Disturbed Sleep Model Study.

A Double-blind, Double-dummy, Randomised, Placebo-controlled,Four-way Crossover Study to Investigate the Effect of Single Oral Doses of SB-649868 and of Zolpidem in a Model of Noise Induced Situational Insomnia in Healthy Male Volunteers.

Subjects will be screened within 28 days. Each treatment session will consist of 2 PSG nights, study drug administration and noise model is conducted on second night.

Inclusion Criteria:

• 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;
• The subject shows a normal sleep pattern on the basis of the evaluation of both PSG screening nights. Normal sleep will be defined as follows: LPS (Latency to persistence Sleep) <30min., SE (Sleep Efficiency) >85%, apnea/ hypopnea index < 10, periodic leg movements (PLM) with arousal index < 10. The apnea/hypopnea index is defined as "the number of apneas and hyponeas divided by the total sleep time (TST) expressed in hours". PLMI is defined as "the number of periodic leg movements associated with arousals or awakening divided by the total sleep time (TST) expressed in hour".

Exclusion Criteria:

• A positive result for the pre-study urine drug/ alcohol breath screen.
• Abuse of alcohol.
• Subject complains of sleep disturbances and /or is receiving treatment for sleep disorders.