Brain rhythms and sleep Flashcards
(127 cards)
1
Q
What is EEG, and what is its primary medical use today?
A
EEG stands for “electroencephalogram.” It measures electrical activity from the surface of the scalp and is primarily used for diagnosing neurological conditions, especially epilepsy seizures. Additionally, EEG is used for research, such as studying sleep stages and cognitive processes during wakefulness.
2
Q
What is the typical amplitude of the voltage fluctuations measured in EEG, and how are different brain regions examined using EEG?
A
EEG records small voltage fluctuations, typically a few tens of microvolts (μV) in amplitude. Different brain regions, such as anterior and posterior or left and right, can be examined by selecting appropriate electrode pairs.
3
Q
What generates the fluctuations and oscillations of an EEG?
A
An EEG measures voltages generated by the currents flowing during synaptic excitation of the dendrites of many pyramidal neurons in the cerebral cortex. The electrical contribution of a single cortical neuron is very small, so it takes many thousands of neurons activated together to generate a measurable EEG signal.
4
Q
What factors strongly influence the amplitude of the EEG signal? What happens to the EEG signal when neurons are excited synchronously?
A
-The amplitude of the EEG signal depends on how synchronous the activity of the underlying neurons is. When neurons are excited simultaneously, their signals sum to generate a larger surface signal. Conversely, when excitation is spread out in time, the summed signals are smaller and irregular.
-When neurons are excited synchronously, the resulting EEG signal consists of large, rhythmic waves
5
Q
How is rhythmic EEG activity described in terms of amplitude?
A
Rhythmic EEG signals are described in terms of their relative amplitude, which indicates the degree of synchrony in the underlying neuronal activity.
6
Q
What is magnetoencephalography (MEG)? How does the generation of magnetic fields by neurons compare to other environmental magnetic sources? and what is required to detect the brain’s magnetic signals effectively using MEG?
A
-MEG stands for magnetoencephalography, a technique used to record the rhythms of the cerebral cortex by measuring the minuscule magnetic fields generated by neuronal currents
-the magnetic fields generated by neurons are extremely weak, about one billionth the strength of the Earth’s magnetic field, which makes them challenging to detect amidst the much larger magnetic “noise” from sources like power lines and metal objects.
-To detect the brain’s magnetic signals, a specially screened room is needed to shield out environmental magnetic noise, along with a large and expensive instrument equipped with highly sensitive magnetic detectors cooled with liquid helium to -269°C.
-it complements other methods by excelling in localizing deep brain neural activity, recording rapid neural fluctuations, and directly measuring neuronal activity.
7
Q
How does MEG compare to EEG in terms of localizing neural activity?
A
MEG is better than EEG at localizing the sources of neural activity, especially deep within the brain.
8
Q
What distinguishes MEG from fMRI and PET in terms of brain function measurement?
A
-MEG directly measures neuronal activity, while fMRI and PET detect changes in blood flow and metabolism, which can be influenced by various factors.
-MEG cannot provide the spatially detailed images of fMRI
9
Q
What are some applications of MEG in neuroscience and clinical diagnosis?
A
MEG is used in experimental studies of brain function, cognitive processes, and aids in diagnosing conditions like epilepsy and language disorders
10
Q
What are the main categories of EEG rhythms based on their frequency range?
A
The main EEG rhythms are categorized by their frequency range. They include:
-Delta rhythms (less than 4 Hz)
-Theta rhythms (4–7 Hz)
-Alpha rhythms (about 8–13 Hz)
-Mu rhythms (similar in frequency to alpha -rhythms)
-Beta rhythms (about 15–30 Hz)
-Gamma rhythms (about 30–90 Hz)
-Spindles (brief 8–14 Hz waves)
-Ripples (brief bouts of 80–200 Hz oscillations).
11
Q
What is the significance of delta rhythms in EEG?
A
Delta rhythms, which are slow (less than 4 Hz), large in amplitude, and hallmark deep sleep states.
12
Q
Which part of the brain is associated with alpha rhythms in EEG?
A
Alpha rhythms (about 8–13 Hz) are largest over the occipital cortex and are associated with quiet, waking states.
13
Q
What do gamma rhythms in EEG indicate?
A
Gamma rhythms, which are relatively fast (about 30–90 Hz), signal an activated or attentive cortex.
14
Q
What are spindles and ripples in the context of EEG rhythms?
A
Spindles are brief 8–14 Hz waves associated with sleep, while ripples are brief bouts of 80–200 Hz oscillations.
15
Q
What is the significance of theta rhythms in EEG, and when can they occur?
A
Theta rhythms, which have a frequency of 4–7 Hz, can occur during both sleeping and waking states.
16
Q
What is associated with high-frequency, low-amplitude EEG rhythms?
A
High-frequency, low-amplitude EEG rhythms are associated with alertness, waking, or the dreaming stages of sleep.
17
Q
What are low-frequency, high-amplitude EEG rhythms associated with?
A
Low-frequency, high-amplitude EEG rhythms are associated with nondreaming sleep states, certain drugged states, or the pathological condition of coma.
18
Q
Why is the cortex’s activity level relatively high but unsynchronized during alertness and waking?
A
During alertness and waking, the cortex’s activity level is relatively high but unsynchronized because each neuron or a small group of neurons is actively engaged in different aspects of complex cognitive tasks, resulting in rapid but unsynchronized firing. This leads to low synchrony and low EEG amplitude, with gamma and beta rhythms dominating.
19
Q
What characterizes the activity of cortical neurons during deep sleep?
A
During deep sleep, cortical neurons are not engaged in information processing, and many of them are phasically excited by a common, slow, rhythmic input. This results in high synchrony and high EEG amplitude.
20
Q
What are the two fundamental ways in which the activity of a large set of neurons can produce synchronized oscillations? What is the first mechanism of synchronized oscillations, and what is it analogous to? What is the second mechanism of synchronized oscillations, and what is it analogous to?
A
-The activity of a large set of neurons can produce synchronized oscillations in one of two fundamental ways: (1) They may all take their cues from a central clock or pacemaker, or (2) they may share or distribute the timing function among themselves by mutually exciting or inhibiting one another.
-The first mechanism of synchronized oscillations is when neurons take their cues from a central clock or pacemaker. This mechanism is analogous to a band with a leader, where each musician plays in strict time to the beat of the leader’s baton.
-The second mechanism of synchronized oscillations involves neurons sharing or distributing the timing function among themselves by mutually exciting or inhibiting one another. This mechanism is analogous to a jam session in music, where timing arises from the collective behavior of cortical neurons.
21
Q
How can thalamic neurons generate rhythmic action potential discharges?
A
Some thalamic cells have a particular set of voltage-gated ion channels that allow each cell to generate very rhythmic, self-sustaining discharge patterns even when there is no external input to the cell.
22
Q
What forces thalamic neurons to conform to the rhythm of the group? How are the coordinated rhythms passed to the cortex from the thalamus?
A
Synaptic connections between excitatory and inhibitory thalamic neurons force each individual neuron to conform to the rhythm of the group. These coordinated rhythms are then passed to the cortex by the thalamocortical axons, which excite cortical neurons. In this way, a relatively small group of centralized thalamic cells (acting as the band leader) can compel a much larger group of cortical cells (acting as the band) to march to the thalamic beat
23
Q
Why are there so many cortical rhythms in the brain? What is one hypothesis regarding sleep-related rhythms in the brain?
A
-The purpose of the numerous cortical rhythms in the brain is not definitively understood, and various hypotheses exist. One idea is that sleep-related rhythms serve to disconnect the cortex from sensory input during sleep. While this concept has intuitive appeal, it does not explain why rhythms are necessary instead of simply inhibiting the thalamus to allow the cortex to rest quietly. This is achieved through the thalamus entering a self-generated rhythmic state, preventing organized sensory information from reaching the cortex.
24
Q
How might synchronized cortical rhythms during different neural activities contribute to brain function?
A
Synchronized cortical rhythms could potentially bind together various neural components into a single perceptual construction, allowing the brain to unify disjointed pieces of information and form meaningful groups of neurons.
25
What is the current understanding of the functions of rhythms in the cerebral cortex?
he functions of rhythms in the cerebral cortex are still largely a mystery. One hypothesis suggests that most rhythms may not have a direct function but are rather by-products of strongly interconnected brain circuits with various forms of excitatory feedback. These oscillations may be an unavoidable consequence of the brain's extensive feedback circuitry. While they may not have a specific function, EEG rhythms provide a window into the brain's functional states.
26
Why might the cerebral cortex exhibit rhythmic activity, according to one hypothesis?
one hypothesis suggests that the cerebral cortex exhibits rhythmic activity as a result of its extensive feedback circuitry. When circuits in the brain are highly interconnected and include excitatory feedback, oscillations can arise as an unintended consequence.
27
What is the most extreme form of synchronous brain activity? What is a partial seizure?
-Seizures
-It involves only a circumscribed area of the cortex
28
Why are seizures usually accompanied by very large EEG patterns?
Because the neurons within the affected areas fire with synchrony that doesn't occur during normal behavior.
29
What percentage of the general population has experienced at least one isolated seizure in their lifetime?
7-10%
30
What is the condition known as when a person experiences repeated seizures? Approximately how many people worldwide have epilepsy? In which populations is epilepsy more common, and why?
-Epilepsy, About 0.7% (50 million people)
-Epilepsy is more common in developing countries, particularly in rural areas, likely due to higher rates of untreated childhood epilepsy, infections, and poor pre- and postnatal care.
31
When does the diagnosis of epilepsy typically occur in individuals?
It occurs most often in young children and among the elderly.
32
What are the main causes of childhood epilepsy and elderly-onset epilepsy?
Childhood epilepsy is usually congenital, caused by genes or a disease/abnormality present at birth, while elderly-onset epilepsy tends to be acquired due to conditions like stroke, tumors, or Alzheimer's disease.
33
Are there identified genetic factors associated with epilepsy, and what kinds of proteins do these genes code for?
Yes, there are identified genetic factors associated with epilepsy. These genes code for a variety of proteins, including ion channels, transporters, receptors, and signaling molecules.
34
How do mutations in sodium channel proteins relate to epilepsy?
Mutations in sodium channel proteins can lead to epilepsy. These mutations tend to keep sodium channels open longer than normal, allowing more sodium current to enter neurons and making them hyperexcitable.
35
How can mutations affect synaptic inhibition mediated by GABA and contribute to epilepsy?
Mutations can impair synaptic inhibition mediated by GABA by affecting its receptors, enzymes essential for its synthesis or transport, or proteins involved in its release.
36
What factors can trigger seizures in the brain?
Seizures can be triggered by factors such as an upset in the balance of synaptic excitation and inhibition, excessively strong excitatory interconnections, drugs that block GABA receptors, and the withdrawal of chronic depressant drugs like alcohol or barbiturates.
37
How do anticonvulsant drugs work to suppress seizures?
Anticonvulsant drugs work in various ways to counter excitability. Some of them prolong the inhibitory actions of GABA, while others decrease the tendency for certain neurons to fire action potentials at a high frequency
38
What factors determine the behavioral features of a seizure?
The behavioral features of a seizure depend on the neurons involved and the patterns of their activity
39
What happens during most forms of generalized seizures?
-During most forms of generalized seizures, virtually all cortical neurons participate, leading to complete disruption of behavior for many minutes.
-Consciousness is lost, while all muscle groups may be driven by tonic (ongoing)
activity or by clonic (rhythmic) patterns, or by both in sequence, the so-called tonic–
clonic seizure
40
Describe the characteristics of an absence seizure.
Absence seizures are characterized by less than 30 seconds of generalized, 3 Hz EEG waves accompanied by a loss of consciousness. Despite dramatic EEG patterns (voltage patterns are
extraordinarily large, regular, and rhythmic and are generated synchronously across
the entire brain), the motor signs are subtle, often involving only fluttering eyelids or a twitching mouth.
41
What can partial seizures originating in a small area of motor cortex cause?
Clonic movement of part of a limb.
42
What happens if seizures begin in a sensory area?
They can trigger an abnormal sensation or aura, such as an odd smell or sparkling lights
43
What are some of the more well-formed auras that partial seizures can elicit?
Déjà vu (the feeling that something has happened before) or hallucinations.
44
How can partial seizures involving the cortex of the temporal lobes, including the hippocampus and amygdala, affect memory, thought, and consciousness?
They can impair memory, thought, and consciousness.
45
What can happen in some cases when partial seizures spread uncontrollably?
They can become generalized seizures.
46
What is the approximate amount of time spent sleeping during one's life? How much of our sleep time is typically spent in a state of active dreaming?
Approximately one-third of our lives is spent sleeping. About one-quarter of our sleep time is spent in a state of active dreaming.
47
Is sleep universal among higher vertebrates and perhaps all animals?
Yes, research suggests that even animals like fruit flies may sleep.
48
What is the definition of sleep?
Sleep is a readily reversible state of reduced responsiveness to, and interaction with, the environment. (Coma and general anaesthesia are not readily reversible and do not qualify as sleep.)
49
What are the two distinct phases or states of sleep experienced during the night?
Rapid eye movement sleep (REM sleep) and non-REM sleep.
50
Describe REM sleep.
-During REM sleep, the EEG looks more awake than asleep, the body (except for the eye and respiratory muscles) is immobilized, and vivid, detailed dreams occur.
-During REM sleep, the brain is highly active, and vivid, detailed dreams occur. The body is also typically immobilized during this stage.
- Dreams during REM sleep are often visually detailed, lifelike, and can have bizarre storylines.
-REM sleep is characterized by an EEG pattern that resembles an awake, active brain, earning it the nickname "paradoxical sleep." During REM sleep, the brain's oxygen consumption is higher than when awake and engaged in complex mental tasks. The body experiences near-complete loss of skeletal muscle tone (aka atonia), leading to paralysis, except for muscles controlling eye movement and the inner ear, which remain active.
-The body's temperature control system stops working, and core temperature begins to decrease.
-Heart and respiration rates increase and become irregular during REM sleep.
-The clitoris and penis become engorged with blood and erect during REM sleep, although this is not necessarily related to sexual dreams.
51
What are the characteristics of Non-REM sleep?
(Non-REM sleep is also sometimes called slow-wave sleep because of its domination by large, slow EEG rhythms.)
-During non-REM sleep, the brain exhibits its lowest rate of energy use and general firing rates of neurons. Large-amplitude EEG rhythms suggest that cortical neurons oscillate with high synchrony. Most sensory input cannot reach the cortex during this state.
-Mental processes hit their daily low during non-REM sleep. People often recall nothing or only brief, fragmentary, and plausible thoughts with few visual images. Detailed, entertaining, and irrational dreams are rare during this state
- Non-REM sleep is a period of reduced muscle tension and minimal movement. Body temperature and energy consumption decrease during this state. The parasympathetic division of the autonomic nervous system becomes more active, resulting in slower heart rate, respiration, and kidney function, along with accelerated digestive processes.
52
What are ultradian rhythms?
Ultradian rhythms are biological rhythms that have faster periods than circadian rhythms and include cycles such as the transitions between non-REM and REM sleep during a night's sleep.
53
What are the characteristics of stage 1 non-REM sleep?
Stage 1 non-REM sleep is transitional sleep. During this stage, the EEG alpha rhythms of relaxed waking become less regular and wane. The eyes make slow, rolling movements. Stage 1 is fleeting and usually lasts only a few minutes. It is the lightest stage of sleep, meaning that individuals are most easily awakened.
54
What are the characteristics of stage 2 non-REM sleep?
Stage 2 non-REM sleep is slightly deeper than stage 1 and may last 5–15 minutes. theta waves. It is characterized by occasional 8–14 Hz oscillations of the EEG called sleep spindles, which are generated by a thalamic pacemaker. Additionally, a high-amplitude sharp wave called the K complex is sometimes observed during this stage. Eye movements almost cease during stage 2.
55
Describe stage 3 non-REM sleep.
During stage 3 non-REM sleep, the EEG shows large-amplitude, slow delta rhythms. Eye and body movements are relatively few during this stage, indicating a deeper level of sleep.
56
What are the characteristics of stage 4 non-REM sleep?
Stage 4 non-REM sleep is the deepest stage of sleep, characterized by large EEG rhythms of 2 Hz or less, delta waves. During the first cycle of sleep, stage 4 may persist for 20–40 minutes. It represents a very deep and restorative phase of sleep.
57
What follows stage 4 non-REM sleep in the sleep cycle?
After stage 4 non-REM sleep, sleep begins to lighten and ascends through stage 3 to stage 2 for 10–15 minutes. Following this, the sleep cycle enters a brief period of REM sleep, characterized by fast EEG beta and gamma rhythms and sharp, frequent eye movements.
58
What is a normal night's sleep duration for adults?
-Research suggests that normal sleep requirements among adults vary widely, ranging from about 5 to 10 hours per night. The average duration is approximately 7.5 hours.
-About 68% of young adults sleep between 6.5 and 8.5 hours per night
59
Why might teenagers find it challenging to get enough sleep?
Research indicates that sleep requirements for teenagers do not decrease compared to preadolescence, but changes in circadian timing mechanisms can make it progressively harder for teenagers to fall asleep early in the evening. This shift in sleep patterns often coincides with the start of high school and an earlier school day, contributing to chronic sleep deprivation among many students.
60
What are the two main categories of theories explaining the function of sleep?
The two main categories of theories explaining the function of sleep are theories of restoration and theories of adaptation.
61
What does the theory of restoration propose about the function of sleep?
The theory of restoration suggests that we sleep in order to rest, recover, and prepare to be awake again.
62
What does the theory of adaptation propose about the function of sleep?
The theory of adaptation suggests that we sleep to keep us out of trouble, hide from predators, avoid harmful aspects of the environment, or conserve energy when we are most vulnerable.
63
Is sleep primarily a time for increased tissue repair in the body?
No, evidence indicates that sleep is not primarily a time for increased tissue repair in the body.
64
Is it possible for some brain regions, like the cerebral cortex, to achieve a form of essential "rest" during non-REM sleep?
Yes, it is possible that certain brain regions, such as the cerebral cortex, may achieve some form of essential "rest" during non-REM sleep
65
What occurs when individuals who have been deprived of REM sleep are allowed to sleep undisturbed?
When allowed to sleep undisturbed, individuals who have been deprived of REM sleep experience REM rebound and spend more time in REM sleep proportional to the duration of their deprivation.
66
Does REM deprivation cause major psychological harm during the daytime?
Most studies have found that REM deprivation does not cause major psychological harm during the daytime. However, it's important not to interpret REM deprivation as dream deprivation, as dreams may still occur during sleep onset and non-REM periods
67
What did Sigmund Freud propose as the primary function of dreams?
Freud suggested that dreams were disguised wish fulfilment, a way for us to express unconscious sexual and aggressive fantasies.
68
How do recent theories of dreaming, like the activation-synthesis hypothesis, differ from Freud's ideas? According to the activation-synthesis hypothesis, why are some dreams bizarre and nonsensical?
-Recent theories, such as the activation-synthesis hypothesis proposed by Allan Hobson and Robert McCarley, reject Freudian psychological interpretations and suggest that dreams are a result of random discharges of the pons during REM sleep, which elicit memories and associations in the cerebral cortex.
-The activation-synthesis hypothesis suggests that during REM sleep, the pons' random activity triggers various images and emotions in the cerebral cortex. The cortex then attempts to synthesize these disparate elements into a coherent narrative, leading to bizarre and nonsensical dreams.
69
What are some criticisms or limitations of the activation-synthesis hypothesis regarding dreams?
While the activation-synthesis hypothesis explains the weirdness of dreams and their correlation with REM sleep, it doesn't fully explain how random activity can generate complex and recurring dream narratives.
70
What role does REM sleep play in memory?
REM sleep is thought to aid in the integration or consolidation of memories. Depriving humans or rats of REM sleep can impair their ability to learn various tasks. Some studies indicate an increase in REM sleep duration after intense learning experiences.
71
How did Avi Karni's study support the idea that REM sleep is related to memory? What effect does depriving individuals of non-REM sleep have on performance in Karni's study?
-Avi Karni and his colleagues conducted a study where people were trained to identify the orientation of a small line in their peripheral visual field. Their performance improved between evening and morning after a night's sleep. However, when people were deprived of REM sleep, their learning did not improve overnight. This suggests that REM sleep may play a role in certain types of memory consolidation.
-Depriving individuals of non-REM sleep actually enhanced their performance in Karni's study, which contrasts with the negative impact of REM sleep deprivation on learning
72
How does the sensory input affect an animal's sleep-wake cycles?
Blocking sensory afferents to an animal's brain does not prevent cycles of waking and sleeping, indicating that sleep is an active process.
73
What are the key principles of the control systems for sleeping and waking?
1. Neurons involved in diffuse modulatory neurotransmitter systems are critical for controlling sleeping and waking.
2. Brain stem modulatory neurons using norepinephrine, serotonin, and acetylcholine play roles in enhancing different aspects of the sleep-wake cycle.
3. Thalamus controls EEG rhythms of the cerebral cortex, with slow, sleep-related thalamic rhythms blocking sensory information flow to the cortex.
4. Descending branches of the diffuse modulatory systems are involved, including the inhibition of motor neurons during dreaming.
74
What did lesions in the brain stem suggest about its role in sleep and wakefulness?
Lesions in the brain stem suggested that specific brain stem regions are crucial for regulating sleep and wakefulness.
75
What were the effects of lesions in the midline structures of the brain stem on an individual's state? (moruzzi's research)
Lesions in the midline structures of the brain stem caused a state resembling non-REM sleep in individuals.
76
What did lesions in the lateral tegmentum of the brain stem affect? (moruzzi's research)
Lesions in the lateral tegmentum of the brain stem interrupted ascending sensory inputs but did not produce non-REM sleep-like states.
77
Describe the effects of electrical stimulation of the midline tegmentum, within the reticular formation, in the midbrain. (moruzzi's research)
Electrical stimulation of the midline tegmentum in the midbrain transformed the cortex's EEG activity from slow, rhythmic non-REM sleep patterns to a more alert and aroused state, resembling wakefulness.
78
What did Giuseppe Moruzzi call the region of stimulation within the midbrain, and what did it represent?
Giuseppe Moruzzi referred to the stimulated area within the midbrain as the ascending reticular activating system (ARAS). This region represents a complex network that influences various ascending modulatory systems, contributing to wakefulness and arousal regulation.
79
Which sets of neurons are involved in arousal and awakening?
Neurons involved in arousal and awakening include cells in the locus coeruleus (norepinephrine-containing), raphe nuclei (serotonin-containing), brain stem and basal forebrain (acetylcholine-containing), midbrain (histamine-using), and hypothalamus (using hypocretin or orexin).
80
What neurotransmitters are released by neurons in the locus coeruleus, raphe nuclei, brain stem and basal forebrain, midbrain, and hypothalamus, for anticipation of awakening
Neurons in the locus coeruleus release norepinephrine, the raphe nuclei release serotonin, neurons in the brain stem and basal forebrain use acetylcholine as their neurotransmitter, midbrain neurons utilize histamine, and neurons in the hypothalamus communicate with hypocretin or orexin as their transmitter.
81
What is hypocretin? What is the role of hypocretin (orexin) in the brain? What sleep disorder is associated with the loss of hypocretin (orexin) neurons?
-Hypocretin, also known as orexin, is a small peptide neurotransmitter primarily expressed by neurons in the lateral hypothalamus.
-Hypocretin (orexin)-secreting neurons project widely in the brain and excite various modulatory systems, including cholinergic, noradrenergic, serotonergic, dopaminergic, and histaminergic systems. It plays a role in promoting wakefulness, inhibiting REM sleep, facilitating specific motor behaviors, regulating neuroendocrine and autonomic systems and feeding behaviours.
-The loss of hypocretin (orexin) neurons is linked to a sleep disorder called narcolepsy.
82
What happens to the firing rates of most brain stem modulatory neurons during the onset of non-REM sleep? What happens to a subset of cholinergic neurons in the basal forebrain during non-REM sleep?
-There is a general decrease in the firing rates of most brain stem modulatory neurons (those using NE, 5-HT, and ACh) during the onset of non-REM sleep.
-A subset of cholinergic neurons in the basal forebrain increases their firing rate with the onset of non-REM sleep and is silent during wakefulness.
83
How is synchronization of activity during spindle or delta rhythms achieved?
Synchronization of activity during spindle or delta rhythms is due to neural interconnections within the thalamus and between the thalamus and cortex. The strong, two-way excitatory connections between these brain regions contribute to this synchronization.
84
How do brain activity patterns differ between REM sleep and waking in PET and fMRI? What does the heightened limbic activation during REM sleep suggest? and What happens in the frontal lobe during REM sleep?
-Brain imaging studies using PET and fMRI have shown that during REM sleep, extrastriate cortical areas and parts of the limbic system are significantly more active than during waking. In contrast, regions of the frontal lobes are less active during REM sleep. This suggests that during REM sleep, there is an increase in extrastriate activity, possibly related to dreaming, but the primary visual cortex remains less active, indicating that extrastriate excitation is internally generated.
- The heightened limbic activation during REM sleep suggests that the emotional component of dreams may be derived from this increased limbic activity.
-The frontal lobe shows low activity during REM sleep, suggesting that high-level integration or interpretation of extrastriate visual information may not occur during this sleep state, leaving individuals with a buzz of uninterpreted visual imagery.
85
What controls REM sleep and its onset in the brain? What happens to the firing rates of the locus coeruleus and the raphe nuclei before the onset of REM sleep?
-REM sleep is controlled by diffuse modulatory systems in the core of the brain stem, particularly the pons.
-The firing rates of the locus coeruleus and the raphe nuclei decrease to almost nothing before the onset of REM sleep.
86
What is the role of ACh-containing neurons in the pons during REM sleep?
ACh-containing neurons in the pons show a sharp increase in firing rates during REM sleep, and they are believed to induce REM sleep. ACh's action during REM sleep causes the thalamus and cortex to behave similarly to the waking state.
87
What prevents us from acting out our dreams during REM sleep? and what is REM sleep behavior disorder, who is most commonly affected by it, and hat is the possible basis for REM sleep behavior disorder??
-The core brain stem systems that control sleep processes actively inhibit spinal motor neurons, preventing motor activity during REM sleep. This inhibitory mechanism is an adaptive function to protect us from physically acting out our dreams.
-REM sleep behavior disorder is a condition in which individuals act out their dreams during REM sleep. It is most commonly seen in elderly men.
-REM sleep behavior disorder may result from disruption of brain stem systems that mediate REM muscle atonia, allowing dream-related motor activity to occur.
88
What is adenosine, and what role does it play in sleep?
-Adenosine levels in the brain increase during prolonged wakefulness and sleep deprivation, and they decrease during sleep. Adenosine is considered an important sleep-promoting factor.
-Adenosine has an inhibitory effect on the diffuse modulatory systems for acetylcholine (ACh), norepinephrine (NE), and serotonin (5-HT) that tend to promote wakefulness.
-Adenosine levels increase with neural activity in the awake brain, leading to increased inhibition of the modulatory systems associated with wakefulness. This enhances the suppression of "wakeful" systems and promotes the transition into the slow-wave synchronous activity characteristic of non-REM sleep. As sleep progresses, adenosine levels slowly decrease, and activity in the wakefulness-promoting modulatory systems gradually increases, eventually leading to wakefulness.
89
How do substances like caffeine affect adenosine receptors and sleep?
Caffeine and theophylline are antagonists of adenosine receptors, and they are known to keep people awake by blocking the effects of adenosine. This is why they are commonly found in beverages like coffee, tea, and cola
90
What is another important sleep-promoting factor besides adenosine, and how does it promote sleep?
Nitric oxide (NO). NO is a small, gaseous molecule that can easily diffuse across membranes and serves as a retrograde messenger between certain neurons. Brain NO levels are highest during waking and rise rapidly with sleep deprivation. NO promotes sleep by triggering the release of adenosine, which, in turn, promotes non-REM sleep by suppressing the activity of neurons that help sustain waking.
91
What was identified in the spinal fluid of sleep-deprived goats, and what role does it play in sleep?
A muramyl dipeptide was identified, which facilitates non-REM sleep. Muramyl peptides are usually produced by bacteria and can stimulate immune responses.
92
What are cytokines, and how are they related to sleep regulation? and what effect does interleukin-1 have when given to humans?
-Cytokines are small signalling peptides involved in the immune system. Interleukin-1, a cytokine synthesized in the brain by glia and macrophages, has been implicated in the regulation of sleep. Its levels increase during waking and promote non-REM sleep.
-When given to humans, interleukin-1 induces fatigue and sleepiness
93
What is melatonin, and how does it relate to sleep patterns and sleep-promoting treatments?
-Melatonin is a hormone.
-It is secreted by the pineal body.
-Melatonin is often referred to as the "Dracula of hormones" because it is released in response to darkness, typically at night.
-Its release is inhibited by exposure to light.
-In humans, melatonin levels tend to rise in the evening, peak in the early morning hours, and return to baseline levels upon awakening.
-Melatonin is believed to play a role in initiating and maintaining sleep.
-It is available as an over-the-counter sleep-promoting drug.
-Melatonin has shown promise in addressing issues like jet lag and insomnia in older adults.
94
What are immediate early genes, and how are they related to sleep and wakefulness?
Immediate early genes are genes that code for transcription factors influencing the expression of other genes. Some of these genes are associated with changes in synaptic strength. During sleep, the low expression of these genes may be linked to the absence of significant learning and memory formation.
95
What did Chiara Cirelli and Giulio Tononi's research on gene expression in rats during sleep and wakefulness reveal?
Chiara Cirelli and Giulio Tononi's research showed that the vast majority of genes in rats were expressed at the same level during sleep and wakefulness. However, approximately 0.5% of genes exhibited different levels of expression between the two states.
96
What is the significance of genes related to mitochondria in the context of sleep and wakefulness?
Genes related to mitochondria were among those that showed increased expression during wakefulness. This increased expression may be associated with meeting the higher metabolic demands of the awake brain.
97
What is the third group of genes mentioned for sleep and wakefulness?
The third group of genes is related to responses to cellular stress.
98
Genes that increased in awake rats:
intermediate early genes and mitochondrial genes
99
Genes that increased in sleeping rats:
genes that contribute to protein synthesis and plasticity mechanisms
100
What was the first evidence of a biological clock? and who conducted this
The mimosa plant's daily leaf-raising and lowering, which persisted even in darkness. French physicist Jean Jacques d’Ortous de Mairan in 1729.
101
What did Augustin de Candolle's observations of a similar plant in the dark suggest?
The plant likely had an internal biological clock since it followed a 22-hour cycle, different from the sun's 24-hour cycle.
102
What are zeitgebers?
Zeitgebers are environmental time cues that include factors like light/dark, temperature, and humidity variations.
103
How do animals respond to zeitgebers in terms of their activity cycle?
In the presence of zeitgebers, animals become entrained to the day–night rhythm and maintain an activity cycle of exactly 24 hours.
104
What happens to the activity cycle of animals when they are completely deprived of zeitgebers?
When completely deprived of zeitgebers, animals settle into a rhythm of activity and rest that often has a period more or less than 24 hours, referred to as free-running rhythms.
105
What is the natural free-running period for mice, hamsters, and humans? and what is the impact of isolated environments like deep caves on human activity rhythms?
-In mice, the natural free-running period is about 23 hours, in hamsters it is close to 24 hours, and in humans, it tends to be 24.5–25.5 hours.
-Mammals completely deprived of zeitgebers settle into rhythm of activity and rest but drift out of phase with 12-hour day/light cycle.
-In isolated environments like deep caves, human activity rhythms may initially settle into a 25-hour rhythm, but over time, they may start to free-run with a longer period, often 30–36 hours.
106
What happens to the rhythms of temperature and sleeping-waking when people experience desynchronization of their cycles?
When rhythms become desynchronized, the body's lowest temperature may drift, first moving earlier into the sleep period and then into waking time. This desynchronization can impair sleep quality and waking comfort.
107
What is jet lag, and how can it be alleviated?
Jet lag occurs when the body is forced suddenly into a new sleep-wake cycle due to travel. Bright light is an effective way to help resynchronize the biological clocks and alleviate jet lag.
108
In isolation experiments, what happens to the synchronization of body temperature and sleeping-waking cycles when people are entrained on a non-24-hour "day" with artificial lighting?
In isolation experiments, body temperature and other physiological measures may continue to change reliably over a 24-hour cycle even if people are entrained on a different, non-24-hour "day" with artificial lighting. This can lead to desynchronization of the rhythms of temperature and sleeping-waking, affecting sleep quality and comfort.
109
What are the components of a biological clock responsible for circadian rhythms?
Light sensor --> clock --> output pathway
110
What are the suprachiasmatic nuclei (SCN), and where are they located?
-The SCN is a biological clock in mammals, tiny neuron clusters in the hypothalamus, located on either side of the midline, bordering the third ventricle.
-Each SCN has a volume of less than 0.3 mm^3
111
How do lesions in the SCN affect circadian rhythms?
Lesions in the SCN abolish circadian rhythmicity of physical activity, sleeping, waking, feeding, and drinking.
112
Can sleep "regulation" continue without an intact SCN?
Yes, sleep regulation can persist without an intact SCN, primarily depending on the amount and timing of prior sleep.
113
What is the retinohypothalamic tract responsible for?
The retinohypothalamic tract is responsible for entraining sleeping and waking cycles to night and day by transmitting light information to the suprachiasmatic nuclei (SCN) in the hypothalamus.
114
How does the retinohypothalamic tract transmit light information to the SCN?
The retinohypothalamic tract consists of axons from ganglion cells in the retina that synapse directly on the dendrites of SCN neurons, allowing them to respond to light stimuli.
115
What distinguishes SCN neurons from visual pathway neurons?
SCN neurons have very large, nonselective receptive fields and respond to the luminance of light stimuli rather than their orientation or motion, unlike the more familiar neurons of the visual pathways.
116
What specialized type of ganglion cells in the retina was discovered by David Berson and his colleagues, and what is their unique feature that makes them light-sensitive?
David Berson and his colleagues discovered a specialized type of ganglion cell in the retina known as light-sensitive ganglion cells. These ganglion cells express a unique type of photopigment called melanopsin, which allows them to be slowly excited by light. Their primary role is to send a signal directly to the suprachiasmatic nucleus (SCN) to reset the circadian clock in response to light.
117
What is the primary neurotransmitter used by almost all SCN neurons? and describe the outputs of SCN neurons
use GABA as primary neurotransmitter, SCN output axons to parts of the hypothalamus, midbrain, diencephalons
118
How do neurons of the SCN keep time? and what happens to SCN cells when isolated in a tissue culture dish?
-Each SCN cell is a tiny clock with molecular machinery that produces regular ticks and tocks. Even when isolated in a tissue culture dish, these cells continue to exhibit rhythms in action potential firing, glucose utilization, vasopressin production, and protein synthesis, all with a period of about 24 hours, similar to their behavior in the intact brain.
-SCN cells in culture, when isolated from the brain and each other, maintain their basic rhythmicity with a period of about 24 hours. However, they can no longer be entrained to light–dark cycles since input from the eyes is necessary for this entrainment to external cues.
119
What happens to SCN neurons when tetrodotoxin (TTX), a sodium channel blocker, is applied? and how does the SCN clock behave when TTX is removed after blocking action potentials?
-When TTX is applied to SCN cells, it blocks their action potentials but has no effect on the rhythmicity of their metabolism and biochemical functions.
-When TTX is removed, action potentials resume firing with the same phase and frequency they had originally, indicating that the SCN clock continues to run even without action potentials.
120
What is the significance of the SCN cells' ability to maintain rhythms in isolation?
The ability of SCN cells to maintain their rhythms even when isolated from the brain and external cues suggests that they possess intrinsic molecular clocks responsible for keeping time. These clocks continue to function independently, regulating various cellular processes with a circadian period.
121
What is the nature of the biological clock that functions without action potentials?
The biological clock that functions without action potentials is a molecular cycle based on gene expression. This molecular clock is similar in humans, mice, fruit flies (Drosophila), and even bread mold.
122
What are some important clock genes involved in the molecular clock in mammals?
Some important clock genes in mammals include period (per), cryptochrome, and clock.
123
Describe the basic scheme of the molecular clock in circadian rhythms. the Joseph Takahashi experiment
The basic scheme of the molecular clock involves a negative feedback loop. Clock genes are transcribed to produce mRNA, which is then translated into proteins. After a delay, these proteins send feedback to interact with the transcription mechanism, causing a decrease in gene expression. This cycle, taking about 24 hours, repeats to create circadian rhythms.
124
How does the SCN coordinate the thousands of cellular clocks within it?
The coordination of rhythms between SCN cells seems to be independent of action potentials and normal synaptic transmission. Additionally, the SCN communicates directly with other SCN neurons, and this communication involves various mechanisms, including chemical signals, electrical synapses (gap junctions), and the participation of glia.
125
What drives the circadian clocks in peripheral tissues, such as the liver, kidney, and lung? and under what conditions do cells from peripheral tissues like the liver and kidney exhibit circadian rhythms? and what governs the clocks in peripheral tissues throughout the body's organs?
-Gene transcription feedback loops similar to those in the SCN (suprachiasmatic nucleus).
-When grown in isolation.
-The SCN (suprachiasmatic nucleus) in the brain, which acts as the master control
126
How does the SCN influence the body's circadian clocks in peripheral tissues? and what effect does body temperature have on the clocks of peripheral tissues? and what can desynchronize the body's circadian clocks?
-Through signaling pathways that affect the autonomic nervous system, core body temperature, adrenal gland hormones, neural circuits for feeding, movement, and metabolism.
-Body temperature drops each night under the influence of the SCN, helping to synchronize the internal organ clocks with the daily rhythms of the SCN and the environmental light-dark cycles.
-Odd feeding schedules, chronic use of methamphetamine, and extreme living conditions like long-term cave dwelling.
127
which brain mechanisms modulate sleep?
Suprachiasmatic nucleus (SCN) of the hypothalamus:
- Brain’s biological clock (“clock genes”);
- Can be modulated by light via retino-hypothalamic tracts
- Its output controls sleep onset and duration as well as associated bodily changes
