Schmidt hippocampus 3

Question 1

What led to the discovery of Jennifer Aniston cells?

Answer 1

Patients with pharmacologically-resistant epilepsy had an implantation of electrodes to detect the focus of the seizure onset
Targeted areas in the medial temporal lobe including the hippocampus and presented large numbers of visual stimuli whilst recording neuronal responses
Found that neurons responded with increase in firing rate to pictures of Jennifer Aniston and not as much with pictures of other celebrities

Question 2

What are the features of the Jennifer Aniston cells?

Answer 2

It was invariant to the specific picture type and more related to the abstract concept so even the written name of the person could evoke a response
Been debated before with Grandmother cells
And could see similar neuronal responses for other things such as Sydney Opera house

Question 3

What are the implications for place cells from Jennifer Aniston cells?

Answer 3

Place cell properties may apply to this, suggesting a generalisation of hippocampal function from place cells
It may also have relations with episodic memory

Question 4

What is episodic memory?

Answer 4

According to Tulving (1972): information about temporally-dated episodes, autobiographic events and tempero-spatial relations among these events.
Part of declarative memory and requires consciousness

Question 5

What did Clayton introduce?

Answer 5

The concept of ‘episodic-like memory’

Question 6

What is episodic-like memory?

Answer 6

Refers to the behavioural criteria of episodic memory without requiring conscious experience
Relevant for animal studies as they may lack consciousness

Question 7

What are the 3 key criteria for this retrospective aspect of episodic-like cognition?

Answer 7

1. Content: a what-when-where memory of a single past experience
2. Structure: what-when-where components are bound together to discriminate overlapping memories e.g. in the sample place but different events at different times
3. Flexible deployment: use the information to generalise across episodes e.g. learn from past experiences

Question 8

What is the network of place cells like within CA3?

Answer 8

Can be connected with each other with different strengths, usually a one-way projection from neuron to neuron.
If the connection is strong the neuron projected to will be affected more by an action potential from the projecting neuron
The relation between different spatial locations may be stored in the connections between place cells

Question 9

What other connections could be made in the CA3?

Answer 9

In the CA3 of humans, relations between more abstract concepts, e.g. persons, may be stored

Question 10

What is synaptic plasticity?

Answer 10

Changes in synaptic strengths, possibly the neural correlate of learning?

Question 11

Outline spike timing dependent plasticity

Answer 11

• Neuron 1 has an excitatory connection to neuron 2
• If neuron 1 fires briefly BEFORE neuron 2, it strengthens the connection from neuron 1 to neuron 2
• If neuron 1 fires briefly AFTER neuron 2, then it will weaken the connection from neuron 1 to neuron 2

Question 12

What does spike timing dependent plasticity relate to?

Answer 12

Correlation coding

Question 13

How do we organise the timings of action potentials?

Answer 13

Through looking at oscillations, as the relative timing of APs in 2 connected neurons may be important for learning

Question 14

What are oscillations?

Answer 14

They reflect behavioural states and can be measured through EEG or local field potentials using electrodes

Question 15

What do oscillations reflect?

Answer 15

A temporal organisation of large networks of neurons

May provide a temporal reference similar to a clock - thereby the timing of APs of different neurons can be investigated

Question 16

Which oscillations are looked at in relation to hippocampus spikes?

Answer 16

Theta oscillations, which are around 8Hz, important for organising the timing of spikes

Question 17

What is a spike phase?

Answer 17

The phase tells us what the relation is between spikes and the oscillation
Can be seen that spikes don’t occur at random times relative to the oscillations

Question 18

Give an example of phase locking

Answer 18

Spikes occur at a preferred phase e.g. always occurring at the peak, which indicates that the neuron activity is modulated by the oscillation
Can visualise this in a histogram of spike phases (X axis = 0-360^, Y axis = No. of spikes)

Question 19

What happens when there is more variability in phase locking?

Answer 19

There will be a broader distribution on the histogram

Question 20

What can be said about phase locking in hippocampal neurons?

Answer 20

Different types of neurons are active at different theta phases e.g. pyramidal cells have different phase locking patterns to PV basket cells

Question 21

What is phase precession?

Answer 21

From cycle to cycle the spike phase decreases
Can use this phenomenon to understand how the spike times are organised in the hippocampus
This systematic precession happens in the place cells of the hippocampus relative to theta oscillations
Spike sequences that reflect behavioural sequences

Question 22

What is an example of phase precession research in animals?

Answer 22

An animal is at one side of a linear track with food at the other end.
As the animal crosses the track, there will be multiple cells in the hippocampus that have this place field and will become more active at these points, thus producing respective spike trains
Looking at the produced spike trains in relation to the theta oscillations can see the space advancement and phase precession

Question 23

What can be found when looking at multiple place cells in phase precession?

Answer 23

You can see the organisation between (for example) place cell A, B and C, with A firing just before B and B firing just before C
If looking just at A and C can see the greater distance in place fields reflected in the spike train organisation
Important because as the animal walks along the linear track it will experience a sequence of place cells also represented in phase precession within each theta cycle

Question 24

What can these sequences of phase precession be used for?

Answer 24

Storing spatial-temporal relations between place cells, relating back to spike-time dependent plasticity and strengthening the connection from A to B and B to C

Question 25

What does this phase precession also relate back to?

Answer 25

Episodic memory, through storing this sequence into a network using spike timing dependent plasticity
May be a simple form of an episode for an animal, same principle may apply for more abstract concepts in humans

Question 26

What can the place cell sequences be described as?

Answer 26

The sequences are compressed from a behavioural timescale (seconds) to a synaptic timescale (milliseconds)