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An introduction to entorhinal cortex, its layers and cells present in different layers in addition to a very brief introduction to Grid & Place cells.

An introduction to entorhinal cortex, its layers and cells present in different layers in addition to a very brief introduction to Grid & Place cells.

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EC, grid & place cells EC, grid & place cells Presentation Transcript

  • The Entorhinal cortex, Grid & Place cells Chinmaya Sadangi AG I. Vida & AG D. Schmitz 2013.12.12
  • Outline • Entorhinal cortex – Location & Morphology, Cell types in different layers • Grid & place cells – Brief introduction
  • Entorhinal cortex • EC or the brodman area 28. Lateral area – 28a & medial area 28b • Nodal point between hippocampal formation & association with the cortex • Medial subdivision cells are spatially modulated but absent in LEC. LEC convey olfactory & somatosensory information • Anteriorly, the EC meets with olfactory & amygdaloid cortices & medially it merges with the structures belonging to the hippocampal formation. Laterally it meets the perirhinal cortex.
  • a b a: Ramon Y Cajal b: Cathrin B. Canto et al: What does the anatomical organization of the entorhinal cortex tell us?: Neural plasticity (2008)
  • Layer I • Horizontal cells & Multipolar neurons (MPNs). MPNs • MPN are abundant & non- or sparsely spiny. • Positive for Calretinin (CR) & GABA • Diameter of dendritic tree varies between 100 um to 150 μm • Axons of layer I neurons travel towards layer II & layer III HORIZONTAL CELLS • Horizontal cells present between layers I & II. Spherical to elongated soma of 13 – 15 μm. • Spine free dendrites. • Are GABAergic in LEC and dendritic terminal in MEC stains positive for cholecystokinin
  • Layer II • Densely packed, large & medium sized pyramidal & stellate cells. STELLATE CELLS • Abundant cell type & more common in MEC. • Soma is variable, but characteristic spiny dendritic tree. • Dendritic arbor has multiple, roughly equally sized primary dendrites branching widely. • Thick axon. Gives very thin collaterals, branching repeatedly & reaching superficial layers & colocalizing with entire dendritic tree. • Excitatory using glutamate for transmission & stain CB positive.
  • FAN CELLS • Common in LEC. • Large polygonal soma, with spiny primary dendrites mostly in horizontal & ascending direction. • Differs from stellate cells in MEC as fan cells have small descending dendrites. PYRAMIDAL CELLS • Medium sized triangular or ovoid shaped soma. • Located in deep portion of layer II. • Spiny thick apical dendrite. Basal dendrites are spiny, thin, short & straight with extensive branching.
  • L2S 2010: Prateep Beed: Micro circuitry in the entorhinal cortex L2P
  • • Smooth & thin axons, giving off collaterals & distributing in layers I-III. • Subtype of pyramidal –like cells known as horizontal pyramidal cell located in superficial part of layer II. • Another subtype has thick & sparsely or nonspiny apical dendrite branching in layer II. INTERNEURONS • MPNs, bipolar, basket & chandelier cells. MPNs - polygonal, fusiform or round cell bodies with multiple spiny dendrites reaching layer I and deep into layer III. Axons travel to layer II.
  • • Bipolar cells – Soma located in layer II and border to layer I. Dendrites orient horizontally. Vertical bipolar cells have spindle shaped soma with one ascending & one descending primary dendrite & branch into thinner dendrites. • Fast spiking basket –like cells – small spherical soma, sparsely spiny dendrites projecting to layer I. Axon confined to layer II and form basket –like complex around soma of other cells. Basket cells in whole EC contains PV. • Chandelier cells – vertical aggregations of axonal boutons called candles. Medium sized & variable shaped soma. Nonspiny, poorly ramyfying dendrites stays within layer II/III. Vertically oriented axonal tree. GABAergic, PV – positive cells.
  • Layer III • Spiny & non-spiny pyramidal cells SPINY PYRAMIDAL CELLS (SPCs) • Present in the LEC. • Somata gives rise to prominent apical dendrite that bifurcates, becomes spiny & branches. Axon projects towards the subiculum. NONSPINY PYRAMIDAL CELLS (NSPCs) • Triangular to spherical shaped somata. • Non spiny apical dendrite branches closer to soma & also branches in superficial layers.
  • STELLATE CELLS • Somata are elongated, polygonal or spherical. • Spiny dendrites and dendrites branching in layer I. • Axons forms collaterals in layer III. PRINCIPAL MPN SOMATA • Small & Spherical. Largest located in outer half of layer III. • Cell body is 15-18 um with spiny dendrites branching in all directions. Axons reach the hippocampus. INTERNEURONS RESEMBLING PYRAMIDAL CELLS • Pyramidal looking interneurons (PLI). Also known as type 3-(Gloveli) or type 1-(Kumar) cells. • Pyramidal shaped cell body & non spiny basal & apical dendrites. Dendrites collateral through layer II reaching layer I. Axons extend into layer III.
  • • F 2010: Prateep Beed: Micro circuitry in the entorhinal cortex L3P
  • Layer IV • Pyramidal shaped neurons border to layer III & layer V. • Similar properties of layer III & layer V pyramidal neurons. • Also present are Bipolar cells. • Dendrites grow horizontally and axons collaterals travel towards superficial layer III & deep layers.
  • Layer V • No difference between MEC & LEC principal cells. PYRAMIDAL CELLS • Located below the layer IV. • Soma varies from pyramidal form to star shaped. • Large and spiny apical dendrite branching close to the soma. Spine occurs after the first or second bifurcation. • Small pyramidal cells have more basal dendrites & densely occupied with spines. Main axon reaches out to the dentate gyrus. HORIZONTAL CELLS • Soma is polygonal. Sparsely spiny apical dendrite branching in layer I. In MEC, primary dendrite is spinier.
  • • Axons branches into layer V & VI. POLYMORPHIC MPNs • Soma varies from spherical to pyramidal. • Multipolar spiny dendrites. Axon branches within layer V but reaches out to subiculum via the dentate gyrus. BIPOLAR CELLS • Spindle like soma. • Dendrites are spiny and extend from the soma to the subiculum unidirectional & extensive branching in layer I & II. Axons reaches the dentate gyrus. GLOBULAR CELLS • Soma branches within layer III – V. Axons projects towards layer V.
  • LAYER VI • MPNs are present throughout layer VI. Have spherical soma & spiny dendrites. Axon reaches the subiculum. • Also present are classical pyramidal cells. Soma are medium sized. Dominant dendrites descend towards the subiculum. Axons branches at subiculum.
  • Navigation & the Hippocampus • Hippocampus function is based on two discoveries: - Amnestic consequence as a removal of hippocampus - Spiking activity of hippocampal neuron with spatial position. • Navigation is based on two mechanisms: - Map based or Allocentric navigation - Integration of motion & knowledge of previous positions
  • • Navigation guiding involves the hippocampus & the entorhinal cortex. Declarative memory Semantic Episodic • Neural system for navigation should have the capacity to store large quantities
  • Memory • Episodic memory is the memory of our experiences. Relevant to recent & remote events. Also known as Implicit memory. • Semantic memory is more structural record of facts, meanings, concept & knowledge. Similar to allocentric map which defines a location largely independent of how the animal got there. • Semantic memory is derived from episodic memory and we learn new facts or concepts from our experiences & episodic memory supports the semantic memory
  • Buzsaki & Moser: Memory, navigation & theta rhytm in hippocampal – entorhinal system. Nature neuroscience review (2013)
  • • Semantic memory depends on the hippocampal – entorhinal system. • Still debatable if semantic acquired information becomes hippocampus independent or hippocampus dependent forever. • Animal’s spatial coordinates are encoded by striking firing patterns from hippocampal “place cells” & entorhinal “grid cells”.
  • Grid cells • Present throughout the MEC & in the pre - & parasubiculum. Abundant in layer 2 of MEC. • Arranged along the dorsal to ventral axis of the MEC. • Small grid scales present in dorsal part & large grid scales present in large parts. • Deep layers are intermingled with head directional cells. • Grid cell provides a neural representation of space and head directional cells provide a directional reference frame. • These cells are active in all environment & behave in a coherent manner.
  • a b c a & b: Buzsaki & Moser: Memory, navigation & theta rhytm in hippocampal – entorhinal system. Nature neuroscience review (2013) c: Burgess et al: Evidence for grid cells in a human memory network. Nature (2010)
  • Place cells • Place cells are the basic elements of a distributed noncentered map-like representation. (O’Keefe & Nadel – 1978). • Abundant in the Hippocampus. • Place cell provides the animal with a dynamic and continuously updated representation of allocentric space and its own position in that space. • Fire selectively when an animal occupies a particular position. • They fire differentially in different environment. • After hippocampal damage rats are terrible at spatial problem solving & appear lost in space.
  • a b c a: Buzsaki & Moser: Memory, navigation & theta rhytm in hippocampal – entorhinal system. Nature neuroscience review (2013) b: Burgess et al: Evidence for grid cells in a human memory network. Nature (2010) c: The Knierim Lab (John Hopkins university)
  • Conclusion • Hippocampal place cells behave as a navigator. Updates estimate of location using dead reckoning & sightings. • Grid cells provide the path integration input.
  • Vielen Dank. Wishing everyone a merry christmas and a happy new year