GAMMA WAVE SYNCHRONY AND CONSCIOUSNESS
By Junius
[Junius authored a science fiction book 'Persephone Wakes' under the name Jack Junius with theories of consciousness as its theme. He is presently working on another fiction book (a sort of Dan Brown of the Cotswolds) with altered states of consciousness and religion as its theme. He maintains a Website/Blog on Consciousness and Fundamental Physics at: www.quantum-mind.co.uk
I am very grateful to him for the concise write up on Gamma Synchrony explaining the intricacies in a lucid manner.
I have also added at the end the Abstract from the Paper by A. Lutz et al (2004) (including the explanation by David Dobbs (2005)), a few comments from the work of Z. Josipovic (2010) and the work of E.C. Leuthardt (with regard to Gamma band and anesthesia) -- ramesam]
GAMMA WAVE SYNCHRONY AND CONSCIOUSNESS
By Junius
This write up on Gamma Synchrony is based on the research by Lucia Melloni and Wolf Singer at the Max Planck Institute published in 2010. For further reading see, 'New Horizons in the Neuroscience of Consciousness'. The authors discuss studies that show that conscious perceptions produce different types of brain activity from unconscious percepts. In particular, consciousness is demonstrated to produce long-range synchronisation of gamma oscillations in widely separated neural assemblies. The approx. 30-90 Hz oscillation of neuronal spiking, known as the gamma wave can become synchronised across large areas of the brain. The authors suggest that the synchronisation of widely distributed neuronal activity meets some of the requirements for explaining how conscious experience arises in the brain.
The brain comprises specialised although connected processing areas, and for these to become unified, it has to overcome the problem of representation in different modalities, such as hearing, seeing etc. In this research, it is proposed that the processing of spatially separated neuronal assemblies is bound together by means of the gamma synchrony.
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| Gamma Waves in EEG (from Wikimedia) |
The brain comprises specialised although connected processing areas, and for these to become unified, it has to overcome the problem of representation in different modalities, such as hearing, seeing etc. In this research, it is proposed that the processing of spatially separated neuronal assemblies is bound together by means of the gamma synchrony.
Neurons are known to be synchronised into coherent assemblies, and these assemblies are suggested to signal the presence of particular features to other neural assemblies. This process is suggested to give rise to a distributed representation of the external environment. Neuronal assemblies form and dissolve rapidly, which could account for the easy shifting of consciousness from one focus to another.
Synchronisation also allows better control of interaction between neurons. Thus excitatory inputs are seen to be effective at a particular point of the oscillation cycle, but are ignored at other times. This means that groups of neurons that oscillate in synchrony will be able to signal to one another, and that groups that are out of synchrony will be ignored. This mechanism can function within neural assemblies, but also between spatially separated assemblies. The frequency and phase of oscillation can alter to influence signaling.
Studies suggest that local processing is unconscious, whereas large scale activity such as reciprocal signaling between separate neural assemblies is a correlate of consciousness. This is argued to be a 'small worlds' system, where there is co-existence between local and long-range networks. In the brain, it is suggested that the local networks are between neurons only a few hundred micrometers apart within layers of the cortex, while the long-range networks run mainly through the white matter, and thus link spatially separated areas of the cortex. It is these latter that can establish the global coordination that is correlated to consciousness.
The authors propose that masking experiments are a good way of studying consciousness, because this allows the same stimuli to be either unconscious or conscious. In a study undertaken by the authors, words could be perceived consciously in some trials but unconsciously in others (Melloni et al, 2007). Local gamma synchronisation was similar in both cases, but with consciously perceived words there was a burst of long-distance gamma synchrony between the occipital, parietal and frontal cortices. Also subsequent to this burst, there was activity that could have indicated a transfer of information to working memory, while an increase in frontal cortex theta wave activity may have indicated material being held in working memory. Words processed at the unconscious level could lead to an increase in the power of the gamma frequency range, but only conscious stimuli produced increases in long-distance gamma synchronisation, plus possibly theta activity looks to be a requirement for consciousness.
Even the authors admit that the gamma synchronisation is just a correlate, and does not explain how consciousness actually arises. However, it does look like providing an explanation of how conscious perceptions are unified. The redness of fruit in one assembly is synchronised or entrained with the greenness of leaves in another assembly, and the blueness of sky in still another, plus the humming of bees and song of birds in the more distant but still synchronized assemblies of the auditory cortex.
One aspect which is touched on, but not enlarged on in the mainstream literature is that there is a zero or near zero time lag in the synchronisation of spatially separated neural assemblies, which bears the signature of quantum entanglement. Between 2007 and 2010, studies of photosynthetic organism demonstrated the existence of possibly functional quantum coherence and entanglement in biological systems even at room temperature, partly refuting the claims of the much-hyped (Tegmark 2000) paper.
As for constructing something that could communicate qualia, in principle anything that is physical can be built, but the prospects for something like the above in the near term looks daunting. The photosynthetic studies suggest working at the level of coherent electrons within the interior of neurons, bearing in mind that a neuron is said to be more complex than London. The difficulties of the relatively more straight forward requirements for quantum computing are not encouraging in this respect.
The gamma synchrony is just a correlate and does not explain how consciousness arises. It does, however, seem plausible that the physical basis of consciousness is in some way related to this process. At the same time, indefinite pursuit of correlates of consciousness will not by itself yield a theory of consciousness, as correlation is not the same as identity. One of the benefits, if the gamma synchrony was seen to resolve the binding or unity of consciousness problem, would be to allow efforts to be concentrated on qualia or subjectivity which looks like the real hard problem. One has to be wary of a tendency to get bogged down in areas that are not the essential problem in consciousness studies.
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2. From: A Lutz et al (2004), “Long-term meditators self-induce high-amplitude gamma synchrony during mental practice”, PNAS, 101(46), 16369–16373.
Abstract
Practitioners understand “meditation,” or mental training, to be a process of familiarization with one's own mental life leading to long-lasting changes in cognition and emotion. Little is known about this process and its impact on the brain. Here we find that long-term Buddhist practitioners self-induce sustained electroencephalographic high-amplitude gamma-band oscillations and phase-synchrony during meditation. These electroencephalogram patterns differ from those of controls, in particular over lateral frontoparietal electrodes. In addition, the ratio of gamma-band activity (25-42 Hz) to slow oscillatory activity (4-13 Hz) is initially higher in the resting baseline before meditation for the practitioners than the controls over medial frontoparietal electrodes. This difference increases sharply during meditation over most of the scalp electrodes and remains higher than the initial baseline in the postmeditation baseline. These data suggest that mental training involves temporal integrative mechanisms and may induce short-term and long-term neural changes.
3. From: Zen Gamma By David Dobbs, Sci Amer, March 24, 2005.
Researchers at the University of Wisconsin-Madison have found that during meditation, Zen Buddhist monks show an extraordinary synchronization of brain waves known as gamma synchrony--a pattern increasingly associated with robust brain function and the synthesis of activity that we call the mind.
Brain waves are produced by the extremely low voltages involved in transmitting messages among neurons. Most conscious activity produces beta waves at 13 to 30 hertz, or cycles per second. More intense gamma waves (30 to 60 or even 90 Hz) generally mark complex operations such as memory storage and sharp concentration.
The Wisconsin study took electroencephalograms (EEGs) of 10 longtime Buddhist practitioners and of a control group of eight college students who had been lightly trained in meditation. While meditating, the monks produced gamma waves that were extremely high in amplitude and had long-range gamma synchrony--the waves from disparate brain regions were in near lockstep, like numerous jump ropes turning precisely together. The synchrony was sustained for remarkably long periods, too. The students' gamma waves were nowhere near as strong or tuned.
Such results connote more than spiritual harmony; they reflect the coordination of otherwise scattered groups of neurons. Gamma synchrony increases as a person concentrates or prepares to move. And lack of synchrony indicates discordant mental activity such as schizophrenia. Finally, a growing body of theory proposes that gamma synchrony helps to bind the brain's many sensory and cognitive operations into the miracle of consciousness.
That hypothesis certainly agrees with the monks' gamma readings, seemingly confirming that Zen meditation produces not relaxation but an intense though serene attention. Trained musicians also show superior gamma synchrony while listening to music--another form of calm but intense focus.
4. From Josipovic, Z., “Duality and nonduality in meditation research”, Consciousness and Cognition (2010), doi:10.1016/j.concog.2010.03.016.
Travis and Shear suggest that the differences between meditation styles should be evident as fairly simple distinctions in EEG signatures. There is elegance and parsimoniousness to this idea, but the reality may be more complicated. The EEG signatures of meditation tend to be fairly complex across all bands and differ, as well, with the degree of the subject’s proficiency (Cahn & Polich, 2006). Changes in the gamma band, which the authors use as one of the indicators of focused attention style, have been found in other styles of editation as well (Cahn, Delorme, & Polich, 2010). It is also questionable whether compassion meditation (Lutz, Greischar, Rawlings, Ricard, & Davidson, 2004) which produced some of the largest changes in the gamma band found in meditation to date, belongs to the focused attention style, as the authors suggest. The non-referentiality of compassion makes it more akin to meditations in the nondual or ‘automatic self-transcending’ category. Most importantly, certain aspects of synchrony in the gamma range await further clarification due to artifacts from scalp muscles and eye movement (Yuval-Greenberg, Tomer, Keren, Nelken, & Deouell, 2008).
5. From ScienceDaily, Feb. 9, 2011: Gamma Band under Anesthesia:
Dr. E. C. Leuthardt and his colleagues have used the grids to watch consciousness fade under surgical anesthesia and return when the anesthesia wears off. They found each frequency gave different information on how different circuits changed with the loss of consciousness.
Their results also showed a series of changes that occurred in a specific order during loss of consciousness and then repeated in reverse order as consciousness returned. Activity in a frequency region known as the gamma band, which is thought to be a manifestation of neurons sending messages to other nearby neurons, dropped and returned as patients lost and regained consciousness.
6. From "Neuroskeptic" of 4 July 2011:
(http://neuroskeptic.blogspot.com/2011/07/gamma-waves-brains-clock-or-neural.html )
If you believe some recent claims, gamma waves are the answer to all the mysteries of life and the universe. They're said to underlie the symptoms of schizophrenia andautism, and they've been invoked to answer deep questions such as the binding problem and maybe conciousness itself. You can even buy a Nintendo game that promises to boost them.
A new paper from Burns et al casts doubt on all of these grand claims. Gamma-based theories of brain function all assume that gamma waves act a bit like a clock, with a consistent rhythm of about 40 Hz. Activity of about 40 Hz is indeed observed in brain recordings but is that just because the brain is randomly generating all kinds of signals, and only the 40 Hz ones "get through"?
6. From "Neuroskeptic" of 4 July 2011:
(http://neuroskeptic.blogspot.com/2011/07/gamma-waves-brains-clock-or-neural.html )
If you believe some recent claims, gamma waves are the answer to all the mysteries of life and the universe. They're said to underlie the symptoms of schizophrenia andautism, and they've been invoked to answer deep questions such as the binding problem and maybe conciousness itself. You can even buy a Nintendo game that promises to boost them.
A new paper from Burns et al casts doubt on all of these grand claims. Gamma-based theories of brain function all assume that gamma waves act a bit like a clock, with a consistent rhythm of about 40 Hz. Activity of about 40 Hz is indeed observed in brain recordings but is that just because the brain is randomly generating all kinds of signals, and only the 40 Hz ones "get through"?
