3. Episodic Memory and Neural Coding Flashcards
episodic memory
receives and stores information about temporally dated episodes or events, and temporal spatial relations among these events (Tulving, 1972)
- memory of autobiographical events
requires consciousness, can you study it in animals then?
episodic-like memory
refers to behavioural criteria of episodic memory without requiring conscious experience (can study in animals)
- retrospective aspect of episodic like cognition, 3 criteria:
Clayton and Emery (2015)
hippocampus and episodic memory
- different networks of place cells in hippocampus representing different areas of the environment
- relation between spatial locations may be stored in the connection between place cells
- relationships between mire abstract concepts may be stored in CA3 of humans (episodic memory)
- connection strength related to amount of excitation/inhibition of presynaptic neurons (higher level function? - people or more abstract items maybe linked here)
Clayton and Emery (2015)
- content = what, when, where memory of single past experience
- structure = what, when, where components are bound together to discriminate overlapping memories (separate time, what happened…)
- flexible deployment = use the information to generalise across episodes
synaptic plasticity and learning
synaptic plasticity = the change in strength of a synapse
spike timing dependent plasticity = depends on the timing of AP’s.
- if N1 fires just before N2 and has an excitatory connection, the connection will become stronger
- if N2 fires just before N1, the connection will become weaker
- correlation coding in spike trains!
organising the timings of AP’s
oscillations reflect behaviour states
- extracellular recording through EEG = brain states
- oscillations reflect temporal organisation of large networks of active neurons
- may provide a temporal reference similar to a clock organising the AP’s of many neurons, perhaps related to plasticity
- timings of AP’s of different neurons can be orchestrated
- theta oscillations important in hippocampus
- Buzsaki (2002)
theta oscillation
8Hz (4-12Hz)
Buzsaki (2002)
recorded from 16 different sites in the hippocampus through the layers
- signals dominated by oscillations, shifting when going deeper into hippocampus
- important for organising the timing of spikes throughout the hippocampus
spike phase
shows the relationship between spikes and oscillations
- spike occur at peak of phase of oscillation
- if spikes occur at a preferred phase = phase locking - can be at peaks or troughs (usually not perfect, shows some variability)
- can be represented in histograms
- in the hippocampus different types of neurons are active at different theta stages
- phase precession = from cycle to cycle the spike phase decreases (systematic change in spike timing relative to theta oscillations)
phase precession
- vary on cell type, region and their neuromodulators
- systematic precession (advancement) of the spike phase relative to theta oscillations
- leads to a formation of spike sequences that represent spatial-temporal relations (behaviour sequences)
- strengthens synapses between place cells
- can use multiple place cells. strength of network represents an event in the outside world
- go through one place field, enter the second a little later represented in theta in short time scale (ms) - synapse gets stronger
storing spatial-temporal relations between place cells
neuron 1 excitatory connection to neuron 2
N1 fire > (ms) > N2 fires = stronger connection
- when walking through the environment the place cells synapses are strengthened (N1 > N2 > N3)
- place cells relate to each other in space and time in a network using spike time plasticity
- can be used to learn spatial-temporal relations between place cells
- place cells are sequences compressed from a behavioural timescale to a synaptic timescale (animals can learn about the succession of locations, could be how humans combine events in a timescale - precursor of episodic memory?)
