Marr’s influence on the standard model of hippocampus, and the need for more theoretical advances

David Marr’s classic 1971 paper laid the foundation for a standard model of the hippocampus combining pattern separation (Marr’s codon hypothesis) and pattern completion. His paper discusses functions that became components of a standard theoretical model of hippocampal function within the field, and inspired further studies on more detailed analysis of pattern separation in the dentate gyrus and pattern completion by attractor dynamics in region CA3. This theoretical framework has been the focus of a number of experimental tests over the years, including neurophysiological studies of patterns of neuronal activity in behaving rats, tests of behavioural effects with selective genetic manipulations, and fMRI studies of hippocampal activity in humans. This chapter also reviews subsequent research related to the dynamics of pattern completion, as well as subsequent modeling that addressed network dynamics in the hippocampus including theta rhythm oscillations, theta phase precession and the patterns of grid cell firing in entorhinal cortex. Finally, this chapter addresses the need for future breakthroughs by researchers that combine sophisticated mathematical techniques with detailed knowledge of the anatomy and neurophysiology of cortical structures.