WEEK 5 - 7 Flashcards
(87 cards)
~WEEK 5~
Central Physiology
Brain tem rituclar formation
= - thalamus
- hypothalamus - basal forebrain
The main areas involved in sleep are:
- the brain stem,
- hypothalamus,
- pineal gland,
- the limbic system,
- and the cortex
- The brain stem reticular formation branches out to the thalamus and the hypothalamus
- the hypothalamus contains the sleep switch so it is a key area for sleep
- The suprachiasmatic nucleus is the coordinator of Process C and is located at the anterior of the hypothalamus alongside the pineal gland where melatonin is secreted
- melatonin sets the stage for sleep several hours later
- The thalamus is a sensory relay system and although information continues to arrive via the senses during sleep, it is important to have a sensory blockade so that meaningless information is not processed all through the night
- Without this blockade we would wake up continuously
- The basal forebrain branches out from the hypothalamus to other cortical areas
- cortical areas responsible for logic and planning, such as the prefrontal area, are largely inhibited during sleep
Where Does Sleep Emanate/originate from?
- the seat of wakefulness is the ascending reticular activating system (ARAS)
The ARAS is a system that includes:
- the pons,
- brain stem,
- reticular formation,
- pontine,
- mesencephalic tegmentum,
- and caudal diencephalons
- The pontine and midbrain areas also project to hypothalamocortical areas
- Much of what we know about these systems we learned by stimulating different circuits to produce wakefulness
- In other words, the cells within this system produce wakefulness
The cells implicated in wakefulness include (not an exhaustive list):
- Noradrenergic cells in the locus coeruleus (LC):
- We know this because when we monitor a single cell in an experiment, we observe that these cells fire at their highest rate when awake and decrease while falling asleep
- These cells completely stop firing during REM
- administering drugs that stimulate noradrenergic cells in the LC produces wakefulness - Serotonergic (5HT) cells in the raphe nuclei (RN)
- Like the noradrenergic cells, single cell experiments tell us that serotonergic cells fire at their highest rate when awake and decrease while falling asleep
- they completely stop firing during REM - Cholinergic cells in the pedunculopontine tegmentum:
- Activating these cells promotes wakefulness
- a series of cat studies by Garcia-Rill and colleagues showed that electrical stimulation of this area of the brain caused wakefulness - Dopaminergic cells in the substantia nigra and ventral tegmental area:
- If you administer a dopamine antagonist (an antagonist is a drug that blocks the action of that chemical), you can produce sleep, including SWS
- So, if you block dopamine and it produces sleep—it means that this cell’s function is the opposite, which is wakefulness - Hypocretins/orexin:
- Their discovery was around the same time and two different labs named this chemical two different things, so it is always confusing as to whether you should call it orexin or hypocretin
- For the sake of convenience, we will always refer to it as orexin in this class**
- Orexin is produced in the hypothalamus, and these cells have projections into the LC and dorsal raphe
- They are excitatory peptides
- They appear to consolidate sleep and integrate metabolism and sleep
- If you block orexin, you fall asleep
- Those with narcolepsy have deficits in orexin and fall asleep involuntarily or lose muscle tone like they are asleep, even when awake
- Remember the video of a Doberman Pinscher with an orexin deficiency - Histamine:
- Histamine is produced in the hypothalamus and is an excitatory neuron
- It is blocked by GABA when sleep is produced
- When you have a cold or allergies, you may take a drug that blocks histamine (an antihistamine) and antihistamines have sedating properties
Sleep occurs when the ascending reticular activating system (ARAS) is deactivated and when the sleep switch in the hypothalamus is turned on. There are a variety of chemicals associated with sleep and sleepiness. For example:
- Adenosine:
- When cells are working, they produce a byproduct called adenosine that accumulates in the basal forebrain over the waking hours
- from the moment you are awake and your cells start to work and produce this chemical, you begin building a drive for sleep that night
- The greater the amount of adenosine build-up, the greater the drive for sleep (the sleepier you become)
- While this build-up of Process S occurs, you are also receiving alerting signals from the clock at increasing intensity across the day so that you will not continuously fall asleep because of the adenosine build-up
- You want a sufficient build-up of adenosine in order to sleep deeply, so chemicals that block the build-up interfere with sleep quality
- One such chemical is caffeine
- Caffeine blocks adenosine and interferes with sleep quality - GABA:
- Gamma-aminobutyric acid (GABA) is one of the primary sleep chemicals
- GABA inhibits wakeful chemicals such as histamines, 5HT, and acetylcholine activity
- GABA promotes sleep by exerting effects in the basal forebrain and hypothalamus
- it exerts effects on the sleep switch in the ventrolateral preoptic area (VLPO)
- Most sleeping pills act on GABA - Melatonin:
- Produced by the pineal gland with receptors in the SCN and hypothalamus (where thermoregulation occurs)
- Exogenous melatonin has sedative properties when endogenous melatonin is not present
- This means that if you took a melatonin pill when melatonin was not present (e.g., 4 p.m.) you could expect some sedation
- If you took the same melatonin pill at your normal bedtime (e.g., 11 p.m.), the pill would have little effect because melatonin was secreted hours earlier
Respiration During Sleep
- Let’s move away from central physiology to consider cardiovascular physiology
- In order to meet the metabolic needs of the body, we exchange gases and regulate the balance between CO2, O2, and the pH in the blood = we breathe
- Breathing is rhythmic; we take in/inhale O2 and expel/exhale CO2
- although breathing rates can increase or decrease, the rhythm more or less remains constant
- When we are awake we have some control over our breathing—we can even hold our breath for a certain amount of time
- However, during sleep, breathing is not volitional
- During sleep, breathing is a steady rhythm generated by pontomedullary neurons
- During wakefulness, there is limbic, motor cortex, and pontine input into breathing but during sleep, breathing is under brain stem control
- During slow wave sleep, breathing slows down considerably and is the most rhythmic
- During REM sleep breathing can become less regular and more closely resembles breathing during wakefulness
- There can be inter-breath variability; blood pressure increases as does heart rate, but the most important thing to note is the variability
- The unusual variability in REM sleep may relate to the phasic activity (e.g., PGO spikes) or even to dream content
Wakefulness reflective (brainstem) behavioural (motor cortex) emotional (limbic system) = respiratory muscles
Sleep
brainstem = respiratory muscles
NOT motor cortex or limbic system
Obstructive Sleep Apnea
Obstructive Sleep Apnea (OSA):
- a breathing disorder in which breathing stops for a minimum of ten seconds and the brain wakes up (often outside of awareness) to reinitiate breathing
- OSA is caused by an obstruction or narrowing of the airway
- there may be too much soft tissue in the palate or upper airway or hypertrophy of the muscles in the upper airway (e.g., hypertrophied adenoids or tonsils) or abnormal bony structures
- Imagine that your airway is like a cloth tube, if there is air being pushed or sucked through it, the tube is open but once the air stops the tube deflates
- The pharynx, or pharyngeal muscle, loses tone during sleep, particularly in REM sleep wherein we lose muscle tone through most of our body
- Other factors influencing collapsibility is weight, particularly in the neck
- Weight pushing down on the airway narrows the path for which air can enter and leave
- During the day, people can compensate for an obstruction in the airway by stiffening the airway but this does not occur at night and they cannot compensate for the reduced flow coming through a small airway
- The result of apneic events is severe sleep deprivation as well as cardiovascular and insulin problems
SIDs
Sudden Infant Death Syndrome or SIDS:
- occurs in the less than 1% of babies under the age of one-year-old
- It is unknown as to what causes SIDS but it is believed that the baby asphyxiates and is unable to reinitiate breathing or to wake up to eliminate the obstruction (e.g., if the baby is face-down they may not wake up to unblock their nose or mouth)
- There may be a vulnerability to SIDS (e.g., abnormal brain stem 5HT receptors or immature respiratory system because of premature birth) that interacts with environmental problems such as sleeping face-down or smoking in the home
Blood Pressure (BP) and Heart Rate (HR)
- HR and BP are lower during sleep and BP dips by about 10%
- If you deprive someone of sleep they do not show the dipping so it may not be circadian—it may relate to sleep itself
- BP and HR decrease from stages 1 to 3/4NREM
- NREM is a time of parasympathetic activity
- In REMS both increase and there is considerable variability
- Arousals are associated with sympathetic activity
- Thus disturbances in sleep are associated with sympathetic activity
Endocrinology and Sleep
- Sleep is an active time for your endocrine system
- Growth hormone (GH), a hormone important for tissue restoration and protein anabolism, is secreted for the most part exclusively at night
- GH secretion occurs very close to sleep onset and most often coincides with slow wave sleep (SWS)
- GH is associated with a healthy build-up of sleep drive, which you learned about when you learned about the homeostatic system
- Because of its association with SWS and the observed increases after sleep deprivation, some use it as evidence that sleep serves a restorative function
- GH production drops off over the course of the night and GH concentration is quite low in the second half of the night (this is associated with SWS production or lack thereof in the second half of the night)
- Men have a single GH secretion peak but women have several peaks of secretion
- GH is related to the hypothalamic-pituitary-somatotrophic (HPS) system
- Cortisol is a hormone associated with stress—it is released in response to stress but also exhibits a circadian rhythm
- Cortisol reaches its lowest point or nadir in the twenty-four-hour period around sleep onset
- Cortisol stays low but then begins to circulate again around 2 to 3 a.m. and increases towards waking
- Corticotropin-releasing hormone is released by the hypothalamus, which stimulates cortical production in the adrenal cortex—part of the hypothylamic-pituitary-adrenal (HPA) system
- Thus the HPS and HPA systems reciprocally interact with one another to regulate sleep
- Melatonin reaches its peak in the early morning hours and begins secretion in response to the offset of light in the evening
- Renin is a hormone related to the REM/NREM cycle
- Renin oscillates throughout the night and peaks during NREM and reaches a trough (acrophase) during REMS
Sleep and the Autonomic Nervous System
- The autonomic nervous system (ANS) is active during sleep
- The ANS has two branches: the parasympathetic (PNS) and sympathetic (SNS)
- The sympathetic branch is known for its fight or flight response
- it enables us to deal with emergencies by inhibiting less important bodily processes and mobilizing resources to respond to threats
- Parasympathetic activity is known for the conservation or maintenance of resources
- During sleep, the parasympathetic activity is less active except for NREM; for example, digestion slows
- Bodily waste still moves through the body but very slowly
- Saliva is not produced and we do not have a swallowing reflex
- Our blood pressure decreases and our breathing slows
- The one exception is that during REMS, the PNS becomes more active
- Our SNS decreases during sleep, particularly during NREM
- The exception is that during REMS, there can be bursts of activity, described as a storm, wherein there are dramatic and irregular surges of activation/deactivation of organs
- When this SNS activity occurs, we are more prone to arousals and wake ups
Is There an Alarm Hormone?
- Born and colleagues (1999) monitored the blood levels of adrenocorticotropin (A) levels of fifteen people for three nights
- Adrenocorticotropin (A) is a hormone that is secreted just before rising and communicates to the adrenal gland to release cortisol
- Cortisol starts to rise in the morning hours
- Once the researchers collected the baseline levels, their independent variables were a combination of instructions and forced wake-up times
- The dependent variable was what happened to A levels
- In the first condition, they were told the night before that they had to get up at 6 a.m. and they were indeed woken up at 6 a.m
- In this group, A increased in the hour before the scheduled wake-up time
- In the second group, they were told the night before that they had to get up at 9 a.m. and they were indeed woken up at 9 a.m
- Similarly, A increased in the hour before the scheduled wake-up time of 9 a.m
- In the final group, they were told the night before that they had to get up at 9 a.m. but they were woken up (unexpectedly) at 6 a.m
- The result was that there was no rise in A before the unexpected 6 a.m. wake-up time
- This suggests that there is a chemical “expectation” of sorts of rise time and it prepares your body for an awakening
Summary WEEK 5
There are several neurochemicals associated with sleep and wakefulness. These include:
- noradrenaline in the locus coeruleus (LC)
- serotonin in the raphe nuclei (RN)
- acetylcholine in the pedunculopontine tegmentum
- dopamine in the substantia nigra and ventral tegmental area
- hypocretins/orexin and histamine in the hypothalamus
- adenosine in the basal forebrain
- GABA in the basal forebrain and hypothalamus (especially the ventrolateral preoptic area)
- melatonin in the pineal gland
- Breathing during sleep is rhythmic and no longer under volitional control
- During REM sleep, breathing, heart rate, and blood pressure become less regular and more closely resemble breathing during wakefulness
The endocrine system is active during sleep. Key hormones include:
- Growth hormone: the chemical associated with SWS
- Cortisol: a hormone associated with stress that exhibits circadian rhythmicity
- Melatonin: a hormone associated with light offset which also exhibits circadian rhythmicity
- Renin: a hormone related to the REM/NREM cycle
- During sleep, autonomic nervous system activity is low
- During NREM we have increased PNS activity
- During tonic REMS, the PNS becomes more active and during phasic REMS, there are surges of organ activation (SNS activity)
Tonic REM:
- a parasympathetically driven state with no eye movements, decreased EEG amplitude, and atonia
~WEEK 6~
Ryecast video: Sleep and dreams
- we don’t know what’s causing dreams/what’s going on in the brain when we dream
- When looking at the brain during REM sleep, the midline of the brain lights up = all the regions involed in emotions
- looks like when we are sleeping, the logic part of our brain is turned off and the part of our brain that remembers events and sequences is turned off, and cranks up the emotional system
The brain dreams about 3 main things:
- things that are recent
- things that are repetitive
- things that are emotional important
Neurobiology of Dreams
- Dreams in REMS are associated with a greater rate of recall than other stages so most of what we know about dreams from a physiological standpoint has been collected from REMS
- We can discern a lot about dreams from brain activation studies
- Some areas of the brain are not active during dreaming, for example, the prefrontal cortex (PFC)
- The PFC is an area associated with planning and purpose, thus with the PFC largely “asleep,” dreaming is associated with a loss of volition and logic
- There are several areas that are active while dreaming
- limbic structures, associated with emotionality, are highly active during dreaming
- The pontine and midbrain reticular activating system (RAS) areas associated with consciousness are active during dreaming
- The hypothalamus and basal forebrain areas are active, which may explain the primitive instinctual content in dreams
- Visual imagery may be associated with the activity observed during dreams in the visual association cortex
- the cerebellum, an area associated with movement, and primary motor cortices, and areas associated with sensation and movement, are all active during dreaming
- Essentially, during REMS dreaming, acetylcholine, a chemical associated with arousal is active
- Emotion and sensory areas are active but the prefrontal cortex which is associated with planning and volition is quiet
- As the text says, this is why we may be missing the “reality check” in our dreams
- It explains the emotional, instinctual, primitive nature of our dreams as well as the vividness of our dreams
Do We Dream Only in REMS?
- We appear to dream in both REMS and NREM although this is somewhat contested
- The discovery of dreams was during REMS, so there has been a perception that we only dream in this stage of sleep
- There is evidence that we may also dream in NREM, although the recall of dream content is less than half of that of dream content when awoken from REMS
- Some view the activity during NREM to be less consistent with dreams
- There are differential areas of the brain activated during dreaming from REMS versus NREM
- In both REMS and NREM people recall “dreams,” although, as stated above, there is less likelihood of recall when awoken out of NREM
- The type of dream most typically reported out of NREM is one of mundane, brief descriptions of events, sometimes with some of the details obscured
Consider the following dream recalls:
a) Episodic memory sources (hippocampal): “I was at the cottage, but it wasn’t the cottage, during the summer, with Joan, but Joan was someone else.”
b) Emotional content (emotion structures): “I was scared. Maybe someone was after me?”
Which recall is most likely from REMS?
- The answer is B
- It is primarily emotional and less mundane
- Option A is likely NREM because it is an attempt to recall a fairly mundane event without much emotional context, along with some potentially nonsensical material
Why Do We Dream?
There are three general types of theories of dreaming:
- Psychodynamic theories
- Biological theories
- Cognitive theories
- Psychodynamic Theories
- Freud believed that dreams reveal people’s secret wishes and desires and are thus important
- Dreaming was an important activity because it released tension we experience from all of our “unacceptable” wishes
- Our “unacceptable” wishes were thought to appear in a disguised version
- For example, dreaming about a knife was supposed to be a dream about a penis
- Thus, part of Freud’s work was dream interpretation; that is translating disguised dreams into what he believed to be their “actual” meaning
- There is of course no evidence for this**
- Contemporary psychoanalysis continues the tradition of dream interpretation albeit typically with less of an emphasis on sex
- Carl Jung was a contemporary of Freud who broke away from Freud because of differences of opinion
- Both interpreted dreams but one major departure was labelled in the text as “dreams reveal, not conceal”
- The idea here is that Jung thought that dreams were not merely disguising unwanted wishes; sometimes dreams help people to solve waking problems
- This is a more positive view of dreams
- Although there is no evidence for dream interpretation per se, interestingly Dr. Rosalind Cartwright has shown that dreams may have emotionally adaptive purposes
Do we dream to cope?
- Dr. Rosalind Cartwright suggests that during dreams we are trying to “work through” emotional issues
- One of her studies showed that dream content about one’s spouse predicted improvements in depression in women following divorce
- The suggestion is that the dream process was somehow helpful in processing information related to the divorce that ultimately ameliorated the depression
- Sleep may help with emotional adaptation to negative experiences
- If research participants are shown negatively valenced pictures, they show increased negative arousal; that is the pictures are upsetting
- When the same participants sleep that night, those with the greater degree of REMS report better adaptation (i.e., less reactivity) to the pictures the next day
- Biological Theories
- The activation-synthesis hypothesis (Hobson, Pace-Schott, & Stickgold, 2000) explains dreams as a result of particular areas of the brain activating and the brain attempts to create a narrative that synthesizes/integrates the activated material
- For example, during sleep areas of the brain associated with emotion, instincts, sensation of where the body is in space and movement, memory, emotion, sensation (although incoming information is blocked) are activated/firing
- Other areas of the brain are not active—for example, the prefrontal cortex
- Remember that the prefrontal cortex is an area of the brain associated with logic, planning, and executive functioning
- there is plenty of activity in the brain, as areas are firing through the night, and the brain attempts to connect the information into a narrative but the area of the brain that might be able to integrate this most logically, is essentially asleep
- This may be why dreams can be so illogical
- So dreaming can be interpreted to be meaningless using this theory
- However, this theory does not necessarily mean that dreams are meaningless because the narrative is being created by your brain, using your memories, so it is unique to you
- Cognitive Theories
- Cognitive theories of dreaming essentially focus on how information processing differs or is similar to wakeful information processing
- Whereas psychodynamic theories focus on dreams as a clue to the unconscious, and biological theories view dreams as neural activity, cognitive theories see dreams as a type of thought
- Cognitive dream researchers wake participants repeatedly throughout the night and participants speak about their thoughts while being monitored via PSG
- Thought content (i.e., dreams) is reported whenever being awakened but the content becomes more visual and can be hallucinatory
- Another characteristic of cognition in this study is that thought is not under voluntary control as people enter sleep (as verified by the PSG)
- Thus, dreams can be seen as mental content similar to wakefulness but different in the visual experience (i.e., it can be hallucinatory) and not under volitional control
What is Lucid Dreaming?
- Lucid dreaming is when one is aware that one is dreaming while dreaming
- The methodology to study lucid dreaming is essentially to train research participants to signal the experimenter using an eye movement code to signal lucidity
ex. looking left two times and then right once to signal awareness while dreaming - The experimenter then looks at the physiological activity or nature of the subjective recall during this period as compared to a non-signaled segment of time
- There is some evidence that brain activity is different during lucid versus non-lucid dreaming
- The electrical activity during lucidity is characterized by higher frequency activity during lucidity
- research participants shift their EEG power, especially in the 40-Hz range to a higher frequency activity and especially in frontal regions of the brain
- Frontal activity and increased higher frequency activity is most typical of wakefulness; thus, lucid dreaming is best described as a mixed state of REMS and wakefulness
- Those interested in lucid dreaming believe that lucid dreaming could unlock more potential, including clinical potential
- For example, many think that lucid dreaming could be used clinically to work through emotional issues
- The most obvious group in mind are those with post-traumatic stress disorder (PTSD)
- People with PTSD often complain of nightmares, and effective treatments include exposure to the trauma event and a reprocessing/integration of the trauma material
- behavioural sleep medicine specialists have been helping people with PTSD to restructure their dreams for years without invoking the idea of the lucid dreaming label
- The technique is called imagery rehearsal and retraining therapy (IRT)
- In this therapy, nightmares are presumed to be a learned (involuntary) behaviour that can be modified by mentally rehearsing alternative dream scenarios
- Patients are told to write down a nightmare and then write out a dream with alternate content
- They then practice (by using their imagination) the new dream over and over again
- The new content is expected to appear in dreams in place of nightmare content
- Research supports that IRT reduces the number of nights with a nightmare, and results in improved self-reported sleep quality disturbance
- So, invoking the lucid dreaming concept is probably unnecessary
- Moreover, of people that respond to experiment advertisements for this type of study, only a proportion of people can be successfully trained to lucid dream
Can You Intensify Your Dreams?
- There are many medications and substances that can lead to reports of “intensified” dreaming, increased dreaming, or more unusual dream content
- For example, some antidepressant medications called selective serotonin reuptake inhibitors (SSRIs) can have this impact on dreaming
- In addition, when quitting smoking, use of transdermal nicotine (i.e., the patch) can be associated with an increased dreaming report
- Those taking cardiovascular medications called beta blockers, or those with neurologic disorders such as periodic limb movement disorder or restless leg syndrome who take dopaminergic drugs, can report dream intensification as a side effect
- Lastly, drinking alcohol before bed diverts resources to metabolize the alcohol which temporarily suppresses REM sleep
- When REMS is suppressed, pressure builds for REM sleep, such that when REM is permitted to occur, it occurs with greater intensity, and people can report dream intensification
Problems With the Study of Dreams
- There are many challenges in conducting dream research
- We are asking people to tell us about their dreams, but in doing so, they are verbally describing their experience; an experience that is audiovisual
- We must assume that their visual experience of “seeing an elephant” is the same as what we would see as an elephant during wakefulness
- Similarly, we have no way of knowing that someone’s recall of their dreams while awake is a good match for the content while they are dreaming
- Recall relies on memory and our memory may not work in the same way when waking up from a dream
- It is also documented that there is a recency effect in the recall of dreams = we remember the parts closest to the time at which we were awakened
- there may be an expectancy effect in dream recall
Imagine someone agrees to participate in a dreaming study:
- Do you think that people who volunteer for a dreaming study might be different than those who would not volunteer for a dream study?
- What do you think they would expect the experimenter wants?
- There might be an expectation to have a dream so the participant might be particularly attentive to dream-related material when awakening, searching their memory for any potential dreams
- Perhaps there might be some pressure to report a good dream
- If the participant had a dream wherein they were looking over a grocery list, can you imagine that they might feel the need to embellish?
- although there is plenty of dream-related research, there are significant challenges inherent in this type of research
Summary Week 6
- Psychodynamic theories of dreaming emphasize that dreams help to conceal unwanted wishes
- Dreams are interpreted by psychoanalysts because they are viewed as key for emotional growth
- There lacks empirical support for interpreting dreams
- Biological theories of dreaming emphasize spontaneous neuronal firing with an attempt to connect the information into a narrative
- Cognitive theories of dreaming treat dreams as a form of information processing that is different from wakeful processing, e.g., dreams are a type of thinking that tends to be more visual than wakeful thought
- Lucid dreaming is dreaming with an awareness of dreaming. It involves a state between wakefulness and sleep
There are several problems with dream research, including:
- Dreams are mainly a visual experience whereas recall is a verbal endeavor—so we cannot be sure if someone’s verbal (recalled) report is a match for what they actually dreamed
- There may be problems with recall, including a bias towards recency
- There may be expectancy effects