A transition microelectrode (108) can include a micro well array (104) having a plurality of microwells. The transition microelectrode (108) can further include a plurality of neuronal soma oriented within the plurality of microwells. A bioerodible probe guide (106) can be oriented over the microwell array (104). An electrode (103) can be electrically connected with the plurality of microwells. A transition microelectrode array (116) can include an electrode array having a plurality of the transition microelectrodes (108).