Chapter 12 p. 1 (EEG) Flashcards by Julia Boudreau

EEG is an __ monitoring method for recording the __ of the brain using electrodes placed __, although __ electrodes are occasionally used

electrophysiological ; electrical activity; along the scalp; invasive

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__ EEG is the most typical

non-invasive

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2 types of invasive EEG

electrocorticography (ECoG), and stereotactic EEG (sEEG)

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ECoG is used for __

invasive localization of seizures prior to surgery

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sEEG is used for __

deep brain stimulation (DBS)

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EEG measures __ resulting from __ within neurons

voltages; ionic currents

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EEG can be used to measure __ brain waves (e.g. __(3)) or __ brain waves (__)

endogenous; sleep, coma, epilepsy; exogenous; evoked potentials (EPs)

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a common class of EPs consists of __ which are averaged EEG response that are __

event-related potentials (ERPs); time-locked to complex processing stimuli

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ERP research is very common in __ (3)

cognitive science, cognitive psychology, and psychophysiological research

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because electric potentials are difference in __, each EEG signal is the difference between __

voltage between two sites; two voltage waveforms

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an EEG montage represents __

how the signal is obtained

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3 types of EEG montages

monopolar, bipolar, Laplacian

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monopolar montage: the waveform is the difference between __ and __

the signal at the scalp; the signal at a skin location far away (e.g. arm, leg)

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bipolar montage: the waveform is the difference between __

2 scalp electrode signals

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Laplacian montage: the signal is __ minus __

the voltage at some point on the scalp; a weighted average of the surrounding electrodes

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one version of a monopolar montage

the 10-20 montage

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it’s named the 10-20 montage because __

the angle between electrodes is ~10 degrees

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the 10-20 montage uses __ to direct the placement of electrodes

the natural landmarks of the head

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10-20 montage electrodes are typically named based on __

the brain lobe over which they are located

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EEG sources are primarily due to __ along the __

currents; apical dendrites of pyramidal neurons (PY)

pyramidal neurons: somas are in __ and apical dendrites project to __

layer V; layers I and II

types of neurons other than PYs do not typically generate a strong EEG signal because of __ (e.g. in the case of __)

signal cancellation; stellate neurons

within white matter fibers, the net electrical currents __ because action potentials travel __ and thus the scalp signal due to these is __

cancel out; both ways along the fiber; very weak

__ of ions along the dendrite of PY create a __ across the membrane, and the simultaneous activation of PY populations results in a __ which extends to the scalp

influx or efflux; net potential difference; measurable electric field

PY cell populations within a spatial neighborhood on the cortex can __ and their electric signal can be represented using the __

activate simultaneously; current dipole model of EEG

in the current dipole model of EEG, electric currents are approximated by vectors which are __ and whose direction is __

perpendicular to the surface of the cortex; determined by the direction of the electric currents along the apical dendrites of the PY cells

current dipole model of EEG: note that the recorded signal is more __ when a bipolar montage is used, compared to the monopolar montage

focal

active EEG sources produce distinct patterns at the scalp depending on __, as well as on the __

the location where they are generated; orientation of these generators

because the orientation of the generators is predicated upon the __ of the cortex at locations which are __, the __ of the brain determines scalp potential patterns

gyrification; electrically active; anatomic configuration

__ cells generate currents which propagate to the scalp

electrically active PY

the extent to which currents can travel across tissues which are __ is determined by the __ of these tissues, which is a measure of the physical ability of a material to __

interposed between the cortex and the scalp; electrical conductivity; conduct an electric current

there are many layers between the brain and the scalp, and each of these __ (e.g. __)

has a different conductivity (e.g. that of CSF is very high because it contains Na and Cl ions in water, whereas that of bone is very low)

because of the different conductivities of the layers between brain and scalp, the EEG signal is both __ and __, so that scalp potentials provide a measure of __

attenuated; spatially smeared; only the strongest cortical currents

EEG signals may change __ and/or __ in response to __

amplitude; frequency; ERPs

5 canonical frequency bands (in order from lowest to highest Hz/frequency)

delta, theta, alpha, beta, gamma

delta

slow-wave sleep, subcortical lesions

theta

higher in children, drowsiness in adults, encephalopathies

alpha

eye closing, relaxation, inhibition control, coma

beta

attention, alertness, anxiety, decreased by GABA agonists (benzos)

gamma

sensory integration, decreases with cognitive decline

the task of localizing EEG currents based on scalp EEG potential recordings is known as

the inverse problem of EEG

the task of calculating the scalp EEG potential due to a known distribution of electric currents is know as

the forward problem of EEG

solving the forward problem involves computing the __, which specifies the __

lead field of each EEG electrode; areas of cortex from which the electrode can record

__ is the most important step required before solving the __, and the accuracy of __ depends on the accuracy of __

finding the lead fields of EEG; inverse problem; inverse localization; lead field calculation

lead fields are computed based on __

appropriate formulations of Maxwell's Equations

the second step to inverse localization involves __. two examples?

the creation of realistic models of the head; boundary element models (BEMs), and finite element models (FEMs)

BEMs are models which specify the __, and the conductivity within each shell is __ (not particularly accurate due to __)

boundaries between tissues; assumed to be constant; conductivity inhomogeneities

FEMs are models which discretize/divide the head into __, and each of these has its own __ (much more __ than BEM if the __ is high)

small tetrahedra; conductivity; accurate; spatial resolution

once the inverse model has been generated, scalp potentials can be __ and the __ can be determined (ex: __)

localized to the cortical surface; locations of EEG generators; post-traumatic epileptic spiking