Neurophysiological measurements Flashcards
EEG
- records electrical activity of the brain
- uses 21 electrodes on scalp
- 10/20 International system of Electrode Placement
- strenuous hyperventilation used to bring up abnormal discharges
- sometimes strobes of light used
- 24 hour sleep deprivation can lead to activation of paroxysmal EEG discharges in some casees
- EEG recording during sleep can be used when wake tracing is normal
Beta waves
> 13hz
-seen on normal waking EEG
Alpha waves
8-13hz
- dominant wave frequency when eyes are closed and relaxing
- disappears with anxiety, arousal, eye opening or focused attention
- dominance reduces in old age
Theta waves
- 4-8hz
- small amount of sporadic theta seen in waking at frontotemporal area
- prominant in drowsy or sleep EEG
- excessive theta in awake EEG is a sign of pathology
Delta waves
- <4 hz
- not seen in waking EEG
- common in deep sleep
- presence of focal/generalised delta in awake EEG is a sign of pathology
Mu waves
- 7-11 hz
- occurs over motor cortex and is associated with motor activity and limb movement
Lambda
- Single waves
- single occipital triangular, symmetrical sharp wave produced by visual scanning whilst awake or in light sleeo
Fast waves
-alpha (8-12) and beta (13)
Slow waves
-theta (4-8) and delta (<4hz)
Newborns
-dominant delta and theta waves
Infants
-irregular medium to high voltage delta activity
Early childhood
-alpha range develops in posterior areas
Mid adolescence
-EEG essentially has the appearance of an adult tracing by 12-14 years
Adult EEG
-normal dominant alpha rhythm
Diffuse slowing
- most common EEG abnormality
- non-specific
- signifies the presence of encephalopathy
Focal slowing
-suggests local mass lesions e.g haemotoma, focal seizure
Epileptiform discharges
- hallmark of seizure disorder
- but may indicate acute destructive brain lesion
MEG
Magnetoencephalography
- measures magnetic fields produced by electrical activity to the brain
- not very accurate
ERP
- event related potential
- change in electrical brain acitivity stereotyped and time-locked to an event
- low signal to noise ratio
