PATTERNS AND FUNCTIONS OF SLEEP GAURAV MOGHE DEPARTMENT OF BIOCHEMISTRY THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA
SOME FACTS ABOUT SLEEP • Sleep has been regarded “sacred” in many cultures. • Most higher organisms show sleep or sleep-like behavior. • In humans, sleep deprivation causes many health and behavior related problems.
QUESTIONS • How to “define” sleep? • Do all organisms sleep? • How does our own sleep pattern develop after birth? • Why do we spend 1/3rd of our lives sleeping? What is the “function” of sleep?
STAGES OF SLEEP • Sleep has been traditionally judged by behavioral criteria: 1. Minimal movement 2. A typical sleep posture 3. Reduced responsiveness to ext. stimuli • The event of sleep has been physiologically classified into 2 types REM NREM
Distribution of some key sleep regulating neuronal populations plotted on the saggital section of the rat brain Nature, Oct 2005
AMPHIBIANS, REPTILES AND BIRDS • Amphibians and Reptiles have a primitive nervous system that does not generate the same electrophysiological patterns as higher brains of mammals and birds. • 29 bird species have been shown to “sleep” with one of the two eyes closed. • It is suspected that some birds sleep aloft during transoceanic flights
SLEEP IN CETACEANS EEG of adult beluga EEG Of Beluga vs Rat Nature, Oct 2005
SLEEP IN INSECTS AND OTHER INVERTEBRATES • Correlates of sleep have been demonstrated in 1. Drosophila (Molecular markers) Science, March 2000 2. Crayfish (Slow wave activity) PNAS, Aug 2004 3. Cockroaches, wasps
WHAT DOES ALL THIS TELL US? • All higher animals HAVE TO sleep. • The pattern of sleep may vary according to the ecologicalniche of the organism • The NEED for Sleep may have some physiological correlate.
INFANCY TO OLD AGE • Sleep events tend to be fragmented in infancy and in old age • A normal sleep pattern exists for most period of our lives. • How this sleep pattern develops is an interesting aspect to study.
Shows 4388 points of data collected over 616 days for Beatrix Valentina MacNeill
ADOLESCENT SLEEP PATTERNS Current Biology, 2004
DISORDERS DUE TO SLEEP RELATED PROBLEMS • Sleep Apnea • Restless Leg Syndrome • Insomnia • Arousal Disorders • Sleep-Wake transition disorders • REM Sleep associated parasomnias
THEORIES OF FUNCTION The theories that have been proposed are: • Wear and Tear of the body • Memory Consolidation • Ecological niche theory
WEAR AND TEAR HYPOTHESIS GH LEVELS Sleep after deprivation Baseline sleep Deprivation JPN, 1991
MEMORY CONSOLIDATION THEORY • Sensory memories are consolidated during REM or Deep Sleep. • Sleep Deprivation led to poor performance in specific tasks, in 3 studies, and improved after a period of sleep: 1) Visual texture discrimination task 2) Motor sequence learning task 3) Motor adaptation learning task • The improvements showed strong correlations to specific stages of sleep and specific regions in the brain
Motor adaptation learning Visual Texture discrimination
SOME OTHER SUPPORTS • Zebrafinch • Rats • Sheep • Fetal and Neonate psychology
ECOLOGICAL NICHE THEORY • Predator-Prey relationships affect the patterns of sleep • Evidences proposed include: 1) Newborns sleep more than adults 2) This pattern is reversed in aquatic mammals 3) Distinct correlation between predator-prey status and sleep periods • But is this logic sufficient to explain why humans spend 1/3rd of their lives sleeping?
FUTURE DIRECTIONS • Are sleep-like states present in lower organisms, esp those that don’t have a “nervous system”? • What are the cytological and molecular aspects of memory consolidation? • How can the harmful effects of sleep deprivation be prevented?