
• Hospital readmission that includes MV and sedation
• History of cardiac arrest, traumatic brain injury (TBI) with loss of consciousness, genetic disorder, premature birth <32 weeks gestational age, or birth weight <2500 g Sibling control subjects
• Adopted or step siblings
• History of MV and sedation, receipt of general anesthesia, cardiac arrest, TBI with loss of consciousness, genetic disorder, premature birth <32 weeks gestational age, or birth weight <2500 gm.

1. Male or females age 14-18 inclusive 2. Diagnosed with concussion due to sports-related injury. Concussion is defined as: 1. Direct blow to the head, face, neck or a blow elsewhere on the body with an "impulsive" force transmitted to the head. 2. Rapid onset of short-lived impairment of neurologic function in one or more of the following clinical domains that resolves spontaneously: i. Symptoms: somatic (eg, headache), cognitive (eg, feeling like in a fog and/or emotional symptoms (eg, lability). ii. Physical signs (eg, loss of consciousness, amnesia). iii. Behavioral changes (eg, irritability). iv. Cognitive impairment (eg, slowed reaction times). v. Sleep disturbance (eg, drowsiness). c) No abnormality on standard structural neuroimaging studies, if such neuroimaging studies are completed for a clinically-indicated reason. Note: neuroimaging is not a part of this study protocol. Study participants will not undergo neuroimaging as part of this study. 3. Concussion within 4 days of enrollment 4. Presenting for treatment to the Sports Medicine Center at Children's Medical Center 1. Subjects not actively participating in an organized sport at time of enrollment 2. Subjects who received a concussion from an event other than playing a sport (motor vehicle accident, fall, etc.) 3. Subjects who participate in or received a concussion during participation in motorized sports (i.e., motorcross, dirt biking, jet skiing, etc.) 4. Subjects with radiographic evidence of traumatic brain injury (i.e., skull fracture, intracranial hemorrhage, cerebral contusion, etc). 5. Subjects with a prior diagnosed concussion in the previous 6 months. 6. Pregnant women. 7. Subjects sensitive to aspirin 8. Subjects diagnosed with high blood pressure and currently being treated with blood pressure medications 9. Subjects allergic to soy bean oil or corn oil. 10. Subjects currently taking fish oil or DHA supplements.

• Adolescents and young adults aged 10-24, male and female of all races and ethnicity.
• Participants must be English-speaking (because several study assessments are only available in the English language), however the parent(s) or legal guardian may either speak English or Spanish as the consenting process can be conducted bilingually.
• Adults age 18 and older must be able to provide written informed consent; for youth younger than age 18, a parent or legal guardian must provide written informed consent, and the child or teen must provide written informed assent.
• Ability to complete clinical evaluations and neuropsychological testing.
• Individuals who are unable to provide informed consent.
• Participants who are non-English speaking.
• Individuals with any of the following psychotic features: MDD with psychotic features, schizophrenia, schizoaffective disorder, or other Axis I psychotic disorder.
• Individuals with a depression diagnosis or a history of depression diagnosis at the initial visit (participants who develop depression during the longitudinal follow-up will continue in the study).
• A PHQ-9 score of 10 or greater.
• Individuals who are unable to provide a permanent home address and contact information.
• Individuals with any condition for which, in the opinion of the investigator, study participation would not be in their best interest (e.g., compromise their well-being) or that could prevent, limit, or confound the protocol-specified assessments.

•Male or female, age greater than or equal to 45 years at the time of signing informed consent
•Body mass index (BMI) greater than or equal to 27 kg/m^2
•Have established cardiovascular (CV) disease as evidenced by at least one of the following: prior myocardial infarction; prior stroke (ischemic or haemorrhagic stroke); or symptomatic peripheral arterial disease (PAD), as evidenced by intermittent claudication with ankle-brachial index (ABI) less than 0.85 (at rest), or peripheral arterial revascularization procedure, or amputation due to atherosclerotic disease Exclusion Criteria:
•Any of the following: myocardial infarction, stroke, hospitalisation for unstable angina pectoris or transient ischaemic attack within the past 60 days prior to the day of screening
•HbA1c greater than or equal to 48 mmol/mol (6.5 %) as measured by the central laboratory at screening
•History of type 1 or type 2 diabetes (history of gestational diabetes is allowed)

• Outpatient men and women age 18-70 years old with bipolar I or II disorder or schizoaffective disorder (bipolar type)
• English or Spanish speaking
• Current diagnosis of alcohol use disorder with at least moderate severity (DSM-5 terminology)
• Alcohol use of at least 28 drinks a week if male or an average of 21 drinks per week if female and 3 drinking days a week in the 28 days prior to intake
• Current mood stabilizer therapy (defined as lithium, lamotrigine, carbamazepine, oxcarbazepine or an atypical antipsychotic) with stable dose for ≥ 28 days prior to randomization or valproate/divalproex at a stable dose for ≥ 90 days (longer period due to data suggesting valproate may decrease alcohol use in BPD)
• Diagnosis of substance use disorder other than alcohol, caffeine or nicotine is allowed if 1) alcohol is the self-identified substance of choice and 2) severity of other substance use disorder is ≤ moderate
• Mood disorders other than bipolar I or II disorders or schizoaffective disorder bipolar type (e.g. bipolar NOS, cyclothymic disorders, schizophrenia, schizoaffective disorder depressive type, or unipolar depression based on the SCID); other disorders (e.g. anxiety, will be allowed)
• Baseline HRSD17 or YMRS scores ≥ 35 to exclude those with very severe mood symptoms at baseline
• Evidence of clinically significant alcohol withdrawal symptoms defined as a CIWA-Ar score of ≥ 10
• Current (last 28 days) treatment with naltrexone, acamprosate, disulfiram, or topiramate as these may also decrease alcohol use
• Oral contraceptives and hormone replacement therapy. This exclusion is due to a possible interaction with pregnenolone.
• Women with hormone sensitive conditions such as breast cancer, uterine cancer, ovarian cancer, endometriosis, uterine fibroids. These persons are excluded because pregnenolone is converted to estrogens.
• Vulnerable populations (e.g. pregnant, nursing, cognitively impaired, incarcerated)
• High risk for suicide defined as > 1 attempt in past 12 months that required medical attention, any attempt in the past 3 months or current suicidal ideation with plan and intent such that outpatient care is precluded
• Intensive outpatient treatment (defined as ≥3 visits each week) for substance abuse (AA, NA meetings, or less intensive counseling at baseline will be allowed)
• Severe/unstable condition (e.g. cirrhosis, poorly controlled hypertension) or laboratory/physical exam findings consistent with serious illness (e.g. abnormal electrolytes) or AST or ALT >3 times normal

Volunteers with Schizophrenia or other mental illness
• Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR) diagnosis of Schizophrenia or Schizoaffective disorder
• Competent to give informed consent
• All races and ethnicities
• Eyesight corrected to 20-40 or better
• Able to read, speak, and understand English
• No past or current severe mental illness
• All races and ethnicities
• Eyesight corrected to 20-40 or better
• Able to read, speak, and understand English Volunteers with schizophrenia or other mental illness
• Diagnosis of an organic brain disease
• Diagnosis of DSM-IV-TR alcohol or substance abuse within the last month or DSM-IV-TR alcohol or substance dependence within the last three months
• Serious, unstable medical illness
• History of serious head injury
• Pregnant women
• History of psychiatric illness
• Current use of psychoactive drugs excluding nicotine and caffeine
• Diagnosis of an organic brain disease
• Serious, unstable medical illness
• History of serious head injury
• Pregnant women

Inclusion Criteria (all CN participants): 1. Participant with or without subjective memory complaints, verified by a study partner, beyond what one would expect for age 2. Normal memory function documented by scoring above education adjusted cutoffs on the Logical Memory II subscale (Delayed Paragraph Recall, Paragraph A only) from the Wechsler Memory Scale -Revised (the maximum score is 25): 1. 9 for 16 or more years of education 2. 5 for 8-15 years of education 3. 3 for 0-7 years of education 3. Mini-Mental State Exam score between 24 and 30 inclusive (Exceptions may be made for participants with less than 8 years of education at the discretion of the Project Director) 4. Clinical Dementia Rating = 0. Memory Box score must be 0 5. Cognitively normal, based on an absence of significant impairment in cognitive functions or activities of daily living 6. Stability of Permitted Medications for at least 4 weeks: 1. Stable doses of antidepressants lacking significant anticholinergic side effects (if they are currently adequately treated for depressive symptoms and do not have a history of major depression within the past 1 years) 2. Estrogen replacement therapy is permissible 3. Gingko biloba is permissible, but discouraged 4. Washout from psychoactive medication (e.g., excluded antidepressants, neuroleptics, chronic anxiolytics or sedative hypnotics, etc.) for at least 4 weeks prior to screening. Inclusion Criteria (all MCI participants): 1. Participant must express a subjective memory concern as reported by participant, or recalled by study partner or clinician. 2. Abnormal memory function documented by scoring below education adjusted cutoffs on the Logical Memory II subscale (Delayed Paragraph Recall, Paragraph A only) from the Wechsler Memory Scale -Revised (the maximum score is 25): a. < 11 for 16 or more years of education b. ≤ 9 for 8-15 years of education c. ≤ 6 for 0-7 years of education 3. Mini-Mental State Exam score between 24 and 30 inclusive (Exceptions may be made for participants with less than 8 years of education at the discretion of the Project Director) 4. Clinical Dementia Rating = 0.5. Memory Box score must be at least 0.5 5. General cognition and functional performance sufficiently preserved such that a diagnosis of Alzheimer's disease cannot be made by the site physician at the time of the Screening Visit 6. Stability of Permitted Medications for at least 4 weeks: 1. Stable doses of antidepressants lacking significant anticholinergic side effects (if they are currently adequately treated for depressive symptoms and do not have a history of major depression within the past 1 years) 2. Cholinesterase inhibitors and memantine are allowable if stable for 12 weeks prior to Screening Visit 3. Estrogen replacement therapy is permissible 4. Gingko biloba is permissible, but discouraged 5. Washout from psychoactive medication (e.g., excluded antidepressants, neuroleptics, chronic anxiolytics or sedative hypnotics, etc.) for at least 4 weeks prior to screening. Inclusion Criteria (all AD participants): 1. Participant must express a subjective memory concern as reported by participant, or recalled by study partner or clinician.n. 2. Abnormal memory function documented by scoring below education adjusted cutoffs on the Logical Memory II subscale (Delayed Paragraph Recall, Paragraph A only) from the Wechsler Memory Scale -Revised (the maximum score is 25): 1. ≤ 8 for 16 or more years of education 2. ≤ 4 for 8-15 years of education 3. ≤ 2 for 0-7 years of education 3. Mini-Mental State Exam score between 20 and 24 inclusive (Exceptions for scores of 24 and 25 may be made for participants with less than 8 years of education at the discretion of the Project Director) 4. Clinical Dementia Rating = 0.5 or 1.0 5. NINCDS (National Institute of Neurological and Communicative Disorders and Stroke) -ADRDA (Alzheimer's Disease and Related Disorders Association) criteria for probable AD 6. Stability of Permitted Medications for at least 4 weeks: 1. Stable doses of antidepressants lacking significant anticholinergic side effects (if they are currently adequately treated for depressive symptoms and do not have a history of major depression within the past 1 years) 2. Cholinesterase inhibitors and memantine are allowable if stable for 12 weeks prior to Screening Visit 3. Estrogen replacement therapy is permissible 4. Gingko biloba is permissible, but discouraged 5. Washout from psychoactive medication (e.g., excluded antidepressants, neuroleptics, chronic anxiolytics or sedative hypnotics, etc.) for at least 4 weeks prior to screening. Inclusion Criteria Specific to Newly Enrolled Participants 1. Geriatric Depression Scale score less than 6. 2. Age between 55-90 years (inclusive). 3. Study partner who has frequent contact with the participant (i.e., minimum average of 10 hours per week) and is available to accompany the participant to all clinic visits for the duration of the protocol. 4. Visual and auditory acuity adequate for neuropsychological testing. 5. Good general health with no diseases expected to interfere with the study. 6. Participant is not pregnant, lactating, or of childbearing potential (i.e. women must be two years post-menopausal or surgically sterile). 7. Willing and able to participate in a longitudinal imaging study. 8. Modified Hachinski Ischemic Score less than or equal to 4. 9. Completed six grades of education or has a good work history (sufficient to exclude mental retardation). 10. Must speak English or Spanish fluently. 11. Willing to undergo repeated MRIs (3Tesla) and at least two PET scans 12. Agrees to collection of blood for genomic analysis (including GWAS (genome-wide association study) sequencing and other analysis), APOE (Apolipoprotein E) testing and biospecimen banking. 13. Agrees to collection of blood for biomarker testing. 14. Agrees to at least one lumbar puncture for the collection of CSF. 15. Agrees to share genomic data and biomarker samples. Inclusion Criteria Specific to Rollover Participants" The following additional inclusion criteria apply to all diagnostic categories for rollover participants only: 1. Must have been enrolled and followed in ADNI-1, ADNI-GO, or ADNI-2 for at least one year. 2. Willing and able to continue to participate in an ongoing longitudinal study. A reduced battery of tests is allowable if the participant is not able/willing to complete the full battery. Exclusion Criteria (all CN participants): 1. Any significant neurologic disease, such as Parkinson's disease, multi-infarct dementia, Huntington's disease, normal pressure hydrocephalus, brain tumor, progressive supranuclear palsy, seizure disorder, subdural hematoma, multiple sclerosis, or history of significant head trauma followed by persistent neurologic deficits or known structural brain abnormalities Exclusion Criteria (all MCI participants): 1. Any significant neurologic disease other than suspected incipient Alzheimer's disease, such as Parkinson's disease, multi-infarct dementia, Huntington's disease, normal pressure hydrocephalus, brain tumor, progressive supranuclear palsy, seizure disorder, subdural hematoma, multiple sclerosis, or history of significant head trauma followed by persistent neurologic deficits or known structural brain abnormalities. Exclusion Criteria (all AD participants): 1. Any significant neurologic disease other than Alzheimer's disease, such as Parkinson's disease, multi-infarct dementia, Huntington's disease, normal pressure hydrocephalus, brain tumor, progressive supranuclear palsy, seizure disorder, subdural hematoma, multiple sclerosis, or history of significant head trauma followed by persistent neurologic deficits or known structural brain abnormalities. Exclusion Criteria (all participants): The following additional exclusion criteria apply to all diagnostic categories: 1. Screening/Baseline MRI brain scan with evidence of infection, infarction, or other focal lesions or multiple lacunes or lacunes in a critical memory structure 2. Subjects that have any contraindications for MRI studies, including the presence of cardiac pacemakers, or metal fragments or foreign objects in the eyes, skin or body. 3. Major depression, bipolar disorder as described in DSM-IV within the past 1 year. Psychotic features, agitation or behavioral problems within the last 3 months that could lead to difficulty complying with the protocol. 4. Currently treated with medication for obsessive-compulsive disorder or attention deficit disorder. 5. History of schizophrenia (DSM IV criteria). 6. History of alcohol or substance abuse or dependence within the past 2 years (DSM IV criteria). 7. Any significant systemic illness or unstable medical condition, which could lead to difficulty complying with the protocol. 8. Clinically significant abnormalities in B12 or thyroid function tests (TFTs) that might interfere with the study. A low B12 is exclusionary, unless follow-up labs (homocysteine (HC) and methylmalonic acid (MMA)) indicate that it is not physiologically significant. 9. Residence in a skilled nursing facility. 10. Current use of specific psychoactive medications (e.g., certain antidepressants, neuroleptics, chronic anxiolytics or sedative hypnotics). Current use of warfarin or other anticoagulants such as dabigatran, rivaroxaban and apixaban (exclusionary for lumbar puncture). 11. Current use of any other exclusionary medications 12. Investigational agents are prohibited one month prior to entry and for the duration of the trial. 13. Participation in clinical studies involving neuropsychological measures being collected more than one time per year. Exclusion Criteria Specific to AV-1451 PET: The following criteria are exclusionary only for the AV-1451 scanning portion of the study: 1. History of risk factors for torsades de pointes (a cardiac dysrhythmia associated with sudden death) or taking medications known to prolong the QT interval. A list of restricted medications will be provided. 2. Have an ECG obtained prior to the AV-1451 PET scan that in the opinion of the investigator is clinically significant with regard to the subject's participation in the study. Bazett's corrected QT (QTcB) interval must be evaluated and must not exceed 458 msec in males, or 474 msec in females.