What are the different kinds of circuits that may underlie memories?
- Neural chain
- Superordinate/Modulatory ciruits
- Cell assembly
What is a neuronal chain?
- Also called monosynaptic circuit
- Simple neuron to neuron connection
- Can be seen in monosynaptic reflex arcs
What is a superordinate circuit?
• A simple neuronal chain is modulated
by the activity of a third neuron
• Example of this later (eye-blink
conditioning)
What is a cell assembly?
- Many neurons form a complex network
- This is the structure in which memories are most likely stored
- Strengthening or weakening occurs through plastic changes of individual nodes
- Every single neuron can belong to a variety of cell assemblies
How were place cells found and what were the results?
Set up:
• Rat had to walk through a maze
• The activation of various neurons within a rat’s hippocampus were measured
Results:
• The activation of each neuron was restricted to a specific area of the maze
What is the explanation for place cells?
• Only a radical disruption of the environment could change this spatial orientation.
Meaning that after moving through the altered environment the place cells would get
“updated”.
• It could be said that the hippocampus keeps a spatial map of your environment and highly
correlated to episodic memories.
What are possible enhancements of neuronal connections?
- More neurotransmitter (NT) released
- Larger pre-and postsynaptic area
- Interneuron causes increased NT release
- New synapses formed
- Shift in synaptic input
What are the 4 facts of early LTP?
- Works based on existing proteins
- Does not require gene expression
- Can be based on a single stimulation
- Only temporary
What are the 7 steps of early LTP`?
- Single strong activation
- Glutamate released from presynaptic
cell - Glutamate opens AMPA receptors
- Na+ flows through AMPA and
depolarizes postsynaptic cell - Mg²+ leaves NMDA receptor (because of
the depolarization) - Ca²+ flows into postsynaptic cell via the
NMDA receptors and activates protein
kinases (CaM Kinase) - CaMK makes more AMPA receptors
available and further activates the ones
already available
What are the 4 facts of late LTP?
- Requires new protein synthesis
- Requires gene expression
- Requires repeated experience or coactivation
- Long lasting
What are the 7 steps of late LTP?
- Repeated activation/ stimulation
- Calcium activates CaMK (same
mechanism as in early LTP) - The protein kinases (CaMK) activation
leads to activation of CREB - CREB triggers expression of “immediate
early genes - IEGs - IEGs produce RNAs – Proteins
- These proteins activate Late Genes –
LGs - LG expression leads to structural
changes in the neuron, causing longterm
changes in synaptic efficiency (e.g.
more receptors)
What is systems consolidation?
Refers to the changes in neural networks in the brain that result from the combination of all cellular and synaptic changes following an experience
Which lesions lead to semantic memory loss?
Lesions in the association cortex will give lesions that may be more semantic in nature, and may to some extent show modality specifity
Which lesion lead to episodic memory loss?
Anterior temporal lobe lesions including the hippocampus will give deficits dominate by anterograde and retrograde (episodic) memory loss
