Laptev, D.; (2008) Interaction of motion and perception in continuous attractor representations of position. Doctoral thesis , University of London.

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Abstract

The simple relationship of movement to position via temporal integration helps to explain some of the neural representations of position seen in the mammalian brain, such as the representations of eye-position, and of head-direction and self-location within an environment. The positional information also comes from perception, such as vision, and the two sources need not necessarily agree. I construct neuronal firing rate models (introduced in Chapter 2) that utilize both velocity and visual inputs, and test them against physiological data acquired in situations when the two inputs are put in conflict. I start with a model of the oculomotor system (Chapter 3), in which a visual target and integration of the motion signal play distinct roles. The model represents a continuous attractor, stable and unstable regimes of which are analyzed with the latter found to correspond to different clinical disorders. In Chapters 4 to 6 continuous attractors are used to model hippocampal systems for the representation of the animal's location within its environment. Chapter 4 describes the 'standard' model of the integration of self-motion information to maintain a representation of current location in the firing of hippocampal 'place cells'. I demonstrate the stability and invariance under translation of this representation under the model. Using this model, I then consider how abstracted sensory information concerning environmental location is combined with self-motion information to provide the representation of location (Chapter 5). The model is tested by simulation of experimental data on place cell firing in situations where both types of information are put into conflict. Chapter 6 investigates whether the integration of self-motion and environmental information into a single coherent representation could result from a reciprocal interaction between place cells and the recently discovered 'grid cells' in Entorhinal cortex. In this model, integration of self-motion occurs between grid cells and projections from grid cells to place cells provide the self-motion contribution to place cell firing. Conversely, sensory inputs contribute to place cell firing and projections from place cells to grid cells maintain the stability of grid cell firing relative to the environment. This model is tested against experimental data on both place cell firing and grid cell firing in situations where environmental and self-motion information are put into conflict. Testable predictions for future experimental studies are generated by the model. In Chapter 7 we discuss the relationship of our findings to other related approaches, and their implications for the neural organization of spatial behavior.

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