On causal closure and life as an emergent phenomenon.

One of the first things we do when designing the methods of a study is exclude confounding variables if we can. We attempt to close the system from the interference of extraneous agency and events.

Causal closure of the physical prohibits agency to be able to interfere with measurements done of a closed system. Roughly speaking, it means that certain reproducible forms of human telekinesis must be false, nothing else.

Calculating all the influences on the net electrical field in which an electron within the body of a living human moves requires the "closed" system to be so large it is _totally incalculable_ if we include the person's body and environs within the system (just closing it within a couple of meters of the mat where the person under study is lying down, for example).

As a result, the only way causal closure could ever be shown in practice requires that we exclude people and society from our measurements. If a person messes with our equipment from the outside, say by waving a magnet near the chamber, we discard the artifactual changes.

Causal closure could in principle be falsified (reproducible telekinesis would do it), but it cannot actually (empirically) be proven.

Causal closure is thus a philosophical extension of a simplifying method, and the idea is not entailed by the method at all. In fact, as discussed in the paper below, even sub-cellular level biological systems are incalculable within the bounds of the physical universe, and as such may show properties that are non-predictable by the micro-physical laws because those laws require we calculate mathematically the behavior of the biological system, and that is in principle impossible within the bounds of the universe!

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ABSTRACT

Emergent biological principles and the computational properties of the universe

P.C.W. Davies

The claim that life is an emergent phenomenon exhibiting novel properties and principles is often criticized for being in conflict with causal closure at the microscopic level. I argue that advances in cosmological theory suggesting an upper bound on the information processing capacity of the universe may resolve this conflict for systems exceeding a certain threshold of complexity. A numerical estimate of the threshold places it at the level of a small protein. The calculation supports the contention that life is an emergent phenomenon.

Comments: 9 pages. no figures, research paper

Subjects: Astrophysics (astro-ph)

Journal reference: Complexity 10 (2004) 1

Cite as: arXiv:astro-ph/0408014

(or arXiv:astro-ph/0408014v1 for this version)

Astrocytes and Attention to the New

One of the many simplifying assumptions proposed for the brain simulations being attempted by just-starting, very large research programs in Europe and North America is that neural networks can be simulated as networks of neurons alone, abstracting away the influences of supporting cells such as oligodendrocytes and astrocytes, which account for a large portion of normal brain. Astrocytes, for example, make up about 50% of brain cellular mass.

Why might we assume that supporting glial cells like astrocytes can be ignored in simulation brain function, including components of cognition? The feeling has been that such cells are needed for the network of neurons to function at all, but that they did not determine particular aspects of cognition and so their influence could be safely averaged out of the network.

Unfortunately, there is increasing evidence that ignoring, or averaging out, the influence of astrocytes in simulating cognition may not be possible if we want to properly simulate some aspects of attention and memory, at least in mice. The article below, from PNAS this month, documents an influence of astrocytes on the gamma oscillation-dependent behavioral response to novelty in mice.

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ABSTRACT

Astrocytes contribute to gamma oscillations and recognition memory

Hosuk Sean Leea,b,1, Andrea Ghettia,2, António Pinto-Duartec,d,e, Xin Wangc, Gustavo Dziewczapolskia, Francesco Galimif,g, Salvador Huitron-Resendizh, Juan C. Piña-Crespoa,3, Amanda J. Robertsh, Inder M. Vermaf, Terrence J. Sejnowskic,i, and Stephen F. Heinemanna,1

Significance

Astrocytes are well placed to modulate neural activity. However, the functions typically attributed to astrocytes are associated with a temporal dimension significantly slower than the timescale of synaptic transmission of neurons. Consequently, it has been assumed that astrocytes do not play a major role in modulating fast neural network dynamics known to underlie cognitive behavior. By creating a transgenic mouse in which vesicular release from astrocytes can be reversibly blocked, we found that astrocytes are necessary for novel object recognition behavior and to maintain functional gamma oscillations both in vitro and in awake-behaving animals. Our findings reveal an unexpected role for astrocytes in neural information processing and cognition.

Abstract

Glial cells are an integral part of functional communication in the brain. Here we show that astrocytes contribute to the fast dynamics of neural circuits that underlie normal cognitive behaviors. In particular, we found that the selective expression of tetanus neurotoxin (TeNT) in astrocytes significantly reduced the duration of carbachol-induced gamma oscillations in hippocampal slices. These data prompted us to develop a novel transgenic mouse model, specifically with inducible tetanus toxin expression in astrocytes. In this in vivo model, we found evidence of a marked decrease in electroencephalographic (EEG) power in the gamma frequency range in awake-behaving mice, whereas neuronal synaptic activity remained intact. The reduction in cortical gamma oscillations was accompanied by impaired behavioral performance in the novel object recognition test, whereas other forms of memory, including working memory and fear conditioning, remained unchanged. These results support a key role for gamma oscillations in recognition memory. Both EEG alterations and behavioral deficits in novel object recognition were reversed by suppression of tetanus toxin expression. These data reveal an unexpected role for astrocytes as essential contributors to information processing and cognitive behavior.

Hosuk Sean Lee, doi: 10.1073/pnas.1410893111

An alternative to Kim's physicalism

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