title: Speed modulation of hippocampal theta frequency correlates with spatial memory performance.
abstract: Hippocampal theta rhythm is believed to play a critical role in learning and memory. In animal models of temporal lobe epilepsy (TLE), there is evidence that alterations of hippocampal theta oscillations are involved in the cognitive impairments observed in this model. However, hippocampal theta frequency and amplitude at both the local field potential (LFP) and single unit level are strongly modulated by running speed, suggesting that the integration of locomotor information into memory processes may also be critical for hippocampal processing. Here, we investigate whether hippocampal speed-theta integration influences spatial memory and whether it could account for the memory deficits observed in TLE rats. LFPs were recorded in both Control (CTR) and TLE rats as they were trained in a spatial alternation task. TLE rats required more training sessions to perform the task at CTR levels. Both theta frequency and power were significantly lower in the TLE group. In addition, speed/theta frequency correlation coefficients and regression slopes varied from session to session and were worse in TLE. Importantly, there was a strong relationship between speed/theta frequency parameters and performance. Our analyses reveal that speed/theta frequency correlation with performance cannot merely be explained by the direct influence of speed on behavior. Therefore, variations in the coordination of theta frequency with speed may participate in learning and memory processes. Impairments of this function could explain at least partially memory deficits in epilepsy.
authors.affiliation: Department of Neurology, Geisel School of Medicine, Hanover, New Hampshire.
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Richard
authors.forename: Ali
authors.initials: A
authors.lastname: Titiz
authors.forename: Anna
authors.initials: A
authors.lastname: Tyler
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Holmes
authors.forename: Rod C
authors.initials: RC
authors.lastname: Scott
authors.forename: Pierre-Pascal
authors.initials: PP
authors.lastname: Lenck-Santini
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D004567:Electrodes, Implanted; D004569:Electroencephalography; D004833:Epilepsy, Temporal Lobe / Q000139:chemically induced / Q000150:complications; D005508:Food Deprivation; D006624:Hippocampus / Q000503:physiopathology*; D018021:Lithium Chloride / Q000633:toxicity; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology; D008569:Memory Disorders / Q000209:etiology / Q000473:pathology*; D018721:Muscarinic Agonists / Q000633:toxicity; D010862:Pilocarpine / Q000633:toxicity; D051381:Rats; D017207:Rats, Sprague-Dawley; D013028:Space Perception / Q000187:drug effects / Q000502:physiology*; D013826:Theta Rhythm / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
chemical_list: D018721:Muscarinic Agonists; D010862:Pilocarpine; D018021:Lithium Chloride
keywords: Hippocampus; epilepsy; local field potentials; spatial alternation; theta rhythm