![]() ![]() Those results are hard to parse into something meaningful. Losing any one of 1,560 transistors made it impossible for the microprocessor to load any of the games. The experiment netted 1,565 transistors that could be eliminated without any consequences to the games. The effort was akin to what neuroscientists call “lesion studies,” which probe how the brain behaves when a certain area is damaged. They wanted to know which transistors were mission-critical to three important “behaviors”: Donkey Kong, Space Invaders and Pitfall. Using a simulation to run their experiments, the researchers systematically knocked out every single transistor one at a time. In one experiment, they tested what would happen if they tried to break the 6502 bit by bit. Some transistors (locations on microprocessor, left) damaged just one of the games. BREAKING THE GAME With certain transistors shut down, Donkey Kong (blue), Pitfall (red) and Space Invaders (green) no longer worked (Venn diagram, right). Those shared traits make the 6502 a legitimate and informative model organism, Jonas and Kording argue. These units can be organized into specialized modules that allow both “organs” to flexibly move information around and hold memories. Brains and microprocessors are both built from many small units: 86 billion neurons and 3,510 transistors, respectively. Yet there are some undeniable similarities. The methods for understanding one shouldn’t be expected to work for the other, Sejnowski says. The 6502, which debuted in 1975, was designed by a small team of humans, who engineered the chip to their exact specifications. ![]() The human brain has been sculpted over millions of years of evolution to be incredibly specialized, able to spot an angry face at a glance, for instance, or remember a childhood song for years. Synapses grow and connect nerve cells, storing new knowledge.īrains and microprocessors have very different origins, Sejnowski points out. Unlike the microprocessor’s connections, brain circuits morph every time you learn something new. And this hardware changes from minute to minute. “This is not the case in the brain, where the software is the hardware,” Sejnowski says. In microprocessors, the software is distinct from the hardware - any number of programs can run on the same machine. And compared with a microprocessor, the brain has an incredible amount of redundancy, with multiple circuits able to step in and compensate when others malfunction. The brain can behave differently in different situations, a variability that adds an element of randomness to its machinations computers aim to serve up the same response to the same situation every time. Terrence Sejnowski of the Salk Institute for Biological Studies in La Jolla, Calif., for instance, calls the comparison “provocative, but misleading.” The brain and the microprocessor are distinct in a huge number of ways. “And I don’t necessarily disagree.” Differences and similaritiesĬritics, however, contend that the analogy of the brain as a computer is flawed. “Their point is that it’s not clear that the current methods would ever allow us to understand how the brain computes in fundamental way,” he says. The paper “does a great job of articulating something that most thoughtful people believe but haven’t said out loud,” says neuroscientist Anthony Zador of Cold Spring Harbor Laboratory in New York. ![]() Current neuro-science methods might not be up for the job when it comes to truly understanding the brain. The implications are profound - and discouraging. Bottom line of their report: Some of the best tools used by neuro-scientists turned up plenty of data but failed to reveal anything meaningful about a relatively simple machine. On May 26, Jonas and Kording shared their results with a wider audience by posting a manuscript on the website. “And a bunch of people were like, ‘That’s bullshit. I had that idea 10 years ago and never got around to doing it,’ ” Jonas says. “A bunch of people said, ‘That’s awesome. When Jonas presented the work last year at a Kavli Foundation workshop held at MIT, the response from the crowd was split. Their results - or lack thereof - hit a nerve among neuroscientists. ![]() By the end of their experiments, Jonas and Kording had discovered almost nothing. ![]()
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