Functional significance of complex fluctuations in brain activity: from resting state to cognitive neuroscience

D. PapoAvatar Inv

Frontiers in Systems Neuroscience, 8:112 (2014).

Behavioural studies have shown that human cognition is characterized by properties such as temporal scale invariance, heavy-tailed non-Gaussian distributions, and long-range correlations at long time scales, suggesting models of how (non observable) components of cognition interact. On the other hand, results from functional neuroimaging studies show that complex scaling and intermittency may be generic spatio-temporal properties of the brain at rest. Somehow surprisingly, though, hardly ever have the neural correlates of cognition been studied at time scales comparable to those at which cognition shows scaling properties. Here, we analyze the meanings of scaling properties and the significance of their task-related modulations for cognitive neuroscience. It is proposed that cognitive processes can be framed in terms of complex generic properties of brain activity at rest and, ultimately, of functional equations, limiting distributions, symmetries, and possibly universality classes characterizing them.

[Read more in Frontiers in Systems Neuroscience]

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Measuring brain temperature without a thermometer

Avatar InvD. Papo

Frontiers in Physiology, 5:24 (2014).

Temperature has profound effects on a wide range of parameters of neural activity at various scales [1]. At the cell level, ionic currents, membrane potential, input resistance, action potential amplitude, duration and propagation, and synaptic transmission have all been shown to be affected by temperature variations [1-5]. At mesoscopic scales of neural activity, temperature changes can steer network activity toward different functional regimes [6], affecting the duration, frequency and firing rate of activated states during slow frequency oscillations, and the ability to end these states [7]. Temperature also has a substantial effect on chemical reaction rates [8], and affects the blood oxygen saturation level by changing haemoglobin affinity for oxygen [9]. Furthermore, cooling reduces metabolic processes [10], and has been used to silence cortical areas to study their function [11].

[Read more in Frontiers in Fractal Physiology]

Why should cognitive neuroscientists study the brain’s resting state?

D. PapoAvatar Inv

Frontiers in Human Neuroscience, 7:45 (2013).

Cognitive neuroscience studies how cognitive function is produced by the brain. Seen from a reverse angle, cognitive neuroscience studies how brain activity is modulated by the execution of cognitive tasks. In the former case, cognitive function is characterized in terms of neural properties associated with the execution of given cognitive tasks, while in the latter it can be thought of as a probe exposing information on brain dynamics. Brain activity displays dynamics independently of whether a particular task is carried out or not. The question is then: should cognitive neuroscience get interested in the properties of resting brain activity? And, if so, how and to what extent can studying resting brain activity help characterizing the neural correlates of cognitive processes?

[Read more in Frontiers in Human Neuroscience]

Brain temperature: what it means and what it can do for (cognitive) neuroscientists

David PapoAvatar Inv

arXiv:1310.2906v1 (2013).

The effects of temperature on various aspects of neural activity from single cell to neural circuit level have long been known. However, how temperature affects the system-level of activity typical of experiments using non-invasive imaging techniques, such as magnetic brain imaging of electroencephalography, where neither its direct measurement nor its manipulation are possible, is essentially unknown. Starting from its basic physical definition, we discuss
possible ways in which temperature may be used both as a parameter controlling the evolution of other variables through which brain activity is observed, and as a collective variable describing brain activity. On the one hand, temperature represents a key control parameter of brain phase space navigation. On the other hand, temperature is a quantitative measure of the relationship between spontaneous and evoked brain activity, which can be used to describe how brain activity deviates from thermodynamic equilibrium. These two aspects are further illustrated in the case of learning-related brain activity, which is shown to be reducible to a purely thermally guided phenomenon. The phenomenological similarity between brain activity and amorphous materials suggests a characterization of plasticity of the former in terms of the well-studied temperature and thermal history dependence of the latter, and of individual differences in learning capabilities as material-specific properties. Finally, methods to extract a temperature from experimental data are reviewed, from which the whole brain’s thermodynamics can then be reconstructed.

[Read more in ArXiv]