Lecture 9 Flashcards
Sleep
By age 60, will have spent 20 years asleep. Larger animals sleep less than small animals, moderated by the fact that predators are sleeping more and prey are sleeping less.
Our rhythms
Biological rhythms are regular fluctuations in any living process. Circadian rhythms are a pattern of behavioral, biochemical, or physiological fluctuation that has a 24 hour period (e.g. hormone levels, body temp, drug sensitivity). These are the most common rhythms. Ultradian rhythms refer to a rhythmic biological event with a period shorter than a day, usually from several minutes to several hours (e.g. bouts of activity, feeding, hormone release). Infradian rhythms - rhythmic biological event with a period longer than a day (menstrual cycle, breeding in animals).
The circadian rhythm - our biological clock
Diurnal vs nocturnal. Mammals have a precise circadian clock, but it is longer than 24 hours. 24 hr and 7 min if remove circadian cues like sunlight. If rodent doesn’t know it’s day or night, sleeps the same amount of time, but the clock shifts so that it’s eventually sleeping during the day because not getting any cues (slightly longer clock than 24 hour). Environmental stimuli synchronize our biological rhythms. Entrainment - environmental stimuli that link you to biological clock (like alarm clock, link to 24 hour world). Zeitgeber - helps coordinate internal rhythms, any stimulus that would keep you on the 24 hour clock rather than longer one (sun going down ex).
The anatomy of the circadian clock
The SCN within the hypothalamus serves as the biological clock - lesions to SCN portion of hypothalamus eliminate circadian rhythms (rats sleep at very random time). Completely random in dim light - loses all coordination of sleep/wake. Brain transplants prove SCN contains circadian clock. Removed SCN from rats w/ 20 hr running period (allele variation that causes people/rats to have shorter vs longer circadian clock). If you put that into another rat, the rat develops that clock. Therefore, it has a causal role in the circadian system.
Melatonin
Some evidence supplement works for helping you sleep. As night approaches, the pineal gland secretes hormone melatonin. Regulated by SCN. Informs brain about day length of entrainment (synchronization) of circadian rhythms. Exogenous melatonin is a standard treatment for sleep disorders. It is a chronobiotic - slightly advancing the circadian phase by 30 min to 1 hour. It moderates body temperature (a variation that happens as you get closer to sleep), ells body time to sleep with the temp. Advancing movement and trajectory of body temp- decreases body temp.
SCN and retinohypothalamic pathway
The entrainment pathway consists of specialized retinal ganglion cells that project to SCN via the retinohypothalamic tract. This is kind of an offramp of the geniculate path. it bypasses the visual system, direct info from environment for SCN. These cells do not rely on traditional photoreceptors but on a photopigment called melanopsin. Blind people can still have this pathway and can maintain circadian rhythms, some blind people (about 60%) don’t have this and it’s a much more debilitating condition for them. They can’t entrain behaviors to outside world. Photoperiod = what time of day it is. Transgenic mice lacking rods and cones will still maintain a circadian clock if melanopsin containing ganglion cells are present. Most blind adults lack melanopsin containing RGCs and show free-running circadian rhythms. Melatonin can help entrain circadian rhythms among blind individuals. Photoperiod also drives SAD - melanopsin cells important for maintaining mood.
Individual differences
Morning vs evening person. Per gene has variation affecting if you’re morning or evening. Implicated in bipolar disorder - dysregulation of circadian rhythms.
Human circadian rhythm
When isolated from cues about time of day, human circadian rhythm shifts from 24 to 25 hours
Sleep architecture and EEG
Good at measuring sleep, can sleep with EEG cap on, can measure basic electrophysiology that covaries with sleep. Sleep architecture - prototypical profile of electrophysiological activity. Differences in REM vs non-REM. Electromyography- can measure eyes moving. Overall pretty active in REM, suppression of motor activity. REM sleep is referred to as paradoxical sleep - aside from eyes, body is paralyzed and has no muscle tone (atonia). Brainstem profoundly inhibits motor neurons through GABA transmission - motor neurons are hyperpolarized. REM behavior disorder. So you can’t act out dreams.
Sleep and EEG 2
Waking - desynchronization (this is good, supposed to happen), gamma and delta 30 cy/s. Stage 1 - alpha waves, starting to get a little slower 6-12 per second. Stage 2- spindles and K complexes, periods of desynchronization. Stage 3/4 - memory consolidation, immune. Stage 2 accounts for 50% of sleep, REM for 20%. REM sleep lengthens as night goes on (lasts 40 mins or so just before waking). Adolescents shift their circadian rhythms such that they wake later. It goes 1-4 then REM, then 4-2, then REM, then back down and up. Brief awakenings in REM. 2 is prominent in sleep, REM is not. You can have dreams in non-REM (factual), but the REM dreams are more fanciful and bizarre. MDD - reduced REM latency and decreased time spent in delta wave sleep. MDD associated with elevated REM activity/density.
REM and dreams
non-REM dreaming: more cognitive, factual. REM - being transported, microdreams as you fall asleep. Why do we dream? Activation synthesis theory: consolidate info. Nightmare - bad dream. Night terror - wake up in intense fear.
Sleep across species
Nearly all mammals display both REM and slow wave sleep. Certain marine mammals like dolphins do not display REM sleep. Atonia of REM most likely incompatible with needing to come to the surface to breathe. Marine mammals and birds may display unilateral sleep (one hemisphere at a time).
Sleep across the lifespan
Takes approx 16 weeks for a newborn to establish a 14 hour sleep rhythm. Infant mammals spend the majority of time in REM sleep. Sleep amount decreases over age, more awakenings. May be related to memory decline. 50% reduction slow wave by 60, absence at 90. Slow wave critical to memory consolidation and growth hormone secretion.
Functions of sleep
Energy conservation: slow wave sleep in particular is metabolically conservative. Ex. small mammals with high metabolism sleep more. Ecological niche adaptation: out in wild, diurnal not up at same time as predators. Body and brain restoration: growth hormones central to cell reproduction and regeneration secreted in slow wave sleep. Immune system processes occur at night - sleep deprivation can be fatal due to infection. Glial cells flush out waste during sleep. Memory consolidation: you only remember a dream if you wake up (hippocampus otherwise not there, brain does not store new info during sleep), crucial for consolidating memory experienced before bed - ex people perform better on verbal learning task after 8 hours of sleep versus 8 hours of daytime, slow wave sleep critical for consolidation of declarative (factual) memory, REM sleep critical for perceptual skills learning (visual discrimination). Brains connections shrink during sleep - forgetting, it’s adaptive to forget. Devoting resources to critical things, maintaining synapse connections for things we use, up to 15% reduction in receptor volume, pruning.
Tone study
Playing auditory cues during slow wave sleep that were present during initial memory consolidation enhances memory for that event.
