According to this Wired piece, cyberneticist Kevin Warwick and his researchers at the University of Reading in the UK have transplanted brain cells from rats into robots. The cells are alive and can form new connections, so the bots can apparently learn. That rat-bots have are all able to avoid bumping into walls, but they each exhibit different behavior patterns as real mice would. Spooky and just in time for Halloween! (Thanks to Marginal Revolution.)