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Lecture 6

PSY397H5 Lecture Notes - Lecture 6: Timothy Bliss, Long-Term Potentiation, Pyramidal Cell

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Robert Gerlai

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Lecture 6
Long Term Potentiation: The electrophysiology of learning and memory
- Mental time travel: We can go back in the past, analyze our memories, and forecast what will
happen in the future.
- Learning occurs at the synaptic level
- Hippocampal function is important in many species
- Place cells: How can a neuron in the hippocampus put together bits and pieces of information?
o Long term potentiation: Alters the connectivity between neurons. Neurons connect via
synapses, which allow for neuronal connection between one neuron to the next. The
strengthening of the connection between the synapses is what causes long term
LTP is a long-lasting change produced by a brief stimulus
- Electrical signal conversion is not similar to electricity running through a wire. Depending on the
strength of synapse, it will determine whether the AP will go to the next neuron.
- For example: You have 20 neurons that encode for a memory for a specific event. The
hippocampus knows that only these 20 neurons will associate with that specific event, and it is
all due to pyramidal cells.
- Example: If you go to a food court you smell something that reminds you of a food you ate 20
years ago. The neuron in your brain activates when you smell that familiar smell.
- Connectivity between pyramidal cells and cortex is what allows us to recall memories.
- How does it strengthen or weaken in relevant connections with neurons in the brain? LTP
- Long term depression: Weakening of synaptic connections
- Long term potentiation: Strengthening of synaptic connections.
Figure 1
- Memory is stored in the cortex
- Pyramidal cells in the CA1 region strengthens the
connection between neurons and itself
- The triangle represents a pyramidal cell
- The connections represent particle memory pieces
- Particle subset of memory pieces
- Relational connection between multiple memory pieces
episodic memory connects to multiple neurons
- LTP allows for connections to be established between
certain neurons only and gets rid of all other ones.
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The Cellular and Molecular Basis of Organisms/Memories are stored as alterations in the strength of
synaptic connections between neurons in the CNS
- Prior to when neurobiologists discovered strengthening and weakening (or the biology behind
LTP), Hebb wrote a book where he theorized his postulates.
- He as uaare of hat it as alled ad stated it as proess
- After he postulated it as Neuros that fire together ire together
- In terms of memory, we know about the behavioral, place cell, and electrophysiological aspects.
- However, we are unaware of how pyramidal cells connects all neurons in the brain.
The Discovery of LTP
- Timothy Bliss was the person who discovered LTP, along with Lomo
Bliss ad Loos First Published LTP Experiment
- Bliss took out the brains of the rabbits, sliced the hippo campuses, sliced it into chambers, etc
- He had an electrode that recorded unstimulated neurons. It was difficult to do this because any
hage i euroal atiity oulde ee due to other fators like teperature hages
- There was no change for 6 hours. The brain tissue had been placed in the artificial chamber for 6
hours and neurons had been responding to all sorts of factors.
- During stimulation, a single electric pulse (1 hertz) was sent every second. Afterwards neuronal
activity was measured in response to each pulse.
- Electricity was injected into presynaptic terminal. In the post synaptic terminal, NTs were
released and created depolarization and EPSP
o Bliss measured the depolarization
- Tetanus/Tetanic stimulation: Tetanus has the same amplitude of electricity as a single pulse,
however it is of high frequency (100x per second 100 Hz)
o Even though the electric pulse and the tetanic pulse were of same amplitude, there
were more tetai resposes hih the ireased its overall amplitude
o Frequency of stimulation changed
o After a single tetanus, he returned back to the single pulse and measured what the
response was to the single pulses, which was 3 times above the baseline.
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