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Gamma wave

gamma waves, gamma wave frequency
A gamma wave is a pattern of neural oscillation in humans with a frequency between 25 and 100 Hz,1 though 40 Hz is typical2

According to a popular theory, gamma waves may be implicated in creating the unity of conscious perception the binding problem345 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 time6


  • 1 History
  • 2 Relation to Unity of Consciousness
    • 21 History of idea
    • 22 Role in attentive focus
    • 23 Contemporary research
    • 24 Relation to meditation
    • 25 Opposing evidence
  • 3 See also
    • 31 Brain waves
  • 4 References
  • 5 Further reading
  • 6 External links


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 Hz1 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 monkeys7

Relation to Unity of Consciousnessedit

History of ideaedit

The idea that distinct regions in the brain were being stimulated simultaneously was suggested by the finding in 19882 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 19908 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 Later the same authors expressed skepticism over the idea that 40 Hz oscillations are a sufficient condition for visual awareness9

A number of experiments conducted by Dr Rodolfo Llinás, MD, PhD, supports a hypothesis that the basis for consciousness in awake states and dreaming is 40-Hz oscillations throughout the cortical mantle in the form of thalamocortical iterative recurrent activity In two papers entitled "Coherent 40-Hz oscillation characterizes dream state in humans” Rodolfo Llinás and Urs Ribary, Proc Natl Acad Sci USA 90:2078-2081, 1993 and "Of dreaming and wakefulness” Llinas & Pare, 1991, Llinás proposes that the conjunction into a single cognitive event could come about by the concurrent summation of specific and nonspecific 40-Hz activity along the radial dendritic axis of given cortical elements, and that the resonance is modulated by the brainstem and is given content by sensory input in the awake state and intrinsic activity during dreaming According to Llinás’ hypothesis, known as the thalamocortical dialogue hypothesis for consciousness, the 40-Hz oscillation seen in wakefulness and in dreaming is proposed to be a correlate of cognition, resultant from coherent 40-Hz resonance between thalamocortical-specific and nonspecific loops In Llinás & Ribary 1993, the authors propose that the specific loops give the content of cognition, and that a nonspecific loop gives the temporal binding required for the unity of cognitive experience

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: 10

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 focusedit

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 sic, and thereby bringing the precept sic 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 coma4

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 percept 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 problem3

Gamma waves are observed as neural synchrony from visual cues in both conscious and subliminal stimuli111213 14 This research also sheds light on how neural synchrony may explain stochastic resonance in the nervous system15 Gamma Waves are also implicated during Rapid eye movement sleep and anesthesia, which involves visualizations6

Contemporary researchedit

A 2009 study published in Nature successfully induced gamma waves in mouse brains Researchers performed this study using optogenetics the method of combining genetic engineering with light to manipulate the activity of individual nerve cells The protein channelrhodopsin-2 ChR2, which sensitizes cells to light, was genetically engineered into these mice, specifically to be expressed in a target-group of interneurons These fast-spiking FS interneurons, known for high electrical activity, were then activated with an optical fiber and laser—the second step in optogenetics In this way, the cell activity of these interneurons was manipulated in the frequency range of 8–200 Hz The study produced empirical evidence of gamma wave induction in the approximate interval of 25–100 Hz The gamma waves were most apparent at a frequency of 40 Hz; this indicates that the gamma waves evoked by FS manipulation are a resonating brain circuit property This is the first study in which it has been shown that a brain state can be induced through the activation of a specific group of cells16 Pushed by the need of understanding how gamma might affect disease pathogenesis, a recent study published in Nature demonstrates that entraining oscillations and spiking at 40 Hz in the hippocampus of a well-established model of Alzheimer's disease 5XFAD mice reduces Aβ peptides and at the same time activates a microglia response17

Relation to meditationedit

Experiments on Tibetan Buddhist monks have shown a correlation between transcendental mental states and gamma waves1819 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 occurring18 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

As mentioned above, gamma waves have been observed in Tibetan Buddhist monks A 2004 study took eight long-term Tibetan Buddhist practitioners of meditation and, using electrodes, monitored the patterns of electrical activity produced by their brains as they meditated The researchers compared the brain activity of the monks to a group of novice meditators the study had these subjects meditate an hour a day for one week prior to empirical observation In a normal meditative state, both groups were shown to have similar brain activity However, when the monks were told to generate an objective feeling of compassion during meditation, their brain activity began to fire in a rhythmic, coherent manner, suggesting neuronal structures were firing in harmony This was observed at a frequency of 25–40 Hz, the rhythm of gamma waves These gamma-band oscillations in the monk’s brain signals were the largest seen in humans apart from those in states such as seizures Conversely, these gamma-band oscillations were scant in novice meditators Though, a number of rhythmic signals did appear to strengthen in beginner meditators with further experience in the exercise, implying that the aptitude for one to produce gamma-band rhythm is trainable20

Such evidence and research in gamma-band oscillations may explain the heightened sense of consciousness, bliss, and intellectual acuity subsequent to meditation Notably, meditation is known to have a number of health benefits: stress reduction, mood elevation, and increased life expectancy of the mind and its cognitive functions The current Dalai Lama meditates for four hours each morning, and he says that it is hard work He elaborates that if neuroscience can construct a way in which he can reap the psychological and biological rewards of meditation without going through the practice each morning, he would be apt to adopt the innovation21

Opposing evidenceedit

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 activity2223 – to relations to other neural function, such as minute eye movements24

However, proponents like O'Nuallain and Andreas Engel argue that gamma evidence persists even with careful signal separation1825

Moreover, recent studies using magnetoencephalography MEG, which does not suffer the potential artifacts associated with EEG, have identified gamma activity associated with sensory processing, mainly in the visual cortex26272829

A recent study with micro-electrodes in monkey and human 30 showed that gamma oscillations are present and are clearly correlated with the firing of single neurons, mostly inhibitory neurons The gamma oscillations were found in humans during all states of the wake-sleep cycle, and were maximally coherent during slow-wave sleep

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

See alsoedit

Brain wavesedit

  • Delta wave – 01 – 3 Hz
  • Theta wave – 4 – 7 Hz
  • Alpha wave – 8 – 15 Hz
  • Mu wave – 75 – 125 Hz
  • SMR wave – 125 – 155 Hz
  • Beta wave – 16 – 31 Hz
  • Gamma wave – 32 – 100 Hz


  1. ^ a b Hughes JR July 2008 "Gamma, fast, and ultrafast waves of the brain: their relationships with epilepsy and behavior" Epilepsy Behav 13 1: 25–31 doi:101016/jyebeh200801011 PMID 18439878 
  2. ^ a b Ian Gold 1999 "Does 40-Hz oscillation play a role in visual consciousness" Consciousness and Cognition 8 2: 186–195 doi:101006/ccog19990399 PMID 10448001 
  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. ^ Singer, W; Gray, CM 1995 "Visual feature integration and the temporal correlation hypothesis" Annu Rev Neurosci 18: 555–586 doi:101146/annurevne18030195003011 PMID 7605074 
  6. ^ a b Vanderwolf CH Feb 2000 "Are neocortical gamma waves related to consciousness" Brain Res 855 2: 217–24 doi:101016/S0006-89939902351-3 PMID 10677593 
  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 v2, 263-275
  9. ^ Crick, F, Koch, C 2003 "Framework for consciousness" Nature Neuroscience 6 2: 119–26 doi:101038/nn0203-119 PMID 12555104 CS1 maint: Multiple names: authors list link
  10. ^ Andreas K Engel; Pascal Fries; Peter Koenig; Michael Brecht; Wolf Singer 1999 "Temporal Binding, Binocular Rivalry, and Consciousness" Consciousness and Cognition 8 2: 128–151 doi:101006/ccog19990389 
  11. ^ Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E Mar 2007 "Synchronization of neural activity across cortical areas correlates with conscious perception" J Neurosci 27 11: 2858–65 doi:101523/JNEUROSCI4623-062007 PMID 17360907 
  12. ^ Siegel M, Donner TH, Oostenveld R, Fries P, Engel AK Mar 2008 "Neuronal synchronization along the dorsal visual pathway reflects the focus of spatial attention" Neuron 60 4: 709–719 doi:101016/jneuron200809010 PMID 19038226 
  13. ^ Gregoriou GG, Gotts SJ, Zhou H, Desimone R Mar 2009 "High-frequency, long-range coupling between prefrontal and visual cortex during attention" Science 324 5931: 1207–1210 Bibcode:2009Sci3241207G doi:101126/science1171402 PMC 2849291  PMID 19478185 
  14. ^ Baldauf D, Desimone R Mar 2014 "Neural mechanisms of object-based attention" Science 344 6182: 424–427 Bibcode:2014Sci344424B doi:101126/science1247003 PMID 24763592 
  15. ^ Ward LM, Doesburg SM, Kitajo K, MacLean SE, Roggeveen AB Dec 2006 "Neural synchrony in stochastic resonance, attention, and consciousness" Can J Exp Psychol 60 4: 319–26 doi:101037/cjep2006029 PMID 17285879 
  16. ^ <J Cardin, M Carle, K Meletis, U Knoblich, F Zhang, K Deisseroth, Li-Huei Tsai and Christopher Moore 2009 Driving fast-spiking cells induces gamma rhythm and controls sensory responses Nature, 459: 663-668>
  17. ^ Iaccarino, Hannah F; Singer, Annabelle C; Martorell, Anthony J; Rudenko, Andrii; Gao, Fan; Gillingham, Tyler Z; Mathys, Hansruedi; Seo, Jinsoo; Kritskiy, Oleg; Abdurrob, Fatema; Adaikkan, Chinnakkaruppan; Canter, Rebecca G; Rueda, Richard; Brown, Emery N; Boyden, Edward S; Tsai, Li-Huei 7 December 2016 "Gamma frequency entrainment attenuates amyloid load and modifies microglia" Nature 540 7632: 230–235 doi:101038/nature20587 
  18. ^ 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 42
  19. ^ Kaufman, Marc January 3, 2005 "Meditation Gives Brain a Charge, Study Finds" The Washington Post Retrieved May 3, 2010 
  20. ^ Lutz A; Greischar LL; Rawlings NB; Ricard M; Davidson RJ 2004 "Long-term meditators self-induce high apmlitude gamma synchrony during mental practice" Proceedings of the National Academy of Sciences USA 101: 16369–16373 Bibcode:2004PNAS10116369L doi:101073/pnas0407401101 PMC 526201  PMID 15534199 
  21. ^ "Scientific American:Meditation On Demand" 
  22. ^ Whitham EM, Pope KJ, Fitzgibbon SP, et al Aug 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:101016/jclinph200704027 PMID 17574912 
  23. ^ Whitham EM, Lewis T, Pope KJ, et al May 2008 "Thinking activates EMG in scalp electrical recordings" Clin Neurophysiol 119 5: 1166–75 doi:101016/jclinph200801024 PMID 18329954 
  24. ^ Yuval-Greenberg S, Tomer O, Keren AS, Nelken I, Deouell LY May 2008 "Transient induced gamma-band response in EEG as a manifestation of miniature saccades" Neuron 58 3: 429–41 doi:101016/jneuron200803027 PMID 18466752 
  25. ^ Dynamic predictions: Oscillations and synchrony in top-down processing, AK Engel, P Fries, W Singer, Nature Reviews Neuroscience, 2001
  26. ^ Adjamian, P; Holliday, IE; Barnes, GR; Hillebrand, A; Hadjipapas, A; Singh, KD 2004 "Induced stimulus-dependent Gamma oscillations in visual stress" European Journal of Neuroscience 20: 587–592 doi:101111/j1460-9568200403495x 
  27. ^ Hadjipapas A; Adjamian P; Swettenham JB; Holliday IE; Barnes GR 2007 "Stimuli of varying spatial scale induce gamma activity with distinct temporal characteristics in human visual cortex" NeuroImage 35 2: 518–30 doi:101016/jneuroimage200701002 
  28. ^ Muthukumaraswamy SD, Singh KD 2008 "Spatiotemporal frequency tuning of BOLD and gamma band MEG responses compared in primary visual cortex" NeuroImage 40: 1552–1560 doi:101016/jneuroimage200801052 PMID 18337125 
  29. ^ Swettenham JB, Muthukumaraswamy SD, Singh KD 2009 "Spectral properties of induced and evoked gamma oscillations in human early visual cortex to moving and stationary stimuli" Journal of Neurophysiology 102: 1241–1253 doi:101152/jn910442008 PMID 19515947 
  30. ^ Le Van Quyen M; Muller LE; Telenczuk B; Halgren E; Cash S; Hatsopoulos N; Dehghani N; Destexhe A 2016 "High-frequency oscillations in human and monkey neocortex during the wake-sleep cycle" Proceedings of the National Academy of Sciences USA 113 33: 93639368 doi:101073/pnas1523583113 PMID 27482084 

Further readingedit

  • Kaufman, Marc January 3, 2005 "Meditation Gives Brain a Charge, Study Finds" WashingtonPostcom Retrieved June 16, 2005 
  • Bruce Bower 2004 "Synchronized thinking Brain activity linked to schizophrenia, skillful meditation" Science News 166 20: 310 doi:102307/4015767 JSTOR 4015767 

External linksedit

  • EpilepsyHealthcom - 'A Sampling from Chapter 3' Biofeedback, Neurofeedback and Epilepsy, Sally Fletcher 2005
  • Gamma: Insight, Consciousness, or Microsaccades - A summary of recent research 6/26/2009
  • How Thinking Can Change the Brain, dalailamacom 2007-01-29

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