Chips under construction in Taiwan contain 20 ARM processor cores, each modelling 1000 neurons. (New Scientist) With 20,000 neurons per chip, 50,000 chips will be needed to reach the target of 1 billion neurons. Steve Furber hopes to have a 10,000-processor version working later this year.
Furber won’t come close to copying every property of real neurons, says Henry Markram, head of Blue Brain. Big Blue is an IBM project attempt to simulate a brain with unsurpassed accuracy on a Blue Gene supercomputer. Brain-inspired chips can only produce brain-like functions. However, that is good enough for Furber, who wants to start teaching his brain-like computer about the world as soon as possible. His first goal is to teach it how to control a robotic arm, before working towards a design to control a humanoid. A robot controller with even a dash of brain-like properties should be much better at tasks like image recognition, navigation and decision-making.
A memory chip next to each processor stores the changing synaptic weights as simple numbers that represent the importance of a given connection at any moment. Initially, those will be loaded from a PC, but as the system gets bigger and smarter, says Furber, “the only computer able to compute them will be the machine itself”.
Another brain-like behaviour his chips need to master is to communicate coordinated “spikes” of voltage. A computer has no trouble matching the speed at which individual neurons spike – about 10 times per second – but neurons work in very much larger, parallel groups than silicon logic gates.
In a brain there is no top-down control to coordinate their actions because the basic nature of individual neurons means that they work together in an emergent, bottom-up way.
Spinnaker cannot mimic that property, so it relies on a miniature controller to direct spike traffic, similar to one of the routers in the internet’s backbone. “We can route to more than 4 billion neurons,” says Furber, “many more than we need.”
While the Manchester team await the arrival of their chips, they have built a cut-down version with just 50 neurons and have put the prototype through its paces in the lab. They have created a virtual environment in which the silicon brain controls a Pac-Man-like program that learns to hunt for a virtual doughnut.
The SpiNNaker project’s architecture DOI-Link mimics the human brain’s biological structure and functionality. This offers the possibility of utilising massive parallelism and redundancy to provide resilience in an environment of unreliability and failure of individual components.
In the human brain, communication between its computing elements, or Neurons, is achieved by the transmission of electrical “Spikes” along connecting Axons. The biological processing of the Neuron can be modelled by a digital processor and the Axon connectivity can be represented by messages, or information packets, transmitted between a large number of processors which emulate the parallel operation of the billions of Neurons comprising the brain.
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