Brain rhythms and sleep Flashcards
What is EEG, and what is its primary medical use today?
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.
What is the typical amplitude of the voltage fluctuations measured in EEG, and how are different brain regions examined using EEG?
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.
What generates the fluctuations and oscillations of an EEG?
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.
What factors strongly influence the amplitude of the EEG signal? What happens to the EEG signal when neurons are excited synchronously?
-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
How is rhythmic EEG activity described in terms of amplitude?
Rhythmic EEG signals are described in terms of their relative amplitude, which indicates the degree of synchrony in the underlying neuronal activity.
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?
-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.
How does MEG compare to EEG in terms of localizing neural activity?
MEG is better than EEG at localizing the sources of neural activity, especially deep within the brain.
What distinguishes MEG from fMRI and PET in terms of brain function measurement?
-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
What are some applications of MEG in neuroscience and clinical diagnosis?
MEG is used in experimental studies of brain function, cognitive processes, and aids in diagnosing conditions like epilepsy and language disorders
What are the main categories of EEG rhythms based on their frequency range?
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).
What is the significance of delta rhythms in EEG?
Delta rhythms, which are slow (less than 4 Hz), large in amplitude, and hallmark deep sleep states.
Which part of the brain is associated with alpha rhythms in EEG?
Alpha rhythms (about 8–13 Hz) are largest over the occipital cortex and are associated with quiet, waking states.
What do gamma rhythms in EEG indicate?
Gamma rhythms, which are relatively fast (about 30–90 Hz), signal an activated or attentive cortex.
What are spindles and ripples in the context of EEG rhythms?
Spindles are brief 8–14 Hz waves associated with sleep, while ripples are brief bouts of 80–200 Hz oscillations.
What is the significance of theta rhythms in EEG, and when can they occur?
Theta rhythms, which have a frequency of 4–7 Hz, can occur during both sleeping and waking states.
What is associated with high-frequency, low-amplitude EEG rhythms?
High-frequency, low-amplitude EEG rhythms are associated with alertness, waking, or the dreaming stages of sleep.
What are low-frequency, high-amplitude EEG rhythms associated with?
Low-frequency, high-amplitude EEG rhythms are associated with nondreaming sleep states, certain drugged states, or the pathological condition of coma.
Why is the cortex’s activity level relatively high but unsynchronized during alertness and waking?
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.
What characterizes the activity of cortical neurons during deep sleep?
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.
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?
-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.
How can thalamic neurons generate rhythmic action potential discharges?
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.
What forces thalamic neurons to conform to the rhythm of the group? How are the coordinated rhythms passed to the cortex from the thalamus?
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
Why are there so many cortical rhythms in the brain? What is one hypothesis regarding sleep-related rhythms in the brain?
-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.
How might synchronized cortical rhythms during different neural activities contribute to brain function?
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.
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.
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.
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
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.
What percentage of the general population has experienced at least one isolated seizure in their lifetime?
7-10%
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.
When does the diagnosis of epilepsy typically occur in individuals?
It occurs most often in young children and among the elderly.
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.
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.
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.
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.
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.
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
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
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
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.
What can partial seizures originating in a small area of motor cortex cause?
Clonic movement of part of a limb.
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
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.
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.
What can happen in some cases when partial seizures spread uncontrollably?
They can become generalized seizures.
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.
Is sleep universal among higher vertebrates and perhaps all animals?
Yes, research suggests that even animals like fruit flies may sleep.
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.)
What are the two distinct phases or states of sleep experienced during the night?
Rapid eye movement sleep (REM sleep) and non-REM sleep.
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.
