Evaluation of a Handheld Event Related Potential (ERP)/Quantitative Electroencephalography (qEEG) System (COGNISION™) as a Useful Cognitive Biomarker for Alzheimer's Disease.

Inclusion Criteria: AD Cohort: Subjects between 60 and 90 years old meeting NINCDS-ADRDA criteria for probable AD2 and DSM-IV criteria for dementia of the Alzheimer's type3 will be recruited in the AD cohort (MMSE ≥21, ≤26). Memory complaint by subject and/or study partner SRP-1418 N Page: 8 of 26 Abnormal memory function score on Logical Memory II subscale (Delayed Paragraph Recall) from the Wechsler Memory Scale - Revised (adjusted for education. Maximum score is 25): i. \< 10 for 16 or more years of education ii. \< 6 for 8-15 years of education iii. \< 4 for 0-7 years of education Clinical Dementia Rating (CDR) = 0.5, 1.0 or 2.0 Modified Hachinski Ischemic Scale (HIS) ≤ 4 Geriatric Depression Scale (GDS) \< 6 For subjects that decide to provide a CSF sample: Platelet count ≥ 100,000/μL, Prothrombin Time (PT) = 11 to 16 seconds, International Normalized Ratio = 0.8 to 1.2 Study partner or caregiver to accompany subject to all scheduled visits Fluent in English Adequate visual acuity to allow neuropsychological testing Adequate auditory acuity to allow neuropsychological and ERP testing Good general health with no additional diseases expected to interfere with the study Willing to undergo neuroimaging and provide blood. The subject may optionally provide a CSF sample by lumbar puncture. Normal Controls: Healthy subjects matched for age, gender, and education level will be recruited as normal controls (MMSE ≥ 27). Normal memory function will be documented by scoring at specific cutoffs on the Logical Memory II subscale (Delayed Paragraph Recall) from the Wechsler Memory Scale - Revised: i. ≥ 10 for 16 or more years of education ii. ≥ 6 for 8-15 years of education iii. ≥ 4 for 0-7 years of education Study partner or caregiver Fluent in English Adequate visual acuity to allow neuropsychological testing Adequate auditory acuity to allow neuropsychological and ERP testing Exclusion Criteria: AD Cohort: Severe or unstable forms of diabetes, heart disease, HIV, drug or alcohol abuse, etc. including severe AD: MMSE ≤20 Platelet count \< 100,000/μL, Prothrombin Time (PT) \> 16 seconds, International Normalized Ratio \> 1.2 (for subjects that choose to provide a CSF sample by lumbar puncture). Medical or psychiatric disorders that might complicate the assessment of dementia (i.e., mental retardation, alcohol abuse, drug abuse, HIV) A disability that may prevent the subject from completing all study requirements (e.g., blindness, deafness, language difficulty) Recent intake of drugs known to cause major organ system toxicity or CNS alteration (e.g. sedation) Diseases of the dementia type other than AD (i.e., vascular dementia, frontotemporal dementia, Lewy Body Disease, Huntington's disease) Presence of non-MRI compatible implants/devices Prohibited Medications: Warfarin or other anticoagulants (for subjects that choose to provide a CSF sample by lumbar puncture), investigational agents. Normal Controls: Severe or unstable forms of diabetes, heart disease, HIV, drug or alcohol abuse, etc. A disability that may prevent the subject from completing all study requirements (e.g., blindness, deafness, language difficulty) Use of psychoactive drugs (only SSRI's are allowed) Psychiatric disorders (schizophrenia, bipolar, etc.) Depression (GDS \> 6) Vascular dementia (HIS \> 4) Other dementia (CDR \> 0) Abnormal memory function score on Wechsler Memory Scale -Logical Memory II subscale (delayed Paragraph Recall) from the Wechsler Memory Scale - Revised (the maximum score is 25): I. \< 10 for 16 or more years of education II. \< 6 for 8-15 years of education III. \< 4 for 0-7 years of education