100+ Free ABCN CNP Practice Questions

Explanation: The 10-20 system is named because electrodes are placed at distances that are 10% or 20% of the total front-to-back (nasion-to-inion) or right-to-left (preauricular) measurements of the skull. The outermost electrodes sit 10% from the landmarks, and inner electrodes are spaced at 20% intervals. This proportional method ensures consistent placement across different head sizes.

Explanation: The longitudinal (front-to-back) measurement runs from the nasion, the depression between the forehead and nose, to the inion, the bony prominence at the back of the skull. The transverse measurement runs between the two preauricular points. These landmarks anchor the proportional placement of all scalp electrodes.

Explanation: The alpha rhythm, or posterior dominant rhythm, is 8-13 Hz in the normal awake adult, best seen posteriorly with the eyes closed and relaxed. It attenuates with eye opening or mental effort. A frequency below 8 Hz in an awake adult is abnormal slowing.

Explanation: Beta activity spans roughly 13-30 Hz and is usually symmetric and frontally predominant in the awake adult. It is enhanced by certain medications such as benzodiazepines and barbiturates. Beta is a normal finding, unlike excessive delta in the awake state.

Explanation: A bipolar montage links pairs of adjacent electrodes in chains, so each channel displays the voltage difference between two active sites. This arrangement is excellent for localizing focal activity through phase reversal. In contrast, a referential montage compares each active electrode to a common reference.

Explanation: In a bipolar chain, the electrode closest to a focal source produces a phase reversal, where the deflections in adjacent channels point toward (negative) or away from (positive) each other. The electrode at the point of phase reversal marks the location of maximal potential. This is a cornerstone of bipolar localization.

Explanation: A routine EEG typically uses a low-frequency filter (high-pass) around 1 Hz, which attenuates slow drift and sweat or movement artifact while preserving relevant slow waves. The high-frequency filter is usually set near 70 Hz. The low-frequency filter is called a high-pass filter because it allows higher frequencies to pass.

Explanation: The notch filter selectively attenuates 60 Hz (50 Hz in many countries) power-line interference. It should be used judiciously because it can also distort or obscure genuine EEG and may mask poor electrode connections that cause the interference. Fixing high impedance is preferred over relying on the notch filter.

Explanation: Sleep spindles are 11-16 Hz bursts lasting at least 0.5 seconds and are recorded maximally over the central (vertex) leads. They are a defining feature of stage N2, along with K complexes. K complexes, by contrast, are most prominent over the frontal regions.

Explanation: The mu rhythm is an alpha-frequency (arch-shaped) rhythm over the central sensorimotor regions that appears when the limbs are at rest and attenuates with movement or the intention to move the contralateral extremity. Unlike the posterior alpha rhythm, mu does not block with eye opening. It reflects sensorimotor cortex idling.