Sleep & Dreaming Flashcards
What is sleep?
Reversible state
Recurring
Reduced responsiveness to the environment
Reduced or absent consciousness
Suspended sensory activity, inactivity of nearly all the voluntary muscles
What are endogenous and exogeneous influences?
Endogenous influences: are influences originating from inside the body, specifically from the nervous system
Exogenous influences: are influences originating from outside the body e.g. light, temperature, environment
What are circannual rhythms?
e.g. animals story food for winter
animals can’t rely on external cues only
e.g. animals need to start storing food before it gets too cold
What are circadian rhythms?
Regulates the frequency of eating and drinking, body temperature, secretion of hormones, urination, sensitivity to drugs
Are there any cues for endogenous rhythms? What is the purpose of these rhythms? How long are they?
Purpose: keep our internal workings in phase with the outside world
Rhythm is slightly longer than 48 hours
No exogenous cues
What are zeitgebers? What is the most important zeitgeber?
Zeitgeber: stimulus that resets the circadian rhythm
Light is crucial to reset this
Other zeitgeber: exercise, noise, temperature. These are less effective than light
In the study by Roenneberg et al (2007) what was the procedure and results for the ‘sun time’ in Western and Eastern Germany?
The whole of Germany is on the same time zone
But the sun rises 30 mins earlier in the East
People from both sides reported the times they were waking up and going to bed
The midpoint was calculated
East Germans midpoint was 30 minutes earlier than West Germans
How does melatonin and cortisol fluctuate during the day and night?
High cortisol during the day, with low melatonin
More active
High melatonin during the night, with low cortisol
Sleeping
What are examples of disruptions to circadian rhythms? Why is there a disruption? Can everyone adapt to these disruptions?
e.g. monday morning blues, daylight savings in spring, jet lag, shift work
Mismatch between internal circadian clock and external time
Easier for some, more difficult for others
What is jet lag? What are phase delays? What are phase advances? How does this affect sleep and body temperature?
Sleepiness during the day but sleeplessness at night
Travelling west: phase delays (late to go to bed and late to get up) Difficulty going to sleep
Travelling east: phase advances (go to bed earlier and wake up earlier) Difficulty staying asleep
Facilitated by body temperature, lowest temperature when asleep
Is it easier to fly west or east? Why? How long are our endogenous cycles, so how can this help with phase delays and phase advances?
Easier to adapt to jet lag when flying west because the day of the travel is lengthened
This is shortened when travelling east
Endogenous cycle is 25 hours, so we can cope better with phase delay than phase advance
How can shift work be an example of phase delay and phase advance? Why is disrupting a worker’s sleep cycle bad?
Rising early or retiring to bed earlier is a phase advance
Going to bed late or getting up late is a phase delay
Accidents can happen when a worker’s sleep cycle is disrupted by a night shift
e.g. more lorry accidents between 4am and 7am, chernobyl occurred between 1am and 4am
How does sleep change as an infant newborn and during adulthood? What is the duration? Is it disrupted? When do they sleep?
In adulthood you can sleep throughout the night with no disruptions. This duration of sleep of sleep is shorter
Newborn infants need a longer duration of sleep. This is more disputed. they sleep throughout night and day on and off.
How does sleep change in old age? How long is it, is it broken up, when do they wake up? Why?
Amount of sleep decreases
More fragmented
Shifts earlier
More occasional wake ups
But is this due to a reduced need of sleep or decreased capacity of sleep mechanisms?
Where is the Suprachiasmatic nucleus located? How does it help circadian rhythms? If it is damaged, what happens?
Parts of the hypothalamus located above the optic chiasm
The main control centre of circadian rhythms of sleep and temperature
Damage to the CSN results in less consistent body rhythms that are no longer synchronised with environmental patterns of light and dark
How does the SCN help circadian rhythms? What happens regarding action potentials and genetics?
Cells in the SCN fire their action potentials in a particular rhythm
The circadian rhythm generated by the SCN are genetically controlled
How does the SCN receive light information? What is the optic nerve, the retinohypothalamatic path and melanopsin?
Light resets the SCN via a small branch of the optic nerve (the retinohypothalamatic path)
Travels from retina to the SCN
The retinohypothalamatic path comes from a special population of retinal receptors that have their own photopigment called melanopsin.
These cells respond directly to the light and do not require any input from the rods or cones
Are blind mole rats able to follow sleep/wake cycles? Why is this the case in regards to melanopsin cells?
Blind mole rats
There are eyes but no muscles to lift the lids nor lenses
Able to follow steady sleep and wake cycles
The melanopsin cells are fully functional in the absence of functioning rods and cones
Where is the pineal gland located? How does the SCN regulate the pineal gland? What hormone does the pineal gland secrete? How does this help circadian and circannual rhythms?
The SCN regulated waking and sleeping by controlling activity levels in other areas of the brain such as the pineal gland
Located posterior to the thalamus
Secretes melatonin, a hormone that increases sleepiness
Melatonin also regulates circadian and circannual rhythms
There are 2 proteins which generate the circadian rhythm. What is the period and timeless protein? What happens to the sleep/wake cycle when they are high or low?
Period: produces proteins called PER
Timeless: produces proteins called TIM
When they’re high they induce sleepiness, low induces wakefulness
What is an actigraph?
Actigraph watch is a recording device with an accelerometer (movement sensor)
What is polysmonography?
Uses multiple methods to look at brain, heart, muscle and eye movement activity
What are some advantages of using an EEG?
Equipment is cheap
Low invasiveness
Can be used to study the brain activity over an extensive period of time
Can be used on a wider range of patients e.g. babies and dogs
How does an EEG detect brain activity? How does it work in regards to neurons?
Record electrical activity in the brain
Measures the changes in the potential of the postsynaptic neurons
Groups of neurons firing at the same time
Electric activity is detected by placing electrodes on scalp and amplifying them and displaying them on a screen
What happens in stage 1 sleep? Is there any frequency waves? What happens to brain activity?
The EEG is dominated by irregular, jagged, low voltage waves
Brain activity begins to decline
Alpha waves present
State of relaxation
5% of sleep
What happens in the stage 2 of sleep. What is the K complex? What are the frequency waves?
Sleep spindles
12 to 14 Hz waves
K complex: a sharp high amplitude slow negative wave followed by a smaller, slower positive wave
50% of sleep
In stage 3 of sleep, what are the type of amplitude waves? Is there neuron activity?
Slow, large amplitude waves (delta)
Slowing heart rate, breathing rate, and brain activity
Highly synchronised neuronal activity
Represents 15-20% of sleep
In stage 4, what wave patterns are seen? Is it a deep sleep? What happens to the postural muscles? When does REM occur?
Deep sleep but light sleep in other ways
Irregular, low voltage and fast
Postural muscles of the body are more relaxed
REM
20-25% of sleep
What did Von Econom find on dead autopsy patients? What had happened to these patients? What is the wakefulness centre and the sleep centre?
Autopsies on patients who died from Spanish flu where some would be lethargic and go into coma before dying, others wouldn’t sleep for several days then die
Found:
wakefulness centre: at the posterior hypothalamus or the upper midbrain, for those that were lethargic and comatose before dying
sleep centre: at the preoptic area of the anterior hypothalamus, for those that were sleepless before dying
How does the brain stem and reticular formation help the wakefulness centre? What happens when these areas are damaged?
Brain stem
(including the posterior hypothalamus and reticular formation)
Receives sensory information
Brain stem plays an essential role by maintaining the state of wakefulness
Damage leads to coma
Stimulation of the reticular formation awakens animals from normal sleep or energises those already awake
What happens if the anterior hypothalamus (controls the sleep centre) is damaged?
Anterior hypothalamus
Damage leads to sleepiness
How can inhibitory and excitatory neurotransmitters affect wakefulness and sleep? What are the types of drugs for each of these? How do they affect hormones?
Inhibitory (GABA): decrease temperature and metabolic rate, decrease stimulation of neurons
Excitatory (Acetylcholine, Norepinephrine, Histamine, Orexin): increase arousal, maintain wakefulness, increases cortical activity
PET scans can see REM sleep. There is increased and decreased activity in specific brain areas to trigger this… what are they?
Post Emission Tomography (PET)
Increased activity in the pons triggers REM sleep
Increased activity in the limbic system (emotional systems), parietal cortex and temporal cortex
Decreased activity in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex
What are PGO waves? What areas does it look at to measure REM sleep?
Pons Geniculate Occipital
Looks at waves in the occipital cortex, geniculate and pons
According to the evolutionary theory, how can the sleep/wake cycle help to conserve energy in regards to food? How can body temperature during the night conserve energy?
To conserve energy
e.g. food for bats is easily found at night time but for cows it’s during the day
During sleep body temperature decreases, this also saves energy as there’s no movement
What happens if humans go without sleep? Why is sleep important after working hard all day?
Sleep enables the body and brain to repair itself after working hard all day
Going without sleep: irritable, dizzy, hallucinate, impaired concentration
How much you sleep, doesn’t depend on how much we worked that day
What is the evidence that goes against the repair and restoration theory? In regards to physical/mental exertion, external cues, performance deficits, permanence of adverse effects and cognitive tasks?
None of the adverse effect are permanent
Disturbances after sleep deprivation is mainly due to attention tasks not cognitive tasks
No correlation between duration of sleep deprivation and the magnitude of performance deficits
Heavy physical or mental exertion increases sleep but only slightly
Without external cues, sleep tends to be shorter following long periods of wakefulness
What is the sleep dependent memory processing model (memory consolidation)? What happens in this model?
Model of sleep-dependent hippocampal-neocortical memory consolidation. At encoding the hippocampus rapidly integrates information within distributed cortical modules. Successive sleep-dependent reactivation of this hippocampal–cortical network leads to progressive strengthening of cortico-cortical connections, which over time, allow these memories to become independent of the hippocampus and gradually integrated with pre-existing cortical memories.
The sleep dependent memory processing model was adapted to the two stage model of memory consolidation. What happens in this model?
During waking, memory traces are encoded in both the fast-learning, temporary store and the slow-learning, long-term store (in the case of declarative memory these are represented by the hippocampus and neocortex, respectively). During subsequent slow wave sleep (SWS), active system consolidation involves the repeated re-activation of the memories newly encoded in the temporary store, which drives concurrent re-activation of respective representations in the long-term store together with similar associated representations (dotted lines). This process promotes the re-organization and integration of the new memories in the network of pre-existing long-term memories. However, declarative memory, because of its integrative nature (it binds features from different memories in different memory systems), benefits more from SWS-associated system consolidation, whereas procedural memories, because of their specificity and discrete nature, might benefit more from REM sleep-associated synaptic consolidation in localized brain circuits
The stage model of memory was adapted further. This created the sleep dependent memory processing (system consolidation) model. What occurs in this model?
A key issue of long-term memory formation, the so-called stability–plasticity dilemma, is the problem of how the brain’s neuronal networks can acquire new information (plasticity) without overriding older knowledge (stability). The two-stage model of memory offers a widely accepted solution to this dilemma. The model assumes two separate memory stores: one store allows learning at a fast rate and serves as an intermediate buffer that holds the information only temporarily; the other store learns at a slower rate and serves as the long-term store. Initially, new events are encoded in parallel in both stores. In subsequent periods of consolidation, the newly encoded memory traces are repeatedly re-activated in the fast-learning store, which drives concurrent re-activation in the slow-learning store, and thereby new memories become gradually redistributed such that representations in the slow-learning, long-term store are strengthened. Through the repeated re-activation of new memories, in conjunction with related and similar older memories, the fast-learning store acts like an internal ‘trainer’ of the slow-learning store to gradually adapt the new memories to the pre-existing network of long-term memories. This process also promotes the extraction of invariant repeating features from the new memories. As both stores are used for encoding information, in order to prevent interference, the re-activation and redistribution of memories take place off-line (during sleep) when no encoding occurs. Because in this model consolidation involves the redistribution of representations between different neuronal systems that is, the fast- and slow-learning stores, it has been termed ‘system consolidation’. For declarative memories, the fast- and slow-learning stores are represented by the hippocampus and neocortex, respectively.
What is the activation synthesis hypothesis? How can this explain dreams? How does the cortex, amygdala and pons guide this?
Begin with spontaneous activity in the pons
This activates many parts of the cortex (amygdala for emotion)
The cortex synthesises a story from the patterns of activation
Normal sensory information cannot compete with the self generated stimulation and hallucination as a result
What is the neurocognitive hypothesis? How does it differ from the activation synthesis hypothesis? How can sensory information and memories guide dreams according to this theory?
Dreams begin with arousing stimuli that are generated within the brain
Stimulation is combined with recent memories and any information the brain is receiving from the senses
Less emphasis on the pons or REM sleep
Suggests that dreams are similar to thinking, just under unusual circumstances
How can the brain generate images without constraint in dreams? What brain area is associated with this? How can we lose track of what is happening in a dream? What brain area is associated with this? What dictates the motivational and emotional content of a dream? What brain area is associated with this?
The brain is getting little information from sense organs, so other brain areas are free to generate visual images without constraints. Activity is high in the inferior part of the parietal cortex, which is important for visuo-spatial information.
Activity in the prefrontal cortex is suppressed, impairs working memory during dreaming, this means we can lose track of what’s happening in a dream
Activity is high in the hypothalamus and amygdala. Accounts for emotional and motivational content of dreams
There is a study with an animal following colours when awake. What happens whilst they were asleep?
Animal follows colours when awake: red, blue, purple, green
When the animal goes to sleep, they repeat the same pattern
This animal was able to follow the animals at a faster pace
