EEG Intro Flashcards
Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants
When was the first known neurophysiologic recordings of animals performed? Who was it?
Performed By Richard Caton in 1875
When was the first known neurophysiologic recordings of humans performed? Who was it?
Hans Berger, German Psychiatrist in 1924
What is the main utility of EEG?
Evaluation of Dynamic Cerebral Functioning
EEG is particularly useful for evaluating patients with suspected seizures, epilepsy, and unusual spells. With certain exceptions, practically all patients with epilepsy will demonstrate characteristic EEG alterations during an epileptic seizure (ictal, or during-seizure, recordings). Most epilepsy patients also show characteristic ______ termed spike
(<70 µsec duration), spike and wave, or sharp-wave (70–200 µsec duration) discharges.
interictal (or between-seizure) epileptiform discharges (IEDs)
What are some other clinical indications that EEGs can find?
Monitor depth of anesthesia during surgical procedures; EEG waveforms may also be averaged, giving rise to evoked potentials (EPs) and event-related potentials (ERPs), potentials that represent neural activity of interest that is temporally related to a specific stimulus.
The EEG is thought to be primarily generated by —– neurons in the —– that are oriented perpendicularly to the brain’s surface. The neural activity detectable by the EEG is the summation of the — and — postsynaptic potentials of relatively large groups of neurons firing synchronously. Conventional scalp or cortical surface–recorded EEG is unable to register the — arising from neuronal action potentials.
The EEG is thought to be primarily generated by cortical pyramidal neurons in the cerebral cortex that are oriented perpendicularly to the brain’s surface. The neural activity detectable by the EEG is the summation of the excitatory and inhibitory postsynaptic potentials of relatively large groups of neurons firing synchronously. Conventional scalp or cortical surface–recorded EEG is
unable to register the momentary local field potential changes arising from neuronal action potentials.
What is an unfortunate reality of EEG? How can electrical signals be detect on the scalp surface?
An unfortunate reality of EEG is that cerebral activity may be overwhelmed by other electrical activity generated by the body or in the environment.
To be seen on the scalp surface, the miniscule, cerebrally generated EEG voltages must first pass through multiple biological filters that both reduce signal amplitude and spread the EEG activity out more widely than its original source vector. Cerebral voltages must traverse the brain, CSF, meninges, the skull, and skin prior to reaching the recording site where they can be detected. Additionally, other biologically generated electrical activity (by scalp muscles, the eyes, the tongue, and even the distant heart) creates massive voltage potentials that frequently overwhelm and obscure the cerebral activity.
What does a typical EEG display on the graph?
Voltages - Vertical Domain
Time - Horizontal Domain
Provides a near real-time display of ongoing cerebral activity
What can the interpreter adjust the sensitivity of the recording? What is the other name for sensitivity in EEG recordings?
Sensitivity == Gain [microvolts per milimeter]
Interpreter can adjust the sensitivity of the recording to increase or reduce the display height of waveforms.
Why should one be carful in applying digital filters?
Digital filters may also be applied to reduce artifact in certain settings but must be used
with great caution since they also filter EEG activity of interest and may distort EEG waveforms severely.
What amplification priciples does EEG use? How are EEG waveforms generated? What are the two electrodes used?
EEG uses the principle of differential amplification, or recording voltage differences between different points using a pair of electrodes that compares one active exploring electrode site with another neighboring or distant reference electrode. Only through measuring differences in electrical potential are discernible EEG waveforms generated. By convention, when the active
exploring electrode (termed G1, for “Grid 1,” a historical convention from analog amplification) is more negative than the reference electrode (G2), the EEG potential is directed above the horizontal meridian (i.e., an upward wave), whereas if the opposite is true, where the reference electrode is more negative, the EEG potential vector is directed below the horizontal meridian (downward potential).
How does MEG work?
utilizes sensors to capture magnetic fields generated by the brain.
How does MEG complement EEG?
MEG provides complementary information to the EEG by demonstrating the activity of magnetic cerebral dipole. MEG dipoles may produce more accurate locations for cerebral epileptiform generators than EEG.
What is Epileptiform activity?
Epileptiform activity on EEG is indicative of cortical hyperexcitability, which carries an increased risk for seizures and the presence of an epileptic network within the brain.
What are different types of epileptiform
Single Discharges(Sharps and Spikes), rhythmic and/or periodic activity.
How can epileptiform be useful?
It is important to note that the presence of epileptiform activity is not sufficient for a diagnosis of epilepsy in a patient with no history of seizures. In a patient with a history of seizures, epileptiform activity in between seizures (interictal activity) is useful in helping to localize seizure onset.
What is epileptiform discharge?
disruption of the usual functioning of the brain, and sharps and spikes are perhaps the most classic type.
What are the classic types of epileptiform discharge?
Sharps and Spikes
What is “Sharps” in epileptiform discharge?
A sharp is a single epileptiform discharge defined by its duration lasting between 70-200ms, and by its disruption of the EEG background
What is the difference between “Sharps” and “Spikes”?
A sharp is a single epileptiform discharge defined by its duration lasting between 70-200ms, and by its disruption of the EEG background. A spike is very similar to a sharp but faster, with a duration from 20-70ms. Realistically, the cutoff between them is not very important clinically, as one isn’t known to be any more “severe” than the other.
Sharp - 70-200ms
Spike - 20-70ms
