Methods: High-density polyimide-based ECoG MEAs with submillimetre recording/stimulation sites were micro-fabricated, using electrodeposited PEDOT-CNT as neural interface material. To manage recording and stimulation, an ad-hoc electronics is introduced. The system is able to acquire, filter and digitalize the signals, perform signal processing algorithms and produce, on the selected electrode, an appropriate stimulation output in real time. Thus, the device is able to perform closed loop algorithms on local electrodes.Results: The ECoG MEAs have a total device thickness as low as 6 μm and adhere tightly to the brain surface. The PEDOT-CNT coating has very low impedance (7.2±2.2 kΩ@ 100Hz for 50μm diameter electrodes), allowing high signal to noise ratio signal recording. It also shows high charge transfer capability (> 30mC/cm 2), enabling high current density stimulation on ultrathin polymeric …