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Author Topic: Are theta and gamma neural oscillations an example of self organisation?  (Read 653 times)


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Gamma and Theta Oscillations are thought to be key to spatial and episodic memory and have been implicated in navigation. Phase locking and Cross Frequency coupling between gamma and other rhythms within the same and different brain regions has been well documented, including modulation by theta. G Buzsáki - ‎2012.

It has been suggested that neural oscillations might encode time and space (A Kösem - ‎2014).  Such encoding may also be found in the BZ reaction.   It might be the case that a reaction diffusion type memory process is taking place.

Patterns and waves in excitable or oscillatory reaction–diffusion media are able to perform such processor tasks as counting, logical operations, signal transformation, and finding the shortest path through a maze.

Since the brain may be thought of as a reaction–diffusion system, these capabilities are perhaps not so remarkable, though the simplicity of the systems employed is striking. Kuhnert et al. demonstrated that the photosensitive Belousov–Zhabotinsky (BZ) oscillating chemical reaction is capable of briefly (for a few periods of oscillation, that is, several minutes) storing and smoothing an image as complex as a human face....It has been shown that a photosensitive BZ-AOT system can store spatial information for up to an hour, even without replenishment of reactants. A Kaminaga - ‎2006

When an activator-inhibitor system undergoes a change of parameters, patterns that emerge include stripe or hexagonal patterns, spiral waves and target patterns, vortices and lattices.

Theta Oscillations and Grid Cells.

Theta oscillations have been closely linked to neural grid cells.  Also see J O’ Keefe (2014)

Although each individual grid cell responds to multiple positions in space, the overall activation patterns have been found to form virtual hexagonal lattices. The hexagonal symmetry characteristic of grid-cell activation patterns (and of more familiar structures such as the honeycomb) affords the highest possible spatial resolution.... It is suggested that the brain encodes higher-dimensional sensory or cognitive variables with populations of grid-cell-like neurons whose activity patterns exhibit lattice structures at multiple, nested scales. A Mathis et al (2015).

There has been speculation about the role of interference patterns between two theta-like waves on information processing and storage in the hippocampus (O'Keefe 1985).   Theta waves are associated with grid cells and are typically 4-10 Hz in rats, but are thought to be slower in humans (around 1-4 Hz) - see Joshua Jacobs (2013)

Grid cells combine with one another to form moiré interference patterns, referred to as “moiré grids,” that replicate the hexagonal lattice over an infinite range of spatial scales.It has been proposed propose that dMEC grids are actually moiré grids formed by interference between much smaller “theta grids,” which are hypothesized to be the primary source of movement-related theta rhythm in the rat brain. H T Blair et al 2007.

Connections have been made between the regularity of both the Turing symmetry breaking and the grid cell phenomenon. B L. McNaughton et al 2006. E I. Moser et al 2014 and J Orchard et al 2013 and 2015, further explore oscillatory interference models of grid cells and attractor networks based on local excitaton and long range inhibition connnectivity which spontaneously generate grid-cell-like activity patterns).

Microsaccades and Gamma Neural Oscillations

Studies have reported microsaccades that bent and jerky. Zhang and Li (2012) reported that the drift-tremor combination took a complex, curling trajectory. If fixation between microsaccades tracks the central phase singularity of a drifting spiral wave (Winfree, 1991), then complex, curling fixational drift-tremor trajectories would be a natural outcome. N Wilkinson et al 2013.

Microsaccades are thought to trigger binocular rivalry, which is itself a bistable state resulting in Hysteresis.

Gamma oscillations have been described in several areas of the neocortex, entorhinal cortex amygdala, hippocampus, striatum, olfactory bulb and thalamus as well as other areas.

Microsaccades have also be strongly linked to gamma neural oscillations (typically around 40Hz).  See more on

Initially this lead to a questioning of the importance of gamma oscillations, but more recently a number of studies also suggest that eye movement may be involved in memory retrieval.

By measuring vertical and horizontal eye position, researchers have been able to predict with reliable confidence a research participants next chosen number -- before it was spoken. T Loetscher et al  2010. This suggests that we somehow link abstract number representations in the brain with movement in space.

Research on episodic memory has established that spontaneous eye movements occur to spaces associated with retrieved information even if those spaces are blank at the time of retrieval.  results provide novel evidence of an active and facilitatory role of gaze position during memory retrieval and demonstrate that memory for the spatial relationship between objects is more readily affected than memory for intrinsic object features. R Johansson 2014.  This study suggested that the more closely the participants’ eye movements during information encoding corresponded with those that occurred during retrieval of the information, the better they were at remembering the objects.

In humans it has been shown that eye movement can influence moral decision. Philip Pärnamets et al 2015. This demonstrated that if eye movements are tracked moment by moment, it is possible to track the person’s decision-making process and steer it in a pre-determined direction,” Previous studies which have shown that for simpler choices, such as choosing between two dishes on a menu, eye movements indicate what will be eaten before an actual decision is made.

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