Monday, May 2, 2011

New Research on Gamma Brainwaves and Perception

I found this article yesterday over on Flight of Hermes, and it simply is awesome. It summarizes several scientific studies relating gamma brainwaves (the highest frequency, ranging from 30 to 200hz) to how the brain processes and perceives information. As it is written in academic language I'm guessing it's a little confusing to anyone without a background in experimental psychology or neuroscience, so I'm going to go ahead and offer a "translation" and relate it back to my earlier post on Information and Energy. As I discuss in that article, I believe that these high-frequency brainwaves are an important part of not just how we perceive information, but also how we can perform effective magical operations.

In the last two decades advances in neuroscience and the use of electroencephalography (EEG), and magnetoencephalographic (MEG) techniques have solidified the observation that brain regions communicate by synchronizing the firing of neurons. The rhythmic input that is produced in the extracellular field potential results in brain oscillations represented by delta (0–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), beta (12–30, Hz) and gamma (30–200 Hz) frequencies respectively. Previously thought to be a byproduct of waking, sleeping, and dreaming states, research in the past two decades has uncovered the possibility of these frequencies (especially those in the gamma range) representing a more causal roles in normal cognitive processes including memory, attention, perceptual binding and the experience of consciousness. Experimental data shows that gamma oscillations become highly correlated during different perceptual tasks amongst long-range neural networks which may lead to the creation of a unified field of perception.

"Extracellular field potential" means the magnetic field that is produced by the combined activity of neural cells in the brain. This is how an EEG works, by measuring fluctuations in this field through electrodes connected to the scalp. "Unified field of perception" refers to our experience of the world as a whole. When we interact with an object our mind somehow arranges our sensory inputs so that what we experience is a sort of internal model of that object as a whole. "Perceptual binding" is the name given to the process by which the brain combines the various inputs together to create this model. The term "long-range neural networks" refers to areas of the brain that are not directly adjacent to one another but nonetheless communicate back and forth.

Initial experimentation by Singer and Grey (1989) analyzing the visual cortex of cats presented with moving bars of varying orientations produced results showing that gamma oscillations work to synchronize inter-columnar input in the cortex when the bars were perceived. During a cycle of gamma frequency oscillations the neurons in different parts of the cortex fired “in phase” (i.e at the same time) leading to the proposition that gamma oscillations helped to “bind” different aspects of the scenery and convey a unified representation (Williams 2010).

So what was done here was to show an image of a bar at various angles to convey a sense of movement. We've all seen this effect in, for example, a theater marquee sign, in which lights turn on and off in such a way that what we see is movement even though the lights are all stationary. This phenomena is called Phi by psychologists. This research is suggesting that brainwaves at gamma frequencies communicate information back and forth between areas of the visual cortex to produce this illusory sense of movement.

Further studies have found that the firing of cells in the visual cortex and elsewhere can become highly correlated over distances of many millimeters during perceptual tasks (Robinson 2007). Most studies of cortical network dynamics have focused on “random wiring” or “neighborhood couplings” however, recent studies point to more complex state of activity by utilizing local and long-range “patchy connections” (horizontal connections). Patchy projections seem to provide an exceptionally efficient way of wiring, as the resulting networks use significantly reduced wiring costs. Furthermore,” the eigenvalue spectra, as well as the structure of common in and output of the networks suggest that different spatial connectivity patterns support distinct types of activity propagation” (Voges 2009).

So rather than neurons communicating with only adjacent cells there in fact seems to be a mixture of adjacent and "long range" (even several millimeters is "long" when you're talking about brain cells) connections. This allows for greater efficiency in terms of the number of cells required to process incoming signals, as the cell groups involved can communicate directly rather than passing the signal through intermediate cells. In brainwave terms, "distinct types of activity propogation" means that short-range and long-range connections operate on different brainwave frequencies.

In particular, the existence of strong two-point correlations in inter-columnar processing was closely associated with the oscillatory behavior in the gamma range. Two-point correlations of firing rates or local field potentials often show peak near-zero-time lag, even amongst easily detectable axonal conduction delays between the cells of interest.

Long-range connections in particular seem to run in the gamma frequency range. The function of this is that the fast firing means that even though information is being passed back and forth between two areas over one of these connections they activate almost simultaneously. This makes intuitive sense - if a connection covers a longer distance, the neural firing needs to run at a faster rate to get the information where it needs to go.

Correlations between cells are found to be highest when subjects are called upon to use similar preference features (line orientation, ocular dominance, etc.) and lessened as the disparity of presented stimuli increased (Robinson 2007).

So, for example, a bunch of identical lights turning on an off in a pattern suggests movement, whereas if the lights all looked different the suggestion would be far weaker.

In cases where multiple stimuli were presented simultaneously, neural-cells partitioned off in “highly correlated groups each of which corresponded to one stimulus with little correlation between groups” (Robinson 2007). In comparison, the arousal of the same cells when presented with only one stimulus resulted in activity amongst all cells.

When the brain constructs an internal model involving multiple objects or sets of stimuli, it seems that the cells form into specific groupings, with each group concentrating on a particular set of stimuli. If only a single stimulus is presented all the cells concentrate upon it.

Although changes in gamma activity were found to be statistically insignificant when a stimulus was perceived and not perceived, the level of correlation of gamma activity increased dramatically between cells depending upon the type of stimulus perceived (i.e multiple or singular).

Simple interpretation - perceiving nothing still behaves like a singular perception, so the brain activity looks similar when you're perceiving nothing and when you're perceiving a single stimulus. But as soon as multiple stimuli are presented the gamma activity increases.

Mean-field theory, normally applied to fluid, static, and plasma physics presents working formulae which show how mm-scale patchy connections can support the properties of gamma oscillations with the proper frequencies needed for spatial structure even when motivated by uncorrelated points. These occur via resonances associated with the periodic modulation of the network connections rather than being due to single-cell properties.

The gamma-frequency brainwaves behave collectively in such a way that groups of cells can act in concert regardless of where the neural stimulation is coming from. In effect, the connections unify their activity into a coherent whole. This allows the integration of multiple sensory paths into a single, consistent, internal model of the world.

Building on the initial experiments of Singer and Grey, experiments by Bartos et al (2007) found that cortical and thalamic regions display accelerated sub-threshold gamma oscillations of neuronal membranes. Synchronization of these rhythmic movements were shown to be facilitated by intra-laminar neurons which fire rhythmic spike bursts in the gamma frequency range and exhibited wide-spread cortical projections.

The gamma firing in both the cortex and thalamus seems to be synchronized by bursts of gamma activity issued by neurons with wide-ranging connections throughout these areas of the brain. The cortex is involved in cognitive processing and the thalamus mediates spatial sense and perceptual information.

Experiments focusing on the hippocampus of mice in the temporal lobe showed that gamma oscillations arise from the precise interplay of the action potential firing of excitatory glutamatergic pyramidal neurons and inhibitory GABAergic inter-neurons. Consequently, alternating pairs of current sinks and sources occur in the tissue, which require enhanced Na+/K+- ATPase activity to restore ionic gradients and to maintain excitability.

Glutamate and GABA are neurotransmitters, chemicals that allow neural signals to pass between cells. Within the cell neurons signal along a membrane that holds sodium ions on one side and potassium ions on the other. As signals travel along the axon (the "wire" along which the signal moves) gates in the membrane open in sequence allowing the ions to momentarily pass back and forth. This creates an electrical potential travels through the cell. ATPase is an enzyme that helps move the ions back to their respective sides of the membrane. So for a neuron to fire in the gamma range more of this substance must be present in order to allow the various sections of the membrane to "reset" quickly enough to support this fast signaling.

ATPases enzymes are responsible for catalyzing the decomposition of adenosine trihosphate (ATP) in the andesonine diphosphate (ADP) and a free phosphate ion. Dephosphorylation reactions are responsible for the release of energy which is used to drive other chemical reactions. The local ATP consumption in neurons is rapidly counterbalanced by mitochondria via oxidative phosphorylation, mainly in response to changes in substrates and intracellular Ca2 +. The process requires sufficient glucose and O2 supply as well as proper activities of mitochondrial enzymes.

This is a description of the ATP cycle which provides the energy for all of our body's organ systems including the brain. These reactions happen in the mitochondria, the tiny "power plants" that allow cells to continue living and performing their particular functions. Intracellular calcium is important because it is involved in the release or neurotransmitters at the synpse (the gap between neurons). Changes in calcium levels corellate to changes in the rate of signaling, and when this signaling speeds up more energy is required from the ATP cycle. Faster firing requires more glucose and oxygen fed into the energy cycle.

Results obtained by experimentation of gamma wave frequency oscillations and perception emphasize that neural synchrony does not require temporally synchronous inputs, but can be instead draw from a variety of seemingly non-related stimuli. Activated patchy connections in turn help to compose seemingly unrelated events and perceived objects into a coherent perception. It is also apparent that the fundamental cause for gamma oscillation synchrony is governed by the network eigenmode rather than single cell properties (although mean cellular characteristics determine wave properties) and correspond to biological functions in the brain such as ion gradients and enzyme catalyzation.

Essentially all the cells involved in these firing patterns work together as an integrated whole, bringing together signals from our various senses and combining them into the coherent picture of the world around us that we experience from moment to moment.

I touched on how "energy work" facilitates this process in my Information and Energy article, and here it is spelled out in chemical terms. Breathwork provides more energy by increasing oxygenation of the blood, which in turn supports gamma-frequency firing in the brain. You also need more glucose, but that doesn't pose much of a problem for anyone eating a typical Western diet. As the experience of samadhi also seems to be related to gamma brainwaves and is among the mystical states of consciousness that facilitate effective magical operations, it should be clear that "energy work" generates real biochemical energy and enhances magick through cognitive processes similar to those that results in both mental coherence and spiritual realization.

Many thanks to Soror FSO for posting this article. I hadn't seen some of this research yet, and I'm really starting to get the sense that experimentation along these lines is starting to close in on the inner workings of consciousness.

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phornepax said...

Excellent work, Scott.

Anthony VanWagner

Ananael Qaa said...

Thanks! I may work in IT, but it's nice to know that experimental psych degree is good for something!

Knight of Pan said...

Very interesting article.