A brain structure involved in episodic memory and spatial processing. In computational accounts, dentate gyrus input transformation, recurrent hippocampal CA3 processing and hippocampal CA1 output processing supply complementary operations; these assignments are hypotheses constrained by recordings and interventions.
Hippocampus circuitry drawn by Santiago Ramón y Cajal, 1911
. Historical drawing of the rodent hippocampus by Santiago Ramón y Cajal, attributed on Commons to his Histologie du Système nerveux de l'Homme et des Vertébrés, Paris: A. Maloine, 1911. Public domain under the life-plus-70-year term recorded on Commons. This is an anatomical illustration, rather than a recording of episodic memory. Source usage terms. Source.
Reactivation of representations associated with experience during pauses or sleep, sometimes as temporally compressed sequences. Ensemble coactivation, sequence replay, prospective simulation and transfer to cortex are related but distinct claims and require different evidence. Early sleep recordings demonstrated experience-related coactivity rather than every one of these properties.[ref]
Reactivation of hippocampal ensemble memories during sleep by Matthew A. Wilson and others. Abstract; Science 265, pp. 676–679, place-cell coactivation before and after spatial experience
Generation of new neurons in the adult hippocampal dentate region. Whether it mediates a particular drug effect depends on species, age, task and intervention; a rodent dependency does not prove a universal human clinical mechanism.
A brief coordinated hippocampal population event with a sharp-wave component and fast ripple oscillation. Such events occur in quiet waking as well as sleep, so effects of their disruption cannot automatically be assigned to sleep alone.
A circuit-level hypothesis combining sparse input coding and pattern separation in the dentate gyrus, recurrent autoassociation in hippocampal CA3, and learned pattern association through hippocampal outputs. It explains a route from an incomplete cue to reinstated event content. Context, event order, interference and changing cortical dependence remain requirements beyond a simple fixed-point memory.
A hippocampal input structure with sparse granule-cell activity. Expansion and synaptic competition can reduce overlap between similar inputs, motivating its role in pattern separation. Input and output population comparisons test that computation more directly than firing-rate differences alone.
A hippocampal subfield receiving both CA3 and entorhinal input and contributing to hippocampal output. Heteroassociative memory models assign learned transformations to its converging inputs and outputs, but a computational role requires more evidence than anatomical resemblance.
A hippocampal subfield with recurrent collateral connectivity, motivating autoassociative memory accounts of pattern completion. Its computations also depend on the input conditions, inhibition and synaptic plasticity; it is not exclusively a retrieval circuit.
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