A model of hippocampal-parietal interaction in spatial navigation, imagery and episodic recall.

Allen Cheung(1), Suzanna Becker (2) and Neil Burgess (1)
1:Department of Anatomy and Institute of Cognitive Neuroscience, UCL
2:Department of Psychology, McMaster University

We present a computational model of the neural mechanisms in the parietal and temporal lobes that support spatial navigation, imagery, and episodic recall. Long term representations are stored in the hippocampus and associated with object and texture information in the surrounding medial temporal lobe. Translation into a viewpoint-dependent representation occurs in parietal cortex to enable construction of an imagined retinotopic scene and generation of appropriate body movements. This model allows recall and imagery of locations and objects and selection of the appropriate direction of movement in complex environments. The model can execute simple navigational planning strategies by either heading directly for the goal, or by searching for the next best direction to get around obstacles. Imagined movement through a familiar environment can occur in our model by shifting activations on the egocentric parietal map in a stereotyped way analogous to optic flow, using hard-wired connections that are gated by the movement signal; if the movement is a large advance, use of the temporal module is then required to fill in the locations of new objects that may be brought into view. Finally, by damaging part of the parietal model, we have simulated hemispatial neglect in mental imagery that rotates with the imagined perspective of the observer, as in the famous Milan Square experiment reported by Bisiach and Luzatti (1978). Acknowledgements: NB is a Royal Society University Research Fellow. This work was supported by a research grant from the MRC to NB and a research grant from NSERC, Canada to SB.

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