What is the function of the human retrosplenial cortex?

The retrosplenial cortex (RSC) comprises Brodmann areas 29/30 and is an integral part of a brain system that is engaged by spatial navigation, scene processing, recollection of the past and imagining the future. Damage involving the RSC in humans can result in significant memory and navigation deficits, while the earliest metabolic decline in Alzheimer's disease is centred upon this region. The precise function of the RSC, however, remains elusive. In this thesis I sought to determine the key contribution of the RSC in a series of six studies that each comprised behavioural and functional magnetic resonance imaging (fMRI) experiments. Specifically, I discovered that the RSC is acutely responsive to landmarks in the environment that maintain a fixed, permanent location in space, and moreover is sensitive to the exact number of permanent landmarks in view. Using a virtual reality environment populated with entirely novel ‘alien’ landmarks I then tracked the de novo acquisition of landmark knowledge and observed the selective engagement of the RSC as information about landmark permanence accrued. In three further studies I established the parameters within which the RSC operates by contrasting permanent landmarks in largeand small-scale space, by comparing landmark permanence with orientation value, and by investigating permanence in non-spatial domains. In parallel lines of inquiry, I uncovered evidence that a fully functional RSC may be a prerequisite for successful navigation, while also characterising RSC interactions with other brain regions, such as the hippocampus, that could have importance for constructing reliable representations of the world. Together my findings provide new insights into the role of the RSC in a range of cognitive functions. The RSC’s processing of permanent predictable features may represent a key building block for spatial and scene representations that are central to navigation, recalling past experiences and imagining the future. What is the function of the human retrosplenial cortex? Acknowledgements 4