the principle of coherence in multi-level brain information processing

Review neuroscientific article authored by Matej Plankar, Simon Brežan and Igor Jerman explains the principle of coherence in multi-level brain information processing,  where coherence can be viewed as an integral part of brain  mechanisms responsible for synergetic processes / synergy of mind and behaviour. One of the authors of the article, Simon Brežan, is also part of the Synergy project.

“The tendency of natural systems to achieve order and harmony in their behaviour is a manifestation of open systems’ selforganising capacity, existing everywhere in nature (Osipov et al., 2007). Synchronisation, a process whereby objects of a different nature adjust their internal rhythms to a collective operation regime due to their mutual interactions, is one of the most captivating phenomena encountered in complex systems, and has become a major scientific tool to explain this tendency. Technically, synchronisation refers to the establishment of stable phase relationships among the oscillating components within a system of coupled oscillators due to phase locking or frequency entrainment, whose oscillatory characteristics are more generally described as the coherence. [2] Synchronisation phenomena are encountered in areas as diverse as physics, chemistry, engineering, biology, medicine, economics, and social sciences, which implies its deep significance and explanatory power (Arenas et al., 2008; Osipov et al., 2007; Pikovsky et al., 2001).

Organisms are highly excitable dissipative systems whose responses to external and internal perturbations and energy flow throughout the system must be precisely and efficiently coordinated in time and space. Synchronisation phenomena have been observed at all basic levels of biological organisation e from the precisely coordinated gene expression and metabolic cycles (for example, glycolytic oscillations) to collective physiological rhythms [3] and social interaction dynamics. [4] The functional significance of coherent oscillatory dynamics lies in the collective summation of outputs of individual elements, which enables a powerful response to a weak external input, efficient communication between different systems (that is, transfer of energy and information) and encoding information in terms of the phase, frequency, or amplitude of the oscillating system. In other words, the power (or meaning) of coherence arises from a reduction in the uncorrelated degrees of freedom into a collective operation mode, which enables long range order and coordination of biological processes (Arenas et al., 2008; Bianchi, 2008; Binhi and Rubin, 2007; Goldenfeld and Woese, 2011; Ho, 2008; Klevecz et al., 2008; Strogatz, 2003; Winfree, 2001). Coherence and synchronisation are thus important concepts in biological organisation and systems biology (Plankar et al., 2011).

Synchronised oscillations of large neuronal groups, whose frequency range spans several orders of magnitude, represent one of the most prominent characteristics of brain information processing (Buzsáki and Draguhn, 2004). It has been proposed for over twenty years that dynamic neuronal interactions rely on precise temporal coordination of single neuronal discharges and population activity in distributed neuronal assemblies. This phenomenon, generally termed neuronal synchrony, has been found to correlate strongly with cognitive functions: perception, attention, sensorimotor integration, learning, memory, consciousness, decision making etc., and pathological synchrony patterns appear in many different brain disorders. It is strongly argued that coherent neuronal oscillations are not merely an epiphenomenon, but have a direct functional relevance and a causal role in encoding representations, coordinating neuronal communication and regulating synaptic plasticity (Fell and Axmacher, 2011; Fries, 2009; Fries et al., 2007; Jensen et al., 2007; Senkowski et al., 2008; Singer, 2009; Uhlhaas et al., 2009; Uhlhaas and Singer, 2010).

There is however another type of coherence that may also be important for neuronal information processing, but which operates at the level of individual molecules and molecular complexes. The coherence of molecular dynamics has long been theoretically elaborated (Del Giudice et al., 1985; Fröhlich, 1968; Ricciardi and Umezawa, 1967), only recently gaining wider acceptance, when quantum coherence was experimentally demonstrated to directly coordinate energy flow, maximising efficiency of excitation transfer in several photosynthetic complexes (Collini et al., 2010; Engel et al., 2007; Lee et al., 2007). On the other line of research, the neuronal cytoskeleton or, more generally, the intraneuronal matrix (Woolf et al., 2009) e is increasingly acknowledged to have an important role in modifying the gating properties of ion channels and in coordinating neuronal plasticity (Janmey, 1998; Priel et al., 2010; Woolf, 2006; Woolf et al., 2009). Moreover, much theoretical and experimental effort has been focussing on the coherent properties and long-range signal transfer within cytoskeletal elements, most notably in the microtubules (Bandyopadhyay, 2010; Cifra et al.,2010; Jibu et al., 1994; Mershin et al., 2006; Priel et al., 2006a; Sahu et al., 2011; Tuszynski et al., 1997). It is hypothesised that such intrinsic information processing capacity could provide the neurons with greater autonomy in response (Woolf et al., 2009), complementary to their classical membrane-dependent characteristics.

Footnotes
[2] Although not identical, the terms coherence and synchronisation are often used interchangeably. Throughout this review, we will use both according to their traditional use in respective fields.
[3] These include, for example, heart contraction, brain oscillations, circadian rhythms, hormonal secretion, locomotion, etc.
[4] Common examples are synchronised signalling in crickets and fireflies, the dynamic behaviour of dense groups of animals, such as bird flocks or fish schools, bacterial quorum sensing, collective hunting strategies, etc. An interested reader may find further examples in the cited literatute.”

The article was published by Matej Plankar, Igor Jerman, Simon Brežan in renowned international scientific journal Progress in Biophysics and Molecular Biology in 08/ 2012 and is available at this link: The principle of coherence in multi-level brain information processing.

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