Researchers at Harvard have taken a new look at how electricity can make neurons fire in the brain. The scientists found some surprising things: if you stick an electrode in the brain and apply current, you don’t just make a small group of neurons fire — many neurons fire a long way away from the electrode. That’s probably because instead of activating the cell bodies of the neurons, their axons fire. Those axons are the wiring of the brain. Your cerebral cortex is something like a big pile of unwound yo-yos — if you stick an electrode into the cortex, you’re much more likely to hit the strings (the axons), and the yo-yo connected to the string can be really far away. So, how will you ever hook up a computer to your brain? This data shows that we need to rethink how to do that with electrical current. If you stick an electrode in one place, neurons in a totally different place will fire. New optogenetic methods (e.g. using viral delivery of proteins) might work. Or possibly we will figure out how to make the brain learn to interpret these sparse, widespread electrical patterns. New optical techniques have made a dramatic impact on neuroscience recently, and this study uses pulsed-laser-scanning microscopy (two-photon microscopy) to take pictures of neurons deep inside the living brain. The academic paper (PDF) is available on the author’s site.