This is a study where AZD5213 or placebo is given to patients with Mild Alzheimer's Disease or Mild Cognitive Impairment in a blinded and random assignment. The main study objective is to estimate the relationship of sleep duration versus dose after 4 weeks of treatment.

A Phase IIa Safety and Tolerability Study to Investigate the Effect on Sleep of 3 Doses of AZD5213 and Placebo in Patients with Mild Alzheimer's Disease and Mild Cognitive Impairment During 4 Weeks of Treatment, Designed as a Randomized, Double-Blind, Multi-Center, Parallel Group, Placebo-Controlled Study

Inclusion Criteria:

• Patient and study partner to sign informed consent before initiation of any study-related procedures.
• Clinical diagnosis of Alzheimers (AD) or mild cognitive impairment (MCI) disease.
• Single caregiver for at least 6 months prior to Screening, capable of accompanying the patient on clinic visits as needed. The caregiver must either be living with or visiting the patient at least 10 hours per week, split over multiple (at least 2) days, for the duration of the study.
• Single study partner, for at least several months prior to Screening, capable of accompanying the patient on clinic visits as needed. The study partner must either be living with or visiting the patient at least 3 days per week for the duration of the study.
• A body mass index (BMI=weight/height2) of 18 kg/m2 to 32 kg/m2.

Exclusion Criteria:

• Significant neurological disease or dementia other than AD or MCI.
• Current episode or symptoms of major depressive disorder or other major psychiatric disorder.
• History of self-reported sleep duration of less than 4 hours per night or less than 4 hours average total sleep time per night during Baseline PSG assessment.
• History or present symptoms of a sleeping disorder such as sleep apnea.
• History of cancer in the last 5 years.
• Use of anti-AD drugs (including off-label drugs and herbal medications) with the exception of donepezil, memantine, and/or rivastigmine transdermal system, as monotherapy or in combination in the following conditions: treatment with donepezil (5 mg to 10 mg daily), memantine, and/or rivastigmine transdermal system or combination regimens for at least 3 months and a stable dose(s) for the last 2 months prior to randomization is allowed.