lecture 5 - memory traces

What are the three main stages of the multi-store model of memory and their approximate durations?

Sensory memory (~300 ms) → Working memory (~20 s) → Long-term memory (decades).

How is short-term memory maintained according to the multi-store model?

By reverberating activity in networks of neurons.

How is long-term memory stored according to the multi-store model?

By changing the strength of connections between neurons in a network.

What happens during the recall of a memory?

An assembly (network) of neurons is reactivated; the reactivation is a partial match to the original experience due to differential synaptic strength.

What does reverberating neural activity in closed-loop circuitry mean?

Neurons continuously excite each other in a feedback loop, allowing a signal to persist after the original stimulus stops.

Who was Donald Hebb and what did he propose?

A key theorist who proposed that each significant event or thought corresponds to activity in a specific cell assembly—a group of interconnected neurons.

What is Hebb’s famous principle about synaptic strengthening?

“Cells that fire together, wire together.”

What does Hebbian learning explain about the association of inputs?

Two signals arriving close together in time can strengthen each other’s synaptic connections, linking their activity.

What evidence supports synapse strengthening in learning?

Artificial electrical stimulation can produce long-term synaptic strengthening.

Define long-term potentiation (LTP).

A long-lasting increase in synaptic strength following repeated or strong stimulation, thought to underlie learning and memory.

Define synaptic plasticity.

The ability of synapses to strengthen or weaken over time in response to activity or experience.

What happens when glutamate binds to AMPA receptors during LTP?

Na⁺ enters the postsynaptic neuron, depolarizing it and helping remove the Mg²⁺ block from NMDA receptors.

What occurs when NMDA receptors are unblocked?

Ca²⁺ enters the cell, activating pathways (e.g., CaMKII, PKC) that insert more AMPA receptors and strengthen synapses—producing LTP.

Describe the setup of the Morris water maze experiment.

A rat/mouse swims in opaque water to find a hidden platform using visual cues around the room.

What does the Morris water maze test?

Spatial learning and memory.

What happens to rodents given an NMDA antagonist during the water maze task?

They show decreased performance in finding the platform—indicating NMDA receptors are crucial for learning.

Give an example of an NMDA antagonist.

Ketamine.

What happens to a memory each time it is retrieved?

It becomes labile (unstable) and can be modified before being reconsolidated.

How can the reconsolidation process be therapeutically useful?

It can be targeted to modify or weaken traumatic memories, such as in PTSD treatment.

What enzyme is important for maintaining LTP?

Protein kinase M zeta (PKMζ).

What is ZIP (zeta-inhibitory peptide) and what does it do?

It inhibits PKMζ, blocking its activity.

What are the experimental effects of ZIP?

It can erase established LTP and disrupt long-term memory maintenance, though it does not prevent new memory formation.