Lesions of the Postsubiculum Disrupt Path Integration
Previous research has shown that the postsubiculum (PoS) is involved in allocentric spatial navigation. Indeed, rats with PoS lesions were severely impaired in the Morris water maze and radial arm maze tasks, suggesting that this region is necessary for accurate orientation in allocentric space. In addition, electrophysiological recordings have revealed that the PoS contains two types of spatially tuned neurons - head direction (HD) cells and grid cells. Further, a study that coupled PoS lesions and recording of HD cells in anterodorsal thalamus showed the importance of this region in visual landmark control over the HD signal. Indeed, HD cells in lesioned animals showed a dramatic reduction in their ability to follow a salient visual cue when it was rotated. This result suggested that the PoS conveys visual information into the HD circuit and maintains the stability of the system in allocentric space. The afferent connections of the PoS (visual cortex, retrospenial cortex, the anterior and laterodorsal thalamic nuclei) make it a good candidate for an interface between the HD signal and visual information, but we wanted to determine whether the PoS also plays an important role in processing idiothetic information. We therefore used a path integration task where animals did not rely on visual cues for performance, but needed to rely on self-motion cues to continuously update their orientation. The PoS of female Long-evans rats was neurotoxically lesioned bilaterally and the animals were then tested in two versions of the food hoarding task: (i) in light conditions, the animals could use visual cues for orientation and return accurately to the refuge, (ii) in dark conditions, they had to path integrate in order to perform the task. Both groups were able to learn the task in a similar amount of training session. As expected, in the light condition, PoS lesioned animals (n = 7) were significantly impaired compared to sham lesioned controls (n = 6), in all our accuracy measures (heading error, number of errors). Importantly, PoS lesion rats were also impaired in the dark condition, which required them to return to the refuge using a path integration strategy. These results confirm the importance of PoS in navigation based on visual cues, but also show that the PoS is necessary for accurate path integration. It further indicates that the role of the PoS is not restricted to the visual modality, but may play a more general role in maintaining the stability of spatial representations, which is necessary for both visual allocentric navigation and in path integration.
Biological Psychology | Psychology
Stephane Valerio, Benjamin J. Clark, Ryan M. Yoder, and Jeffrey S. Taube (2011).
Lesions of the Postsubiculum Disrupt Path Integration. Presented at Neuroscience 2011, Washington, DC.