Mechanisms of Learning and Memory Exam 2

What local field potential oscillations are prominent during wake, REM sleep and slow wave sleep?

-During waking/spatial exploration & REM, theta is the prominent oscillation

-During slow wave sleep, the prominent oscillation is the sharp wave ripple (also during immobility/eating)

*Theta & sharp wave ripple waves never occur at the same time

*Ripples are essential for memory consolidation

How are local field potentials generated?

Local field potential is reflective of membrane potential --> this is the physical mechanism where ions are moving through receptors which generates the electrical current

What is the difference between rate- and temporal-coding?

-Rate: the number of spikes in response to each stimulus (count spikes)

-Temporal: the timing of firing of neurons, relation to an ongoing oscillation (pattern)

What are theta sequences?

A compression of a sequence that can tell you where you were, are, and are going- this is because of phase precession or temporal coding that contains past, present, and future spikes.

What is the difference between theta oscillations and theta sequences?

Theta oscillations are rhythmic electrical activity in the brain, while theta sequences are specific patterns of hippocampal place cell firing that occur within those oscillations, representing compressed spatial trajectories.

Sharp Wave Ripples

High-amplitude bursts of EEG activity in the hippocampal region of the brain. Sharp wave ripples are associated with memory consolidation

What is replay?

Sequential activation that was activated during behavior during sharp wave ripples (to reach high spike dependant plasticity)

All that information can be compressed into a theta cycle while the animal is running (8x compression) -> then stops and switches to immobility and sharp ripple events and all the same neurons that were active are now active all at once (in about 50 milliseconds (20x compression)).

What is one way the THC decreases memory performance?

-THC messes up the coding processes - thus you can't properly encode those memories (can't replay and consolidate)

-Degrading neuronal coordination: THC messes up the spiking pattern of neurons (aka neuronal coordination/communication) - thus the neurons can't communicate to encode memories

-THC leads to less co firing of neurons

EEG

Monitors electrical activity of the first ~ 1nm of brain tissue; electrodes form a blanket over the cortex

Advantages of EEG

- Allows researchers to measure multiple brain regions at once

- Non-invasive

- Easy to administer

- Relatively cheap

- High temporal resolution

Disadvantages of EEG

- Does not measure deep, subcortical regions of the brain

- Low spatial resolution

- Only records the brain surface

PET Scans

Measures metabolic activity of the brain using radioactive ligands that are delivered through the bloodstream. These analogs can bind to receptors in the brain, which the researcher is interested in

Advantages of PET

- Whole brain imaging

- Specific to the ligand of choice

Disadvantages of PET

- Ethics?

- Difficult to administer

- VERY expensive

- Need radio-labeled ligand

What is BOLD response?

The change in blood oxygenation that accompanies neural activity. BOLD is not a proxy for neuronal signaling, because there is a lag behind the neuronal activity. Simply, BOLD is the response of the brain to neuronal activity

fMRI

A form of magnetic resonance imaging of the brain that registers blood flow to functioning areas of the brain

Advantages of fMRI

- Non-invasive

- Easy to administer

- Measures activity of the whole brain

Disadvantages of fMRI

- Low temporal resolution

- Signal source related to neural activity is not 100% known