Brain On a Chip
Are we humans – with our carbon-based neural net “wetware” brains – at a point in history when we might be able to imprint the circuitry of the human brain using transistors on a silicon chip?
A well-covered recent article in MIT’s Technology Review reports that a team of European scientists may have taken the first steps in creating a silicon chip designed to function like a human brain.
What’s involved in this seemingly Herculean task? The brain is a parallel processor. The colorful blue jay I see flitting from tree to tree in my garden appears as a single image. But the brain divides what it sees into four components: color, motion, shape, and depth. These are individually processed – at the same time – and compared to my stored memories (blue things, things with feathers, things that fly, other blue jays that I’ve seen).
My brain then combines all of these processes into one image that I see and comprehend. And that’s just vision aspect of a multiplexed moment of perception. At the same time, I smell the fragrant flowers in my garden, hear the neighbors talking about a party, feel my muscles relax as I sit in my lounge chair, and daydream about the beaches of Fiji while I answer my cell phone.
The MacBook Pro Intel core duo that I’m using to type this article is also doing several things at once. At the highest level, its world consists of programs with multiple computational threads running at the same time. Parallel processing makes programs run faster because there are more CPUs or cores running them.
Today’s most powerful supercomputers are all massively parallel processing systems with names like Earth Simulator, Blue Gene, ASCI White, ASCI Red, ASCI Purple, and ASCI Thor’s Hammer. Through Moore’s Law – which states that the number of transistors on a chip double every eighteen months – single chips that function as parallel processor arrays are becoming cost effective. Examples include chips from Ambric, picoChip, and Tilera.
The brain is also massively parallel, but currently on a different scale than the most powerful supercomputers. The human cortex has about 22 billion neurons and 220 trillion synapses. A supercomputer capable of running a software simulation of the human brain doesn’t yet exist. Researchers estimate that it would require at least a machine with a computational capacity of 36.8 petaflops (a petaflop is a thousand trillion floating point operations per second) and a memory capacity of 3.2 petabytes – a scale that supercomputer technology isn’t expected to hit for at least three years.
Enter the team of scientists in Europe that has created a silicon chip designed to function like a human brain. With 200,000 neurons linked up by 50 million synaptic connections, the chip is still orders of magnitude from a human brain. Yet, the chip can “mimic the brain’s ability to learn more closely than any other machine” – thus far.
“The chip has a fraction of the number of neurons or connections found in a brain, but its design allows it to be scaled up.” So says Karlheinz Meier, a physicist at Heidelberg University in Germany, and the coordinator of the Fast Analog Computing with Emergent Transient States project, or FACETS.
Henry Markram, head of the Blue Brain project at the Ecole Polytechnique Fédérale de Lausanne, uses the same databases of neurological data as FACETS. Among the challenges he faces is “recreating the three-dimensional structure of the brain in a 2-D piece of silicon.”
Markram admits that the simulations of biological brain functions using a silicon chip are still crude. "It’s not a brain. It’s more of a computer processor that has some of the accelerated parallel computing that the brain has," he says.
Markram doubts that the FACETS hardware approach will ultimately offer much insight into how the brain works. For example, unlike the Blue Brain project, researchers aren’t able to perform drug testing – simulating the effects of drugs on the brain using silicon. "It’s more a platform for artificial intelligence than understanding biology," he says.
Markram’s Blue Brain project is the first comprehensive attempt to reverse-engineer the mammalian brain. The brain processes information by sending electrical signals from neuron-to-neuron using the “wiring” of dendrites and axons. In the cortex, neurons are organized into basic functional units – cylindrical volumes – each containing about 10,000 neurons that are connected in an intricate but consistent way. These units operate much like microcircuits in a computer. This microcircuit, known as the neocortical column, is repeated millions of times across the cortex.
The first step of the project is to re-create this fundamental microcircuit, down to the level of biologically accurate individual neurons. The microcircuit can then be used in simulations such as a genetic variation in particular neurotransmitters, mimicking what happens when the molecular environment is altered using drugs.
Brains In Silicon, an interdisciplinary program at Stanford, also combines neurobiological research with electrical engineering. The program has two complementary objectives: to use the existing knowledge of brain function to design an affordable supercomputer that can then itself serve as a tool to investigate brain function, “feeding back and contributing to a fundamental, biological understanding of how the brain works.”
Kwabena Boahen, Brains In Silicon principal investigator and an associate professor of bioengineering at Stanford, has been working on implementing neural architectures in silicon. One of the main challenges to building this system in hardware, explains Boahen, is that each neuron connects to others through 8,000 synapses. It takes about 20 transistors to implement a synapse. Clearly, building the silicon equivalent of 220 trillion synapses is not an easy problem to solve.
The quest to reverse-engineer the human brain is described in detail in Jeff Hawkins’ well-known book On Intelligence. Hawkins believes computer scientists have focused too much on the end product of artificial intelligence. Like B.F. Skinner, who held that psychologists should study stimuli and responses and essentially ignore the cognitive processes that go on in the brain, he holds that scientists working in AI and neural networks have focused too much on inputs and outputs rather than the neurological system that connects them.
Hawkins’ company, Numenta, is creating a new type of computing technology modeled on the structure and operation of the neocortex. The technology is called Hierarchical Temporal Memory, or HTM, and is applicable to a broad class of problems from machine vision, to fraud detection, to semantic analysis of text. HTM is based on the theory of the neocortex first described in Hawkins’ book.
In The Singularity Is Near, Ray Kurzweil comments that, “…hardware computational capacity is necessary but not sufficient. Understanding the organization and content of these resources – the software of intelligence – is even more critical and is the objective of the brain reverse-engineering undertaking.” He goes on to famously say that once a computer achieves a human level of intelligence, it will necessarily soar past it.
h+ contributor Ben Goertzel (like Kurzweil) has stated that – given the problems facing humanity – we may not be able to wait on advances in hardware and the reverse-engineering of the brain to achieve the AI vision of human-like intelligence (or greater). His Novamente Artificial General Intelligence (AGI) software is not dependent on a specific hardware architecture, although it will obviously benefit from massively parallel supercomputer architectures. Key cognitive mechanisms of the system include a probabilistic reasoning engine based on a variant of probabilistic logic and an evolutionary learning engine that is based on a synthesis of probabilistic modeling and evolutionary programming. It’s a different approach than reverse-engineering the brain, but one that may yield results more quickly.
With research and development converging on all fronts – hardware and software – it would seem to be only a matter of time until a brain with human-level complexity is available using a massively parallel architecture on silicon chip. Karlheinz Meier’s FACETS group now plans to further scale up their chips, connecting a number of wafers to create a superchip with a total of a billion neurons and 1013 (10 trillion) synapses, well on the way to the 22 billion neurons and 220 trillion synapses of the human brain.
If Ray Kurzweil is right, superchip development won’t stop at 22 billion neurons, even if Moore’s law is no longer applicable and it becomes impossible to get additional transistors on a piece of silicon. Physicist Freeman Dyson at Princeton University has visualized spheres extracting usable stellar energy. Currently the stuff of SciFi, a “Class B stellar engine” would consist of a series of nested Dyson spheres – a Matryoshka brain like a series of Russian dolls enclosed inside each other – and composed of nanoscale computers powered by a star.