Week 6-Sleep Flashcards
What are 3 Psychophysiological measures for sleep stages
-Looks at how we sleep and how our muscles respond
- Electroencephalogram (EEG): electrodes attached to the scalp record electrical activity of the brain
- Electromyogram (EMG): electrodes attached to the chin monitor muscle (muscle twitching/mouth opening) activity whilst sleeping
- Electro-oculogram (EOG): monitors eye movements (Important for REM stage as rapid fast eye movements)
What brain activity occurs during Stage 1 of Sleep? (alpha wake stage)
-Slower waves than that of alert wakefulness but still low-voltage (amplitude) and high-frequency (alpha: 8-12 Hz)
-As we progress from Stage 1 sleep through Stages 2, 3 and 4, there is a gradual increase in voltage (amplitude) and decrease in frequency
What are EEG recordings characterised by?
Frequency (number of waves per second) and amplitude (size of a wave e.g., much bigger in stage 3)
What brain activity occurs during Stage 2 of Sleep?
-Increase in theta wave activity (4-7 Hz) and the body goes into a stage of deep relaxation (heart rate slows down and blood pressure decreases)
-Theta waves are interrupted by brief bursts of activities known as sleep spindles (high-frequency)
-Spindles are 1-2 second bursts of 12-14 Hz waves (high frequency bursts)
-A K-complex can also be observed - a very high amplitude pattern of brain (large negative wave and single positive wave which goes downwards)
What brain activity occurs during Stage 3 of Sleep?
Deep sleep or slow-wave sleep is defined by the occasional presence of delta waves - largest and slowest waves (1-2 Hz)
-Large and slow delta waves in EEG phase
What brain activity occurs during Stage 4 of Sleep?
Predominance of delta waves - we stay in stage 4 for a time before retreating back through sleep stages to stage 1
Stage 3 and 4 together are referred to as slow-wave sleep (SWS)
How does Stage 1 differ after a full cycle of sleep?
-After stage 4, we return to stage 1 but sleep activity is NOT the same
Initial Stage 1: First period of stage 1, not marked by major EMG or EOG activity changes (no muscle twitches, atonia or eye movements seen)
Emergent Stage 1: Subsequent stage 1 periods, marked by loss of muscle tone and characterised by rapid eye movements (REMs)
-All other stages of sleep are known as non-REM (NREM) sleep
What is brain activity like in the 90 minute sleep cycle?
Awake and Alert: Beta brain waves (has received a lot of attention lately in terms of drugs, pharmacological treatments for anxiety etc.,)
Awake but Drowsy: Alpha brain waves
50-70 minutes:
Stage 1 NREM Sleep: Mixture of alpha and theta brain waves
Stage 2 NREM Sleep: Sleep spindles, K complexes, theta brain waves, and beginning of delta waves
Stage 3 NREM Sleep: Mixture of thelta and delta brain waves
Stage 4 NREM Sleep: Delta brain waves
5-15 minutes:
REM Sleep: Fast, active brain waves accompanied by rapid eye movements (REMs)
-Never completing a full cycle=poor quality sleep
What do we observe in REM sleep in terms of brain activity and dreaming?
-During REM sleep we observe high brain activity and lack of muscle tone
-REM sleep is thought to be the physiological correlate of dreaming as 80% of dream recalls happen during awakenings from the REM sleep - while only 7% arise from NREM (not full narratives but isolated experiences e.g., “I was falling”)
-Along the night, the proportion of REM increases and NREM decreases. REM periods increase in length and frequency towards the morning (as cycle repeats)
How was the 2 key brain areas in the hypothalamus involved in sleep regulation discovered?
-The 2 key brain areas involved in sleep regulation was discovered during World War 1 by Constantin von Economo - a Viennese neurologist
-He examined victims of a serious viral infection - encephalitis lethargica - which led to the deaths of about 1.5 million people in a 1915-1926 epidemic
-The majority of patients slept for more than 20 hours per day (lethargy), arising only to eat and drink. Their cognitive function was intact and could communicate, but they would soon return to sleep
-A minority of patients had difficulty sleeping
-The neurologist wanted to look at the difference between those who slept for 20 hours and those who struggled to sleep to determine the region responsible for sleeping too much and for being awake
What 2 key brain areas in the hypothalamus were found to be involved in sleep regulation?
-He found that deceased victims with excessive sleep symptoms had damage in the posterior hypothalamus (wakefulness is associated with PH), whilst victims with the opposite problem had damage in the anterior hypothalamus (sleep is associated with AH)
-His findings and assumptions about the hypothalamus were later confirmed by lesion and animal experimental studies (look at fMRI studies and neuroimaging for additional reading)
What did Bremer (1936) discover after severing the brain stems of cats in several areas?
- Cut between the inferior and superior colliculi to disconnect their forebrains from ascending sensory input to not go to the upper part of the cortex (“cerveau isole” (upward dash on e), or isolated forebrain) –> continuous SWS (slow-wave sleep)
- Transection (cutting through) caudal to the colliculi (“encepale isole”) (upward dash on 2nd e and i), or isolated brain) cutting most of the same sensory fibers –> normal sleep cycle)
-This suggested that the structure involved in wakefulness was located somewhere in the brainstem between these two transections
What are the 4 pieces of evidence that the reticular activating system is involved in sleep? (based on Bremer’s cat study)
- Cats with a midcollicular transection (i.e., a cerveau isole preparation) displayed a pattern of continous slow-wave sleep in their cortical EEGs.
- Lesions at the midcollicular level that damaged the core of the reticular formation, but left the sensory fibers intact, produced a corticial EEG indicative of continous slow-wave sleep.
- Electrical stimulation of the pontine reticular formation desynchronised the cortical EEG and awakened sleeping cats.
- Cats with a transection of the caudal brain stem (i.e., and encephale isole preparation) displayed a normal sleep-wake cycle of cortical EEG.
-Together, these 4 findings suggest that a wakefulness-producing area was located in the reticular formation between the cerveau isole and the encephale isole transections
What were 2 more findings which indicated this structure was the reticular formation?
- Partial transections at the cerveau isole level disrupted normal sleep-wake cycles of cortical EEG BUT only when they severed the reticular formation core of the brain stem.
- Electrical stimulation of the reticular formation of sleeping cats awakened them
-Based on these 4 findings Moruzzi and Magoun (1949) proposed that low levels of activity in the reticular formation produce sleep and that high levels produce wakefulness –> reticular formation known as the reticular activating system.
What do similarities between REM and wakefulness suggest + what is REM sleep controlled by?
-Similarities between REM and wakefulness suggest that the same brain area might be involved in controlling both.
REM sleep is controlled by nuclei in the caudal reticular formation, each controlling a different aspect of REM:
-Atonia (loss of muscle tone)
-Rapid eye movements
-Cardiorespiratory changes
What is the Neurochemical control of sleep?
-Sleep is regulated - suggesting a monitoring mechanism
-Do sleep-promoting substances or wakefulness promoting substances exist?
-Substances do not appear to circulate in the blood just produced in the brain (NMs or NTs)
-Controlled by chemicals that are produced and act within the brain
-Because REM and NREM sleep are regulated independently there might be two substances (related to 2 brain regions mentioned prior)
The amount and timing of sleep is regulated by what 2 major factors?
- Homeostatic drive (the body’s need for sleep)
- Circadian rhythm (the body’s biological clock for the sleep-wake cycle)
-The control of sleep can also be allostatic (the need to be awake) in nature; under some circumstances it is important to stay awake, as for example when reacting to stressful events in the environment (danger, lack of water) –> override homeostatic control
What is adenosine?
-It’s a substance/ NT that accumulates with waking hours and drives the pressure to sleep
-Caffeine promotes wakefulness by acting as an antagonist of adenosine (slows it down delaying pressure to sleep)
-The need for sleep, or pressure to sleep is lowest after a good night’s sleep and then starts to build up as we awaken. The need to sleep will rise until we get to sleep.
What is the role of adenosine in the Neurochemical control of sleep?
-Adenosine is a neuromodulator that has an inhibitory (i.e., decreases) effect on neural activity
-In terms of increased brain activity glycogen stored in the astrocytes is converted into glucose to fuel neurons
-When glycogen levels start to fall (energy depletion), adenosine starts to accumulate
-Caffeine blocks adenosine receptors (to remain awake longer)
-During SWS, neurons in the brain rest and the astrocytes renew their stock of glycogen (taking adenosine levels back to normal)
-If wakefulness is prolonged even more adenosine accumulates
-Since adenosine inhibits neural activity, it can produce the cognitive and emotional effects/impairments seen during sleep deprivation.
