Sleep and Circadian Rhythms Flashcards
Information surrounding sleep
- Sleep is a natural, periodic state that involves reduced responses to environmental stimuli and decreased mobility
- It is a behaviour observed in all humans across cultures and numerous other species, even in unicellular organisms – humans spend a third of their lives sleeping
- Sleep is a type of behaviour that always fascinated people, especially because it involves dreaming (mythology, Sigmund Freud etc)
- In the last few years there has been a renewed interest in the scientific study of sleep
- Sleep differs from states such as coma (extended period of unconsciousness), vegetative state or brain death (no sign of brain activity and no response to stimuli)
- Sleeping is very different to resting
What are the 2 processes sleep is controlled by?
Homeostatic (S) if we do not sleep we accumulate sleep debt (the more we’re awake the more we want to go to sleep)
Circadian (C) – sleep tends to happen at a particular time during the 24-hour cycle
Two-process model of sleep
Circadian rhythm is regular, we are active during the day then we are less active during the night and this has a regular pattern.
For the homeostatic drive we start off with very little of this homeostatic drive and when we wake up we’re very alert but this drive accumulates the more we stay awake and then theres a point we want to go to sleep.
The Study of Sleep
Polysomnography
- The ‘gold standard’ of sleep research
- Discovered by Hans Berger 1929
- Used initially in cats but now it is used for research and for clinical purposes
- Involves recordings of electrical activity from multiple sources “poly” somnography
- Recordings revealed a specific sleep architecture (the way that things are changing)
Polysomnography: list the types of recordings
- EEG recordings (electroencephalogram): recordings of activity of populations of neurons in the brain underneath the skull
- EOG recordings (electrooculogram): recordings of activity of the muscles around the eyes to decipher eye movements
- EMG recordings (electromyogram): recordings of the activity of the muscles in the body
- These recordings can be combined with others such as heart rate, temperature, breathing (O2) etc.
During wakefulness, what are the different types of neuronal activity which are observed in the EEG recording?
Beta waves consist of irregular activity of 13–30 Hz.
- fast activity
- Beta activity takes place when the brain is processing information
- The person is alert and attentive to events in the environment or engaging in cognitive processes
Alpha waves consist of activity of 8–12 Hz.
- Occur when a person is resting quietly, not particularly aroused or excited and not engaged in strenuous mental activity
Stages of brain activity during sleep
- Sleep begins with a state of relaxation, feeling drowsy
- Stage 1 (3.5–7.5 Hz): presence of theta activity - it is a transition between sleep and wakefulness
- Stage 2: Sleep begins – characterized by irregular activity and also sleep spindles (12-14Hz) although these occur in other stages of sleep and K complexes which are only found during stage 2.
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Stage 3: High-amplitude and low-frequency delta activity (less than 3.5 Hz)
– Synchronized, regular waves, reflecting synchrony and coordination in the activity of neurons in underlying brain areas
– There is a slowing down of brain activity as well as other bodily functions, such as heart rate, breathing, temperature, kidney function, etc
– Sometimes referred to as slow-wave sleep (SWS), or deep sleep.
– hard to wake people up when they are in this stage
REM Sleep
1- what is and and characterised by?
2- what did Aserinsky and Kleitman,1953 find?
3- what did Michel Juvet, 1959 find?
4- what happens
1- A sleep phase characterized by increased brain activity and asynchrony in brain waves accompanied by muscle atonia
2- Aserinsky and Kleitman,1953: Sleep characterized by rapid eye movements - Rapid Eye Movement sleep (REM)
3- Michel Juvet, 1959: deep sleep, in terms of muscle activity but light sleep, in terms of brain activity (he thought the more we sleep the more our muscles relax)- Paradoxical sleep
4- Facial twitches, erections, vaginal secretions and dreaming occur during this stage
Brain activity during sleep
- Sleep recordings revealed four distinct patterns of activity, three stages of sleep (NREM), 1, 2, 3 and an additional REM sleep episode
- We cycle through each stage and back, with each cycle lasting approximately 90 minutes
Findings in other species?
SIMILAR FINDINGS
In other species/ mammals we can get very similar activity and similar recodings from EEG, EMG and EOG.
We can distinguish the 3 stages of sleep- in slow wave sleep we have little muscle activity and slowing of brain activity where as in REM we have more theta activity and brain is more active but very little recording in EMG.
Cycle of sleep on a typical night
Starts with wakefulness then goes through the different stages (stage 1 then stage 2), going into deeper levels of sleep (slow wave sleep) at stage 3. Then we come up to stage 2 and stage 1 then we might get a short REM episode and then go down again into deeper stages of sleep, then come up again and have another REM episode a bit longer this time. This processes repeats throughout the night.
Things to point out:
- we spend more time in slow wave/ deeper stages of sleep earlier in the night where as we may not even go to the slow wave sleep phase later in the night. (circadian component). It does make a difference what time we go to bed because we may miss some circadian patterns.
- the opposite happens for REM sleep- it starts off with short episodes but then we start to spend more time in REM sleep when closer to wakefulness.
Dreams:
1- discovered by?
2- considered important in?
3- what are most dreams related to?
4- what did Calvin Hall et al (1982) find?
1- Discovered by Dement and Kleitman, 1957 when participants were awakened from REM sleep. They tended to report vivid dreams
2- Considered important in psychoanalysis:
- Freud thought of dreams as the ‘royal route to the unconscious’ and an opportunity to realise our secret wishes
- Jung viewed dreams as a glimpse into the collective unconscious
3- Most dreams are related to events that happen in a person’s life
4- Calvin Hall et al (1982): analyzed 10,000 dreams of healthy people and found that more than 64% are associated with sadness, anxiety or anger whereas 18% are happy dreams and only 1% involved sexual content
Contemporary views on dreaming
Allan Hobson (2004)
Activation-synthesis hypothesis (bottom-up view on dreams)
- The brainstem is activated during REM and sends signals to the cortex which creates images with actions and emotions from memory
- The frontal cortex is less activated during dreaming so there is no logic in the timing or the sequence of events, although the person tries to organise the content into a logical story when awake
- There is no meaning in dreaming although dreams are based on each person’s experiences
Contemporary views on dreaming
Valli and Revonsuo (2009)
Argued that dreams are biologically adaptive and they lead to enhanced coping strategies
- Coping Hypothesis (also known as ClinicoAnatomical Hypothesis) (top-down view on dreams)
- People dream about events that they find threatening in their lives and this helps to find solutions to their problems
- Support for this hypothesis is the evidence that problem solving occurs during sleep (“sleep on it”)
The neural basis of sleep
1- idea of?
2- what produce sleep-wake cycles?
3- _____ secreted by ____ during _____ promotes sleepiness
- Idea of a sleep-inducing substance perhaps due to the fact that many natural substances cause sleep i.e. morphine
- Neurochemicals and hormones produce sleep-wake cycles
- Melatonin secreted by the pineal gland during the dark promotes sleepiness but it is not the only one
Adenosine
- Accumulates during the day, after prolonged wakefulness and promotes sleep
- Caffeine antagonises the effects of adenosine and decreases sleepiness
- Released by astrocytes and it is a way to signal that there is very little energy. So astrocytes start to release adenosine to slow down the activity of our neurons. When we go to sleep (especially during slow wave sleep) the adenosine gets moved away and then we are able to function well. We have discovered that is we drink caffeine when we are really sleepy, we’re able to extend our wakefulness.
Observations and Discovery:
What did Constantine von Economo early 20th century observe and findings
- observed patients with encephalitis
findings:
- Most had continuous sleepiness and would wake up only to eat and drink and these had damage in the base of the brain
- Fewer patients displayed insomnia and they had damage in an area of the anterior hypothalamus
Observations and Discovery
- what brain area was discovered and what does it contain?
- what does damage to this area cause?
- what does electrical stimulation to this area cause?
- This area of the anterior hypothalamus was later identified as the ventrolateral preoptic area (vlPOA) which contains inhibitory neurotransmitters such as GABA
- Damage to this area causes insomnia in rats and they eventually die
- Electrical stimulation of this area causes sleepiness and sleep
Brain Areas involved in Wakefulness and Arousal
- who discovered these regions accidentally?
- what did they do?
- what resulted in waking the animal?
- Moruzzi and Mogoun (1949) discovered these regions accidentally
- While recording from anaesthetized cats they stimulated the cat’s brainstem and noticed that the delta waves were replaced by beta waves
- Stimulating the brainstem in a sleeping cat resulted in waking the animal
Brain Areas involved in Wakefulness and Arousal
- what brain area promotes arousal?
- list the neurotransmitters important
The reticular formation (Reticular Activating System-RAS) is comprised by several nuclei in the brainstem that extend to the forebrain to promote arousal
- Locus coeruleus (LC - NE/NA)
- Raphé nucleus (RN – 5HT) - producing serotionin
- Tuberomammillary nucleus (TMN-Histamine) antihistamines
- Nucleus basalis of Maynert (NBM-Ach) also high during REM sleep
Key components of ascending arousal system and key projections from the VlPOA to areas of the ascending arousal system
The ventral lateral pre-optic area is inhibiting/ shutting down this arousal system using GABA because we want to sleep
The arousal system is doing the opposite, it is activating, releasing the neuron transmitters. They’re all promoting their individual neurotransmitters and sending projections to different brain areas and the cortex because we want to be alert and processing information.
