As the blog-title “Brain Explorer” suggests, in this blog we will take you on a journey through the brain. Wonsang You and Sarah Moens, the writers of this blog (see the “About”- section for more information about the authors), want to take you on a wonderful journey through the brain, explore the complexity and the beauty of an impressive organ where sensations of the world around us come together, a multitude of information is processed, movement is initiated and learning expressed, just to name a few.
Since we both have different backgrounds, i.e. computational neuroscience and behavioral neuroscience, we hope to cover topics in a complementary way and cover a wide range of topics that could be of interest to a wider audience interested in neuroscience. Some advanced topics will be discussed as well, but in the end we want to make this blog accessible to everyone interested in neuroscience and hope to foster that interest and foster constructive discussions that could emerge from the ideas, questions and comments of fellow readers. So we definitely want and need your input, to make this a vivid, inspiring community page.
Blog messages will concern recent neuroscience news facts, published articles, neuroscience introductions, discussions…
Although the goal is to cover a wide range of topics, the authors are particularly interested in functional brain networks on the one hand and sleep on the other hand, so these topics will get some extra attention and will be discussed more elaborately.
Any comments on the progress of this blog and your input is appreciated. We hope you join us on our journey!
Wonsang and Sarah
Self-organized criticality is a concept which was first proposed by Bak et al. (1988) in the field of physics. What is the critical state of a dynamical system? Simply describing, it can be regarded as a critical point of phase transition. You can imagine the zero degree as a critical boundary between water and ice. In this critical state, water is in the form of snowflakes, and is known to have fractal structure and self-similarity. In general, any system in the critical state exhibits fractal scaling properties. Indeed, Bak et al. proposed that the 1/f noise is a temporal sign of self-organized criticality.
The concept is useful to investigate any natural or spontaneous system without any external stimulation or behavior. Let us think of the brain in resting state. If we observe the spontaneous activity of the brain in resting state, does the brain exhibit any fingerprint of self-organized criticality? The answer is ‘yes’. Plenz and Thiagarajan (2007) showed spatiotemporal patterns of spontaneous neuronal activity in the brain cortex, and they call such a phenomenon ‘neuronal avalanche’. Such patterns have fractal scaling properties in terms of probability density distribution of delay duration of consecutive active neurons.
Measuring neuronal activity through local field potential (LFP) and the groups of consecutive active neurons (TRENDS in Neurosciences)
The self-organized criticality is consistently observed not only in micro-scale recordings but also the macro-scale neuroimaging data. Kitzbichler et al. (2009) observed the criticality properties both in MEG and in functional MRI data by using newly defined measurements such as the phase locking interval (PLI) and the global lability of synchronization. The probability density distribution of phase locking intervals has power-law scaling, i.e., linear relationship in logarithmic scales.
The probability distribution of phase locking interval of functional MRI data (Ed Bullmore et al. 2009)
Self-organized criticality is a very promising concept for resting state brain analysis since it is dedicated to analyze spontaneous dynamic systems. Recently, some scientists are investigating the relationship between self-organized criticality and fractal behavior of the brain.
- P. Bak, C. Tang, K. Wiesenfeld, Self-organized criticality, Physical Review A. 38 (1988).
- D. Plenz, T.C. Thiagarajan, The organizing principles of neuronal avalanches: cell assemblies in the cortex?, Trends In Neurosciences. 30 (2007) 101-10.
- M.G. Kitzbichler, M.L. Smith, S.R. Christensen, E. Bullmore, Broadband criticality of human brain network synchronization., PLoS Computational Biology. 5 (2009) e1000314.
- E. Bullmore, A. Barnes, D.S. Bassett, A. Fornito, M. Kitzbichler, D. Meunier, et al., Generic aspects of complexity in brain imaging data and other biological systems., NeuroImage. 47 (2009) 1125-34.
In this talk, we address two issues on (1) how to apply fractal theories to the functional connectivity analysis of the brain, and (2) to introduce the concept of fractal connectivity as the convergence of wavelet correlation in long memory processes.