Reevaluation of the phenomena of the first night effect.

Thirty subjects, who were between the ages of 24 and 60 years and were free of sleep disorders, were evaluated for impotency by use of polysomnograms recorded over 2 consecutive nights. No statistical differences between the first and second nights' recordings were found in latency to rapid eye movement and stage 4 sleep, sleep efficiency, and movement time with or without awakening. No differences were noted in times spent in different sleep stages, nor between the first 3 h and the second 3 h of sleep across both nights of polysomnography. This confirms previous findings that questioned the efficacy of the first night effect. This study also emphasizes the need to compare sleep disorder patients with matched normal controls.