12-SystemsElectrophysiology2

Crowd Synchronization on London Millennium Bridge

pedestrians walk in step -> bridge swings

feedback btw bridge’s oscillations and walking rhythm

Male Fireflies Flashing in Unison

synchronize flashing to attract mates

-> adjust rhythms in response to neighboring fireflies

• Action potential (~1ms, tens of mV)

• Synaptic currents (tens of ms, few mV)

• Dendritic spikes, Ca spikes (10-100 msec, 10-50 mV)

• Intrinsic currents and resonances (10-500 msec, up to tens mV ), activity dependent

originates from synaptic inputs that generate transmembrane synaptic current, which include

• current sink (I1(t)), where positive ions flow in neuron

• current source (I2(t)), where positive ions flow out neuron

r1, r2 = distances to sink and source

σ = extracellular conductivity

• monopole: field decreases 1/r

  e.g stimulating monopolar electrode

• dipole: field decreases 1/r^2

  e.g synaptic currents in distal dendrites

• multipole: field decreases 1/r^3

  e.g action potentials involving multiple dipole

in closed field dipoles (e.g nuclear morphology)

minimal spatial separation btw sinks and sources result in weak contributions to LFP

in open field dipoles (e.g laminar morphology)

substantial spatial separation btw sinks and sources allows for stronger contributions to LFP

through different mechanisms:

• Perisomatic inhibition (e.g., basket cells, axo-axonic cells) control output of pyramidal neurons

• Dendritic inhibitory neurons (e.g., O-LM cells, bistratified cells)

  regulate input processing by controlling synaptic integration

• Interneuron-targeting interneurons (e.g., VIP cells)

  perform disinhibition, which can facilitate specific circuit activation

-> coordinate timing of excitatory neuronal firing, contributing to synchronization and generation of oscillatory rhythms

LFPs are extracellular recordings that reflect synchronous synaptic activity

key components:

• Low-freq bands (<300 Hz): synaptic input from distant sources

• High-freq bands (>500 Hz): capture spiking activity from local neurons

• Dipole contributions: LFP amplitude influenced by spatial configuration of current sources and sinks

  • open-field dipoles contribute strongly

  • closed-field dipoles contribute weakly

= phenomenon where firing of place cells shifts progressively earlier in theta oscillation cycle as an animal moves through place field

• observed by O’Keeve & Recce (1993) -> encoding of sequential locations within single theta cycle

• compresses real-world spatial sequences into short time scales -> useful for predicting future locations and recalling past positions

Hippocampal SWRs = high-freq bursts that occur primarly during slow-wave sleep and rest

• represent synchronized neuronal activity, involved in replaying past experiences

• sequences of place cells activity during awake states are replayed during SWRs

• Suppressing SWRs impairs spatial memory, suggesting they are curcial for consolidating newly acquired information

• SWRs coordinate with cortical slow oscillations and sleep spindles, facilitating memory transfer to the neocortex for long-term storage

Theta (4-10 Hz) and gamma (40-100 Hz) oscillations coordinate hippocampal activity by facilitating phase-amplitude coupling (PAC):

• Theta rhythm provides a slow temporal framework that aligns neuronal activity across different regions.

• Gamma bursts occur at specific phases of theta cycles, allowing precise information encoding and retrieval.

• Phase-specific gamma oscillations contribute to different processing tasks:

  • CA1 gamma: Links with entorhinal input for memory retrieval.

  • CA3 gamma: Supports pattern completion and memory storage.

  • Dentate gyrus gamma: Facilitates pattern separation.

• This interaction enables efficient communication between the hippocampus and cortex during learning and memory tasks.