THE PHYSIOLOGICAL AND BEHAVIORAL CORRELATESOF SLEEP AND DREAMING • Outline • 1. Three Psychophysiological Measures of Sleep • 2. The Five Stages of Sleep EEG • 3. REM Sleep and Dreaming • 4. Why Sleep? • a. Recuperation Theories • b. Circadian Theories • 5. Comparative Analysis of Sleep • 6. Circadian Sleep Cycles • 7. Effects of Sleep Reduction • a. Total Sleep Deprivation • b. REM Deprivation • 8. Effects of Long-Term Sleep Reduction • 9. Neural Mechanisms of Sleep • 10. The Circadian Clock • a. The Suprachiasmatic Nucleus • b. Mechanisms of Entrainment
Neural Mechanisms of Sleep • Bremer • First major theory of sleep physiology • Proposed a passive theory of sleep • Sleep occurs because of a reduction of sensory input to the forebrain • Cut the brainstem between the superior and inferior colliculi (cerveau isolé) • produced a state of almost continuous slow-wave sleep • This theory was replaced by the reticular activating system theory of sleep.
Reticular Activating System Theory of Sleep Three findings contributed to this new theory: 1) Cutting the brainstem at the caudal end encephalé isolé) did not affect sleep, Damaged the same sensory pathways as the cerveau isolé preparation 2) The cerveau isolé preparation also impaired sleep when it transected only the reticular activating system core of the brainstem – leaving sensory pathways intact.
3) Electrical stimulation of the reticular activating system in sleeping cats awakened them • Suggests that slowing of the reticular activating system leads to sleep. • Increasing the reticular activating system leads to wakefulness
Three Brain Regions Thought To Be Involved In Sleep • 1) the raphe nuclei • A thin cluster of serotonin-releasing nuclei that lie along the midline of the caudal reticular formation • Lesions here produce insomnia • 80-90% destruction of raphe nuclei in cats • Complete insomnia for 3-4 days • 2.5 hours after that (all slow wave)
2) The basal forebrain, including the anterior hypothalamus • Patients with small basal forebrain tumors have difficulty sleeping • Lesions here reduce sleep duration • Single cell recordings have revealed neurons that increase their activity here during sleep.
3) The caudal reticular formation REM-sleep circuits • Various sites in the brainstem control different aspects of REM sleep
The Circadian Clock • Sleep-wake cycles persist in the absence of cues from the environment • Must be an internal timing mechanism • Where is it? • Lesions of the medial hypothalamus • More specifically the suprachiasmatic nuclei (SCN), disrupts various circadian cycles • Cells in the SCN maintain circadian cycles even when surgically cut off from the rest of the brain • Internal clock?
Mechanisms of Entrainment • Connections between the retina and the SCN • Cut the optic nerves before they reach the optic chiasm • Eliminated light and dark entrainment • Cut the optic nerves after they left the optic chiasm • Light and dark entrainment remains • Led to the discovery of the retinohypothalamic tracts • Nerve tract that leaves the optic chiasm and goes to the suprachiasmatic nuclei • Rods and cones not necessary for entrainment. • From transgenic mouse studies