From Wikipedia, the free encyclopedia
A gamma wave is a pattern of brain
waves, with a frequency between 25 to 100 Hz,
though 40 Hz is prototypical.
According to a popular 20-year-old theory, gamma waves may be
implicated in creating the unity of conscious perception (the binding
However, there is no agreement on the theory; as a researcher
- Whether or not gamma wave activity is related to subjective
awareness is a very difficult question which cannot be answered
with certainty at the present time.
Gamma waves were initially ignored before the development of
digital electroencephalography as analog
electroencephalography is restricted to recording and measuring
rhythms that are usually less than 25 Hz.
One of the earliest reports on them was in 1964 using recordings of
the electrical activity of electrodes implanted in the visual
cortex of awake monkeys.
Linked to unity of
The idea that distinct regions in the brain were being
stimulated simultaneously was suggested by the finding in 1988
that two neurons oscillate synchronously (though they are not
directly connected) when a single external object stimulates their
respective receptive fields. Subsequent experiments by many others
demonstrated this phenomenon in a wide range of visual cognition.
In particular, Francis Crick and Christof Koch in
that there is a significant relation between the binding problem
and the problem of visual consciousness and, as a result, that
synchronous 40 Hz oscillations may be causally implicated in visual
awareness as well as in visual binding.
A lead article by Andreas K. Engel et al in the journal
Consciousness and Cognition (1999) that argues for
temporal synchrony as the basis for consciousness, defines the
gamma wave hypothesis thus: 
- The hypothesis is that synchronization of neuronal discharges
can serve for the integration of distributed neurons into cell
assemblies and that this process may underlie the selection of
perceptually and behaviorally relevant information.
The suggested mechanism is that gamma waves relate to neural
consciousness via the mechanism for conscious attention:
- The proposed answer lies in a wave that originating in the
thalamus, sweeps the brain from front to back, 40 times per second,
drawing different neuronal circuits into synch with the precept,
and thereby bringing the precept into the attentional foreground.
If the thalamus is damaged even a little bit, this wave stops,
conscious awarenesses do not form, and the patient slips into
Thus the claim is that when all these neuronal clusters
oscillate together during these transient periods of synchronized
firing, they help bring up memories and associations from the
visual precept to other notions. This brings a distributed matrix
of cognitive processes together to generate a coherent, concerted
cognitive act, such as perception. This has led to theories that
gamma waves are associated with solving the binding
Gamma waves are observed as neural
synchrony from visual cues in both conscious and subliminal
research also sheds light on how neural synchrony may explain stochastic resonance in the
nervous system.. They
are also implicated in rapid-REM sleep, which involves
visualizations, and also during anesthesia.
Experiments on Tibetan Buddhist monks have shown
a correlation between transcendental mental states and gamma
suggested explanation is based on the fact that the gamma is
intrinsically localized. Neuroscientist Sean O'Nuallain suggests
that this very existence of synchronized gamma indicates that
something akin to a singularity - or, to be more prosaic, a
conscious experience - is occurring.
This work adduces experimental and simulated data to show that what
meditation masters have in common is the ability to put the brain
into a state in which it is maximally sensitive and consumes power
at a lower (or even zero) rate, briefly. The "Zero power
hypothesis" suggests that the lower power states may correspond to
a "selfless" state and the more typical non-zero state, in which
gamma is not so prominent, corresponds to a state of empirical
Recently, attempts to induce gamma waves in mice brains using optogenetics have
been successful ,
leading to possibilities of testing many other implications.
Many neuroscientists are not convinced of the gamma wave
argument. Arguments against it range from the possibility of
mismeasurement - it has been suggested that EEG-measured gamma
waves could be in many cases an artifact of electromyographic
- to relations to other neural function, such as minute eye
However, proponents like O'Nuallain and Andreas Engel argue that
gamma evidence persists even with careful signal separation.
Even within the theory, however, a number of questions remain
unexplained, especially regarding details of exactly how the
temporal synchrony results in a conscious awareness, and also how a
new percept "calls for"
the synchrony, etc.
- ^ a
Hughes JR. (2008). Gamma, fast, and ultrafast waves of the brain:
their relationships with epilepsy and behavior. Epilepsy Behav.
Jul;13(1):25-31. PMID 18439878
- ^ a
Ian Gold (1999). "Does 40-Hz
oscillation play a role in visual consciousness?".
Consciousness and Cognition 8 (2):
- ^ a
Buzsaki, György (2006). "Cycle 9, The Gamma
Buzz". Rhythms of the brain. Oxford. http://www.amazon.com/Rhythms-Brain-Gyorgy-Buzsaki/dp/0195301064/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1229021222&sr=8-1.
- ^ a
Robert Pollack, The Missing Moment,
- ^ W. Singer and C.M. Gray,
Visual feature integration and the temporal correlation hypothesis.
Annu. Rev. Neurosci. 18 (1995), pp. 555-586
- ^ a
Vanderwolf CH (Feb 2000). "Are neocortical gamma waves
related to consciousness?". Brain Res
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Hughes JR. (1964). Responses from the visual cortex of
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Crick, F., & Koch, C. (1990b). Towards a neurobiological theory
of consciousness. Seminars in the Neurosciences v.2, 263-275.
Andreas K. Engel, Pascal Fries, Peter
Koenig, Michael Brecht, Wolf Singer (1999). "Temporal Binding,
Binocular Rivalry, and Consciousness". Consciousness and
Cognition 8 (2).
Melloni L, Molina C, Pena M, Torres
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Ward LM, Doesburg SM, Kitajo K,
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- ^ a
O'Nuallain, Sean. "Zero Power and Selflessness:
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Dynamic predictions: Oscillations and synchrony in top-down
processing, AK Engel, P Fries, W Singer, Nature Reviews