The abrupt transition from theta to The abrupt transition from theta to hyper-excitable spiking activity in hyper-excitable spiking activity in
stellate cells from layer II of the medial stellate cells from layer II of the medial entorhinal cortexentorhinal cortex
Horacio G. RotsteinHoracio G. RotsteinDepartment of Mathematical SciencesDepartment of Mathematical Sciences
New Jersey Institute of TechnologyNew Jersey Institute of TechnologyNetwork Synchronization: From dynamical systems to neuroscience Network Synchronization: From dynamical systems to neuroscience
Leiden (NL) - May 27, 2008Leiden (NL) - May 27, 2008
Collaborators
Tilman Kispersky Program in Neuroscience - Boston University
Nancy Kopell Math & Center for BioDynamics – Boston University
Martin Wechselberger Math – University of Sidney
John White Biomedical Engineering – University of Utah
Entorhinal Cortex & Hippocampus
Photomicrograph of a section through the rat hippocampal region (Gluck & Myers). Adapted from Amaral & Witter (1989).
Photomicrograph of a section through the rat hippocampal region (Gluck & Myers). Adapted from Amaral & Witter (1989)
Stellate cells (SCs)
Entorhinal cortex (EC) is the interface between the neocortex and the hippocampus.
Information flows from the neocortex to the hippocampus through the superficial layers (II and III) of the EC. SCs are the most abundant cell type in layer II of the EC.
SCs are putative grid cells.
Subthreshold oscillations (STOs)
SCs develop rhythmic STOs at theta frequencies (8 – 12 Hz).
Spikes occur at the peaks of STOs but not at every cycle.
Interaction between two currents: h- and persistent sodium.
Single cell phenomenon
Depolarization increases from 1 to 3 (Adapted from Dickson et al., J. Neurophysiol., 2000)
SCs: Theta regime (background)
SCs have intrinsic biophysical properties that endow them with the ability to display rhythmic activity in the theta frequency regime (8 – 12 Hz)
Subthreshold oscillations (STOs): interaction between a persistent sodium and a hyperpolarization-activated (h-) current.
Spikes
Mixed-mode oscillations (MMOs): STOs interspersed with spikes
R., Oppermann, White, Kopell (JCNS – 2005) R., Wechselberger, Kopell (Submitted) Focus issue on MMOs (Chaos 2008)
SCs – Hyperexcitable regime (this project)
SCs have intrinsic biophysical properties that endow them with the ability to display spiking activity in the “gamma” frequency regime (~60 Hz).
This time scale can be uncovered by phasic excitation.
The frequency regime depends on a combination of intrinsic and network properties.
Kispersky, White & R. , Work in Progress.
SC dynamic structure
Nonlinearities and multiple time-scales in the subthreshold regime:
How are they created?
How do they depend on the intrinsic SC biophysical properties?
How do they interact with synaptic (excitatory and inhibitory) inputs?
SC biophysical model
SC biophysical model
SC biophysical model
Subthreshold oscillations (STOs) and spikes in the SC model
STOs generated by persistent sodium channel noise in the SC model
Subthreshold Regime: Reduction of Dimensions
Multiscale analysis: Identification of the active and inactive currents Identification of the appropriate time scales
Subthreshold Regime: Reduction of Dimensions
Multiscale analysis: Identification of the active and inactive currents Identification of the appropriate time scales
Subthreshold regime: reduced SC model
SC biophysical model Subthreshold regime
Subthreshold regime: reduced SC model
Subthreshold regime: reduced SC model
Subthreshold regime: reduced SC model
SC biophysical model Subthreshold regime
Subthreshold regime: reduced SC model
Nonlinear Artificially Spiking (NAS) SC model
Nonlinear Artificially Spiking (NAS) SC model
Nonlinear Artificially Spiking (NAS) SC model
Inhibitory inputs can advance the next spike by “killing” an STO.
Transition from theta to hyper-excitable (gamma) rhythmic activity
Experimental (in vitro) results:
There exist recurrent connections among SCs.
These connections are “similar” in normal (control) and epileptic cells.
Recurrent inhibitory circuits are reduced in epileptic cells as compared to normal (control) ones.
Recurrent circuits in layer II of MEC in a model of temporal lobe epilepsy. Kumar, Buckmaster, Huguenard, J. Neurosci. (2007)
Minimal S-I network model
Minimal S-I network model
A minimal S-S network reproduces the experimentally found transition form normal activity to hyper-excitability in SCs due to lack of inhibition
Minimal S-I network model
A minimal SIS network reproduces the experimentally found transition form normal activity to hyper-excitability in SCs due to lack of inhibition
Minimal SC network model (no inhibition)
A small increase in the SC recurrent synaptic conductance causes an explosion of the SC firing frequency
Minimal SC network model (no inhibition)
A small increase in the SC recurrent synaptic conductance causes an explosion of the SC firing frequency
Minimal S-I network model
A small increase in the inhibitory input to the SCs brings their frequency back to the theta regime
Single SC + autapse (no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC model representing a population of synchronized (in phase) SCs.
Single SC + autapse (no inhibition)
Effects of changes in the maximal conductances
Single SC + autapse (no inhibition)
Effects of changes in the maximal conductances
Single SC (no autapse - no inhibition)
Single SC (no autapse - no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC (no autapse - no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC (no autapse - no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC (no autapse - no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC (no autapse - no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC (no autapse - no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC (no autapse - no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC (no autapse - no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC + autapse (no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC + autapse (no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC + autapse (no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC + autapse (no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC + autapse (no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC + autapse (no inhibition)
The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation
Single SC + autapse (no inhibition)
Tilman Kispersky & John White
Dynamic clamp experiments
Dynamic clamp experiments
Voltage record of a stellate cell coupled to itself.
Inset: close up view of a single burst
Under control conditions
Dynamic clamp experiments
Voltage record of a stellate cell coupled to itself.
Inset: close up view of a single burst
Under linopiridine application (M-channel blocker)
Dynamic clamp experiments
Freq. vs. current under control conditions
Dynamic clamp experiments
Minimal S-I network model
Summary
SCs have intrinsic biophysical properties that endow them with the ability to display rhythmic activity in the theta and “gamma” frequency regimes (nonlinearities and time scale separation)
In “normal” conditions SCs display theta rhythmic activity (STOs and MMOs.
Abrupt transitions resulting from recurrent excitation.
Theoretical predictions confirmed by dynamic clamp experiments (Tilman Kispersky)