Final Report Summary - DEVSPACE (The development of the hippocampal spatial representation system)
The research funded by this grant has studied the early post-natal development of the neural map of space (or ‘cognitive map’) in the hippocampal formation. We have uncovered, for the first time, which aspects of cognitive map development depend on sensory experience, and which aspects proceed independently of sensory input. We have also tracked how the sensory modalities supporting spatial cognition change over development. We have shown that early in development, place cells (which code for an animal’s current position) provide stable and accurate spatial signalling only when close to the boundaries of an environment, whereas later in life the place cell map becomes accurate throughout space. This developmental switch in place cell accuracy coincides with the emergence of grid cells, a finding which is consistent with grid cells’ putative role in providing an accurate distance metric for the cognitive map. We looked for how proximity to boundaries could be signalled in the developing brain, and found evidence for the presence of neurons responsive to barriers to movement, in 2-3 week old pups. We studied the development of Head Direction (HD) cells, which code for the current heading orientation of the animal, providing a neural ‘compass’ for the cognitive map. We found that HD cells are foundational to other spatial signals in the brain, emerging before all others. HD cells emerge before eye-opening, meaning that they do not need access to visual information in order to develop. Instead, local non-visual cues (e.g. touch or odour cues) can provide the necessary input for stable and accurate directional signalling, before vision emerges. We have also found evidence that the internal structure (the connectivity between neurons) of the HD cell network is present even before any stable directional signalling can be observed, suggesting that network architecture of this brain circuit is assembled independently of an instructive external sensory input.