Brain Prosthesis

Slashdot and others have covered this story an artificial hippocampus chip. The hippocampus is an area of the brain that’s necessary for the formation of new memories. People with memory disorders like the guy in the movie Memento have damage to their hippocampus. It is also known to be crucial for navigation. Rats have “place cells” in their hippocampus that only fire when they’re in specific places in a maze.

While the idea of brain prostheses is interesting, this has the markings of a lot of hype, so far. Especially since they they’re just beginning to test the chip on “tissue from rat’s brains”. In other words, they’re not even close to actually testing it in a brain, despite their 6-month prediction. The thing that makes me the most dubious, however, is this quote: “No one understands how the hippocampus encodes information. So the team simply copied its behavior. Slices of rat hippocampus were stimulated with electrical signals, millions of times over, until they could be sure which electrical input produces a corresponding output. Putting the information from various slices together gave the team a mathematical model of the entire hippocampus.” This is clearly a journalistic oversimplification, but the chip designers’ paper [1] seems to describe the process in more detail, and they’re definitely using a learning technique to learn the I/O mapping of the hippocampus, but since the hippocampus learns, i.e. changes it’s I/O behavior in response to input, I don’t know how they can learn a model of it this way.

[1] Tsai RH, Sheu BJ, Berger TW. A VLSI neural network processor based on a model of the hippocampus. Analog Integrated Circuits and Signal Processing 15 (1998).

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