Alpha peak frequency is the dominant frequency in the range. For example, if you looked at bars on the power spectrum in the alpha range, the bar that was tallest would be the peak frequency.

This is another way of looking at level of activation. Alpha peak frequency should be around 10Hz (especially in the front) in most adults. Lower peak frequencies indicate EEG slowing with the problems related to that (language and attention difficulties, depression, etc.); higher peak frequencies in the front indicate fast EEG with potential issues of anxiety, compulsivity, etc.

Alpha peak frequency slows as we age beyond about 50, and also in people who run very fast EEG’s over a period of years (just one more way stress ages us prematurely). It is also slower in children, generally with a peak around 8 for 8-year-olds and then sliding up to ten as we mature.

Peak frequencies in the back of the head can be higher without necessarily indicating anxiety; there is even some evidence that faster PF in the back relates to better performance on IQ scores, though not all studies agree on this.

Beta PF is a good measure of OCD, addictive and anxiety issues. For most adults it is around 16-20 (depending on how high up you go with the range you are measuring), while addicts have been found to have PF in beta up in the middle 20’s or above.

Overall PF can be another good measure of overall slowing or speeding of the EEG. Around 10 is pretty good. Much higher suggests fast EEG; much lower suggests slow EEG.