Chapter Six: Sleeping, Dreaming and Biological Rhythms PDF

Chapter Six Sleeping, Dreaming and Other Biological Rhythms  Biological rhythms Biological rhythms are cyclical patterns within biological systems that have evolved in response to environmental influences, e.g. day and night  There are two key factors that govern...

Chapter Six Sleeping, Dreaming and Other Biological Rhythms  Biological rhythms Biological rhythms are cyclical patterns within biological systems that have evolved in response to environmental influences, e.g. day and night  There are two key factors that govern biological rhythms: endogenous pacemakers (internal factors), the body’s biological clocks, and exogenous zeitgebers  Circadian Rhythms One biological rhythm is the 24-hour circadian rhythm (often known as the ‘body clock’), which is reset by levels of light. The word circadian is from the Latin ‘circa’ which means ‘about’, and ‘dian’, which means ‘day’.  The sleep-wake cycle is an example of a circadian rhythm, which dictates when humans and animals should be asleep and awake Light provides the primary input to this system, acting as the external cue for sleeping or waking.  Light is first detected by the eye, which then sends messages concerning the level of brightness to the suprachiasmatic nuclei (SCN). The SCN then uses this information to coordinate the activity of the entire circadian system.  Sleeping and wakefulness are not determined by the circadian rhythm alone, but also by homoeostasis. When an individual has been awake for a long time, homeostasis tells the body that there is a need for sleep because of energy consumption  Body temperature is another circadian rhythm. Human body temperature is at its lowest in the early hours of the morning and at its highest in the early evening  Sleep typically occurs when the core temperature starts to drop, and the body temperature starts to rise towards the end of a sleep cycle  Endogenous Pacemakers Endogenous pacemakers are internal mechanisms that govern biological rhythms, in particular, the circadian sleep-wake cycle. They are internal biological clocks, they can be altered and affected by the environment.  The most important endogenous pacemaker is the suprachiasmatic nucleus, which is closely linked to the pineal gland, both of which are influential in maintaining the circadian sleep/wake cycle  The suprachiasmatic nucleus (SCN), which lies in the hypothalamus, is the main endogenous pacemaker (or master clock). It controls other biological rhythms, as it links to other areas of the brain responsible for sleep and arousal.  The SNC sends signals to the pineal gland, which leads to an increase in the production of melatonin at night, helping to induce sleep their activity is responsive to the external cue of light  (SCN)- is a tiny region located in the hypothalamus, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms.  Low level of light (retina) Melanopsin carries signal to SNC Axon pathway to pineal gland Melatonin Induced sleep Exogenous Zeitgebers (time givers) these can be described as environmental events that are responsible for resetting the biological clock of an organism They can include social cues such as meal times and social activities, but the most important zeitgeber is light (sunlight)  Light is responsible for resetting the body clock each day, keeping it on a 24-hour cycle. Melanopsin, which is a protein in the eye, is sensitive to light and carries the signals to the SCN to set the 24- hour daily body cycle.  In addition, social cues, such as mealtimes, can also act as zeitgebers and humans can compensate for the lack of natural light, by using social cues instead.  Infradian Rhythms Infradian rhythms last longer than 24 hours and can be monthly or annually. A monthly infradian rhythm is the female menstrual cycle, which is regulated by hormones that either promote ovulation or stimulate the uterus for fertilization  the usual menstrual cycle is around 28 days, there is considerable variation, with some women experiencing a short cycle of 23 days and others experiencing longer cycles of up to 36 days.  A second example of an infradian rhythm is related to the seasons. Research has found seasonal variation in mood, where some people become depressed in the winter, which is known as seasonal affective disorder (SAD). SAD is an infradian rhythm that is governed by a yearly cycle  Psychologists claim that melatonin, which is secreted by the pineal gland during the night, is partly responsible  Ultradian Rhythms Ultradian rhythms last fewer than 24 hours and can be found in the pattern of human sleep The anterior hypothalamus and adjacent basal forebrain region have the most potent sleep-promoting effects seen in the brain  Sleep is defined behaviorally by four criteria: _ (1) reduced motor activity, _(2) decreased response to stimulation, _(3) stereotypic postures (for example, lying down with eyes closed in humans), and _(4) relatively easy reversibility (distinguishing it from coma, hibernation and estivation).  REM sleep is generated by mechanisms located at the junction of the midbrain and pons Many of the neurons critical for REM sleep are responsive to acetylcholine Consists of five stages. The cycle starts at light sleep, progressing to deep sleep and then REM sleep.  Stages 1 and 2 are ‘light sleep’ stages Stages 3 and 4 are ‘deep sleep’ Finally, Stage 5 is REM (or dream) sleep. Here is the body is paralyzed (to stop the person acting out their dream) On average, the entire cycle repeats every 90 minutes and a person can experience up to five full cycles in a night  Stage1: light sleep _muscle activity slow down Stage 2: _breathing pattern and heart rate become slow Stage 3: deep sleep begins _rhythmic breathing and limited muscle activity  Stage 4: very deep sleep Stage 5: _Rapid eye movement (Active Form of Sleep) _Dreaming occur _Muscle relax and heart rate increases _Breathing is rapid and shallow  Another ultradian rhythm is appetite or meal patterns in humans. Most humans eat three meals a day and appetite rises and falls because of food consumption  Narcolepsy-chronic neurological disorder involving the loss of the brain's ability to regulate sleep-wake cycles normally  Dreaming REM and non-REM, they also studied the relation of these phases to dreaming. Dreams were far more likely to be recalled when subjects were awakened from REM sleep (longer).  REM sleep is the phase from which dreams may be most reliably elicited, REM sleep is not necessary for dreaming. Dream reports are elicited on awakenings from non-REM phases that occur before the first REM phase of the night  Although reports of non-REM dreams tend to be shorter, less emotional, and more coherent than reports of REM dreams Dreaming varies with cognitive abilities as well as sleep stages.  Dreaming may be absent in a variety of neurologically damaged patients In spite of a lifetime of discriminating between dreams and reality, we can make the discrimination only after awakening  Dreaming per se does not require stimulus input either before or during sleep, since we normally have several dreams a night under a variety of stimulus conditions Even immediate pre-sleep experiences do not appear to affect our dreams consistently  References Antrobus, J.S., and Bertini M. (eds.) 1992. The Neuropsychology of Sleep and Dreaming. New Jersey: Lawrence Erlbaum Cavallero, C., and Foulkes, D. (eds.) 1993. Dreaming as Cognition. London: Harvester Wheatsheaf  Rechtschaffen, A. 1973. The psychophysiology of mental activity during sleep. In F.J. McGuigan, and R.S. Schoonover (eds.), The psychophysiology of thinking. New York: Academic Press, pp. 153-205