Our research is focused on the neural representation of space that is contained within the hippocampal formation. These neural ‘maps’ support the ability of organisms to locate themselves in an environment, and navigate to a goal. They are based on at least four types spatially-tuned neuron: place cells, which code for location; head direction cells, which code for orientation; grid cells, which use a regular hexagonal ‘grid’ of firing to estimate distance travelled; and boundary-responsive cells, which signal the presence of a barrier to movement. Collectively, these spatially-tuned neurons constitute the necessary elements for a map of space.
The aspects of hippocampal function that we are currently investigating include:
1) The emergence of the hippocampal map of space during post-natal development.
Together with Dr Francesca Cacucci (UCL Dept of Neuroscience, Physiology and Pharmacology), we recently published the first study charting the emergence of spatially-tuned neurons during post-natal development (Wills, Cacucci et al. Science, 2010). The questions we are currently investigating include:
- As grid cells are the last spatial neurons to develop (contrary to previous theoretical models), what supports place cell firing at early ages? Which sensory inputs are necessary? Do other spatially-tuned neurons drive place cell firing early in development? (See Muessig et al, 2015, Neuron).
- What is the role of experience and sensory input in the development of the neural map of space? Are there any internal processes that are experience-independent?
- We also use our data to inform theoretical models of neural circuit development. For example, how do head-direction cells develop in the absence of visual information (see Tan, Bassett et al, 2015, Curr Biol)?
2) Place cells as a spatial memory system: how are memory networks formed, in adulthood and in development?
Since the famous case of Henry Molaison (‘patient H.M.’), who became severely amnesic after bilateral surgical removal of his medial temporal lobes, much research has been directed at understanding the role of the hippocampus in long-term memory. We are interested in how place cells encode spatial memory, with the aim of also understanding more general memory encoding in the hippocampus. Topics of research include:
- Are memories stored as attractor states in hippocampal activity (see Wills et al, 2005, Science)? If so, how are these attractor networks created? We are currently investigating the role of neural activity and Hebbian plasticity using in vivo optogenetic stimulation and inhibition of place cells.
- How do memory networks emerge in post-natal development? Do place cells encode long-term memories in early development, and can they serve as a model for infantile amnesia?