Sunday, May 20, 2007

Is the Brain a Spintronic Device?

Spintronics is a new paradigm of electronics based on the spin degree of freedom of the electron. Either adding the spin degree of freedom to conventional charge-based electronic devices or using the spin alone has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices.

All spintronic devices act according to the simple scheme: (1) information is stored (written) into spins as a particular spin orientation (up or down), (2) the spins, being attached to mobile electrons, carry the information along a wire, and (3) the information is read at a terminal. Spin orientation of conduction electrons survives for a relatively long time (nanoseconds, compared to tens of femtoseconds during which electron momentum decays), which makes spintronic devices particularly attractive for memory storage and magnetic sensors applications, and, potentially for quantum computing where electron spin would represent a bit (called qubit) of information.

Given the incredible intricacies of the brain's ultrastructure and the billions of years it has had to evolve, it is conceivable that the brain may utilize spintronics. Of course, any talk of quantum mechanical effects in the brain is often greeted with scepticism, thanks to the shameless shenanigans of Roger Penrose and Stuart Hameroff involving Bose-Einstein condensates and microtubules. However, there may be a role for quantum mechanical effects in neural computation yet. The 'brain as spintronic device' idea is speculative, but perhaps worth further consideration, bearing in mind that one potential problem with spintronics is whether spin states are stable long enough to be used in neural computation.

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