Hippocampal place fields: relationship between degree of field overlap and cross-correlations within ensembles of hippocampal neurons.
The capacity to record from multiple neurons in awake freely moving animals provides a means for characterizing organizational principles of place field encoding within ensembles of hippocampal neurons. In this study, cross-correlations between pairs of hippocampal place cells and degree of overlap between their respective place fields were analyzed during behavioral performance of delayed matching (DMS) or non-matching sample (DNMS) tasks, or while the same rats chased pellets in a different environment. The relationship between field overlap and cross-correlations of neural spike activity within ensembles was shown to be a positive, exponentially increasing, function. Place fields from the same neurons were markedly "remapped" between the Delay and Pellet-chasing tasks, with respect to physical location and size of fields. However individual pairs of place cells within each ensemble retained nearly the same degree of overlap and cross-correlation even though the spatial environment and the tasks differed markedly. This suggested that place cells were organized in functional "clusters" which exhibited the same inter-relations with respect to place field overlap and cross-correlations, irrespective of actual field of location. When cross-correlations between place cells were compared to placement of the array recording electrodes within the hippocampus, the strongest correlations were found along previously defined posterior-projecting fiber gradients between CA3 and CA1 subfields (Ishizuka et al. [1990], J Comp Neurol 295:580-623; Li et al. [1994] (J Comp Neurol 339:181-208). These findings suggest that the functional organization of place fields conforms to anatomical principles suspected to operate within hippocampal ensembles.
Hampson
R E
RE
Department of Physiology and Pharmacology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27157-1083, USA.
Byrd
D R
DR
Konstantopoulos
J K
JK
Bunn
T
T
Deadwyler
S A
SA
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001931:Brain Mapping; D002450:Cell Communication / Q000502:physiology; D004567:Electrodes, Implanted; D004594:Electrophysiology; D006624:Hippocampus / Q000166:cytology* / Q000502:physiology*; D008297:Male; D009474:Neurons / Q000502:physiology*; D009949:Orientation / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013028:Space Perception / Q000502:physiology; D014743:Videotape Recording