Declarative Memory System

Question 1

Who made one of the firsts attempts to dissociate the circuitry for declarative and non-declarative memory? What experimental paradigm did they use?

Answer 1

Packard and McGaugh. The T-maze

Question 2

What strategy did rats initially adopt on Packard and McGaugh’s t-maze? What happened after another week of training?

Answer 2

Initially adopted a place strategy (made a left turn on the rotated maze). Switched to a response strategy (made an incorrect right turn on the rotated maze).

Question 3

What was initial acquisition of the food on P & M’s t-maze guided by? What resulted from subsequent ‘overtraining’?

Answer 3

Cognitive map. Subsequent overtraining led to a response habit developing

Question 4

In general, when do rats use a place strategy?

Answer 4

When salient extra-maze cues are present

Question 5

In general, when do rats use a response strategy?

Answer 5

When over-trained, or salient extra-maze cues are absent

Question 6

After one week of training on the P & M t-maze, what effect did lidocaine injection into the hippocampus have on probe trial success? And into the striatum?

Answer 6

Hippocampus - abolished memory (no preference for left or right turn).

Striatum - no effect

Question 7

After two weeks of training on the P & M t-maze, what effect did lidocaine injection into the hippocampus have on probe trial success? And into the striatum?

Answer 7

Hippocampus - no effect (all made habitual response)

Striatum - abolished ‘response memory’, but rats did not have random preference (92% made place response)

Question 8

What type of maze did Eichenbaum’s lab employ?

Answer 8

Adapted T-maze (arms joined back up with bottom of the central arm

Question 9

In the delayed non-match to sample odour task, when did they record hippocampal neuron activity? What did this allow them to correlate firing rate with?

Answer 9

Position, odour and other aspects of the task (e.g. whether the odour was a match or a non match)

Question 10

In the delayed non-match to sample odour task, what percentage of cells fired in response to one or more task variables?

Answer 10

65%

Question 11

In the delayed non-match to sample odour task, what did most hippocampal cells fire to a combination of? What does this provide evidence for?

Answer 11

Cup position, odour, match/mismatch and start of approach to the cup. Provides evidence to suggest that the hippocampus, in particular area CA1, combined elements of spatial, non-spatial and contextual cues to form an episodic memory

Question 12

What did Eichenbaum suggest the hippocampal network represents an episodic memory as? What does each cell within this network encode?

Answer 12

A sequence of events and places.

Each cell encodes a small segment of the episode.

Question 13

When may memories overlap? Give an example.

Answer 13

At common points.
E.g. entering a particular spatial location may bring other memories containing that spatial location unto consciousness.

Question 14

Why is a heteroassociative network a good model for episodic memory?

Answer 14

Because it allows information to be recalled in the sequence it was experienced.

Question 15

What has been proposed to be the cellular instantiation of the short term memory buffer? Why?

Answer 15

The gamma cycle.
Because the number of gamma cycles on each theta wave is 7+/- 2.
Ebbinghaus suggested the short term memory capacity is 7+/- 2 items.

Question 16

When is theta rhythm robustly displayed in the animal hippocampus

Answer 16

When the animal is exploring its environment.

Question 17

At what point of the theta cycle do place cells fire when the animal is in the centre of the associated place field? What information does this encode?

Answer 17

The trough . This encodes the current position of the animal

Question 18

At what point of the theta cycle do place cells fire when the animal is entering the place field?

Answer 18

Before the positive peak

Question 19

At what point of the theta cycle do place cells fire when the animal is leaving the place field?

Answer 19

Earlier on the theta cycle than when the animal is entering, and in the middle of, a place field.

Question 20

What is the position of the animal across a linear track encodes by?

Answer 20

The phase of theta at which the place cell fires.

Question 21

How can phase precession be seen as an episodic memory?

Answer 21

Phase-specific firing provides a running record of where the animal was, is and will be. Thus, the hippocampus is sequencing the positional information over time to make up the spatial elements of an episodic memory.