EEG and Evoked Potentials Flashcards
What are brain waves and on what scale are they recorded?
They are voltage fluctuations generated at the surface of the scalp, measured in voltage versus time.
How many electrodes are used to generate a channel, and how many are there generally? What is noise?
Two electrodes: a reference and a recording electrode. Only those signals which are not cancelled out are recorded. Each electrode is regularly spaced about the head to prevent any “straight” lines. The noise will cancel out.
There are 8-40 channels in a standard multichannel recording
What is the scale on which brainwaves are measured?
Microvolts, but they are amplified to near megavolt levels by the amplifier.
What is the significance of Fourier Transforms for EEGs?
They convert the wave data from being a function where voltage varies with time to show how much of the EEG signal on a channel occurs due to a given FREQUENCY
-> very useful for determining the type of waves
What is an artifact?
Disturbances in the EEG caused by technical defects, and are usually transitory. I.e. muscle movements, touching of the head, loss of electrode contact, sweating, etc
How many Hz are associated with gamma, alpha, beta, theta, and delta waves?
gamma: >40 Hz
alpha: 8-13 Hz
beta: 13-40 Hz
theta: 4-8 Hz
delta: <4 Hz
What are gamma waves? What do they do?
The highest frequency waves which are expressed widely in brain areas that are active at the same time. They reflect “binding”, and serve to integrate all of our senses into a single consciousness. It is the rhythm / refresh rate of the brain
What are beta waves? Where are they found?
High frequency, low amplitude waves seen on both sides symmetrically, primarily frontally. Dominant rhythm in patients who are alert or anxious, or have their eyes open
What are alpha waves? Where are they found? How does their amplitude vary with dominance?
Slightly lower frequency than beta. They are best seen in posterior regions of head, and are higher in amplitude on the dominant side. It is the major rhythm in normal, rested adults (past age 13), or if eyes are closed. If thinking or calculating, waves will shift to beta
What are theta waves and at what ages is this normal / abnormal when awake? What part of the brain is theta at rest?
It is considered abnormal in awake adults, but is normal in sleeping adults or awake children <13 years.
Seen normally in hippocampus (not by surface EEG).
What types of brain damage are theta waves seen in?
Will be seen in generalized distribution in metabolic encephalopathies or diffuse disorders, or focally in focal subcortical lesions
What are delta waves? When are they normal?
Highest amplitude, lowest frequency waves. Normal in NREM stages 3-4 of sleep, and correlates with non-moving, low levels of arousal.
Present also normally in newborn infants
When are delta waves abnormal?
Not normally seen in adult EEGs. If they are seen, it’s a sign of disease
How does EEG Brain Topography work?
Larger number of electrodes are configured in a geometric array and spaced about the head. A computer makes a “weathermap” or topography of brain activity, with brighter colors to depict higher amplitudes
What is EEG Brain Topography used for?
Used for detection of disorders of brain conduction. Will not be useful for diseases like depression where the electrical conduction of the brain is not interfered with.
For instance: epilepsy, stroke, AV malformations, psychoactive drug withdrawal
