Rat Spatial Navigation Flashcards
Ideothetic cues
Internal cues
Vestibular, propioception, corollary discharge, optic flow
Provide PATH INTEGRATION, continuous movement/distance estimate
Allothetic cues
External cues
5 senses
3 tasks for spatial learning
Radial arm maze, learn to visit each arm once (hippo damage = repeat visited arms, perseveration)
Morris water maze, learn to swim to platform (hippo damage = swim randomly)
Circular platform maze, learn which hole had tunnel
morris/circle require external cue
Types of memory
Declarative explicit -spatial memory!/facts
Procedural implicit - skills/habit
Consolidate working memory into long term, prefrontal cortex does working memory
Amnesia types and H.M.
Retrograde - memory loss before trauma
Anterograde - no new memories (H.M./Dory)
H.M. bilateral temporal lesion - caused anterograde amnesia, unable to form new delcarative, PROCEDURAL AND WORKING INTACT (stored elsewhere)
Hippocampus Pathways
Perforant Pathway - Entorhinal cortex -> Dentate Gyrus
Mossy fiber - Dentate -> CA3
Schaffer collateral - CA3 -> CA1 (CA1 has pyramidal PLACE CELLS)
Hippo grew for taxi drivers, used in spatial!
Place cells
CA1 region hippo
have place field influnced by external and internal cues
spike at specific points, create COGNITIVE MAP
Time Cells
hippo Fire at successive moments in a temporal structure
at least one cell fire at each moment
Head Direction Cells
Postsubiciculum
compass for direction
same preference in any environment, intenral/external cues
Grid Cells
Entorhinal Cortex
Positioning system
different cells have grids of diff sizes and orientation, all stacked on top each other allow for a POPULATION CODE of location, grids scaled to each other at possibly sqrt of e
Speed cells
Medial entorhinal cortex
Linear firing rate to speed
updates position rep with head direction and grid cells
Border Cells
Fire at proximity to boundaries
important to anchor grid cells and create geometric reference frame
All cells working together
Each place in local enviro has unique combo of cells firing (grid cell overlap), hippo place cells
Medial entorhinal cortex MAJOR INPUT TO HIPPO, allow modifiable place cell synapses
Where does synaptic plasticity occur in hippo
Schaffer collateral, LTP between CA3/1
Inducing LTP
Induce axons with tetanus stimulus, allows EPSPs of post axon to heighten
input specific, diff input wont actiavte
BOTH ACTIVE WHEN POST STRONGLY DEPOL
2 required things for LTP (PRE/POST ACTIVE TOGETHER FIRE TOGETHER WIRE TOGETHER)
High freq stim causes temporal summation
Spatial summation across synapses needs to happen
LTP Mediated by what
NMDA receptors
Ligand and voltage gated
AMPA binds with glutamate, depols the post cell
NMDA receptor voltage unlocked (Mg blokc removed)
Channel opens, Ca enters
NMDA IS COINCIDENCE DETECTOR FOR PRE/POST BEING ACTIVE
LTP Mechanisms
Ca entering NMDA activates protein kinases
Kinases phosphorylate AMPA, more efficient
Insert new AMPA receptors
Inducing LTD
Long term depression
give tetanus of LOW freq stim
input specific, diff input wont activate
BOTH ACTIVE WHEN POST WEAKLY DEPOL
Bidirectional Plasticity
Ca can induce LTP or LTD, synapses can change both ways
Protein kinases = high Ca, LTP
Protein phosphatases = DEPHOSPHORYLATE PROTEINS, low Ca, LTD. AMPA dephosphorylated = LTD
AMPA receptor balance
LTP creates need for more room on emmbrane for synapses,
Newly formed AMPA receptors have GLuR1 subunit to allow to fit into membrane
LTD leads to need for smaller membrane
Knockout Mice types
NMDA Blocker = never learn, NMDA needed for memory, swim randomly. Impair LTP, less precise
CAMK11 Knockout = lack Ca-dependent kinases = IMPAIR LTP, fewer place cells/less precise/less stable, impaired spatial learning
