Hippocampal function: navigation & memory

Question 1

What is egocentric navigation?

Answer 1

Navigation that needs limited sensory input –> follows stimulus-response learning
e.g. nightstand is on the right

Question 2

What is allocentric navigation?

Answer 2

Navigating from spot to spot without having a specific route –> requieres an internal cognitive map of the environment
e.g. central station is north

Question 3

What does Thorndike’s Law of effect state?

Answer 3

If stimulus –> response –> reward
Then: strengthen the connection between neurons for stimulus and those for response & you can chain associations to make a path (Egocentric navigation)

Question 4

Whats up with path intergration?

Answer 4

Path intergration starts with egocentric navigation but can result in allocentric mapping with good memory

Question 5

What do patients with bilateral hippocampal lesions suffer from?
1. Anterograde amnesie
2. Retrograde amnesia
3. Amnesia with Ribot gradient

Answer 5

All

Question 6

What is Ribot’s gradient?

Answer 6

Its a law that states that there is a time gradient in retrograde amnesia, so that more recent memories are more likely to be lost then the more remote memories

Question 7

What is retrograde amnesia?

Answer 7

Inability to access memories/information from before an injury or disease occured

Question 8

What is anterograde amnesia?

Answer 8

Inability to create new memories after an event that caused amnesia.

Question 9

What is a cognitive map?

Answer 9

A representation of relationship between entities (places,stimuli,persons,concepts) that is used to perform a cognitive task

Question 10

What are place fields?

Answer 10

The receptive fields of hippocampal cells –> place where the neurons fire

Question 11

What happens during global remapping (new environment)?

Answer 11

Place cells show spatial shift in place field or lose it in the new environment

Question 12

What is rate mapping?

Answer 12

Whe something changes within the same space –> receptive field stay at the same place field, but have a lower amplitude

Question 13

Where are grid cells located and what is a function?

Answer 13

Medial entorhinal cortex –> they help determine distance between locations, the cells together indicate where the animal is

Question 14

Where does the spatial representation of a goal happen?

Answer 14

Medial prefrontal cortex

Question 15

What does the hippocampus generate?

Answer 15

It generates a unique code for stimulus-context combinations
- for task relevant variables

Question 16

Why is space then so prominently coded by the hippocampus?

Answer 16

• Space entails a lot of information about associations between sensory elements
• researchers have not been looking that deep into it (only at spatial variables)

Question 17

What does the hippocampus do in context of memory traces & replay?

Answer 17

Hippocampal ensemble recordings can replay –> spontaneous reoccurence of firing patterns –> can happen awake (forward/backward) and asleep (forward)

–> Replay may subserve memory consolidation, retrieval, internal simulation & planning

Question 18

The ventral striatum is a target area of the hippocampus, in what context is there a strong connection?

Answer 18

In reward expectation –> motivation

Question 19

What are all the evolving concepts of hippocampal function?

Answer 19

• Hippocampus as cognitive map
• Hippocampus as spatial map
• Hippocampus as general-purpose encoder for task-relevant variables
• Hippocampus for retrieving memory traces by replay (non-local coding)