Of maps and grids

Abstract

Neuroscience has made remarkable advances in accounting for how the brain performs its various functions. Consciousness, too, is usually approached in functional terms: the goal is to understand how the brain represents information, accesses that information, and acts on it. While useful for prediction, this functional, information-processing approach leaves out the subjective structure of experience: it does not account for how experience feels. Here, we consider a simple model of how a "grid-like"network meant to resemble posterior cortical areas can represent spatial information and act on it to perform a simple "fixation"function. Using standard neuroscience tools, we show how the model represents topographically the retinal position of a stimulus and triggers eye muscles to fixate or follow it. Encoding, decoding, and tuning functions of model units illustrate the working of the model in a way that fully explains what the model does. However, these functional properties have nothing to say about the fact that a human fixating a stimulus would also "see"it - experience it at a location in space. Using the tools of Integrated Information Theory, we then show how the subjective properties of experienced space - its extendedness - can be accounted for in objective, neuroscientific terms by the "cause-effect structure"specified by the grid-like cortical area. By contrast, a "map-like"network without lateral connections, meant to resemble a pretectal circuit, is functionally equivalent to the grid-like system with respect to representation, action, and fixation but cannot account for the phenomenal properties of space.