Linking neurons and behaviour: The parietal window hypothesis of spatial memory..

Evidence from both behavioural and electrophysiological experiments in animals and humans demonstrates the existence of world-centered (allocentric) and viewer-centered (egocentric) representations of space in the brain.  At the neural level, allocentric representations tend to be associated with the medial temporal lobes and, hence, long-term memory, while egocentric representations tend to be associated with posterior parietal cortex and are often of a more transient nature.  How the neural populations that support these different representations of space interact to allow the brain to generate adaptive behaviour is not well-understood.  For the case of long-term spatial memory, I will propose that the layouts of familiar environments are encoded as allocentric representations in the medial temporal lobes and that these stored representations are accessible only via a limited egocentric ``window´´ supported by circuitry of the posterior parietal cortex.  I will support this claim by presenting a neural network model of medial temporal-posterior parietal circuitry based upon this ``window´´ principle.  The model, which is constrained by neuroanatomical and electrophysiological data, is able to explain experimental findings at both the behavioural and neural levels.  At the core of this long-term memory model is a hand set neural circuit that transforms between egocentric and allocentric representations.  I will also present principles that might underlie the learning of such a transformation ability, along with modeling work which demonstrates that these principles can lead naturally to the learning of place cell responses under certain circumstances.