Gamma Oscillations in Rat Hippocampal Subregions Dentate Gyrus, CA3, CA1, and Subiculum Underlie Associative Memory Encoding

• Published in: Cell reports (Cambridge) Vol. 21; no. 9; pp. 2419 - 2432
• Main Authors: Trimper, John B., Galloway, Claire R., Jones, Andrew C., Mandi, Kaavya, Manns, Joseph R.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 28-11-2017; Elsevier
• Subjects: CA1; CA3; dentate gyrus; electrophysiology; gamma oscillations; hippocampus; memory; object; subiculum; synchrony; dentate gyrus; CA1; memory; hippocampus; electrophysiology; CA3; gamma oscillations; subiculum; synchrony; object
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2017.10.123

Neuronal oscillations in the rat hippocampus relate to both memory and locomotion, raising the question of how these cognitive and behavioral correlates interact to determine the oscillatory network state of this region. Here, rats freely locomoted while performing an object-location task designed to test hippocampus-dependent spatial associative memory. Rhythmic activity in theta, beta, slow gamma, and fast gamma frequency ranges were observed in both action potentials and local field potentials (LFPs) across four main hippocampal subregions. Several patterns of LFP oscillations corresponded to overt behavior (e.g., increased dentate gyrus-CA3 beta coherence during stationary moments and CA1-subiculum theta coherence during locomotion). In comparison, slow gamma (∼40 Hz) oscillations throughout the hippocampus related most specifically to object-location associative memory encoding rather than overt behavior. The results help to untangle how hippocampal oscillations relate to both memory and motion and single out slow gamma oscillations as a distinguishing correlate of spatial associative memory.
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•Slow gamma activity characterized hippocampal LFPs when rats explored objects•Slow gamma increase could not be explained by cessation of locomotion•Slow gamma during familiar object exploration correlated with novelty•Slow gamma during novel object exploration related to subsequent associative memory
Hippocampal local field potentials are modulated by both memory and behavior. Trimper et al. describe how these factors interact to influence the hippocampal network state and demonstrate that slow gamma activity in particular correlates with associative memory encoding.