Lecture 9 - Hiippocampus the spatial representation circuit

Question 1

Who discovered the hippocampus?

Answer 1

Julius Caeser Aranzi

Question 2

What is the hippocampus for?

Answer 2

Learning and normal memory functions

Spatial tasks

Question 3

What is empiricism?

Answer 3

the theory that knowledge comes only or primarily from sensory experience

Question 4

Outline John O’Keefe’s work

Answer 4

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.

Question 5

What are place cells?

Answer 5

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

Question 6

Is there a connection between neighbouring place cells?

Answer 6

No, they are randomly situated

Question 7

How are different environments represented in the hippocampus?

Answer 7

Place fields shift from one place to another in an unpredictable manner

Question 8

What test was performed to idenify whether the hippocampus was involved in social learning?

Answer 8

Morris used the hidden platform test and then blocked NMDAR

Question 9

Are place cell maps present on first exposure to the environment or are they acquired?

Answer 9

Both - they fire from the very beginning but take time to stabilize

Question 10

What disrupts place field formation?

Answer 10

The application of an NMDAR blocker

Question 11

Describe the experiment which showed that the environment itself can cause a freezing response

Answer 11

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

Question 12

What is theta phase precession in the hippocampus?

Answer 12

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

Question 13

What do the boundary cells in the subiculum do?

Answer 13

They respond to the presence of an environmental boundary at a particular distance/direction from the animal

Question 14

What is the function of head direction cells and where are they located?

Answer 14

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

Question 15

What are grid cells?

Answer 15

They are entorhinal and have spatial fields with a paeriodic hexagonal structure, they are used for self-localization.

Question 16

How do entorhinal grid cells work?

Answer 16

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

Question 17

What are the 3 paramaters of grid cells?

Answer 17

Grid Phase
Scale
Orientation

Question 18

What is grid phase?

Answer 18

Displacement in the x and y direction relative to an external reference

Question 19

How is the spatial field of grid cells distributed?

Answer 19

Scattered like a salt and pepper organisation

Question 20

How does the grid module system adapt to different environments?

Answer 20

similar to a combination lock, in which the modules themselves are rigid however each module can shift and rotate independently

Question 21

Outline the 2 possible theories of formation for the grid

Answer 21

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

Question 22

How come the animal moves at different speeds but the firing pattern is regular?

Answer 22

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

Question 23

How does the animal know how to get to it’s goal position?

Answer 23

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

Question 24

How is object information in the environment processed?

Answer 24

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