Independent hydraulic positioning for an implantable multi-electrode array

We report on a new hydraulic drive system for a microdrive, which enables the recording of multi-unit activity of waking animals. Our principal motivation for inventing this device was to simplify the task of positioning electrodes, which consumes a considerable amount of time and requires a high level of skill. The microdrive is cylindrical and has a diameter of 23.5 mm, a height of 37 mm, and a weight of 15 g. It allows for up to 22 electrodes, which are arranged on a 0.35 mm grid. The new microdrive is based on hydraulics to reduce its size and to facilitate its construction such as wiring of the electrodes. Fine movement of electrodes is realized by computer-controlled fluid supply system which can control a minimum of 0.004 mm³ amount of fluid. Although in a single-direction movement, each electrode can be positioned at any depth up to approximately 4 mm. The microdrive was evaluated under acute and chronic recording experiments and is shown to be capable of automatically positioning each electrode and successfully recording the neural signals of waking rats.