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Learning, Memory And Cognition > Hippocampus And Spatial Memory > Flashcards

Hippocampus And Spatial Memory Flashcards

1
Q

What are the two major mechanisms for navigation?

A

Path integration and cognitive map

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2
Q

What type of cells within the hippocampal formation support path integration?

A

Direction and grid cells

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3
Q

What type of cells within the hippocampal formation support the cognitive map?

A

Place cells

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4
Q

What type of animal is a good model for path integration?

A

Ants

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5
Q

What 3 W’s studied navigation of desert ants?

A

Wittinger, Wehner and Wolff (2006)

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6
Q

Theoretically, what are the two possible ways an ant could navigate back to the nest?

A
  1. Remember the path exactly

2. Use motor system and sense of direction (from polarised light) as well as distance travelled

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7
Q

What is the evidence that ants might use their motor system information, sense of direction and distance travelled to navigate back to the nest?

A

They take the most direct route back to the nest, so they must have a sense of distance traveled, and be able to compute and integrate this information with direction when navigating back to the nest

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8
Q

What were Wittinger, Wehner and Wolff (2006) interested in finding out?

A

Whether animals actually count their steps back to the nest

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9
Q

What was the main idea of 3W’s experiment

A

If you make the legs of an ant shorter or longer you can change the distance of the step and thus observe whether ants actually step count

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10
Q

Describe the methodology of the 3 W’s experiment

A
  1. Train ants to navigate from nest to source of food
  2. Modify length of ants legs (short, normal or stilts)
  3. Let them navigate back to the nest
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11
Q

What were the main findings of the 3Ws experiment?

A

Normal ants navigated back to the nest fine
Ants with stunk legs stopped before the nest
Ants with stilts stopped after the nest

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12
Q

What did the 3 W’s find happened when they did the same task on the modified ants the next day?

A

The ants were able to compensate for their modified legs as they travelled the correct distance to the nest

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13
Q

So what type of information do ants use to navigate? What is this evidence of?

A

They use their own motor information to navigate. This is evidence of path integration

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14
Q

What is a cognitive map?

A

Internal representation of the outside world based on sensory information

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15
Q

What are the advantages of path integration?

A

Animals can navigate between locations by integrating linear and angular self motion

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16
Q

What are the disadvantages of path integration

A

Longer journeys tend to accumulate errors

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17
Q

What are the advantages of a cognitive map

A

Highly accurate

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18
Q

What are the disadvantages of a cognitive map

A

Cannot support navigation between locations

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19
Q

What type of navigation is path integration

A

Egocentric

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20
Q

What type of navigation is a cognitive map

A

Allocentric

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21
Q

Why is learning to navigate a new environment ‘unsupervised learning’

A

The animal is not rewarded for learning the layout of the new environment. There is no explicit learning outcome

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22
Q

Who first believed that there were detailed internal maps within the rat brain, and coined the term ‘cognitive map’

A

Tolman

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23
Q

How did Tolman show that rats use unsupervised learning

A

Set up a maze experiment whereby one set of rats is trained to retrieve food from the end of the maze, and the other set of rats was just left to explore the maze.
Of the rewarded rats, deviation from the optimal path decreased with time. Rats were operating at s low error rate near the end of the experiment
On the 11th day of the experiment the un-rewarded rats were given food to retrieve.
These rats found the food as easily as the rats that had been trained to retrieve the food. End up performing slightly better due to greater exploration of the maze
Shows that unrewarded rats are learning about the maze

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24
Q

How did Tolman show that rats possess a cognitive map

A

Used a maze with a series of blockage manipulations.
Rats firstly given free reign on the maze - eventually learn to take the shortest of three possible routes to the food.
Then put in block A - blocks the shortest route, rats take the shortest detour
Then put in block B - blocks shortest route and shortest detour.
Rats take the longest, but only possible, detour.
Evidence of rats using knowledge of maze to guide behaviour

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25
Q

Where does the rodent hippocampus receive major cortical inout from

A

The entorhinal cortex

26
Q

What is the trisynaptic circuit in the rodent hippocampus

A

EC to DG
DG to CA3
CA3 to CA1

CA1 then projects back to EC

27
Q

What types of mazes can we use to test for spatial memory in rats?

A

Radial arm maze - David Olton

Water Maze - Richard Morris

28
Q

When is reference memory used in the radial arm maze

A

Used between trials, when the same arm(s) is bated with food each trial.
Reference memory error would be choosing an arm that has never been bated before

29
Q

When is working memory needed in the radial arm maze

A

When all arms are bated with food each trial and the animal must remember which arms it has visited.
A working memory error would be visiting the same arm twice

30
Q

How would you test if the animal has spatial memory of the platform in the Morris water maze

A

Remove the platform and record the amount of time animal spends swimming in the quadrant where the platform used to be

31
Q

What are the two version of the water maze and radial arm maze you can employ

A

Spatial vs. Cued

32
Q

How would you provide a cue in the Morris water maze

A

Put a flag on the platform

33
Q

How would you provide a cue in the Radial arm maze

A

Signal a visited arm by turning on a light

34
Q

What is different about cued versions of the radial arm maze and the water maze

A

They do not require spatial memory

35
Q

How do animals with a hippocampal lesion perform on cued mazes

A

Normal performance

36
Q

How do animals with hippocampal lesion perform on spatial Versions of the mazes. What does this provide good evidence for

A

Poor performance. Provide good evidence that the hippocampus is the site of the cognitive map

37
Q

How did O’Keefe show that the hippocampus contains place cells

A

Used an electrode implant in the rat hippocampus. Recorded the activity of the cells whilst simultaneously monitoring the position of the rat with a camera. Every time a cell fires a; action potential you label that with the position of the animal.
Can make a map of where particular cells have fired

38
Q

What do place cells do?

A

Fire action potentials whenever the rat is in the corresponding place field

39
Q

What is a place field

A

The area in space where the corresponding place cell fires maximally

40
Q

What is a hyperdrive

A

It’s a recording tool with 14 independent tetrodes, each recording 3-6 cells (giving 40-90 simultaneous recordings)

41
Q

Place cells are non-topographic, what does this mean?

A

Adjacent place cells in the hippocampus do not have adjacent place fields

42
Q

What type of cells are place cells presumed to be?

A

Pyramidal cells. They tend to fire action potentials in complex bursts as the animal moves through a specific location

43
Q

What are a sufficient number of place cells able to do

A

Map a given environment

44
Q

What are place fields resistant to

A

Rotating the environment

45
Q

What does evidence from place cells offer strong support for

A

The involvement of the hippocampus in creating the cognitive map

46
Q

What do place cells provide a very poor neural basis for? Why is this?

A

Path integration. This is because they do not provide information about movement direction or distance covered

47
Q

What cells support path integration?

A

Head direction cells

Grid cells

48
Q

Where are head cells located

A

Presubiculum

49
Q

When do head cells fire?

A

In a 90 degree arc around their preferred direction.

Fire to the same direction in different environments.

50
Q

What is the proposed function of head direction cells?

A

Orient spatial maps in the hippocampus

51
Q

Where are Grid cells located

A

Layer 2 of the Medial entorhinal cortex

52
Q

How do grid cells fire

A

In a regular grid-like pattern across an environment. There is constant spacing between peaks in firing rate. Grid field centres are located at the points of an equilateral triangle.

53
Q

Grid cells are arranged typographically. What does this mean

A

Adjacent grid cells map adjacent positions.

54
Q

What happens to the grid when an animal is in a completely novel environment

A

The grid is initially more spread out but contracts back as the animal becomes more familiar with the environment

55
Q

What are grid cells good at giving information about? What can they not provide information about

A

Good at providing information about distance covered in any. Bad at telling the animal where it is in space because the firing is context independent.

56
Q

What do speed cells provide information about

A

How fast the animal is travelling

57
Q

Where are speed cells located in the hippocampus

A

Medial entorhinal cortex

58
Q

What does the firing of speed cells correlate with

A

The running speed of the animal

59
Q

What is the direct evidence that grid cells play a role in path integration

A

If grid cells are specifically turned off in mEC (through modulation of NMDA receptors) the animals could not path integrate. Place cell firing was not disrupted however

60
Q

What do border cells fire in response to

A

The animal coming up to the edge of an environment (arena experimentally)

61
Q

What do conjunctive cells combine. What does this make them ideal for

A

Grid cell firing and head direction cell firing. Makes them ideal for path integrators

62
Q

Where are conjunctive cells located

A

Deep layers of EC

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