Lecture 8 - Hippocampus, Memory, and Synaptic Plasticity Flashcards
Why are rodents commonly used in memory research?
- Rodents are convenient due to their size, quick learning, and ease of housing.
- Their hippocampus is also large and easily identifiable, making them ideal for memory studies
Where is the hippocampus located and what are its key regions?
The hippocampus is in the medial temporal lobe and includes regions CA1, CA2, CA3, and the dentate gyrus
Who discovered place cells, and what are they?
- O’Keefe & Dostrovsky (1971) discovered place cells, which are hippocampal neurons that fire when an animal is in a specific location
- O’Keefe proposed that they contribute to a “cognitive map” used for spatial navigation
What is the Morris Water Maze, and what does it assess?
- The Morris Water Maze is a test of spatial learning in rats using a hidden platform in opaque water
- Learning is measured by how quickly the rats find the platform and memory by how long they search the former platform location (probe test)
What do hippocampal lesions reveal in the Morris Water Maze?
Rats with hippocampal lesions show impaired place navigation (spatial learning) but intact cue navigation (learning based on visible cues? This suggests the hippocampus is critical for spatial memory.
What did Donald Hebb (1949) propose about learning?
- Hebb’s rule states that “cells that fire together wire together.”
- When two neurons are active together repeatedly, the connection between them strengthens, forming the basis of learning and memory
What is Hebbian synaptic transmission?
- Hebbian synaptic transmission is a learning mechanism where the co-activation of neurons strengthens their synaptic connection
- This principle supports long-term memory formation
How is the hippocampal circuit involved in memory encoding?
- Input: Entorhinal cortex –> Perforant path —> Dentate gyrus –> CA3 –> CA1
- This pathway is key in relaying and processing memory information
What did Boss and Limo (1973) discover about synaptic plasticity?
They found that high-frequency (titanic) stimulation of the perforant path leads to long-lasting increases in synaptic strength in the dentate gyrus, called Long-Term Potentiation (LTP)
What is Long-Term Potentiation?
- LTP is a long-lasting increase in synaptic strength following repeated stimulation
- It is a fundamental mechanism for learning and memory
What are key properties of LTP?
- Long-lasting (can persist for hours or longer)
- Requires co-activation of pre and postsynaptic neurons
- Is input-specific and associative (Hebbian)
What are the roles of NMDA and AMPA receptors in LTP?
- NMDA receptors are essential for LTP. They allow Ca2+ entry only when glutamate binds and the postsynaptic neuron is depolarised
- AMPA receptors mediate normal synaptic transmission
Why is the NMDA receptor called a “coincidence detector”?
- The NMDA only opens when two events occur together: glutamate binds and the postsynaptic membrane is depolarised
- This allows calcium ions (Ca2+) to enter, which is essential for synaptic plasticity
What blocks the NMDA receptor at rest, and how is it removed?
- A magnesium ion (Mg2+) blocks the NMDA channel at rest
- Depolarisation of the membrane removes this block, allowing Ca2+ to enter when glutamate is present
Why is calcium (Ca2+) influx important for LTP?
Ca2+ triggers intercellular processes that strengthen the synapse, solidifying the memory trace
How does LTP support learning and memory?
LTP enhances communication between neurons, making future signal transmission easier and more effective, an essential component of long-term memory storage
What is the overall conclusion about the hippocampus and memory?
- The hippocampus is essential for spatial learning and memory, forming the “where” part of episodic memory
- it supports LTP, which underlies synaptic plasticity and learning
