| Many
cortical and subcortical areas of the brain have spontaneously occurring
36 - 44 Hz (“40-Hz”) activity. Across the scalp, the EEG peak frequency
of 40-Hz is 39.5 Hz. A theory is proposed in which the brain has certain
resident resonant frequencies that are subharmonics of 40-Hz activity.
Some of these EEG frequencies are commonly trained in Neurotherapy. Two
examples are 12-15 Hz and 7-8 Hz activity, which are third and fifth subharmonics.
Other frequencies with known cognitive and mental processing relationships
and mathematical associations too 40-Hz include "Frontal mid Theta" at
6.5 Hz (sixth subharmonic) and Theta at 4 Hz (tenth subharmonic). Exploring
40-Hz and its' subharmonics may provide further insight into the mechanics
of the Neurofeedback process and lead to more effective and efficient
training. It is also anticipated that if the concept of 40-Hz/subharmonics
is explored, the mechanisms of cerebral function might be better understood.
Prior to the availability of the Quantitative (computerized) EEG, the
recording of high frequency (over 30 Hz) electroencephalographic (EEG)
frequencies could only be done with oscilloscopes or with special EEG
amplifiers (often non-commercial) and fast paper speed.
Oscilloscopes
do not lend themselves to the permanent and reproducible recording requirements
of researchers; recording the EEG with fast paper speed requires a major
financial expenditure for chart paper and record storage. The Quantitative
EEG (QEEG) does allow the recording of high frequency EEG data and the
ability to maintain retrievable recordings. However, most EEG clinicians
and researchers use a sampling rate of 128 Hz (cycles per second), restricting
the high frequency response to 32 Hz. Also, if higher sampling rates are
used, very slow (Delta) EEG frequencies are not recorded. As a result,
pathology might be missed clinically and traditionally reported EEG data
are not available for scientific evaluation and publication. As a result
of these technical limitations, frequencies above 30 Hz have received
little attention in either clinical and research EEG.
Nobel
Laureate Francis Crick, codiscoverer of the structure of DNA, has recently
turned his attention to the brain. In a video recorded interview (The
Brain: Our Universe Within), Professor Crick states that he believes that
40-hz pulses control visual mechanisms in the brain. When we focus, certain
neurons fire in a particular pattern (40-Hz) that create a phase lock
with neurons in other areas of the cortex. He amplifies his speculations
in his recent book, The Astonishing Hypothesis: The Scientific Search
for the Soul (Macmillan Publishing, 1994). Upon hearing Crick's comments,
I remembered reading or hearing about 40-Hz EEG biofeedback several years
ago. Rummaging through my library, I finally found a reference under "Beta-Wave
Training" in The Future of the Body by Michael Murphy (Tarcher, 1992).
Running the references, I was amazed to find an large volume of scientific
data regarding 40-Hz EEG and 40-Hz EEG biofeedback.
40-Hz
Activity
In his book, Crick erroneously credits German researchers for the work
behind 40-Hz activity and even makes it seem as if 40-Hz is a new idea.
While the Germans have made important contributions, the early research,
theory and biofeedback work on 40-Hz was done by Americans in work dating
back 30 years.
In strikingly meticulous research, psychophysiologist Daniel Sheer and
a variety of associates have studied a narrow EEG frequency band that
centers near 40-Hz (Sheer, 1967, 1970, 1972, 1973, 1974; Sheer and Grandstaff,
1970; Sheer, Grandstaff, and Benignus, 1966; Sheer and Hix, 1971). Sheer's
research found frequencies in the range of 40-Hz (36 - 44 Hz) in various
zones of the rhinencephalon, specifically the olfactory bulb, prepiriform
cortex and amygdala. Rowland (1968) found 40-Hz activity with conditioned
stimulus in the ectosylvian and lateral cortex, medial geniculate, reticular
formation, centre median thalamus and hippocampus. More recently, these
oscillations were found to be present in the motor and visual cortex (DeFrance
and Sheer, 1988).
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, page 356) He bases his conclusions on studies in which he found
40-Hz activity during visual acquisition of a visual discrimination in
cats (Sheer, 1970), in children mastering tasks involving short term learning
(Sheer, 1974), and visual problem solving in adults (DeFrance and Sheer,
1988). Sheer (1976) also found a deficit of 40-Hz in children with learning
disabilities. For an excellent summary of Sheer's work, see the Theory
section of Biofeedback Training of 40-Hz EEG and Behavior (Sheer, 1975).
German
researchers have confirmed that the average local electrical activity
(the field potential) in the vicinity of increased neural activity often
shows 40-Hz oscillations (Gray & Singer, 1989; Gray, Konig, Engel
and Singer, 1989; Gray, Engel, Konig, and Singer, 1992). Some local neurons
put out spikes, not at random moments, but "on the beat" of other local
oscillations. These 40-Hz neurons may fire a short burst of two or three
spikes that are in close synchrony with fellow neurons. Accordingly, the
pulses "consolidate" (Sheer, 1970) or "bind" (Crick) the various areas
of the cortex needed for memory and to process incoming sensory and motor
information. Field potentials under certain visual conditions may be seen
oscillate in the same phase at two areas of the cortex, even if the electrodes
are much as 7 mm apart.
Confirming
Sheer, et al's work, Giannitrapani (1969) compared the EEG of middle-
and high-I.Q. subjects during mental multiplication activity. A 40-Hz
rhythm occurred just prior to the subject's answering the question.
Forty-hz pulses are thought to lead to synchronization and coordination
of neurons assigned to the processing of incoming sensory stimulation.
Put in "computerese," 40-Hz may be the brain's "operating system" frequency.
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