Tuesday, June 7, 2016

Neuroscience techniques can't even help us understand Donkey Kong

...the MOS 6502 microchip contains 3510 transistors, runs Space Invaders, and wouldn’t even be the most complex object in my pocket. We know very little about how the brain works, but we understand the chip completely.

So, Eric Jonas and Konrad Kording wondered, what would happen if they studied the chip in the style of neuroscientists? How would the approaches that are being used to study the complex squishy brain fare when used on a far simpler artificial processor? ...

Even though the duo knew everything about the chip—the state of each transistor and the voltage along every wire—their inferences were trivial at best and seriously misleading at worst. ...

Last week, the duo uploaded their paper, titled “Could a neuroscientist understand a microprocessor?” after a classic from 2002. It reads like both a playful thought experiment (albeit one backed up with data) and a serious shot across the bow. And although it has yet to undergo formal peer review, other neuroscientists have already called it a “landmark paper”, a “watershed moment”, and “the paper we all had in our minds but didn't dare to write”. ...

Rather than working with an actual chip, Jonas and Kording used a simulation, albeit one accurate enough to run classic games like Donkey Kong, Space Invaders, and Pitfall. That gave them experimental omniscience and omnipotence—they knew everything and could tweak anything. For example, they could disable each of the chip’s transistors one at a time. And by doing so, they found several that were essential for booting up all three games, and others that were essential for just one.

Brain scientists have doing something similar for centuries, either by studying people with localized brain damage or by temporarily shutting down specific brain regions. Through such studies, they’ve labelled different areas as memory centers or language centers or emotional centers. But Jonas and Kording’s work shows why such inferences can be deceptive. They didn’t find “Donkey Kong transistors” or “Space Invaders transistors”; instead, they found components that carry out basic processes that just so happen to be important for those particular games.

They also tried out five other common approaches—the equivalents of analyzing individual neurons, or averaging activity in a small region as in fMRI brain-scanning, or taking a god-like view and look for patterns across the entire brain. None of these told the team anything useful about how the chip works. ...

To move forward, Jonas says that neuroscientists need to put more effort into testing their theories about the brain. “There are a lot of theories about how different parts of the brain might function, but they don’t make falsifiable predictions. They have so many different knobs you can turn that they can be arbitrarily extended to fit arbitrary bits of data. It’s very hard to kick any of these ideas to the curb.”
--Ed Yong, The Atlantic, on the blind men and the elephant