Lecture 9 - Hiippocampus the spatial representation circuit Flashcards
Who discovered the hippocampus?
Julius Caeser Aranzi
What is the hippocampus for?
Learning and normal memory functions
Spatial tasks
What is empiricism?
the theory that knowledge comes only or primarily from sensory experience
Outline John O’Keefe’s work
He studied the movement of rats by implanting tungsten electrodes in the dorsal hippocampus. He found cells that fired alot when dealing with space, he called these place cells.
What are place cells?
Certain CA1 and CA3 cells which are active when dealing with space. Different cells became active in different places and the place fields create a map of space
Is there a connection between neighbouring place cells?
No, they are randomly situated
How are different environments represented in the hippocampus?
Place fields shift from one place to another in an unpredictable manner
What test was performed to idenify whether the hippocampus was involved in social learning?
Morris used the hidden platform test and then blocked NMDAR
Are place cell maps present on first exposure to the environment or are they acquired?
Both - they fire from the very beginning but take time to stabilize
What disrupts place field formation?
The application of an NMDAR blocker
Describe the experiment which showed that the environment itself can cause a freezing response
Used pavlovian contextual conditioning in which a footshock was applied as the unconditioned stimulus. This caused the cell’s place field to be remapped from north east to sout west of the experimental chamber
What is theta phase precession in the hippocampus?
Place cells fire relative the the theta rhythm, when the animal approaches the location a place cell is tuned to, the place cell firing moves to an earlier phase of theta, so the phase offset is the distance from the object
What do the boundary cells in the subiculum do?
They respond to the presence of an environmental boundary at a particular distance/direction from the animal
What is the function of head direction cells and where are they located?
They increase their firing rates only when the animals head is pointing in a certain direction.
They are located in the post-subiculum, retrosplenial cortex, the thalamus, lateral mammillary nucleus, dorsal tegmental nucleus, striatum and entorhinal cortex
What are grid cells?
They are entorhinal and have spatial fields with a paeriodic hexagonal structure, they are used for self-localization.
How do entorhinal grid cells work?
The fields form a grid that covers the entire space available. The place cells give information about where you are in space and the grid cells provide a reference map. This is aligned to the world by the axis of the gird being offset from the walls by an angle of 7.5 degrees therefore minimising symmetry with the borders of the environment
What are the 3 paramaters of grid cells?
Grid Phase
Scale
Orientation
What is grid phase?
Displacement in the x and y direction relative to an external reference
How is the spatial field of grid cells distributed?
Scattered like a salt and pepper organisation
How does the grid module system adapt to different environments?
similar to a combination lock, in which the modules themselves are rigid however each module can shift and rotate independently
Outline the 2 possible theories of formation for the grid
Grid cells with different spacing converge to generate placce cells in a subset of the hippocampal place cell population. Each grid cell belongs to a different grid module
Differential realignment of each of the grid maps induces recruitment of a new subset of place cells
How come the animal moves at different speeds but the firing pattern is regular?
There are speed cells in the MEC which haave firing rates that follow the animals running speed.
the head direction cells in the MEC act like a compass
These are then integrated
How does the animal know how to get to it’s goal position?
Trajectory dependent firing, so when an animal has to follow a path in a T-maze the neurons fire more if they make a right turn, so the mPFC may provide route information to the CA1 region via the nucleus reuniens
How is object information in the environment processed?
By object cells in the Lateral entorhinal cortex which fire at the object and object trace cells which fire at places where objects have been previously
