"Root & Branch Association, Ltd." wrote:

> Medicine/News:  NEW UNDERSTANDING OF A KEY CONTROL MECHANISM IN THE
> BRAIN:  WEIZMANN INSTITUTE FINDINGS COULD PROVIDE NEW INSIGHTS INTO A WIDE
> RANGE OF NEUROLOGICAL DISORDERS, INCLUDING ALZHEIMER'S DISEASE, AUTISM AND
> EPILEPSY
>
> Copyright (c), 2001, the Weizmann Institute of Science
>
> REHOVOT, Yom Shlishi (Third Day -- "Tuesday"), 4 Av, 5761 (Gregorian
> Date:  July 24, 2001) (Hijri Date:  3 Jumad Awal, 1422), Root &
> Branch:  Despite more than a century of research on inhibitory neurons,
> very little is known on how this small population (10-20% of brain neurons)
> exerts its controlling effect on the brain.  Pivotal for normal brain
> development, learning, and memory, it is not surprising that inhibitory
> neurons are involved in most neurological disorders.  A study at the
> Weizmann Institute, published in the January, 2000 issue of Science,
> reveals key principles underlying the design and function of this
> inhibitory system.
>
> By repressing the level of activity in neighboring neurons, inhibitory
> neurons (I-neurons) prevent the brain from quickly spinning out of control
> into hyper-excited states or full-blown epilepsy.  One of the problems that
> children with autism and attention deficit hyperactivity disorders (ADHD)
> have is I-neuron malfunction:  their inhibitory system does not effectively
> suppress unwanted information, impeding their ability to make choices.
>
> I-neuron malfunction is involved in memory disorders (such as Alzheimer's
> disease), neural trauma, and addictions.  It also plays a role in a wide
> range of psychiatric disorders, such as depression, obsessive compulsive
> disorders, and schizophrenia.
>
> In the past, researchers basically thought that I-neurons just sprayed an
> inhibitory neurotransmitter called GABA onto their neighbors.  But this did
> not explain how they inhibited the right neurons at exactly the right time
> and to the right degree.  The new study carried out in the laboratory of
> Professor Henry Markram of the Weizmann Institute's Neurobiology Department
> shows how they achieve this.
>
> CONTROLLING THE NEURON CROWD
>
> The research team found new types of I-neurons, revealing that this tiny
> population is several times more diverse than previously thought.  Further,
> using new methods that they developed, the researchers succeeded in
> recording directly how individual inhibitory neurons control their
> neighbors.  They found that I-neurons build complex synapses (connections)
> onto their target neurons.
>
> The synapses selectively filter inhibitory messages, enabling I-neurons to
> shut down the activity in neighbors as required.  These synapses act as
> fast-switching 'if-then' filtering gates that allow inhibition to be
> applied only at the exact millisecond and to the right degree.
>
> Each I-neuron establishes complex if-then gates onto thousands of
> neighboring neurons and is therefore 'in charge' of controlling their
> activity.  The gates allow I-neurons to rapidly switch their focus onto any
> one neuron that they are connected to.  This ingenious design principle is
> what enables the small group of I-neurons to exert such a sophisticated
> effect, simultaneously 'giving personal attention' to the activity of each
> of the neurons to which they are connected.
>
> AT THE NEGOTIATING TABLE
>
> The researchers showed that a 'discussion' between I-neurons and target
> neurons is involved in deciding which type of if-then gate should be set up
> to filter the inhibitory message.  This decision-making process could allow
> each neuron in the brain to be inhibited in a potentially unique
> way.  Dubbed the  'interaction principle', this process generates maximal
> diversity of if-then gates, allowing more complex and finer control over
> large numbers of neurons.
>
> A POTENTIAL BRAIN-MAPPING TOOL
>
> The researchers went on to reveal a remarkable ability of I-neurons:  they
> can sense neurons that share the same functions in the brain.  I-neurons
> 'select' groups of target neurons to construct the same type of if-then
> gates, possibly enabling the I-neurons to control groups of neurons
> collectively.
>
> It also means that I-neurons can 'smell-out' neurons in the brain that
> collaborate in the most elementary functions even if they seem different in
> almost every other way (i.e., they can identify neurons descended from the
> same 'ancestors').
>
> "I-neurons can trace family trees of neurons.  In other words, they could
> help us to work out how neurons are related to each other.  This could one
> day enable us to map the functional aspect of the brain according to the
> genealogy of neurons -- an organizing principle that we never dreamt
> possible", says Markram.
>
> The researchers believe that the ability to detect functionally related
> groups in the brain, called "the homogeneity principle", results from
> common signal molecules released by target cells.  I-neurons may use the
> signal molecules to determine what kind of if-then gates to build.
>
> Future research designed to identify the nature of these molecules could
> yield a potent tool for mapping the functional structure of the brain.
>
> A color image of an inhibitory neuron interconnecting to three excitatory
> neurons is available upon request.  The image is also posted at:
> http://www.weizmann.ac.il (Media Information).
>
> This research was funded by the Human Frontier Science Program
> Organization, the Israel Ministry of Science, the Israel Science
> Foundation, the U.S. Navy, Minna James Heineman Stiftung, the Abramson
> Family Foundation and the Nella and Leon Benoziyo Center for Neurosciences.
>
> A member of the Weizmann Institute's Neurobiology Department, Professor
> Henry Markram holds the Joseph D. Shane Career Development Chair.
>
> Shavua Tov from Rehovot,
>
> Malka Barkan
> Publications and Media Relations Department
> Weizmann Institute of Science
> Rehovot 76100
> Tel:    972-8-934-3856
> Fax:    972-8-934-4132
> Email:  [log in to unmask]
>
> Please visit the Root & Branch Association website at http://www.rb.org.il,
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