cerebral cortex_525

New theory upends view of how brain is wired

COLUMBIA U. (US) — The long-held view of how signals move through the cerebral cortex of the human brain may be incorrect.

For decades, scientists thought they had a pretty clear understanding of how signals move through the cerebral cortex. By studying the anatomy of nerve axons—the wires that connect nerve cells—they had concluded that information is relayed through a “column” of six layers of specialized nerve cells in a series of hand-offs that begins in the mid-layer of the cortex, then moves to other layers before triggering a behavioral response.

Looking at how sensory information is processed in rats, Columbia University neuroscientist Randy Bruno found that signals are processed in two parts of the cortex simultaneously rather than in series—almost as if there are two brains.

“Our findings challenge dogma,” says Bruno, assistant professor of neuroscience. “The upper and lower layers form separate circuits that do separate things.”

The discovery, he says, “opens up a different way of thinking about how the cerebral cortex does what it does, which includes not only processing sight, sound, and touch but higher functions such as speech, decision-making, and abstract thought.”

The study, co-authored with Christine Constantinople, who earned a PhD at Columbia and is now a postdoctoral researcher at the Princeton Neuroscience Institute, appears in the journal Science.

Rat whiskers and human fingers

The research was conducted in the well-understood sensory system of rat whiskers, which operate much like human fingers, providing tactile information about shape and texture.

This information travels from nerve fibers at the base of the whiskers to the thalamus in the midbrain and then is processed in the cerebral cortex. Past research has mapped each whisker to a specific barrel-shaped cluster of neurons in the brain.

“The wiring of these circuits is similar to those that process senses in other mammals, including humans,” Bruno notes.

The new study relies on a sensitive technique that allows researchers to record how signals move across synapses from one neuron to the next in a live animal by using micropipettes whose tips are just 1 micron wide—one-thousandth of a millimeter.

The recordings showed that signals are relayed from the thalamus to the mid- and deeper layers of the cortex simultaneously with surprisingly robust signaling to the deeper layer.

To confirm that the deeper layer receives sensory information directly from the thalamus, the researchers blocked all signals from the mid-layer using a local anesthetic. Sure enough, activity in the deeper layer remained unchanged.

“This was very surprising,” says Constantinople. “We expected activity in the lower layers to be turned off or very much diminished.”

Upper vs. lower layers

The study suggests that the upper and lower layers of the cerebral cortex form separate circuits that play separate roles in processing sensory information.

Researchers believe that the deeper layers are evolutionarily older—they are found in reptiles, for example, while the upper and middle layers appear in more evolved species and are thickest in humans.

One possibility, suggests Bruno, is that basic sensory processing occurs in the lower layers: for example, visually tracking a tennis ball. Processing that involves integrating context or experience might be done in the upper layers: for example, watching where an opponent is hitting the ball and planning where to return the shot.

German neurobiologist Bert Sakmann, who won a 1991 Nobel Prize for developing the micropipette system of mapping nerve impulses, describes the study as a game changer. “Dr. Bruno has produced a technical masterpiece that now firmly establishes two separate input streams to the cortex,” he says.

Bruno’s lab is now focused on exploring how the various layers of cortex relate to specific behaviors, such as memory and learning.

Source: Columbia University

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8 Comments

  1. Roger D. Masters

    This is fascinating and, based on my research on brain and behavior, very reasonable. What is to be added is the way this dual system relates to the difference between cognitive information processing (which for humans is heavily dependent on language and verbal concepts) and EMOTION (which is processed in different brain structures — AND the complex effects of neurotoxins on both levels of these processing.
    For some introductory examples, see the first entries of articles (a small sample of over a decade of peer-reviewed scientific publications with Myron J. Coplan, a chemist who is retired Vice President of Albany International Chemical Corp.) Of particular importance are the effects of lead, manganese, and either fluorosilicic acid (H2SiF6) or sodium silicofluorides (Na2SiF6). These last two (“silicofluorides”) are toxic compounds that have been added to American public water supplies since 1942 as the means of water “fluoridation” which has been debated violently for over 50 years without considering the fact that sodium fluoride splits apart (“dissociates”) into sodium and fluoride when added to water, and does NOT have harmful side effects, whereas silicofluorides are linked to: higher blood lead levels, lower educational performance, more arrests for driving under influence of cocaine, and higher rates of violent crime.

    Access to several articles in this research are available at: http://www.dartmouth.edu/~rmasters. Fuller information will shortly be available of a separate website to be dedicated to this research project, which is now under construction. The bottom line: the silicofluorides — untested toxins (once officially classified in Australia as “hazardous” substances) that were approved for use in 1950 WITHOUT TESTING, and have multiple harmful effects including an association with higher rates of violent crime and lower scores on standardized educational exams.

    What’s needed is listing the silicofluorides under §5 or §6 of the Toxic Substances Control Act, which by law is done by a decision of the Administrator of the EPA.

    Roger D. Masters, Research Professor & Nelson A. Rockefeller Professor Emeritus,
    Department of Government, Dartmouth College, Hanover, NH 03755 tel. 603 643 4205

  2. Dan

    This is a solid article on brain function, a link to which appeared in an online edition of an American Mensa publication. To be intelligent, humans would need to be of two brains, and one of the most important functions it must do is is to quickly determine what is in our environment that merits our attention, and what doesn’t. In this way, ignorance is an essential quality of intelligence.

    It is ironic that the only comment seems to be from a troll toxicologist who seems to have OCD fixated on the impact of certain substances on the brain, many of which (lead, for instance) are already regulated.

    No mention (by the troll) of the impact of neonicotinoid pesticides in humans with impaired immune systems or head injuries which impact the function of important neurotransmitters and which have caused a pandemic which ravaged colonies of bees worldwide. In Japan where these systemic pesticides were developed, residue of these pesticides are 10 times higher than in the United States, and few human studies have taken head injuries and other factors into account before pesticide and herbicide companies like Monsanto and Bayer have already exposed us all to doses of these chemicals many times higher than a level that cause honeybee brains to stop working, most of them dying in a day with their tongues sticking permanently out.

    Obviously, this troll has some sort of cortical dysfunction. Please get some help from a clinical psychologist to select the appropriate drug to alleviate this debilitating condition.

  3. Mitch

    What is this, the axe-grinding club? Good grief.

    I think Bruno’s study sounds awesome, and I’m looking forward to reading it.

  4. Rick

    Dan,

    Your neonicotinoid commentary renders your entire post fallacious. Give us a break.

  5. Olive

    But Dan read the article on Mensa, so by viture of being thus connected, he must know what he’s talking about. He certainly let us know how he found the article.

  6. John

    Perhaps individuals and their genes survive better when there is an overt learning/acting mind and a covert supervising mind. It is more than just the kind of redundancy that engineers build into spacecraft. The deeper emotional mind keeps the genetic goals firmly in mind, while the higher levels that are built to absorb and categorize information about the environment try to navigate in that environment. This confirmation of two independent brain systems reminds me of how Isaac Asimov thought it best that his character (in the Foundation Trilogy) the genius psychohistorian Hari Seldon create two foundations to shorten the coming dark ages of the Galactic Empire – one foundation was to be the overt actor while the second foundation was to be the covert and guiding supervisor. Only the second foundation knew what were the real goals.

  7. justfound

    7/18/13
    I am also ‘MENSA’, though I’ve let my membership lapse because I need all my student loan money to pay the courses for my Masters studies. I loved not only the ‘how brain is wired’ article, but also (what I consider to be) the very interesting and thought-provoking comment by Roger D. Masters (the first one, at the top). My ‘MENSA IQ’ was discovered while being tested for a learning disability, Mathematics Disorder (commonly called ‘dyscalculia’). When I read, “The discovery, he says, “opens up a different way of thinking about how the cerebral cortex does what it does, which includes not only processing sight, sound, and touch but higher functions such as speech, decision-making, and abstract thought”, my fascination was complete. My ‘abstract reasoning’ is somewhere in the vicinity of Forrest Gump’s, while other parts of my brain are having a wonderful, fulfilling life. Articles like this one help me understand processing disorders,… my own, and that of other people.

    I will add that (although I do not have a background in science) I avoid water and toothpaste which contains sodium fluoride. Decades ago, a chiropractor I knew, told me that sodium fluoride is 40 times more soluble than (the naturally occurring) calcium fluoride, and that sodium fluoride is extremely toxic. Yes, he was a chiropractor, not a scientist. But he was a brilliant man. I’m pasting a link to a site that I haven’t read previously, only to elaborate on this one issue about sodium fluoride. http://www.fluoridationfacts.com/science/papers/aspects_of_toxicity.htm

    BTW, there’s one MENSAN in every 50 people,… top 2% of the populattion,… and most people interested in these ‘brain’ articles could likely ‘make MENSA’ on their first or second try at taking the test. ;-)

  8. Mike

    There is no way that “justfound” could have “made” Mensa if his/her “abstract reasoning is somewhere in the vicinity of Forrest Gump’s.” Furthermore, any current or former member would know that “Mensa” is not supposed to be written in all caps, as “MENSA.” Oops. Mwah-ha-ha-haaaaaaa…!

    -Signed, An Upper Half, 99.1st Percentile Mensan (all you 99.9%’ers, flame away!)

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