EEG Flashcards
What is EEG a measure of?
Electrical activity of the brain
Is EEG an indirect or direct measure of activity?
Direct
What is EEG used for in clinic?
Diagnosis tool for cerebral dysfunction such as epilepsy
Analysing sleep and distinguishing sleep stages
Legal determination of brain death
What exactly does EEG measure?
Sum of extracellular potentials from a group of neurons
Which cell type is largely recorded by EEG?
Cortical pyramidal cells
How are amplitude fluctuations measured on EEG?
uV (microvolts)
What are the advantages of EEG?
Good temporal resolution
Direct measure of brain activity
What are the disadvantages of EEG?
Poor spatial resolution due to filtered signal through blood, tissues, and skull
Measures only a small fraction of total brain activity due to variability in conductivity, mixed orientation of dendrites, and lack of synchronous activity
How has the placement of electrodes been standardized?
International 10-20 system based on scalp measurements, relative to nasion and inion
Where is the nasion?
Between the eyes
Where is the inion?
Base of the skull
What is a series of electrode placements referred to as?
Montage
What are field potentials on EEG?
Extracellular recordings of synchronised activity of a large number of cells
How do field potentials appear on EEG?
Single electrical spikes
What does a single electrical spike indicate on EEG?
Field potential
What type of deflection occurs on EEG following an excitatory post-synaptic potential?
Negative deflection
What type of deflection occurs on EEG following an inhibitory post-synaptic potential?
Positive deflection
What can cause mixed orientation of dendrites?
Folding of cerebral cortex
What does synchrony of neuronal activity cause on EEG?
Large amplitude and low frequency waves
What frequency are beta waves?
13 - 30 Hz
When are beta waves the dominant wave pattern?
Awake and alert, focused on a task
What frequency are alpha waves?
8 - 13 Hz
When are alpha waves the dominant wave pattern?
Awake and relaxed
What frequency are theta waves?
4 - 7 Hz
When are theta waves the dominant wave pattern?
During memory encoding and recall
What frequency are delta waves?
Below 4 Hz
When are delta waves the dominant wave pattern?
During sleep, unconscious
What is the dominant brain wave pattern in infants?
Delta waves
What brain waves are observed in stage 1 NREM sleep?
Theta waves
What brain waves are observed in stage 2 NREM sleep?
Spindles and K complexes
What brain waves are observed in stage 3 and 4 NREM sleep?
Delta waves
What are sensory evoked potentials?
Potentials observed in EEG that are reliably reproduced at specific times in response to particular sensory stimuli
How are sensory evoked potentials extracted from EEG recordings?
Signal averaging of recordings over multiple trials
What does signal averaging do to EEG, when searching for sensory evoked potentials?
Removes/minimises random variations to leave only the stimulus-evoked potential
What are three examples of sensory evoked potentials?
Visual evoked
Auditory evoked
Somatosensory evoked
How can sensory evoked potentials be used in clinic?
Assess neurological function
What condition can be detected in its early stage via abnormal visual evoked potential recordings?
Multiple sclerosis
What change to visual evoked potentials is associated with early stage multiple sclerosis
Delayed VEP
What are the reliably reproducible components of a visual evoked potential?
Negative peak 70ms
Positive peak 100ms
Negative peak at 140ms
For which age range is the visual evoked potential timings reliable?
5 to 60
What change is associated with visual evoked potentials in individuals over the age of 60?
P100 slows with ageing at a rate of approx 1ms per decade
What changes in visual evoked potentials are associated with later stages of multiple sclerosis?
Progressively slower VEPs
What causes alterations in visual evoked potentials in multiple sclerosis?
Progressive demyelination
What are brainstem auditory evoked potentials used to assess for in clinic?
Assess severity of hearing loss
Identify and diagnose hearing impairment in young children
Assess brainstem function
What does each peak of the auditory evoked potential correlate to?
Activity at a different part of the auditory processing pathway
What does wave I of the auditory evoked potential correlate to?
Action potential of vestibulocochlear nerve
What does wave II of the auditory evoked potential correlate to?
Cochlear nucleus and vestibulocochlear nerve
What does wave III of the auditory evoked potential correlate to?
Ipsilateral activation of the superior olivary nucleus
What does wave IV of the auditory evoked potential correlate to?
Nucleus or axons of the lateral lemniscus
What does wave V of the auditory evoked potential correlate to?
Inferior colliculus
What does wave VI of the auditory evoked potential correlate to?
Medial geniculate nucleus of the thalamus
What nerve is stimulated to induce somatosensory evoked potentials?
Cutaneous nerve, usually in the wrist
What are somatosensory evoked potentials used in clinic?
Diagnose/assess multiple sclerosis and other demyelinating diseases
Assess spinal function in spinal conditions or during surgery
What is the definition of epilepsy?
Sudden change in behaviour that is caused by electrical hypersynchronisation of cortical neuronal networks
What percentage of the population will experience a single, isolated seizure?
10%
What percentage of the population experiences recurrent epileptic seizures?
0.5 to 1%
What are potential causes of non-epileptic seizures?
Electrolyte imbalances
Hyper/hypoglycaemia
Drug/alcohol withdrawal
Acute brain injury
What is a ‘partial’ epileptic seizure called and where do they originate?
Focal epilepsy
Originate in a region of abnormal brain tissue that becomes a focal point for the seizure. Some areas of the brain will have normal wave patterns
What is a generalised epileptic seizure?
Involves both hemispheres of the brain
What is electrocorticography?
Electrophysiological measurement method that places electrodes directly on the brain
What are the advantages of electrocorticography over EEG?
Improve spatial resolution and avoids filtering of signal through the skull
What are the disadvantages of electrocorticography over EEG?
Invasive - requires craniotomy
How are intracortical local field potentials recorded?
Electrodes are inserted directly into brain
What is intractable epilepsy?
Drug resistant therapy
How do implanted electrodes aid surgical treatment of intractable epilepsy?
Electrodes are inserted into the brain for presurgical evaluation to determine the location of the seizure origin accurately
