What role does perisomatic cell, dendritic inhibitory neurons and interneuron-targeting interneurons have?
persio.: regulation of output
dend. inhibitory neurons: regulation of input
interneuron-targeting: disinhibition
What transmembrance currents contribute to extracellular potential?
action potential
synaptic currents
dendritic spikes
intrisic currents
What are the forward and inverse models in the context of Local Field Potentials (LFP)? And what are "current dipole scenarios"?
→ Predicts the extracellular voltage (LFP) based on known transmembrane currents. → Uses physical laws (e.g., Laplace’s equation). → Example: Simulating how synaptic currents create a measurable LFP.
→ Estimates the underlying current sources from a measured LFP. → Ill-posed problem (many possible sources → one measurement). → Used in: CSD analysis, source localization.
What is the difference between a short dipole and a long dipole in the context of LFP generation? Why does it matter?
Current source and sink are close together
Electric fields cancel each other out
➤ Weak contribution to the extracellular potential (LFP)
Example: Symmetric, compact neuron activity
Source and sink are far apart (e.g., across cortical layers)
Fields do not cancel, leading to stronger net field
➤ Strong contribution to the LFP
Example: Pyramidal cells with aligned dendrites
Why do hippocampal networks synchronize at theta and gamma frequencies?
Theta (4–10 Hz): Organizes timing of neuronal activity (e.g. for memory, navigation).
Gamma (30–100 Hz): Coordinates local cell assemblies for fast information processing.
Together: Enable precise, layered coding of experience (theta = time frame, gamma = content).
What does the LFP reflect in hippocampal recordings?
LFP = Mixed signal from local recurrent activity + upstream inputs.
Reflects synchronous synaptic currents, not individual spikes.
Represents network-level dynamics.
What does “phase-specific theta dynamics” mean in hippocampal-entorhinal circuits?
Different inputs (e.g. EC2, EC3, CA3) are active at specific phases of the theta cycle.
Leads to phase-locked activation across DG, CA3, CA1.
Enables temporal segregation of information flow → critical for encoding and sequence learning.
What happens when excitability increases in cortical circuits?
Increased excitability leads to high-frequency synchronization of neurons.
Networks shift into fast, rhythmic firing (e.g. gamma range: 30–100 Hz).
Supports attention, sensory processing, and memory encoding.
What are ING and PING models of gamma oscillations?
ING (Interneuron Network Gamma): Oscillations generated by mutual inhibition among interneurons. No excitatory input required.
PING (Pyramidal Interneuron Gamma): Excitatory neurons activate interneurons, which then inhibit them back. Rhythm emerges from E–I feedback loop.
How do brain oscillations coordinate information flow between regions?
Oscillations regulate timing of neuronal communication.
Phase determines when neurons are most receptive.
Enables selective, directed information transfer between sender and receiver regions.
Prevents interference and enhances network efficiency.
What are place cells and what is phase precession?
Place cells fire at specific locations in space (place fields).
Phase precession: As the animal moves through the field, the neuron fires at earlier phases of the theta cycle.
Allows temporal coding of spatial sequences.
Supports navigation, memory, and sequence prediction.
How do theta oscillations support the linking of cell assemblies?
Theta provides a temporal scaffold for organizing neuronal assemblies.
Within each theta cycle, different assemblies fire in sequence.
Phase precession encodes order and timing of spatial or event-related information.
Supports episodic memory, navigation, and prediction.
Front (Question): What is replay during sharp-wave/ripples, and why is it important?
Replay = reactivation of neural sequences from waking experience.
Occurs during sharp-wave/ripple events in sleep/rest.
Supports memory consolidation by strengthening connections and transferring info to cortex.
Blocking ripples impairs memory.
What are slow oscillations (<1 Hz) during sleep, and what is their role?
Slow oscillations are <1 Hz cortical rhythms in deep sleep (SWS)
Alternate between:
Down-state (neurons silent)
Up-state (neurons fire synchronously)
Function:
Synchronize cortical networks
Coordinate with spindles and ripples
Support memory consolidation
What is the system-level model of memory consolidation?
Hippocampus stores new episodic memories quickly
Neocortex stores memories long-term through offline consolidation
During sleep (SWS):
Hippocampus replays memories (ripples)
Cortex synchronizes via slow oscillations & spindles
Together, this allows transfer of memory from hippocampus to cortex
a) Explain the principle of experience-dependent correlated activity in the hippocampus with replay of neural activity in sleep.
During sleep, the hippocampus replays neural activity patterns that were formed during waking experiences — this is called experience-dependent replay. These reactivations occur during sharp-wave/ripple events and are believed to support memory consolidation by strengthening connections and transferring information to the neocortex.
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