title: Contributions of the hippocampus and entorhinal cortex to rapid visuomotor learning in rhesus monkeys.
abstract: The hippocampus and adjacent structures in the medial temporal lobe are essential for establishing new associative memories. Despite this knowledge, it is not known whether the hippocampus proper is essential for establishing such memories, nor is it known whether adjacent regions like the entorhinal cortex might contribute. To test the contributions of these regions to the formation of new associative memories, we trained rhesus monkeys to rapidly acquire arbitrary visuomotor associations, i.e., associations between visual stimuli and spatially directed actions. We then assessed the effects of reversible inactivations of either the hippocampus (Experiment 1) or entorhinal cortex (Experiment 2) on the within-session rate of learning. For comparison, we also evaluated the effects of the inactivations on performance of problems of the same type that had been well learned prior to any inactivations. We found that inactivation of the entorhinal cortex but not hippocampus produced impairments in acquiring novel arbitrary associations. The impairment did not extend to the familiar, previously established associations. These data indicate that the entorhinal cortex is causally involved in establishing new associations, as opposed to retrieving previously learned associations. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.
authors.affiliation: Section on the Neurobiology of Learning and Memory, Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland.
authors.forename: Tianming
authors.initials: T
authors.lastname: Yang
authors.forename: Rachel L
authors.initials: RL
authors.lastname: Bavley
authors.forename: Kevin
authors.initials: K
authors.lastname: Fomalont
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Blomstrom
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Mitz
authors.forename: Janita
authors.initials: J
authors.lastname: Turchi
authors.forename: Peter H
authors.initials: PH
authors.lastname: Rudebeck
authors.forename: Elisabeth A
authors.initials: EA
authors.lastname: Murray
mesh_terms: D000818:Animals; D001245:Association Learning / Q000502:physiology*; D018728:Entorhinal Cortex / Q000187:drug effects / Q000502:physiology*; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007555:Isoxazoles / Q000494:pharmacology; D008253:Macaca mulatta; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory / Q000502:physiology; D009483:Neuropsychological Tests; D011597:Psychomotor Performance / Q000502:physiology*; D013850:Thinking / Q000502:physiology; D013997:Time Factors; D014796:Visual Perception / Q000502:physiology*
chemical_list: D058785:GABA-A Receptor Agonists; D007555:Isoxazoles; C015542:gaboxadol
keywords: associative learning; fornix transection; medial temporal lobe; temporary inactivation
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