Section Two - Neural coding and the function of the hippocampus

Question 1

case study - HM

Answer 1

Bilateral hippocampal removal > severe anterograde amnesia + partial retrograde amnesia

Question 2

episodic memory

Answer 2

declarative
facts and events
happen in medial temporal lobe

Question 3

Animal studies

Answer 3

birds (without cortex) exhibit insight-based cognition

magpies show self-recognition

Question 4

Subregions of hippocampus

Answer 4

denate gyrus (input), granule cells, high neurogenesis

CA3 - dense recurrent networks + pyramidal neurons

CA1 - pyramidal neurons, main output to cortex

subiculum - output structure

Question 5

Neural coding in hippocampus

Answer 5

• pyramidal neurons and interneurons form complex networks (Especially CA3)
• cannabinoid receptors modulate hippocampal microcircuits

Question 5

Tri-synaptic pathway of hippocampus

Answer 5

input = perforant pathway (entorhinal cortex to DG)

mossy fibres (DG > CA3)

Schaffer collaterals (CA3 > CA1)

outputs rom CA1 & subiculum to cortex and limbic structures

Question 5

What is a place cell

Answer 5

neuron in the hippocampus that becomes active when an animal is in a specific location in its environment. They help to form a cognitive map.

Question 5

multi sensory representation of place cells

Answer 5

place cells integrate information from multiple sensory modalities like visual, vestibular (balance), olfactory and proprioceptive (body position) inputs

Question 6

Place cell remapping

Answer 6

occurs when an animal experiences environments that are physically similar but perceived as different contexts

it demonstrates place cells can store multiple maps and switch between them based on the context

Question 6

Place cell remapping experiment - Different box same location - Fyhn et al 2007

Answer 6

Place cells completely change their firing patterns or become silent in Box B
When returning to Box A’, the original firing patterns return
- This demonstrates that place cells respond to the physical features of the environment
- The complete change in firing patterns between environments is called “global remapping”

Question 6

Place cell remapping experiment - same box different location - Fyhn et al 2007

Answer 6

Place cells maintain some aspects of their firing patterns but shift their place fields = spatial remapping where cells update their spatial representation

Question 7

Place cell remapping experiment - change in colour of box walls - Fyhn et al 2007

Answer 7

• When only the colour of the walls changes, the place cells maintain their spatial firing fields. However, the firing rates change significantly
• This suggests that minor environmental changes are encoded by modulating firing rates rather than changing place fields

Question 8

Summary of changes in remapping experiment

Answer 8

Major change (diff box) = global remapping (new map)
Spatial change (new location) = spatial remapping (different place field)

Minor change (colour change) = rate remapping (same field, different rate)

Question 9

What is a cognitive map

Answer 9

mental representation of the spatial environment and the relationships between locations within it

Within hippocampus through integrated navigation of place cells/grid cells

Question 9

Grid cells

Answer 9

fire in a grid pattern

work with place cells to provide a universal metric for spatial navigation

Question 10

Egocentric vs allocentric view

Answer 10

EGOCENTRIC - personal view (e.g. i need to turn right)
ALLOCENTRIC - birds eye view (e.g. place in 30 metres north of ….)

Question 11

Position decoding

Answer 11

Can guess where an animal is based on place cell firing

Question 12

Memory encoding

Answer 12

Place cell patterns provide a spatial framework for associating experiences with locations

Question 12

Jennifer anniston cells

Answer 12

Related to abstract concept = suggests generalisation of place cells
neuron fires when Jennifer appears

Question 13

Synaptic plasticity strenthen vs weaken

Answer 13

Neuron 1 fires before Neuron 2 = strengthen

Neuron 1 fires after Neuron 2 = weaken

Question 13

What cell types are there in the hippocampus in terms of spatial firing properties

Answer 13

place cells
grid cells (entorhinal cortex)
head directional cells (animal head points in specific direction)

Question 14

Theta oscillations

Answer 14

Metronome (timing reference)

associated with active movement and exploration

Question 14

Spike phase

Answer 14

it is a timing relationship between an action potential in a neuron and the ongoing oscillatory rhythm

Cell aligns to peak of theta wave

Question 15

phase procession

Answer 15

As animal moves along place field, timing of cells firing shifts to earlier phase of theta cycle = spike phase decreases

Question 16

Phase locking

Answer 16

Neuron fires at consistent point within each cycle of an oscillation

Question 17

Phase precession experiment

Answer 17

first entry to place field= cell fires near peak of theta cycle animal progresses = spikes occur at earlier phases animal reaches end of place field = spikes occur much earlier in theta cycle Second place cell - fires at same point, starts same phase procession Cells linked together by short time constant which increases synaptic plasticity EARLIER PHASE SPIKE = ANIMAL IS FURTHER ALONG IN THE FIELD

Question 18

place cell sequences

Answer 18

compressed from behavioural timescale (seconds) to synaptic timescale (milliseconds)

Question 19

Episodic like memory

Answer 19

In animals not humans demonstrate behaviours relating to WHAT (specific event) WHERE (spatial location) and WHEN (temporal cortex)

Question 20

How do spikes within a single theta cycle relate to place fields

Answer 20

The order of spikes within a theta cycle recapitulates the exact order of place fields, compressing spatial sequences into millisecond-scale temporal patterns

Question 21

Forward replay

Answer 21

predicts based on past memories place cells activate in sequence at a compressed timescale, representing a path the animal might take

Question 22

reverse replay

Answer 22

reinforces travelled paths place cells fire in a sequence opposite to the order experienced, from the current location back to the starting point

Question 23

Memory consolidation through sleep

Answer 23

neurons fire in the same patterns as those learned earlier in the day, transferring information from hippocampus to neocortex for long-term storage

Question 24

phase procession in schizophrenia

Answer 24

Phase precession doesn't work as well in schizophrenia models, with more spread firing patterns that are poor at consolidating sequences, contributing to hippocampal and episodic memory impairments.

Question 25

Food caching in birds

Answer 25

- six windows with a series of flashing dots (colour of dot associated with different target places e.g. harbour, tent, toilet) - bird gets reward if it remembers sequence - WHAT = colour WHERE = location WHEN = order = EPISODIC LIKE MEMORY - wireless recordings during task - gets single unit recordings