Differential Information Processing by Hippocampal and Subicular Neurons

Abstract: It has been known for some years that hippocampal neurons are critically involved in processing of information necessary for encoding memories. What is less understood is the role of the subiculum in this process. We describe here differential response characteristics of subicular and hippocampal neurons in rats during execution of a delayed‐nonmatch‐to‐sample short‐term memory task. Subicular neurons, unlike hippocampal neurons, fire primarily in the delay interval of the task and appear to provide a temporal linkage between events encoded in hippocampus during the sample and nonmatch phases. Indeed, a large proportion of subicular neurons fire robustly for the entire duration of the delay only. Further analyses using electrical activation methods indicate that subicular neurons that receive short latency inputs from the anterior thalamus and do not project to cingulate cortex are the most responsive to stimuli with behavioral significance.

[1]  M P Witter,et al.  The subiculum: cytoarchitectonically a simple structure, but hodologically complex. , 1990, Progress in brain research.

[2]  R E Hampson,et al.  Hippocampal ensemble activity during spatial delayed-nonmatch-to-sample performance in rats , 1996, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[3]  H. Eichenbaum,et al.  Memory Representation within the Parahippocampal Region , 1997, The Journal of Neuroscience.

[4]  Teuvo Kohonen,et al.  Where the abstract feature maps of the brain might come from , 1999, Trends in Neurosciences.

[5]  D. Finch,et al.  Functional reciprocal connections of the rat entorhinal cortex and subicular complex with the medial frontal cortex: an in vivo intracellular study , 1990, Brain Research.

[6]  R. Hampson,et al.  The significance of neural ensemble codes during behavior and cognition. , 1997, Annual review of neuroscience.

[7]  S A Deadwyler,et al.  Behavioral functions and hippocampal cell types: evidence for two nonoverlapping populations in the rat. , 1986, Journal of neurophysiology.

[8]  H. Eichenbaum,et al.  Neuronal activity in the hippocampus during delayed non‐match to sample performance in rats: Evidence for hippocampal processing in recognition memory , 1992, Hippocampus.

[9]  D. Amaral,et al.  Organization of CA1 projections to the subiculum: A PHA‐L analysis in the rat , 1991, Hippocampus.

[10]  M P Witter,et al.  The organization of the reciprocal connections between the subiculum and the entorhinal cortex in the cat: I. A neuroanatomical tracing study , 1986, The Journal of comparative neurology.

[11]  E. Kang,et al.  Hippocampal modulation of cingulo‐thalamic neuronal activity and discriminative avoidance learning in rabbits , 1998, Hippocampus.

[12]  J. J. Hopfield,et al.  Pattern recognition computation using action potential timing for stimulus representation , 1995, Nature.

[13]  M. Witter,et al.  Subicular efferents are organized mostly as parallel projections: A double‐labeling, retrograde‐tracing study in the rat , 1998, The Journal of comparative neurology.

[14]  S M O'Mara,et al.  The projection from hippocampal area CA1 to the subiculum sustains long‐term potentiation , 1998, Neuroreport.

[15]  T. Kaneko,et al.  Direct projections from the entorhinal cortical layers to the dentate gyrus, hippocampus, and subicular complex in the cat , 1998, Neuroscience Research.

[16]  Robert E. Hampson,et al.  Distribution of spatial and nonspatial information in dorsal hippocampus , 1999, Nature.

[17]  H Eichenbaum,et al.  Thinking about brain cell assemblies. , 1993, Science.

[18]  T. Gloveli,et al.  The perforant path projection from the medial entorhinal cortex layer III to the subiculum in the rat combined hippocampal–entorhinal cortex slice , 1998, The European journal of neuroscience.

[19]  H. Eichenbaum,et al.  Two functional components of the hippocampal memory system , 1994, Behavioral and Brain Sciences.

[20]  D. Gaffan,et al.  Delayed Matching by Fornix-Transected Monkeys: The Sample, the Push and the Bait , 1984, The Quarterly journal of experimental psychology. B, Comparative and physiological psychology.

[21]  M. Stewart.  Antidromic and orthodromic responses by subicular neurons in rat brain slices , 1997, Brain Research.

[22]  H. Niki,et al.  Hippocampal unit activity and delayed response in the monkey , 1985, Brain Research.

[23]  M. Cassell,et al.  Perirhinal cortex projections to the amygdaloid complex and hippocampal formation in the rat , 1999, The Journal of comparative neurology.

[24]  S. Deadwyler,et al.  Control of sensory activation of granule cells in the fascia dentata by extrinsic afferents: septal and entorhinal inputs , 1988, The Journal of neuroscience : the official journal of the Society for Neuroscience.