Fisch EEG Primer Chapter 1 Flashcards
The EEG is generated by cortical nerve cell…
inhibitory and excitatory postsynpatic potentials or neurons underlying the cortex that lasts over ~100ms. NOTE: not by nerve action potentials which only lasts ~1ms
Rythmical cortical EEG activity arises from…
interaction between thalamus and cortex. e.g. sleep spindles generated by thalamic pacemaker cells of the nucleus reticularis, when surgically extracted continue to pace but effected cortical activity ceases
Desynchronization of cortical EEG activity results from
- alteration of subcortical pacemaker (e.g. cells of nucleus reticularis)
- alteration of cortical projection fibers (e.g. ascending cholinergic systems)
- direct damage to or suppression of components any component of rythmic cellular networks
Scalp electrodes best capture postsynaptic potentials of neurons favoring
slow, SIMULTANEOUS pontentials generated in large cortical areas of pyramidal cells situated 90deg to plane of scalp
Tisses that act as a volume conductor to alter recorded EEG activity..
brain parenchyma, dura, CSF, skull, scalp
The Operational Definition of the EEG
difference in voltage between two different recording locations plotted over time. These potentials are the result of excitatory and inhibitory postsynaptic potentials
What is volume conduction?
current flow through tissues between the electrical generator and recording electrode
Describe the inverse problem.
NOTE: related to forward problem
Within scalp recorded EEGs, there are an infinite number of sources within the brain that can explain the recorded potential. It is theoretically IMPOSSIBLE to know EEG gernator location based on scalp recorded EEG.
Describe the forward problem.
NOTE: related to inverse problem
If the anatomical source, intensity, and orientation of the electrical generator are known, scalp EEG recordings can be accurately predicted.
Resting membrane potential of a neuron
-65mV - results from passive and active transport of ions across cell membranes
Excitatory Postsynaptic Potentials (EPSP) results from
transient partial reduction in membrane potential that causes a decreased resting membrane potential (more positive) likely caused by increased permeability to sodium and potassium
Inhibitory Postsynaptic Potentials (IPSP) results from
transient increase (more negative) membrane potential caused by opening chloride channels and possible potassium channels
Facultative Pacemaker Theory
Thalamocortical cells with corresponding thalamic inhibitory interneurons
Scalp EEG tend to filter out
higher frequency potentials and have lower amplitude compared with equivalent cortical recordings (electrocorticogram “ECoG”)
Projected Rythyms
Scalp EEG is intended to measure local potential changes, but cortical potential be detected in more widespread distribution (a.k.a. rythmes a distance)