A recent news release reveals that Elisha Moses and other researchers from the Physics of Complex Systems group at the Weizmann Institute have created functional logical microcircuits from living neuron cells grown in a geometrical design. So far, they've created AND gates, diodes (pictured above), and a threshold device that passes only signals whose strength exceeds a preset limit. The researchers are pulling this off by coaxing nerves to grow along tiny grooves etches in glass. They've also developed a way of triggering the neurons with magnetic fields rather than direct electrical stimulation. What's really interesting is that they've gotten so good at making these neuronal devices, that they'll grow and test a custom design submitted by you. Moses had this to say about the project:

We have been able to enforce simplicity on an inherently complicated system. Now we can ask, ‘What do nerve cells grown in culture require in order to be able to carry out complex calculations?’ As we find answers, we get closer to understanding the conditions needed for creating a synthetic, many-neuron ‘thinking’ apparatus.

It will be interesting to see if the "only brains made of meat can be conscious" crowd are willing to accept the idea of a meat-brained robot. For more information on the research, see the group's web page, Logic Devices from Neuronal Cultures. They've just published a research paper with all the details in Nature, Reliable neuronal logic devices from patterned hippocampal cultures. If you don't want to pay Nature $30, you can find some of the details in their supplementary information document (PDF format).