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Autor     Páraic Scanlon, Seán Commins, Richard Roche
Titel    High Density Event-Related Potentials: Current Theories and Practice
Zeitschrift    The Irish Psychologist
Ausgabe    33
Datum    Jul-Aug 2006 2006
Nummer    1
Seiten    5-8
Anmerkung    The third author is the research supervisor of the author of the thesis.
URL    https://www.academia.edu/639693/High-density_event-related_potentials_Current_theories_and_practice

Literaturverz.   

no
Fußnoten    no
Fragmente    15


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Placing EEG in a historical context, Caton (1875) described the first sensory evoked electrical responses from the surface of the brains of rabbits and monkeys using single electrode recording. Beck (1890) furthered the work of Caton by studying the electrical brain responses of rabbits and dogs to presentation of sensory stimuli. Within 40 years, recordings of electrical brain potentials had moved from animals to humans, and in 1929, Hans Berger published the first recorded study of scalp recordings of human EEGs in which he measured the electrical activity of the human brain by placing an electrode on the scalp, amplifying the signal, and plotting the changes in voltage over time. Caton (1875) described the first sensory evoked electrical responses from the surface of the brains of rabbits and monkeys using single electrode recording. Beck (1890) furthered the work of Caton by studying the electrical brain responses of rabbits and dogs to presentation of sensory stimuli. Within 40 years, recordings of electrical brain potentials had moved from animals to humans, and in 1938 Hans Berger published the first recorded study of scalp recordings of human EEGs, in which he first used the term “Elektrenkephalogramm”.
Anmerkungen

No reference to the source.

The year 1929 seems to be correct: Wikipedia

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In 1939, Davis published a paper in which he extracted the changes in EEG due to a sensory stimulus, naming it an Evoked Potential (EP). Renshaw, Forbes and Morison proposed the possible relationship between the slow potentials of neurons and the oscillations of the EEG in 1940, leading to the foundation of the American EEG Society. Up until the 1950s there was no set method of electrode placement on the scalp, leading to a committee headed by Jasper developing the international 10-20 placement system. A year later, Davis (1939) published a paper in which he extracted the changes in EEG due to a sensory stimulus, naming it an Evoked Potential (EP). Renshaw, Forbes and Morison proposed the possible relationship between the slow potentials of neurons and the oscillations of the EEG in 1940, leading to the foundation of the American EEG Society. Up until the 1950s there was no set method of electrode placement on the scalp, leading to a committee headed by Jasper developing the international 10-20 placement system.
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No reference to the source.

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[Dawson] (1954) extended the EP extraction techniques introduced by Davis (1939), by averaging large numbers of EPs to increase signal-to-noise ratio thereby reducing the amount of conflicting data being recorded for each response. [...] By the 1970s, ERPs were being widely applied in clinical diagnosis, [...] Dawson (1954) extended the EP extraction techniques introduced by Davis (1939), by averaging large numbers of EPs to increase signal-to-noise ratio, beginning the study of Event Related Potentials (ERPs). By the 1970s, ERPs were being widely applied in clinical diagnosis.
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2.3.2 Event-Related Potentials (ERPs)

More specifically for present purposes, ERPs are changes in the ongoing electrical activity of the brain (electroencephalogram, or EEG) which are caused by the specific occurrence of a cognitive, motor or perceptual event. Any changes in EEG due to the demands of the task are amplified, averaged and extracted as ERP waveforms (see Figure 2.1). These wave-forms are measured as the difference between the electrical activity of a baseline reference electrode attached to an electrically inactive site, such as the mastoid bone below the ear or the naison [on the nose, and the electrical activity of the areas of the brain covered by the electrodes.]

Event-Related Potentials (ERPs) are changes in the ongoing electrical activity of the brain (Electroencephalograms, or EEGs) which are caused by the specific occurrence of a cognitive, motor or perceptual event. Any changes in EEG due to the demands of the task are amplified, averaged and extracted as ERP waveforms (see Figure 1). These wave-forms are measured as the difference between the electrical activity of a baseline reference electrode attached to an electrically inactive site, such as the mastoid bone below the ear or the naison on the nose, and the electrical activity of the areas of the brain covered by the electrodes.
Anmerkungen

The source is not given.

Note that there exists no figure 2.1. in the thesis.

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[These wave-forms are measured as the difference between the electrical activity of a baseline reference electrode attached to an electrically inactive site, such as the mastoid bone below the ear or the naison] on the nose, and the electrical activity of the areas of the brain covered by the electrodes. These changes allow neuroscientists to determine what areas of brain are being stimulated at a given time (and therefore which brain areas are involved in a given process), precisely when these areas become activated and what happens in these areas when people make an error. These wave-forms are measured as the difference between the electrical activity of a baseline reference electrode attached to an electrically inactive site, such as the mastoid bone below the ear or the naison on the nose, and the electrical activity of the areas of the brain covered by the electrodes. These changes allow neuroscientists to determine what areas of brain are being stimulated at a given time (and therefore which brain areas are involved in a given process), precisely when these areas become activated and what happens in these areas when people make an error.
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The copied text starts already on the previous page: Jm/Fragment 063 18

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2.3.3 Physiological basis of ERPs

2.3.3.1 Electrical activity in the brain

Communication in the central nervous system takes place through the transmission of electrochemical signals between nerve cells, or neurons (see Figure 2.2). Messages to either excite or inhibit activity in other neurons are passed via the release of neurotransmitter substances from the axon of the efferent (or pre-synaptic) cell to the dendritic tree or cell body of the afferent (or post-synaptic) neuron. The neurotransmitters influence the activity of the neuron by binding to receptors which alter the electrical potential across the membrane of the cell. Due to the constant influx and outflow of both positively and negatively charged ions across this membrane, the equilibrium state, or resting potential, of a neuron is approximately –70 mV. Any deviation from this state will make the cell either more or less likely to generate an action potential. An excitatory signal from a presynaptic cell will cause certain ion channels to open or close, with the result that the membrane potential rises from – 70 mV to 0 mV and possibly higher. Such excitatory impulses are termed Excitatory Post- Synaptic Potentials (EPSPs). If the membrane potential rises above a particular threshold level, approximately +30 mV, then an action potential is generated in the neuron, and [neurotransmitter is released onto another cell.]

Physiological basis of ERPs

Communication in the central nervous system takes place through the transmission of electrochemical signals between nerve cells, or neurons (see Figure 2). Messages to either excite or inhibit activity in other neurons are passed via the release of neurotransmitter substances from the axon of the efferent (or pre-synaptic) cell to the dendritic tree or cell body of the afferent (or post-synaptic) neuron.

The neurotransmitters influence the activity of the neuron by binding to receptors which alter the electrical potential across the membrane of the cell. Due to the constant influx and outflow of both positively and negatively charged ions across this membrane, the equilibrium state, or resting potential, of a neuron is approximately –70 mV. Any deviation from this state will make the cell either more or less likely to generate an action potential. An excitatory signal from a presynaptic cell will cause certain ion channels to open or close, with the result that the membrane potential rises from –70 mV to 0 mV and possibly higher. Such excitatory impulses are termed Excitatory Post-Synaptic Potentials (EPSPs). If the membrane potential rises above a particular threshold level, approximately +30 mV, then an action potential is generated in the neuron, and neurotransmitter is released onto another cell.

Anmerkungen

No reference to the source.

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The rise in membrane potential due to an EPSP is called depolarisation. In contrast, Inhibitory Post-Synaptic Potentials (IPSPs) render cell firing less likely by lowering the membrane potential, thereby pushing it further from the threshold level for action potential propagation. This lowering of the potential across the membrane is called hyperpolarisation. It is the summated effects of these depolarisations and hyperpolarisations (which may collectively be termed Neural Current Sources), rather than the action potentials themselves, that are recorded by EEG and ERPs. The rise in membrane potential due to an EPSP is called depolarisation.

In contrast, Inhibitory Post-Synaptic Potentials (IPSPs) make cell firing less likely by lowering the membrane potential, thereby pushing it further from the threshold level for action potential propagation. This lowering of the potential across the membrane is called hyperpolarisation. It is the summated effects of these depolarisations and hyperpolarisations (which may collectively be termed Neural Current Sources), rather than the action potentials themselves, that are recorded by EEG and ERPs.

Anmerkungen

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Neural Current Sources originate at the cell membrane and represent a deviation from the equilibrium state or resting potential. During an EPSP, a local current sink is produced, which draws positive ions into the cell, thereby moving the potential closer to 0 mV. A sink may be thought of as a negative source. Local sinks are balanced by distant passive sources; as the sink draws ions into the cell, thus depolarising the membrane, these ions move through the neuron and are ejected at some other location, known as a (positive) source. For example, if a sink existed at a branch of the cell’s dentritic tree, the distant source might occur at the cell body, or near the axon hillock. The co-occurrence of the positive source at one location, and the negative sink at another, means that the cell may effectively be viewed as a dipole. In an IPSP, the opposite situation occurs. A local source is produced, which emits positive ions, thereby lowering the membrane potential. This source is balanced by a distant sink, which takes in ions at another location on the cell. Again, this may be considered as a dipole. The EEG gives a macroscopic view of the activity of these sinks and sources. Neural Current Sources originate at the cell membrane and represent a deviation from the equilibrium state or resting potential. During an EPSP, a local current sink is produced, which sucks positive ions into the cell, thereby moving the potential closer to 0 mV. A sink may be thought of as a negative source. Local sinks are balanced by distant passive sources; as the sink draws ions into the cell, thus depolarising the membrane, these ions move through the neuron and are ejected at some other location, known as a (positive) source. For example, if a sink existed at a branch of the cell’s dentritic tree, the distant source might occur at the cell body, or near the axon hillock. The co-occurrence of the positive source at one location and the negative sink at another means that the cell may effectively be viewed as a dipole.

In an IPSP, the opposite situation occurs. A local source is produced, which emits positive ions, thereby lowering the membrane potential. This source is balanced by a distant sink, which takes in ions at another location on the cell. Again, this may be considered as a dipole. The EEG gives a macroscopic view of the activity of these sinks and sources.

Anmerkungen

A reference to the source is missing.

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[Although we] can only provide a brief overview here, a detailed account of the workings of this technique is provided by Nunez (1990).

EEG and ERPs record from the scalp the electrical activity (produced by sinks and sources) of populations of pyramidal cells which form the grey matter of the cortical surface. If a scalp potential records activity due to current sources over an area of less than 1 cm², then the large number of sources may be considered as a single dipole source. Usually, however, scalp potentials are due to larger areas of activity. When a large number of dipoles fire with synchronous activity, and their polarities are the same (i.e. all their positive terminals or sources are adjacent to other positives), as can happen with the densely interconnected pyramidal neurons of the cortical surface, then the group could be considered to form a homogenous dipole layer. However, dipole layers rarely occur with completely homogenous polarities of sinks and sources. The more common occurrence is for the layer to consist of a mixture of polarities of dipoles, in which case the overall potential will reflect the majority of dipole polarities.

Although we can only provide a brief overview here, a detailed account of the workings of this technique is provided by Nunez (1990).

EEG and ERPs record from the scalp the electrical activity (produced by sinks and sources) of populations of pyramidal cells which form the grey matter of the cortical surface. If a scalp potential recorded activity due to current sources over an area of less than 1 cm², then the large number of sources may be considered as a single dipole source. Usually, however, scalp potentials are due to larger areas of activity. When a large number of dipoles fire with synchronous activity, and their polarities are the same (i.e. all their positive terminals or sources are adjacent to other positives), as can happen with the densely interconnected pyramidal neurons of the cortical surface, then the group could be considered to form a homogenous dipole layer. However, dipole layers rarely occur with completely homogenous polarities of sinks and sources. The more common occurrence is for the layer to consist of a mixture of polarities of dipoles, in which case the overall potential will reflect the majority of dipole polarities.

Anmerkungen

A reference to the source is missing

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The captions in the thesis and the source are identical.

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It has been repeatedly demonstrated by correlating scalp-recorded EEG with intracranial neuronal discharges in the monkey and the cat, that the polarity of ERPs, are related to either excitation or inhibition of cells. Comparison of evoked potentials and neuronal spiking activity reveals that neuronal discharges/firing in thalamocortical cells seem to result in negative ERP components, while cellular inhibition underlies positive potentials. Thus EPSPs/depolarisations appear responsible for negative ERP deflections, while IPSPs/hyperpolarisations are the cause of scalp-recorded positivities. Specifically, the scalp recorded negative shifts seem to be due to the depolarisation of pyramidal cell dendrites, which results in an extracellular surface current sink, with the opposite situation the case for scalp recorded positives. The relationship between neuronal activity and scalp-recorded potentials is shown in Figures 2.5 and 2.6 above, from Coenen (1995). Although this polarity reversal between intracranial and scalp recorded activity is true in most cases, the opposite relationship, where scalp positives are due to neuronal excitation and negatives to inhibition, has also been found on occasion. It has been repeatedly demonstrated by correlating scalp recorded EEG with intracranial neuronal discharges in the monkey and the cat that the polarity of ERPs are related to either excitation or inhibition of cells. Comparison of evoked potentials and neuronal spiking activity reveals that neuronal discharges/firing in thalamocortical cells seem to result in negative ERP components, while cellular inhibition underlies positive potentials. Thus EPSPs/depolarisations appear responsible for negative ERP deflections, while IPSPs/hyperpolarisations are the cause of scalp-recorded positivities. Specifically, the scalp recorded negative shifts seem to be due to the depolarisation of pyramidal cell dendrites, which results in an extracellular surface current sink, with the opposite situation the case for scalp recorded positives. The relationship between neuronal activity and scalp-recorded potentials is shown in Figures 3 and 4, from Coenen (1995). Although this polarity reversal between intracranial and scalp recorded activity is true in most cases, the opposite relationship, where scalp positives are due to neuronal excitation and negatives to inhibition, has also been found on occasion.
Anmerkungen

A reference to the source is missing.

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Given that electrical potentials travel through both the bone and skin of the skull and scalp at high speed leading to almost instantaneous recording of the electrical activity of the brain, ERPs provide very [high temporal resolution.] Electrical potentials travel through the bone and skin of the skull and scalp at high speed leading to almost instantaneous recording of the electrical activity of the brain, thus providing very high temporal resolution.
Anmerkungen

A reference to the source is missing. The copied text continues on the next page: Jm/Fragment_071_01

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The time-course of processing in the cortex may be seen with millisecond accuracy. In this particular facet of functional brain activity recording, ERPs are considerably superior to the other major techniques available such as Positron Emission Tomography (PET) and functional Magnetic Resonance Imaging (fMRI). Both of these imaging techniques are constructed upon the concept that increased cognitive processing in an area of cortex requires increased regional cerebral blood flow (rCBF) to support the local energetic demands of the tissue for nutrients and oxygen. There is a significant time-lag involved in such approaches, due to the relatively slow speed at which blood flows through the brain (in comparison to electrical impulses). Also, a blocked design must be used in most imaging studies, such that a real-time record of processing cannot be obtained. The time-course of processing in the cortex

[page 6]

may be seen with millisecond accuracy. In this facet of functional brain activity recording, ERPs is considerably superior to the other major options available, Positron Emission Tomography (PET) and functional Magnetic Resonance Imaging (fMRI). Both of these imaging techniques rely on the idea that increased cognitive processing in an area of cortex requires increased regional cerebral blood flow (rCBF) to support the local energetic demands of the tissue for nutrients and oxygen. There is a significant time-lag involved in such approaches, due to the relatively slow speed at which blood flows through the brain (in comparison to electrical impulses). Also, a blocked design must be used in most imaging studies, so a real-time record of processing cannot be obtained.

Anmerkungen

A reference to the source is missing.

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However, and importantly in terms of present concerns, the major stumbling block encountered with the use of ERPs is the relatively poor spatial resolution it affords both Experimenters and clinicians. Electrical fields are significantly distorted by skull and scalp tissue, such that the pattern of activity recorded on the scalp may bear little resemblance to the regions of cortex responsible for such activity. As such, it is difficult to ascertain with convincing accuracy whether a potential recorded by a dorsolateral prefrontal electrode actually emanated from the dorsolateral prefrontal cortex. PET and fMRI allow for very high spatial resolution, given that the anatomical structures receiving increased blood flow can be represented in three dimensions. Also, because they do not rely on mere scalp recordings, activity in deep sub-cortical regions may also be observed. This disadvantage limits the use of ERPs in Experimental study, and many laboratories have conducted much research on methods to overcome this apparent deficit. The major stumbling block encountered in the use of ERPs is the relatively poor spatial resolution it affords both experimenters and clinicians. Electrical fields are significantly distorted by skull and scalp tissue, so the pattern of activity recorded on the scalp may bear little resemblance to the regions of cortex responsible for such activity. As such, it is difficult to assert that a potential recorded by a dorsolateral prefrontal electrode emanated from the dorsolateral prefrontal cortex. PET and fMRI allow for very high spatial resolution, because the anatomical structures receiving increased blood flow can be represented in three dimensions. Also, because they do not rely on mere scalp recordings, activity in deep sub-cortical regions may also be seen. This disadvantage limits the use of ERPs in experimental study, and many laboratories have conducted much research on methods to overcome this apparent deficit.
Anmerkungen

A reference to the source is missing.

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The Brain Electrical Source Analysis (BESA) technique employed throughout the current thesis attempts to maximize spatial resolution through the use of multiple source algorithms, creating source montages which have been shown to allow the location of ERP potentials to be displayed at a much higher spatial resolution (Scherg, Bast & Berg, 1999) To combat this problem, source analysis software packages have been developed (e.g. BESA; MEGIS software) that attempt to maximize spatial resolution through the use of multiple source algorithms, creating source montages (see Figure 5). This has been found to allow the location of ERP potentials to be displayed at a much higher spatial resolution (Scherg, Bast & Berg, 1999).
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