According to Sheer, 40-Hz activity reflects a focused arousal associated with memory and learning processes. In his words: "...40-Hz reflects repetitive stimulation at a constant frequency for a limited time over a limited circuitry. The circuitry is defined behaviorally by the spatial-temporal patterning of sensory inputs, motor inputs, and reinforcement contingencies. It is 'optimal' for consolidation because repetitive synchronous excitation of cells maximizes the efficiency of synaptic transmission over the limited circuitry." (Sheer, 1975, p. 356)

There are animal studies, human studies in both normal people and the learning disabled (LD), biofeedback studies showing

easily trained

ability to increase and decrease 40 Hz, and long-term follow-up studies.

20 Hz/40 Hz Notes

Another interesting mathematical correlation with 40 Hz is the EEG during meditation. Banquet (1973) found 20- and 40-Hz EEG changes in advanced Transcendental Meditators during the third stage of meditation (considered to be deep meditation or "transcendence"). The EEG was characterized by a dominant Beta rhythm at 20 Hz.
On the ink written record, Beta periods appeared at both 20 and 40 Hz. The amplitude of the background activity reached a surprisingly high voltage of 30-60 yV. Beta was mainly in the anterior head regions, but was sometimes present diffusely. In the compressed spectral arrays (CSA), the 20-Hz Beta power peaks seem to lie on an unvarying straight line with high amplitude, suggesting unusually regular frequency and amplitude. Forty-Hz activity, in comparison, is of significantly lower amplitude and of less steady regularity. The CSA shown in Banquet's article (1973) fits Cricles description of 40 Hz (1994), which he says is "more like a freehand drawing of a wave than a very regular mathematical wave of constant frequency." The spectral array also demonstrated a marked amplitude increase in the Delta range. Unfortunately, the peak frequency of the slow waves is not stated in the study.
Das and Gastaut (1955), recording from seven trained Yogis, reported high amplitude levels of 40-Hz activity during the Samadi state, which is the final, most intense concentration state in this form of meditation. Pollini and Peper (1976) reported Beta activity at 18-20 Hz in subjects during meditation.
In summary, when the body is profoundly relaxed and the mind is in a state of high focus and concentration, 20- and 40-Hz brain activity can be seen in the raw and quantitative EEG of some subjects. It is possible that 18-22 Hz Beta and possibly 40-Hz neurofeedback training may help create a "relaxed body/focused mind" state of consciousness.

Increase Amount of 40Hz not Amplitude

Forty-Hz is thought to be either "off" or "on." For this reason, the neurofeedback objective may be to increase the amount of time that 40 Hz is on, rather than to attempt to increase its amplitude. The audio reward tone is therefore adjusted for a "flat" tone response rather than a "sliding" tone that becomes higher-pitched with increasing amplitude.


It seems important to train 40 Hz in brain areas that are associated with known sensory and motorprocessing, that is, the central and posteriorly placed electrodes (C3, C4, Cz, T5, T6, P3, P4, Pz, 01, and 02). It is important to avoid the midtemporal electrode sites because of the temporalis muscle.

"Gate" Theory

Commonly known clinical EEG frequencies, especially those shown to remediate attention problems and quiet hyperactivity (12-15 Hz), alcohol and drug addictions (Alpha/Theta at 7.5-8 Hz), and mental processing (Theta2 at 6.5 Hz and Theta at 4 Hz) mathematically relate to 40 Hz, an EEG frequency band centering at = 39.5 Hz.
It is proposed that those with attention problems, addictions, and mental processing problems (such as learning disabilities) may have restricted, limited, or no access to critical areas of cognitive and neurological functioning. Neurofeedback aids in the opening of certain critical, frequency-related "gates" in cerebral function to which the trainee previously had restricted, limited, or no access.

"Chord" Theory

Forty-Hz activity represents a chord-a computation- composed of several resident key brain frequencies. If these resonant frequencies are fully and dynamically present, maximum cerebral potential (volitional accessibility to specific neuronal functions, multiple states and levels of consciousness, and attentional flexibility) is available.
Dissonance, deficiency, or excess in one or more key frequencies leads to discordance of 40-Hz activity, which in turn leads to hampered ability (a deficit) of some specific operation in cerebral functioning. Neurofeedback aids in the restoration of specific key resonant frequencies, thereby restoring full clarity to the 40 Hz.