The ultimate goal of neuroscience is to understand the neural basis of subjective experience and behaviour. With our discovery of grid cells as the brain´s metric for space in 2005, spatial navigation became one of the first non-sensory ‘cognitive’ functions of the brain to be accessible for mechanistic analysis. Grid cells are cells with spatially localized firing fields that tile environments with a periodic hexagonal firing pattern in a manner that enables accurate self-localization. Because this activity matrix is generated in the brain, in elaborate neural circuits far away from specific sensory inputs, grid cells provide us with unprecedented access to algorithms of neural coding in the higher cortices. The present proposal will take advantage of this emerging opportunity. The overall objective is to decipher how function is coded, divided and integrated among components of the grid-cell circuit of the medial entorhinal cortex and associated regions. Using a combination of transgenic interventions, intracellular recording and multisite multichannel tetrode recording, we shall establish the mechanisms by which grid cells organize into functionally independent modules, as well as the factors specifying quantitative relationships between grid modules. We shall determine how grid modules are formed during development, test the hypothesis that grid patterns are derived from the local recurrent inhibitory network in layer II, and establish how spatial signals in the entorhinal cortex are transformed to place-cell signals in the hippocampus. Collectively, these studies will pioneer the understanding of functional organization and neural-circuit coding in a non-sensory non-motor mammalian cortex.