Time, Space, and Place

Question 1

What did Ebbinghaus’ experiment reveal?

Answer 1

• participants asked to remember nonsense syllables
• showed the forgetting curve is an exponential decaying curve

Question 2

What was Lashley’s 1950 experiment?

Answer 2

searched for where are the cells that represent stored information by training
rats/mice to do a task and removing % of cortex to try and nail down where it was but it didn’t make much of a difference, only correlated to the more you remove, the more errors they made

Question 3

What is the main brain area responsible for spatial navigation?

Answer 3

the hippocampus - gives us capacity to spatially navigate & is important for declarative episodic memory

Question 4

Patient H.M showed hippocampus is essential for. . .

Answer 4

consolidation of explicit episodic memroy

loss of BOTH hippocampi may result in anterograde amnesia (inability to form and retain new memories) but procedural and short term memory is affected

Question 5

Where does the hippocampus form (primates)

Answer 5

at the edge of the CORTICAL SHEET (as an outgrowth of lateral vesicles) very close to lateral geniculate nucleus (close to THALAMUS)

located in medial temporal lobe

We study on rodent hippocampi for synaptic plasticity because they’re more accessible simpler and still have similar structures and circuits

Question 6

How does info flow into the hippocampus?

Answer 6

Info flows through hippocampus (CA3–CA1) from the cerebral cortex to entorhinal cortex to hippocampus and out the same way

Question 7

What are place cells?

Answer 7

• most hippocampal neurons are place sensitive, encoding a small region of the rat’s environmental position / place but are not topographic
• also integrate declarative and spatial info - respond to place as well as what happened at that location

Question 8

List 3 features of place cells

Answer 8

• Only reactive at specific locations & experiences cause remapping of the spatial map (dynamic & plastic)
• encode where the rat is bu also where it has been recently
• unlike semantic memory, episodic memory is tied to space

Question 9

What happens to place cells with NMDA antagonists?

Answer 9

There is no reconfiguration if there’s a NMDA antagonist, doesn’t abolish place cells - stops them adapting to new environments

Question 10

Because some neurons re-map so rapidly, it is suggested that. . .

Answer 10

there may be a set of skeletal templates that can be selected then further refined as the specific of new environment are encountered

Neighboring cells were not necessarily nearby place fields

Question 11

How does sleep help to consolidate info?

Answer 11

• We dont know why rhythm theta is important for consolidation of information
• Consolidation dependent on sharp wave activity that spreads (ripples) through hippocampus and entorhinal connections at rest/sleep.
• Optimal for LTP and spreads
  via entorhinal cortex to cerebral cortex.

Question 12

Another word for hippocampus

Answer 12

Ammon’s horn

Question 13

Cortical circuits enter hippocampus from the. . .

Answer 13

perforant pathway

Question 14

Why do place cells require LTP?

Answer 14

YOU NEED LTP TO BE FUNCTIONING, to form those maps and maintain them - the maps start to degrade if you don’t have LTP

Question 15

Navigation requires a combination of:

Answer 15

a) ‘dead reckoning’ or self-referenced movement from a known location
b) the generation of landmark-based maps

Question 16

What is declarative memory?

Answer 16

a type of long-term memory that involves conscious recollection of particular facts and events.

Question 17

How do detailed maps form?

Answer 17

It is thought that the formation of a detailed maps relies on repeated experiences with self-referencing explorations, the same way as semantic memories may become context independent with repetition of episodic memories concerning a semantic relationship

o Eventually put episodic memories together (i.e tables in cognitive map)
o Semantic memory comes from declarative memory thinking about how that is incorporated

Question 18

When do grid cells fire and where?

Answer 18

They fire at intervals, metric distances in a grid pattern with different scales, basically respond to distance covered - in entorhinal cortex

fire when a rat is in a multiple of a particular distance

Question 19

Grid cells produce a non-topographical grid

Answer 19

Grid cells produce a non-topographical grid means that they create a pattern of activity that maps spatial locations in a manner that does not directly correspond to the physical layout of the environment. Instead of forming a map where each cell’s activity directly correlates to a specific location (as in a topographical map), grid cells generate a hexagonal, repeating pattern of activation that represents an abstract, coordinate-like system for spatial navigation. This allows the brain to encode and recognize positions in space efficiently, even though the grid pattern itself does not mirror the actual geography of the surroundings.

Answer 20

• grid cells have a denser space dorsally, wider ventrally
• gives reference system for location in environment
• Encode a specific combination of place cell identities for each new environment
• Remember a combination of grid cells for a particular environment which activates place cells which similar configuration
• Select a phase of grid cells = might lead to even more place cell combinations

Question 21

Differences b/w grid and place cells

Answer 21

Mapping: Place cells map specific locations to unique cell activations, creating a place-based representation. Grid cells map space using a regular, repeating pattern that provides a distance-based framework.

Representation: Place cells represent individual locations (e.g., specific rooms or corners). Grid cells represent a coordinate system that helps navigate between these locations.

Function in Navigation: Place cells tell you “where you are” in the environment. Grid cells help you understand “how to get there” by providing a metric for distance and direction.

Question 22

Head direction cells

Answer 22

cells sensitive to direction of head orientation
o 2nd type of cell defining animals place in environment, appears in regions downstream of
hippocampus (ENTORHINAL CORTEX, SUBICULUN)
o Cell fires when animal faces in particular direction relative to environment (not a compass)