Abstract

How do we learn and know? For much of my career it was assumed that neurons respond to external stimuli as if to represent them, but an equally plausible model asserts that neuronal activity is fundamentally internally-organized and instead fit to external features. I will report on our investigations of acquired cognition through studies of spatially-tuned cells in the medial entorhinal cortex and hippocampus. We started with the “noise,” uncertainty of spatially tuned action potential discharge, a clue that cognitive variables might be in that noise. I’ll then discuss the discharge of head-direction cells in the medial entorhinal cortex, which remain internally-organized during navigation, despite their apparent loss of directional tuning to external features. We will then briefly consider how cognitive control training causes learning to learn and persistently altered information processing across synaptic populations of the entorhinal-hippocampal system. Finally, I will discuss recent studies of the remapping phenomenon, in which place fields rearrange according to cell-specific rules when the environment changes. A number of observations challenge the concept of remapping, suggesting instead that hippocampal neural activity is fundamentally internally-organized such that cofiring relationships amongst the cells are largely invariant across distinct environments, despite the cell-specific rearrangement of place fields. Collectively these studies promote a view that rather than represent external information, subjective, internally-organized activity in the entorhinal-hippocampal circuit is actively fit to the environment for processing information that enables navigation and serves cognition.