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Exciting Brain Circuitry News!

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  • Toni Thompson
    Wednesday June 21, 3:04 pm Eastern Time Company Press Release MIT and Bell Labs researchers create electronic circuit that mimics the brain s circuitry Device
    Message 1 of 1 , Jun 21, 2000
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      Wednesday June 21, 3:04 pm Eastern Time

      Company Press Release

      MIT and Bell Labs researchers create electronic circuit that mimics
      the
      brain's circuitry

      Device may help create computers that work more like the brain

      MURRAY HILL, N.J.--(BUSINESS WIRE)--June 21, 2000--Researchers at the
      Massachusetts Institute of Technology and Lucent Technologies' Bell
      Labs report in
      the June 22 issue of Nature that they have created an electronic
      circuit that mimics the biological circuitry of the cerebral cortex,
      the brain's center of intelligence.

      This latest advance in ``neuromorphic'' engineering -- creating
      devices that behave like neural systems -- was achieved by a team
      that included MIT researchers Richard
      Hahnloser, a postdoctoral fellow in the Department of Brain and
      Cognitive Sciences; Rahul Sarpeshkar, assistant professor of
      electrical engineering and computer
      science; and H. Sebastian Seung, assistant professor of computational
      neuroscience.

      ``Like electronic circuits, the neural circuits of the cortex contain
      many feedback loops,'' Seung said. ``But neuroscientists have found
      that cortical feedback seems to
      operate in a way that is unfamiliar to today's electronic designers.
      We set out to mimic this novel mode of operation in an unconventional
      electronic circuit.''

      The circuit was designed in collaboration with Rodney Douglas and the
      late Misha Mahowald from the Institute of Neuroinformatics in
      Switzerland. Much of the
      research was carried out at Lucent Technologies' Bell Labs in Murray
      Hill, N.J., where Sarpeshkar and Seung are consultants.

      In the future, general principles illustrated by this circuit, could
      lead to hardware that efficiently accomplishes complex perceptual
      tasks, such as recognizing objects by
      sight.

      Cooperation and competition among neurons

      The circuit is composed of artificial neurons that communicate with
      each other via artificial synapses. All of these elements are made
      from transistors fabricated on a
      silicon integrated circuit.

      Like neurons in the cortex, nearby artificial neurons affect each
      other. There also is an inhibitory neuron that receives input from
      the 16 excitatory neurons and returns
      inhibition to them. This inhibitory feedback keeps in check
      excitatory feedback that can lead to explosive instability.

      In the brain, synaptic feedback connections are thought to mediate
      neurons' cooperative and competitive interactions. Such interactions
      are expressed most strongly in
      the circuit when multiple stimuli are presented at the same time.

      When simultaneous electrical currents are applied to two artificial
      neurons, the circuit responds to only one stimulus and suppresses its
      response to the other, much like a
      frog choosing which of two flies to strike at.

      Like the brain, there is no single element in the circuit that
      decides which stimulus to suppress. The decision is the outcome of an
      emergent, collective property of all the
      neurons.

      A combination of digital and analog

      A typical neuron in the brain might be connected to 10,000 other
      neurons. Because there are billions of neurons, this makes the brain
      a vast and intricate network.
      ``Biologists like to focus on simple linear pathways through this
      network, ignoring the tangled web of feedback loops, which seem too
      complex to even contemplate,''
      Seung said. ``But it seems unlikely that we could ever understand
      intelligence or consciousness without understanding the role of
      feedback in the neural networks of the
      brain.''

      Because electrical engineers rely heavily on feedback in their
      designs, researchers have been tempted to draw analogies between
      electronic and neural circuits. But
      recent neurophysiological experiments suggest that the brain does not
      use feedback in the same way as conventional electronics, which is
      distinctly analog or digital.

      Perception, the authors write, combines digital and analog aspects.
      When we see an object such as an approaching car, we also receive a
      continuous stream of
      information about its color, its changing size in relation to its
      distance from us, its spatial relations to other objects and so on.
      Nevertheless, the digital component is still
      there because regardless of how the object appears, our brains make
      an either-or decision: Is it a car or not?

      The hybrid analog-digital nature of the brain may be very important
      for its computational efficiency. ``The electronic world is evolving
      more and more towards mixed
      analog-digital computation as the brain has already done,''
      Sarpeshkar said. ``However, the brain's mixed-signal circuits combine
      analog and digital functions in a much
      more intimate way than is done in the electronic world.''

      ``Philosophers and psychologists have long been struck by the duality
      between analog and digital in perception,'' Seung said. ``They have
      further speculated about
      whether the computational operations underlying perception in the
      brain are analog or digital.

      ``Our research suggests that the two sides of this duality are not
      mutually exclusive: the brain's neural circuitry is actually a hybrid
      in which analog and digital coexist.''

      Sarpeshkar, who does research in hybrid electronic circuits, said
      that hybrid electronics has the potential to revolutionize computing
      in the future because it combines the
      digital advantages of programmability, noise immunity and divide-and-
      conquer processing with the analog advantages of efficiency.

      ``The most immediate applications of such biologically inspired
      circuits are likely to be in sensory data processing, where the input
      is analog, and in prosthetic applications
      for the deaf and blind, where mimicing the biology is important,''
      Sarpeshkar said.

      This work was supported by the Swiss National Science Foundation SPP
      Program, Lucent Technologies and MIT.
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