A gamma wave is a pattern of brain waves, with a frequency between 25 to 100 Hz[1], though 40 Hz is prototypical.[2]
According to a popular 20-year-old theory, gamma waves may be implicated in creating the unity of conscious perception (the binding problem) [3][4][5]. However, there is no agreement on the theory; as a researcher suggests:
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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.[1] 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.[7]
The idea that distinct regions in the brain were being stimulated simultaneously was suggested by the finding in 1988[2] 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 1990[8] argued 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: [9] says:
The suggested mechanism is that gamma waves relate to neural consciousness via the mechanism for conscious attention:
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 problem.[3]
Gamma waves are observed as neural synchrony from visual cues in both conscious and subliminal stimuli.[10] This research also sheds light on how neural synchrony may explain stochastic resonance in the nervous system.[11]. They are also implicated in rapid-REM sleep, which involves visualizations, and also during anesthesia[6].
Experiments on Tibetan Buddhist monks have shown a correlation between transcendental mental states and gamma waves.[12][13] A 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[12]. 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 self.
Recently, attempts to induce gamma waves in mice brains using optogenetics have been successful [14], 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 activity[15][16] - to relations to other neural function, such as minute eye movements[17]
However, proponents like O'Nuallain and Andreas Engel argue that gamma evidence persists even with careful signal separation[12][18].
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"[4] the synchrony, etc.
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   | Meditation Gives Brain a Charge, Study Finds - Meditation Gives Brain a Charge, Study Finds (washingtonpost.com) |
| | Are neocortical gamma waves related to consciousness? - Are neocortical gamma waves related to consciousne...[Brain Res. 2000] - PubMed Result |
| | EpilepsyHealth.com - Biofeedback for Epileptic Seizures |
| | Final proof of role of neural coherence in consciousness? - Synchronization of Neural Activity across Cortical Areas Correlates with Conscious Perception -- Melloni et al. 27 (11): 2858 -- Journal of Neuroscience |
| | Brain Waves ("40Hz") Research - Brain waves, or the EEG are electrical signals that can be recorded from the brain, either directly or through the scalp. The kind of brain wave recorded depends on the behavior of the animal, and is the visible evidence of the kind of neuronal (brain cell) processing necessary for that behavior. |
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