Using Pt/TiO₂/Ti planar junctions fabricated with micrometre-sized gaps between electrodes, we found that the application of a bias voltage between the electrodes significantly decreased the resistance of the junction. The nanoscopic resistance profile revealed that the electrical stress modified the bulk as well as the contact resistance. Electrostatic force microscopy was used to investigate the charge distribution and its time evolution in local areas scanned by positively biased Pt-coated tips. Comparative investigations of the transport and scanning probe microscopy results suggest that the electrical stress induced a redistribution of ions, which then modified the junctions\'transport characteristics.