Brain energy use key to understanding consciousness

High levels of brain energy are required to maintain consciousness, a finding which suggests a new way to understand the properties of this still mysterious state of being, Yale University researchers report.

At its simplest, consciousness can be defined as the ability to respond meaningfully to external stimuli. Most studies of consciousness have used imaging technology to try to pinpoint areas of brain activity during tasks such as memorization or problem solving.

There are two problems with such an approach, said Robert G. Shulman, Sterling Professor Emeritus of molecular biophysics and biochemistry at Yale and lead author of the paper, to be published this week in the online edition of the journal Proceedings of the National Academy of Sciences. First, functional magnetic resonance imaging has shown that many areas of the brain, not just one or two, are recruited during tasks such as memory tests and are scant help in studying the state of being conscious. Second, the amount of energy used in such tasks is minute, about one percent of baseline energy available to the brain.

"Neuroimaging has been looking at the tip of the iceberg," Shulman said. "We looked at the rest of the iceberg."

What is the other 99 percent of energy consumption doing?

Shulman and colleagues have proposed that it is needed to maintain a person in a state of consciousness. Heavily anesthetized people are known to show approximately 50 percent reductions in cerebral energy consumption. When the paws of lightly anesthetized rats with rather high baseline energy levels were stroked, fMRI signals were received in the sensory cortex and in many other areas of the brain. In heavily anesthetized rats the signal stopped at the sensory cortex. Both the total energy and the fMRI signals changed when the person or animal lost consciousness.

"What we propose is that a conscious person requires a high level of brain energy," Shulman said.

The finding has profound implications for our understanding of the connection between the brain and consciousness, Shulman said. "You can think of consciousness not as a property of the brain, but of the person."

Anesthesiologists consider a person to be in a behavioral state of consciousness when he or she can respond to simple stimuli. Properties of this state, such as the high energy and the delocalized fMRI signals, allow the person to perform the interconnected activities that make up our everyday lives. Shulman suggests that these more energetic properties of the brain support human behavior and should be considered when interpreting the much weaker signals that are typically recorded during fMRI studies.

Source: Yale University (news : web)

   

• retro - Jun 16, 2009
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  The simple operational definition of consciousness always leaves something to be desired. There's that pesky problem of the subjective experience, as unscientific as that is, since it isn't public and can't be shared. Surely it is possible to have something that meets all objective criteria for "consciousness" and yet, that something might have no subjective component whatsoever. Here is where science meets an obvious limit. When someone tells me they don't know what I am referring to when I mention a "subjective experience" I assume that I am dealing with a robot.
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• am_Unition - Jun 16, 2009
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  "At its simplest, consciousness can be defined as the ability to respond meaningfully to external stimuli."
  
  So what is "meaningful"? Do we draw the line at single-cell organisms... fungi... viruses? Does an electron not respond in a governed, "meaningful" way to a photon of a given energy?
  
  Love to hear any thoughts on this, since in most "professional" environments (and public in general) people stray away from any discussions on things of substance.
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• HenisDov - Jun 19, 2009
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  On Consciousness
  
  
  A. "Out of Our Heads: Why You Are Not Your Brain, and Other Lessons from the Biology of Consciousness" by Alva Noe
  http://www.scienc...lva_Noë
  Review by Bruce Bower
  
  
  B. "Memory, Sentience and Consciousness"
  http://blog.360.y...Q--?cq=1&p=174
  
  As gravity is THE manifestation of the onset of the cosmic inflation cataclysm and consequent universe evolution, so sentience is the manifestation of the onset of consciousness and its consequent neural system evolution.
  
  My definitions, from Merriam-Webster:
  
  Sentience = state of elementary or undifferenciated consciousness as distinguished from perception and thought.
  
  Consciousness = the quality or state of being aware especially of something within oneself and/or of an external object, state, or fact.
  
  I suggest that ALL forms of life possess the attribute of sentience, and that from the base towards the most evolved life forms sentience has been evolving into ever more complex form, consciousness.
  
  
  C. "Life Is Simpler Than They Tell Us"
  http://www.articl...144.html
  
  Evolution of Earth life:
  Genes to Genomes to Monocellular to Multicellular Organisms;
  Direct Sunlight Only To Metabolic Energy, Too;
  Triptophan To Serotonin To Melatonin To Neural System.
  
  Now we can appreciate the fractal nature of life's evolution. It is ever-continuous ever-enhanced ever-complexed cooperation. Now we can understand why, and grosso modo how, all the organs and processes and signals found in multicelled organisms have their origins in the monocells communities. And this includes the functions of serotonin and melatonin and, yes, the evolution of neural cells and the neural systems with their intricate cellular outer-membrane shapes and functionings and with their high energy consumption requirements.
  
  
  D. "Life And Culture Are Virtual Realities"
  http://www.articl...583.html
  
  Culture is the totality of ways of the organisms' dealing with (reaction to, manipulation of, exploitation of) its environment. Culture is a biological entity selected for survival of the genome as means of extending its exploitation capabilities of the out-of-cell circumstances, consequent to the earlier evolution and selection of the genome's organ, its outermost cell membrane, for controlling the inside-of-cell genes'-commune environmental circumstances.
  
  Culture is the ubiqitous biological entity that drives Earth life evolution, by imprinting genetics, by continuously modifying genes' expressions.
  
  "Spiritual matters" are virtual reality affairs. They are feasible only for living organisms that have a culture, i.e. that have a pattern of sensings and reactions to the sensings. Genes, and therefore also genomes, are organisms and display virtual reality phenomena, therefore also multicelled organisms,including humans, display such "spiritual" phenomena.
  
  
  Dov Henis
  (Comments From The 22nd Century)
  Updated Life's Manifest May 2009
  http://www.physfo...ic=14988&st=495&#entry412704
  http://www.the-sc...age#2321
  EVOLUTION Beyond Darwin 200
  http://www.the-sc...age#1407
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