Friday, December 12, 2008

Diodes made of neurons

There are three distinct positions in the philosophy of the mind of greatest contemporary relevance:

1) Eliminative materialism: The brain exists, but the mind does not.

2) Identity theory: The mind and the brain both exist, but the mind can be reduced to the brain in the specific sense that the mind can be identified with the brain.

3) Functionalism: The mind and the brain both exist, and the mind super-
venes on the brain, but the mind cannot be identified with the brain.

Functionalism embraces the notion of substrate-independence, the claim that the mind could supervene upon multiple substrates, of which the brain just happens to be one example; if there are multiple substrates which could support the mind, then one cannot identify the mind with the brain.

The December issue of Nature Physics reports that Ofer Feinerman and colleagues have developed a technique to grow neuronal cell cultures capable of performing any desired computation. By encouraging the self-organization of neuronal networks, Feinerman et al were able to synthesize neuronal diodes, AND gates, and threshold devices. These components are sufficient to assemble any desired logical circuit.

Hence, Feinerman et al appear to have experimentally demonstrated substrate-independence. Diodes, for example, can either be made of neuronal networks, or they can be made of semiconductors.

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