"Neuroscience is one of the fastest-developing areas of science, but it is fair to say that we are still far from understanding how the brain produces subjective experience. For example, simple questions about the origin of thought, imagination, social interaction, or feelings lack even rudimentary answers. We have learnt much about the workings of individual cells and synapses, but psychological phenomena cannot be understood only at this level. These phenomena all emerge from interactions between large numbers of diverse cells in intermingled neural circuits. A major obstacle has been the absence of concepts and tools for investigating neural computation at the circuit level. The aim of this proposal is to combine new transgenic methods for cell type-specific intervention with large-scale multisite single-cell recording to determine how a basic cognitive function self-localization is generated in a functionally well-described mammalian neural circuit. We shall use our recent discovery of entorhinal grid cells as an access ramp. Grid cells fire only when the animal moves through certain locations. For each cell, these locations define a periodic triangular array spanning the whole environment. Grid cells co-exist with other entorhinal cell types encoding head direction, geometric borders, or conjunctions of features. This network is thought to form an essential part of the brain s coordinate system for metric navigation but the detailed wiring, the mechanism of grid formation, and the function of each morphological and functional cell type all remain to be determined. We shall address these open questions by measuring how dynamic spatial representation is affected by transgene-induced activation or inactivation of the individual components of the circuit. The endeavour will pioneer the functional analysis of neural circuits and may, perhaps for the first time, provide us with mechanistic insight into a non-sensory cognitive function in the mammalian cortex."