The contribution of visual and inertial mechanisms to navigation in total darkness

Rats were trained in the Morris water maze to reach a platform in darkness after they had been provided with some information on their initial location. They were given trials with (1) the light on (light condition) and (2) light followed by darkness (dark condition). In this latter condition, the dark period was preceded by either a brief (short group) or a long (long group) initial light period. Although the rats in the short group first oriented accurately toward the platform, their trajectory rapidly deviated in darkness. In contrast, the rats in the long group were able to navigate accurately over a longer distance, but finally also deviated. In transfer trials, the rats in the short group were less accurate than the rats in the long group in the dark; however, both groups performed well in light. This suggests that navigation in darkness depends not only on the use of recent visual and locomotor memory but also on the activation of an inertia-based navigation process.