EEG Chapter 14
Terms
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- Rythmic Frequency
- EEg activity in consisting of waves of approximately constant frequency
- Arrhythmic Frequency
- EEG activity in which no stable rythms are present
- Dysrhythmic Frequency
- EEG activity that refers to patterns or rhythms that characteristically appear in patient groups and are rarely seen in healthy subjects
- Attenuation (synonyms: suppression, depression)
- Reduction of amplitude of EEG activity resulting from decreased voltage
- Hypersynchrony
- increase in voltage and regularity of rhythmic activity, often in alpha, beta, theta range. The term implies an increase in the number of neural elements contibuting to the rhythm
- Paroxysmal
- Activity that emerges from background with a rapid onset, reaching usually quite high voltage, and ending with an abrupt return to lower voltage activity. This is associated with a change in frequency and morphology.
- Morphology
- refers to the shape of the wave form. The shape of a wave or an EEG pattern is determined by the frequencies that combine to make up the waveform and by their phase and voltage relationships.
- Surface polarity
- is described as the negative or positive polarity of a particular activity or waveform at a particular electrode location.
- Monomorphic
- EEG activity appearing to be composed of one dominant frequency
- Polymorphic
- EEG activity composed of multiple frequencies that combine to form a complex waveform
- Sinusoidal
- Waves resembling sine waves. Monomorphic activity is usually sinusoidal.
- Transient
- An isolated wave or pattern that is distinctly different from background activity.
- Spike
- A transient with a pointed peak and a duration from 20 to under 70 msec
- Sharp wave
- A transient with a pointed peak and duration from 70-200 msec
- Complex
- A sequence of two or more waves, not necessarily of the same frequency, with a distinct form or pattern. IE. spike and wave complex, or a sharp and slow wave complex
- Biphasic (diphasic)
- A wave or complex having two distinct components, one surface positive and the oter surface negative
- Triphasic
- A wave or complex having 3 distinct component, such as negative-positive-negative.
- Quantity refers to the ammount of a particular type of EEG activity with respect to percent time present and/or to voltage. There are 4 terms associated with quantity
- Continuous: occuring without interpretation Discontinuous: appearing from time to time Regular and irregular.
- Generalized
- Not limited to a specific area
- Lateral (lateralized)
- Coming from one side. ie. slow activity is present over the right temporal-frontal areas
- Bilateral
- Coming from both sides. ie. Bilateral spike activity in the left and right anterior areas
- Focal
- Coming from a local region
- Symmetry
- Equal distribution of EEG activity over homologous head areas. ie. Alpha activity is seen symetrically in the left and the right occipital areas.
- Synchrony
- is the simultaneous appearance or rhythmic or morphologically distinct patterns over different regions of the head, either on the same side (unilateral) or on both sides (bilateral)
- Periodicity
- refers to the distribution of patterns or elements in time (e.g. the appearance of a particular EEG activity at more or less regular intervals)
- Reactivity
- refers to the reaction of the EEG to stimulation or to a stimulus-related change in morphology.
- Alpha activity
- Range from 8 to 13 Hz about 85% range in 9.5-10.5 Hz 66% average between 20-60 uV with 28% less than 20 uV
- Beta Activity
- frequency faster than 13 Hz but in general range of 18-30 Hz Voltage is between 5 and 20 uV. Can be enhanced by tranquilizers and barbiturates.
- Theta Activity
- between 4-7 Hz voltage less than 15 uV with only 10% 15-25 uV if the amplitude of theta activity exceeds that alpha by more than 50% it may have pathological significance.
- Mu Rythm
- in central areas and about 9 Hz with a range of 7-11 Hz. Has a sharp element with a v;otage up to 80 uV. It can also be in perietal and is blocked by tactile stimulation, fist clenching, or thought of movement.
- Lambda Waves
- Sharp waves with variable polarity seen in the occipital areas when the subject intently scans a complex visual field with horizontal eye movements
- Stage 1 Sleep (drowsiness)
- Alpha attenuates, in the occipital areas, a series of surface positive transients which are called Positive Occipital Sharp Transients. POTS Cz C3 C4 will see a slow sharp transient called a vertex (V) waves
- Stage 2 Sleep
- 11-15 HZ spindle bursts in central vertex area with voltages in 20-100 uV and high as 150 uV. Lasting 0.5- 3 seconds. K complexes are slow waves associated with spindle bursts. Can be seen with/without abrupt auditory stimuli.
- Stage 3 Sleep
- Delta activity with frequencies of 2 Hz or less are present in 20-50% of the time and there are still sleep spindles. K complexes and frontal slow transients may appear.
- Stage 4 Sleep
- Delta activity is present more than 50% with a voltage greater than 75 uV. Sleep spindles slow down to 10 Hz area you will have large regions of the brain appear to discharge synchronously
- REM-Stage Sleep
- EOG electro-oculogram picks up eye movemnt while an EMG electromyogram picks up decreased muscle tone in the chin. Sharp theta waves called saw tooth may appear in central areas. Occurs 5-6 times at intervals of 90 min
- What are the 4 main changes seen in elderly persons?
- 1. decrease in frequency of alpha 2. increase in the amount of beta activity 3. increase in diffuse slow activity 4. development of focal dysrhythmias