The Normal Adult EEG in Wakefulness

Vocabulary terms and definitions related to normal adult EEG waveforms, frequencies, and variants during wakefulness.

Posterior Dominant Rhythm (PDR)

The occipital rhythm in the alpha frequency range ($8-13\,Hz$ in adults) that attenuates with eye opening and appears around 3-4 months of age.

Alpha squeak

A transient increase in the frequency of the Posterior Dominant Rhythm immediately after eye closure.

Slow alpha variant

A subharmonic variant of the alpha rhythm that appears at half the frequency of the patient's normal alpha rhythm.

Fast alpha variant

A superimposed harmonic variant of the alpha rhythm that appears at twice the alpha frequency.

Delta Activity

EEG activity with a frequency of $<4\,Hz$; it is a normal component of sleep but generally not present in the awake adult.

Posterior slow waves of youth

Occipital delta or theta waves fused or mixed with alpha that are maximal between ages 8-14, rare after age 21, and block with eye opening.

Lambda waves

Sharp transients in the occipital region occurring when eyes are open and scanning; they are classically surface positive and equivalent to the $P100$.

Mu rhythm

A comb-shaped central rhythm ($C_3$, $C_4$) with a frequency of $8-12\,Hz$ that blocks with contralateral arm movement or the thought of movement.

Theta activity

EEG activity with a frequency of $6-7\,Hz$ that increases in drowsiness and is predominantly frontocentral in adults.

Frontocentral beta

Activity with a frequency of $>13\,Hz$ and low amplitude ($<20\,\mu V$) that is enhanced by drugs like benzodiazepines, barbiturates, and chloral hydrate.

Breach rhythm

A focal increase in beta activity resulting from skull defects.

Hans Berger

A Berlin psychiatrist who recorded the first human EEG and described the alpha frequency rhythm in the posterior head region.

W. Gray Walter

The English physiologist who described delta activity in 1936.