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Self-organisationCoordination in Behaviour and Cognition Andreas Engel et al In:- Dynamic Coordination in the Brain: From Neurons to Mind - MIT Press (2010) Self-organisation is a key concept in understanding complex systems such as the brain. Self-organisation involves the spontaneous formation of, and change in, patterns in systems that are open to an exchange of information with the environment. In a system such as the brain that is close to instability components of the system rearrange themselves to take account of the environment. Parts of the system may repeatedly revisit a subset of states, and these are referred to as attractor states. Thus systems fall easily into preferred patterns of activity, or attractors in a energy landscape. Mathematical analysis suggests that synchronisation arises from such systems. This tendency is seen as enabling order to arise from the multiplicity of neurons or columns in a brain, and is a candidate to explain unified perceptions. Synchronised oscillatory activity is seen as important to the development of the brain. Stimulation close to the peak of the theta, beta or gamma cycles favours long-term potentiation (LTP), whereas stimulation at the trough of the cycle has the reverse effect of depotentiation. Oscillations are seen as energy-efficient means of coordinating widely distributed neural activity. The synchronisation of beta and gamma frequencies derives from reciprocal links between cells in the same cortical areas, in different cortical areas and even between different hemispheres. GABA-driven interneurons are basic to establishing synchrony in local circuits. A single GABA-driven interneuron has been shown to be capable of synchronising a large population of pyramidal neurons. Dynamic coordination encodes new behaviours, but if behaviour becomes regular, links may arise between neural assemblies that are often activated together. This is a faster system involving a smaller number of neurons, as a prespecified spatiotemporal pattern not needing the flexibility of dynamic coordination. This chapter examines the role of different frequency bands in dynamic coordination. Activity in the theta band relates to working memory, emotional arousal and fear conditioning. Alpha frequencies are related to the awake-resting condition. Beta is associated with sensorimotor processing, and multisensory processing. The uses of the gamma band are diverse but include consciousness, attention, feature integration and sensorimotor activity. Visual stimuli are seen to produce strong responses in the gamma band. Novel or surprising stimuli are seen to produce a high level of gamma activity. Synchronisation of phase and modulation of oscillations in different frequency bands has in particular been suggested as being important to speech processing. Recent studies show that attention produces increased coherence between frontal and parietal cortex in the upper frequency bands, notably gamma. Oscillations are suggested to be important for complex, multi-step computations. An oscillating wave may allow computations to be condensed into a packet that is released when a downstream area is in a state to receive it. Attention in particular appears to be divided into discrete chunks of time. With cognition, studies suggest that sub-ranges of the gamma band relate to particular cognitive functions. |
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