New and Distinct Hippocampal Place Codes Are Generated in a New Environment during Septal Inactivation

• Published in: Neuron (Cambridge, Mass.) Vol. 82; no. 4; pp. 789 - 796
• Main Authors: Brandon, Mark P., Koenig, Julie, Leutgeb, Jill K., Leutgeb, Stefan
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 21.05.2014; Elsevier Limited
• Subjects: Action Potentials - physiology; Animals; Brain Mapping; Codes; Conditioning, Operant - physiology; Environment; Exploratory Behavior - physiology; GABA-A Receptor Agonists - pharmacology; Hippocampus - cytology; Hypotheses; Male; Muscimol - pharmacology; Neural Pathways - drug effects; Neural Pathways - physiology; Rats; Rats, Long-Evans; Rodents; Septum of Brain - drug effects; Septum of Brain - physiology; Space Perception - physiology; Statistics, Nonparametric
• ISSN: 0896-6273; 1097-4199
• DOI: 10.1016/j.neuron.2014.04.013

The hippocampus generates distinct neural codes to disambiguate similar experiences, a process thought to underlie episodic memory function. Entorhinal grid cells provide a prominent spatial signal to hippocampus, and changes in their firing pattern could thus generate a distinct spatial code in each context. We examined whether we would preclude the emergence of new spatial representations in a novel environment during muscimol inactivation of the medial septal area, a manipulation known to disrupt theta oscillations and grid cell firing. We found that new, highly distinct configurations of place fields emerged immediately and remained stable during the septal inactivation. The new place code persisted when theta oscillations had recovered. Theta rhythmicity and feedforward input from grid cell networks were thus not required to generate new spatial representations in the hippocampus. [Display omitted] •Septal inactivation reduced theta power in hippocampus and entorhinal cortex•Theta power was reduced to levels that are known to disrupt entorhinal grid cells•Intact hippocampal place fields appear in a new room during the septal inactivation•The newly established place fields are retained after recovery from inactivation Pharmacological inactivation of the medial septal area is known to disrupt the spatial firing patterns of grid cells. Brandon et al. demonstrate that hippocampal neurons generate distinct and stable spatial firing patterns in a novel room during septal inactivation.