title: Specific responses of human hippocampal neurons are associated with better memory.
abstract: A population of human hippocampal neurons has shown responses to individual concepts (e.g., Jennifer Aniston) that generalize to different instances of the concept. However, recordings from the rodent hippocampus suggest an important function of these neurons is their ability to discriminate overlapping representations, or pattern separate, a process that may facilitate discrimination of similar events for successful memory. In the current study, we explored whether human hippocampal neurons can also demonstrate the ability to discriminate between overlapping representations and whether this selectivity could be directly related to memory performance. We show that among medial temporal lobe (MTL) neurons, certain populations of neurons are selective for a previously studied (target) image in that they show a significant decrease in firing rate to very similar (lure) images. We found that a greater proportion of these neurons can be found in the hippocampus compared with other MTL regions, and that memory for individual items is correlated to the degree of selectivity of hippocampal neurons responsive to those items. Moreover, a greater proportion of hippocampal neurons showed selective firing for target images in good compared with poor performers, with overall memory performance correlated with hippocampal selectivity. In contrast, selectivity in other MTL regions was not associated with memory performance. These findings show that a substantial proportion of human hippocampal neurons encode specific memories that support the discrimination of overlapping representations. These results also provide previously unidentified evidence consistent with a unique role of the human hippocampus in orthogonalization of representations in declarative memory.
authors.affiliation: Department of Neurosurgery, David Geffen School of Medicine and Semel Institute For Neuroscience and Human Behavior, University of California, Los Angeles, CA 90095; Department of Psychiatry and Biobehavioral Sciences, Semel Institute, University of California, Los Angeles, CA 90095; nanthia@g.ucla.edu ifried@mednet.ucla.edu.
authors.forename: Nanthia A
authors.initials: NA
authors.lastname: Suthana
authors.affiliation: Department of Neurosurgery, David Geffen School of Medicine and Semel Institute For Neuroscience and Human Behavior, University of California, Los Angeles, CA 90095;
authors.forename: Neelroop N
authors.initials: NN
authors.lastname: Parikshak
authors.affiliation: Center For Neuroscience and Department of Psychology, University of California, Davis, CA 95616;
authors.forename: Arne D
authors.initials: AD
authors.lastname: Ekstrom
authors.affiliation: Department of Engineering and Centre for Systems Neuroscience, University of Leicester, Leicester LE1 7RH, United Kingdom;
authors.forename: Matias J
authors.identifier: http://orcid.org/0000-0003-2937-8069
authors.initials: MJ
authors.lastname: Ison
authors.affiliation: Department of Psychology, University of California, Los Angeles, CA 90095; and.
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Knowlton
authors.affiliation: Department of Psychiatry and Biobehavioral Sciences, Semel Institute, University of California, Los Angeles, CA 90095; Department of Psychology, University of California, Los Angeles, CA 90095; and.
authors.forename: Susan Y
authors.initials: SY
authors.lastname: Bookheimer
authors.affiliation: Department of Neurosurgery, David Geffen School of Medicine and Semel Institute For Neuroscience and Human Behavior, University of California, Los Angeles, CA 90095; Functional Neurosurgery Unit, Tel-Aviv Medical Center and Sackler School of Medicine, Tel-Aviv University, Tel-Aviv 69978, Israel nanthia@g.ucla.edu ifried@mednet.ucla.edu.
authors.forename: Itzhak
authors.initials: I
authors.lastname: Fried
mesh_terms: D000328:Adult; D001519:Behavior; D001931:Brain Mapping; D004566:Electrodes; D004594:Electrophysiology; D005145:Face; D005260:Female; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D006801:Humans; D007858:Learning; D008297:Male; D008568:Memory / Q000502:physiology*; D008875:Middle Aged; D009474:Neurons / Q000502:physiology*; D009483:Neuropsychological Tests; D010775:Photic Stimulation; D011897:Random Allocation; D021641:Recognition, Psychology; D015203:Reproducibility of Results; D013702:Temporal Lobe / Q000502:physiology; D055815:Young Adult
keywords: discrimination; hippocampus; invariance; memory; selectivity