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[[Image:eeg gamma.svg|right|thumb|Gamma waves |400px|right]]
[[Image:eeg gamma.svg|right|thumb|Gamma waves |400px|right]]
A '''gamma wave''' is a pattern of [[electroencephalography|brain wave]]s in humans
A '''gamma wave''' is a pattern of [[electroencephalography|brain wave]]s in humans
with a frequency between 25 to 100 [[Hertz|Hz]]<ref name="Hughes">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</ref>, though 40 Hz is prototypical. They generate epicranial magnetic fields that tend to alter the conformation of keratine. High gamma waves have been observed in subjects with very curly hair. <ref name=gold/>
with a frequency between 25 to 100 [[Hertz|Hz]]<ref name="Hughes">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</ref>, though 40 Hz is prototypical. They generate epicranial magnetic fields that tend to alter the conformation of keratine. High gamma waves have been observed in subjects with curly hair. <ref name=gold/>


According to a popular 20-year-old theory, gamma waves may be implicated in creating the unity of conscious perception (the [[binding problem]]) <ref name=buzsaki/><ref name=pollack>[[Robert Pollack (biologist)|Robert Pollack]], [http://www.cse.iitk.ac.in/~amit/books/pollack-1999-missing-moment-how.html The Missing Moment], 1999</ref><ref name=singer>
According to a popular 20-year-old theory, gamma waves may be implicated in creating the unity of conscious perception (the [[binding problem]]) <ref name=buzsaki/><ref name=pollack>[[Robert Pollack (biologist)|Robert Pollack]], [http://www.cse.iitk.ac.in/~amit/books/pollack-1999-missing-moment-how.html The Missing Moment], 1999</ref><ref name=singer>

Revision as of 20:28, 11 August 2010

Not to be confused with gamma rays.
Gamma waves

A gamma wave is a pattern of brain waves in humans with a frequency between 25 to 100 Hz[1], though 40 Hz is prototypical. They generate epicranial magnetic fields that tend to alter the conformation of keratine. High gamma waves have been observed in subjects with curly hair. [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:

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.[6]

History

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]

Linked to unity of consciousness?

History of idea

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 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.

Role in attentive focus

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 profound coma[4].

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].

Relation to meditation

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.

Opposing evidence

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].

Bearing this theory in mind, a number of questions remain unexplained regarding details of exactly how the temporal synchrony results in a conscious awareness or how a new percept "calls for"[4] the synchrony, etc.

References

  1. ^ a b 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
  2. ^ a b Template:Cite article
  3. ^ a b Buzsaki, György (2006). "Cycle 9, The Gamma Buzz". Rhythms of the brain. Oxford.
  4. ^ a b c Robert Pollack, The Missing Moment, 1999
  5. ^ W. Singer and C.M. Gray, Visual feature integration and the temporal correlation hypothesis. Annu. Rev. Neurosci. 18 (1995), pp. 555-586
  6. ^ a b Vanderwolf CH (2000). "Are neocortical gamma waves related to consciousness?". Brain Res. 855 (2): 217–24. doi:10.1016/S0006-8993(99)02351-3. PMID 10677593. {{cite journal}}: Unknown parameter |month= ignored (help)
  7. ^ Hughes JR. (1964). Responses from the visual cortex of unanesthetized monkeys. pp. 99–153. In: Pfeiffer CC, Smythies JR, (Eds), International review of neurobiology vol. 7, Academic Press, New York OCLC 43986646
  8. ^ Crick, F., & Koch, C. (1990b). Towards a neurobiological theory of consciousness. Seminars in the Neurosciences v.2, 263-275.
  9. ^ Template:Cite article
  10. ^ Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E (2007). "Synchronization of neural activity across cortical areas correlates with conscious perception". J Neurosci. 27 (11): 2858–65. doi:10.1523/JNEUROSCI.4623-06.2007. PMID 17360907. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  11. ^ Ward LM, Doesburg SM, Kitajo K, MacLean SE, Roggeveen AB (2006). "Neural synchrony in stochastic resonance, attention, and consciousness". Can J Exp Psychol. 60 (4): 319–26. PMID 17285879. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  12. ^ a b c O'Nuallain, Sean. "Zero Power and Selflessness: What Meditation and Conscious Perception Have in Common". Retrieved 2009-05-30. Journal: Cognitive Sciences 4(2).
  13. ^ Kaufman, Marc (January 3, 2005). "Meditation Gives Brain a Charge, Study Finds". The Washington Post. Retrieved May 3, 2010.
  14. ^ http://esciencenews.com/sources/scientific.blogging/2009/04/26/gamma.oscillations.and.the.hunt.for.human.consciousness
  15. ^ Whitham EM, Pope KJ, Fitzgibbon SP; et al. (2007). "Scalp electrical recording during paralysis: quantitative evidence that EEG frequencies above 20 Hz are contaminated by EMG". Clin Neurophysiol. 118 (8): 1877–88. doi:10.1016/j.clinph.2007.04.027. PMID 17574912. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  16. ^ Whitham EM, Lewis T, Pope KJ; et al. (2008). "Thinking activates EMG in scalp electrical recordings". Clin Neurophysiol. 119 (5): 1166–75. doi:10.1016/j.clinph.2008.01.024. PMID 18329954. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  17. ^ Yuval-Greenberg S, Tomer O, Keren AS, Nelken I, Deouell LY (2008). "Transient induced gamma-band response in EEG as a manifestation of miniature saccades". Neuron. 58 (3): 429–41. doi:10.1016/j.neuron.2008.03.027. PMID 18466752. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  18. ^ Dynamic predictions: Oscillations and synchrony in top-down processing, AK Engel, P Fries, W Singer, Nature Reviews Neuroscience, 2001

Further reading

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