label: Absent posterior alpha rhythm
label_lc: absent posterior alpha rhythm
description: "Lack of normal alpha rhythm in the EEG. Alpha rhythm has been defined as a rhythm at 8-13 Hz occurring during wakefulness over the posterior regions of the head, generally with higher voltage over the occipital areas. Amplitude is variable but is mostly below 50 microvolt in adults. It is best seen with eyes closed and under conditions of physical relaxation and relative mental inactivity. It is blocked or attenuated by attention, especially visual and mental effort. One should here note the difference between the terms alpha rhythm and alpha activity: Alpha activity refers to activity in the range of 8-13 Hz and alpha rhythm is the activity of 8-13 Hz with specific characteristics as defined above."