Chapter 12 p. 1 (EEG) Flashcards
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
__ EEG is the most typical
non-invasive
2 types of invasive EEG
electrocorticography (ECoG), and stereotactic EEG (sEEG)
ECoG is used for __
invasive localization of seizures prior to surgery
sEEG is used for __
deep brain stimulation (DBS)
EEG measures __ resulting from __ within neurons
voltages; ionic currents
EEG can be used to measure __ brain waves (e.g. __(3)) or __ brain waves (__)
endogenous; sleep, coma, epilepsy; exogenous; evoked potentials (EPs)
a common class of EPs consists of __ which are averaged EEG response that are __
event-related potentials (ERPs); time-locked to complex processing stimuli
ERP research is very common in __ (3)
cognitive science, cognitive psychology, and psychophysiological research
because electric potentials are difference in __, each EEG signal is the difference between __
voltage between two sites; two voltage waveforms
an EEG montage represents __
how the signal is obtained
3 types of EEG montages
monopolar, bipolar, Laplacian
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)
bipolar montage: the waveform is the difference between __
2 scalp electrode signals
Laplacian montage: the signal is __ minus __
the voltage at some point on the scalp; a weighted average of the surrounding electrodes
one version of a monopolar montage
the 10-20 montage
it’s named the 10-20 montage because __
the angle between electrodes is ~10 degrees
the 10-20 montage uses __ to direct the placement of electrodes
the natural landmarks of the head
10-20 montage electrodes are typically named based on __
the brain lobe over which they are located
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
