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Question 1

how do we cope/navigate a changing world?

Answer 1

construct abstract notion of space so with changes we can figure out how to avoid an obstacle, make due with challenges and get around things
- The tasks we want to do every day involve place type operations but to do the stuff we do in a changing world requires the cognitive maps ⇒ things change in the world
- If you only had a small recollection of sensory input with how we get places that is not going to work because there are different environments, streets, etc.
- All animals live in a changing environment

Question 2

what is the highest cortex region we have to map space?

Answer 2

hippocampus
- entorhinal cortex provides input to hippocampus

Question 3

what does the entorhinal cortex do?

Answer 3

plays a role in making representations, altering it, learning in new environments, etc.

Question 4

what does the hippocampus do?

Answer 4

provides the rest of the brain with a spatial reference map

Question 5

what hippocampal activity do we see when we put mice in a box?

Answer 5

When they head in one direction the cell responds vigorously but when they go in other directions it is mostly silent ⇒ only one location where the cell responds really well
- you have a rat and put it in a box and obscure things ⇒ the rat freely moves around and you take note of where you get response from a single hippocampal neuron

Question 6

how do we know the neuron firing from the rat in the box is not the vestibular system giving information about body orientation instead of place orientation?

Answer 6

if the mouse is heading the same way in a different part of the box there is almost no response at all

Question 7

how do place cells work?

Answer 7

place fields do not depend on which way the animal faces but the position of the animal in an environment
- the strongest firing is in the exact location for all of these ⇒ this is a place cell not a heading cell because there is no variation in the direction the mouse is going
- What they all share is a region in the environment where there is a lot of firing

Question 8

what happens when we make a subtle change in the mouses environment as we record an active place cell?

Answer 8

The neurons often go completely silent with the “new” environment

Question 9

if you put a mouse in 11 different rooms when are the place cells active?

Answer 9

most place cells are active in only 1 or 2 rooms out of the 11 tested ⇒ and if the cells are active, they have different maps in different rooms
- Very few individual cells have any activity for more than 1-2 rooms even though the changes are subtle
- evidence these cells provide flexibility to give information about the environment

Question 10

what happens in the morris water maze when you lesion the hippocampus?

Answer 10

if you lesion the hippocampus on a fully trained rat then the rat starts to go all over the place whereas before the rats remember these experiences so by the 8th trial the rat goes right to the platform

Question 11

when are place cells defined? (2)

Answer 11

place fields are defined relative to landmarks and when the rat moves actively

Question 12

T/F animals need vision for place cells?

Answer 12

False
- a lot of animals are not necessarily visual and need to navigate ⇒ they can often navigate in the absence of vision

Question 13

what did they find when they had a mouse walk a track and then rotated it forward and back?

Answer 13

In this experiment the mice are either blinded or it is dark but they use olfactory for landmarks and they record where the neuron is firing in the hippocampus at different places
- lots of activity at one particular place and if you rotate the whole environment but the landmarks are in the same configuration we see the place cells move => as a control you rotate it back and the place field is consistent
- So when we make subtle changes to the room and watch the cell go silent then the landmarks it cares about have changed or vanished
- In vision we show things and see what happens but in this case the understanding of space is dependent on activity ⇒ integral part is how the animal is navigating through space which needs an explanation

Question 14

what did they find when they had a mouse walk a track vs ride a platform?

Answer 14

When you record from the place cell and he is walking at particular position on the track the neuron fires vigorously and only at that position on the track
- If you put the mouse on the platform then the neuron is non specific with regard to location and fires over a huge range of angles
- Movement seems important and there needs to be references or landmarks ⇒ we need to understand this

Question 15

T/F the source of place signal is internal to the hippocampus?

Answer 15

False
- CA1 cell continued to express place fields after lesion of the intrinsic hippocampal pathway suggesting the source of the place signal is external
- the hippocampus is a big structure and somehow the circuitry within the hippocampus that is responsible for a lot of these things so if we disrupt connections it should have a major effect on place cells which presumably need to derive information with regard to landmarks and movement
- maybe we shouldn’t look for distinct populations in the hippocampus because inputs responsible for place cell generation/maintenance are not in the hippocampus but come from another structure and the hippocampus selectively samples these inputs

Question 16

what are the 2 components of landmarks and what cells are involved in them?

Answer 16

1. External ⇒ border/boundary cells that represent the edges of an environment so that you can orient and position to make judgements of where you are
2. Internal ⇒ grid cells
   - There is an internal representation of distances at regular intervals which are the grid cells in entorhinal cortex
   - Some sense of how far apart things are in the world like an internal map

Question 17

what are the two components and cells of movement/path integration?

Answer 17

1. heading (where you are going) ⇒ heading cells, optic flow cells that on the basis of visual input give you information about where you are going and the direction you are headed
   - Some contribution of cells like this and vestibular cells gives rise to heading cells in entorhinal cortex which only fire when the animal is navigating in a particular direction
2. Speed ⇒ speed cells

Question 18

how do boundary cells function?

Answer 18

(external landmark) place fields scale with the distance between sides of the box => stretched the square out and what happened is the cell stretched out too
- representing positions relative to the environment (I’m in this part of the environment and if it gets longer so does the cell)
- Boundary cells are characterized by placelike things that are near edges and boundaries and are dynamic when you do transformation of the environment ⇒ linked to boarders so they don’t represent place but more likely a place you are relative to the boundary/environment

Question 19

how do our grid cells work?

Answer 19

(internal landmark) The spacing is very regular and the distances between grid points is regular and the angles are regular ⇒ it is a coordinate system like latitude and longitude but it exists within the brain and we don’t see anything labeled to indicate positions are special
- you get hexagonal tessellations of space which is surprising

Question 20

what are the 3 dimensions of variation in grid cells?

Answer 20

• phase
• scale
• orientation

Question 21

how does phase work in grid cells?

Answer 21

nearby cells have a slightly different grid pattern and so forth but their phases change while the scale and orientation do not
- orientation columns have neurons with different phases but in a small patch of entorhinal cortex you have consistent spacing and direction but phase variety

Question 22

how does scale work in grid cells?

Answer 22

there is functional organization cross the entorhinal cortex like other cortical areas and that is the spacing of these grid cells is systematically changing from dorsal to ventral
- Small scale to large scale spacing like a whole set of graph paper to indicate the spacing between objects in the world
- as you get farther from the dorsal boarder you get more spacing (as you go ventral the spacing is larger)

Question 23

how do we know scale, orientation and phase are preserved across environments?

Answer 23

You look at a population of neurons and what the population vector is for each location to see how the activity correlates as a function of spatial location ⇒ way to look at the consistency of grid like representations
- What you find is that if you construct a grid cell map of a population of 6 neurons from environment A and take the animal out and come back the next day to put the animal back in A with the same neurons and look at how the grid cells respond they line up in a regular manner ⇒ elimination of phase for the underlying orientation and spacing of the grid cell population which is really consistent
- if you repeat this experiment with many rats we see the same things ⇒ all that changes is the phase relationship in the environments but underlying regularity and relationship between the grid cells has not changed
- These are shifted versions of each phase but relative phases in the maps are not changing at all ⇒ not context dependent

Question 24

what happens if you look at scale, orientation and phase relationships in the hippocampus?

Answer 24

we find the cells are completely silent in different contexes
- the hippocampus can remap completely

Question 25

what is the evolution of grid cells?

Answer 25

evolutionarily old and speaks to the notion that the basic need to construct maps to understand the environment is shared by many creates and solutions make use of the same mechanisms - been reported in bats, rats, monkeys and humans

Question 26

what is the path integration problem with head direct cells?

Answer 26

in entorhinal cortex we find head direction cells ⇒ sum of all of these potentials in an environment segregated by the direction the animal is heading in - Responds all over the place but are about location

Question 27

what are speed cells useful for?

Answer 27

speed cells are necessary for updating the grid pattern in accordance with the animals movement (distance = speed x time) - respond in a linear way to speed ⇒ increased firing with more speed

Question 28

do speed, grid, border, head etc. cells overlap populations?

Answer 28

no - speed cells are found in all layers and 32% were fast spiking cells (in contrast to 0.5% in the other cell groups) - distinct categories that do not overlap in the entorhinal cortex

Question 29

do grid cells give rise to place cells?

Answer 29

grid activity can be transformed to place cell activity by linear summation of signals from grid cells with different scales - If we take a lot of grid cells with different spatial scales and sum them up then it looks like the wiring diagram of the place cells - If we add up grid cells in a particular phase we get a place cell ⇒ selecting the right grid cells and adding them up

Question 30

how do we make boundary cells? how do they contribute to place cells?

Answer 30

at a point in space we know there is distance from certain boarders so we can sum the distances from edges and come up with a place cell - grid cells and boundary vector cells may provide 2 independent pathways into place representations - you can use grid cells and boundary cells together or independently to provide landmark frames of reference to construct place cells