Brain rhythms and sleep Flashcards
(127 cards)
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.