Subjects will be screened within 28 days, Simvastatin dose and single SB-649868 dose 10 and 7 days prior to repeat dosing respectively, 15 days SB-649868 repeat dosing with safety and cognition function tests.

Inclusion Criteria:

• Healthy adult male subjects aged between 18 and 65 years of age inclusive.
• Body weight =50 kg and BMI within the range 18.5-29.9 kg/m2 inclusive.
• Healthy as judged by responsible physician. No clinically significant abnormality identified on the medical or laboratory evaluation and 12-lead ECG. A subject with a clinical abnormality or laboratory parameters outside the reference range for this age group may be included only if the Investigator and the Medical Monitor considers that the finding will not introduce additional risk factors and will not interfere with the study procedures.
• Subjects will have blood pressure measurements within the normal range for healthy volunteers.

Exclusion Criteria:

• The subject has a positive pre-study urine drug/ alcohol urine screen.
• A positive pre-study Hepatitis B surface antigen, Hepatitis C antibody, or HIV 1/2 result at the screening visit.
• Abuse of alcohol defined as an average weekly intake of greater than 21 units or an average daily intake of greater than 3 units.
• Subject complains of sleep disturbances and/ or is receiving treatment for sleep disorders.