A split microdrive for simultaneous multi-electrode recordings from two brain areas in awake small animals.

Complex cognitive operations such as memory formation and decision-making are thought to be mediated not by single, isolated brain structures but by multiple, connected brain areas. To facilitate studies on the neural communication between connected brain structures, we developed a multi-electrode microdrive for chronically recording ensembles of neurons in two different brain areas simultaneously. The "split drive" contains 14 independently movable microdrivers that were designed to hold tetrodes and to permit day-to-day adjustment of dorsoventral position in the brain. The limited weight of the drive allowed rats to adjust well to the headstage after recovering from surgery and permitted stable recording sessions across at least several weeks. In addition to describing the design and assembly of the split drive, we also discuss some important individual parts of microdrives used for tetrode recordings in general. Furthermore, the split drive was applied to two widely separated and connected brain structures, the hippocampus and ventral striatum. From these two areas, stable ensemble recordings were conducted in rats performing a reward-searching task on a triangular track, yielding group sizes of about 15 and 25 units in the dorsal hippocampus and ventral striatum, respectively.