Phase precession and phase-locking of hippocampal pyramidal cells

We propose that the activity patterns of CA3 hippocampal pyramidal cells in freely running rats can be described as a temporal phenomenon, where the t iming of bursts is modulated by the animal's running speed. With this hypot hesis, we explain why pyramidal cells fire in specific spatial locations, a nd how place cells phase-precess with respect to the EEG theta rhythm for r ats running on linear tracks. We are also able to explain why wheel cells p hase-lock with respect to the theta rhythm for rats running in a wheel. Usi ng biophysically minimal models of neurons, we show how the same network of : neurons displays these activity patterns. The different rhythms are the r esult of inhibition being used in different ways by the system. The inhibit ion is produced by anatomically and physiologically diverse types of intern eurons, whose role in controlling the firing patterns of hippocampal cells we analyze. Each firing pattern is characterized by a different set of func tional relationships between network elements. Our analysis suggests a way to understand these functional relationships and transitions between them. Hippocampus 2001;77:204-215. (C) 2001 Wiley-Liss, Inc.