The post-natal development of hippocampal networks for memory and space
Abstract:
The hippocampal formation contains neurons whose firing represents a code for the position and orientation of an animal in space. Collectively, these cells are thought to constitute a neural map of space, or ‘cognitive map’ (Tolman, 1948; O’Keefe & Nadel, 1978), by means of which an animal can remember locations and navigate to goals. O’Keefe & Nadel (1978) suggested that the hippocampal cognitive map may represent a Kantian synthetic a priori system, not requiring extensive experience of space for its construction, which may therefore emerge early during post-natal development. My research aims to uncover how hippocampal systems for memory and representation of space emerge during the course of post-natal development.
I will review work from my laboratory on the development of head direction cells, the first spatial signal to emerge during development. This work describes which sensory inputs drive the head direction cell network during development, and which aspects of network development appear to proceed independently of experience.
The ability to form and recall spatial memories emerge late during development (paralleling the late development of episodic memory in human children). It remains unknown whether the neuronal basis for such amnesia for early life events lies with deficits in encoding, consolidation or retrieval. I will discuss unpublished work describing the emergence of neural mechanisms for hippocampal consolidation: place cell ‘reactivation’ and ‘replay’ during slow-wave sleep, following awake exploration. ‘Replay’ (rapid sequences of place cell activation, tracing out trajectories through recently explored space) emerges late in development, suggesting that an inability to associate sequences of events may underlie the late development of hippocampal memory.