Scientific Understanding of Consciousness
Complexity, Self-Organization, Emergence — Recent Research
Science 24 November 2006: Vol. 314. no. 5803, pp. 1249 - 1250
Marcus E. Raichle
The adult human brain represents about 2% of the body weight, yet accounts for about 20% of the body's total energy consumption. It is estimated that 60 to 80% of the energy budget of the brain supports communication among neurons and their supporting cells. Intrinsic activity may be far more significant than evoked activity in terms of overall brain function.
In the visual cortex, less than 10% of all synapses carry incoming information from the external world. From a brain energy perspective, the cortex may simply be more involved in intrinsic activities.
Theoretical neuroscience posits that the brain operates as a Bayesian inference engine, designed to generate predictions about the future. Beginning with a set of "advance" predictions at birth (genes), the brain is then sculpted by worldly experience to represent intrinsically a "best guess" ("priors" in Bayesian parlance) about the environment and, in the case of humans at least, to make predictions about the future. The ability to reflect on the past or contemplate the future may have facilitated the development of unique human attributes such as imagination and creativity.
fMRI provides one important experimental approach to understanding the nature of the brain's intrinsic functional activity. A considerable fraction of the variance in the blood oxygen level-dependent (BOLD) signal of fMRI in the frequency range below 0.1 Hz reflects fluctuating neural activity. This activity exhibits striking patterns of coherence within known networks of specific neurons in the human brain in the absence of observable behaviors.
Future research likely will cover a broad range of approaches to the study of spontaneous activity of neurons. Descriptions of slow fluctuations (nominally <0.1 Hz) in neuronal membrane polarization are intriguing. Their functional consequences may be relevant to an understanding of the variability in task-evoked brain activity as well as behavioral variability in human performance.
Science 31 October 2008: Vol. 322. no. 5902, pp. 739 - 742
Experimental Evidence for Spatial Self-Organization and Its Emergent Effects in Mussel Bed Ecosystems
Johan van de Koppel,1 Joanna C. Gascoigne,2 Guy Theraulaz,3 Max Rietkerk,4 Wolf M. Mooij,5 Peter M. J. Herman1
1 Spatial Ecology Department, the Netherlands Institute of Ecology (NIOO-KNAW), Post Office Box 140, 4400 AC Yerseke, Netherlands.
Spatial self-organization is the main theoretical explanation for the global occurrence of regular or otherwise coherent spatial patterns in ecosystems. Using mussel beds as a model ecosystem, we provide an experimental demonstration of spatial self-organization. Under homogeneous laboratory conditions, mussels developed regular patterns, similar to those in the field. An individual-based model derived from our experiments showed that interactions between individuals explained the observed patterns. Furthermore, a field study showed that pattern formation affected ecosystem-level processes in terms of improved growth and resistance to wave action. Our results imply that spatial self-organization is an important determinant of the structure and functioning of ecosystems, and it needs to be considered in their conservation.
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