[Todos] Fwd: charla Jueves 14hs, Horacio Rotstein, LNI

[Ariel Zylberberg]

Hoy a las 14hs en el Laboratorio de Neurociencia Integrativa,
va a dar una charla Horacio Rotstein (http://web.njit.edu/~horacio/).

Abajo va el resumen de la charla, que versa sobre técnicas de dinámica
no lineal aplicadas a modelado neuronal. El que quiera venir por favor
confirme asistencia a arielz at df.uba.ar.

saludos,
Ariel


==============
Frequency preference response to oscillatory inputs in two-dimensional
neural models: a dynamical systems approach to subthreshold amplitude
and phase resonance


We investigate the dynamic mechanisms of generation of subthreshold
and phase resonance in two-dimensional linear and linearized
biophysical (conductance-based) models, and we extend our analysis to
account for the effect of simple, but not necessarily weak, types of
nonlinearities. Subthreshold resonance refers to the ability of
neurons to exhibit a peak in their voltage amplitude response to
oscillatory input currents at a preferred (resonant) frequency. Phase
resonance refers to the ability of neurons to exhibit a zero-phase (or
zero-phase-shift)
response to oscillatory inputs currents at a non-zero (phase-resonant)
frequency. We adapt the classical phase-plane analysis approach to
account for the dynamic effects of oscillatory inputs and develop a
tool, the envelope-plane diagrams, that capture the role that
conductances and time scales play in amplifying the voltage response
at the resonant frequency band as compared to smaller and larger
frequencies. We use envelope-plane diagrams to explain the underlying
mechanisms. In particular we explain why an increase in the time scale
separation causes an amplification of the voltage response in addition
to shifting the resonant and phase-resonant frequencies. We extend
this approach to explain the effects of nonlinearities on both
resonance and phase-resonance. We demonstrate that nonlinearities in
the voltage equation cause amplifications of the voltage response and
shifts in the resonant and phase-resonant frequencies that are not
predicted by the corresponding linearized model. The differences
between the nonlinear response and the linear prediction increase with
increasing levels of the time scale
separation between the voltage and the gating variable, and they
almost disappear when both equations evolve at comparable rates. In
contrast, voltage responses are almost insensitive to nonlinerities
located in the gating variable equation. The method we develop
provides a framework for the investigation of the preferred frequency
responses in higher-dimensional and nonlinear neuronal systems.


==============
Frequency preference in two-dimensional neural models: a linear
analysis of the interaction between resonant and amplifying currents


Many neuron types exhibit preferred frequency responses in their
voltage amplitude (resonance) or phase shift to subthreshold
oscillatory currents, but the effect of biophysical parameters on
these properties is not well understood. We propose a general
framework to analyze the role of different ionic currents and their
interactions in shaping the properties of impedance amplitude
and phase in linearized biophysical models and demonstrate this
approach in a two-dimensional linear model with two effective
conductances gL and g1. We compute the key attributes of impedance and
phase (resonance frequency and amplitude, zero-phase frequency,
selectivity, etc.) in the gL-g1 parameter space. Using these attribute
diagrams we identify two basic mechanisms for the generation of
resonance: an increase in the resonance amplitude as g1 increases
while the overall impedance is decreased, and an increase in the
maximal impedance, without any change in the input resistance, as the
ionic current time constant increases. We use the attribute diagrams
to analyze resonance and phase of the linearization of two biophysical
models that include resonant (Ih or slow potassium) and amplifying
currents (persistent sodium). In the absence of amplifying currents,
the two models behave similarly as the conductances of the resonant
currents is increased whereas, with the amplifying current present,
the two models have qualitatively opposite responses. This work
provides a general method for decoding the effect of biophysical
parameters on linear membrane resonance and phase by tracking
trajectories, parametrized by the relevant biophysical parameter, in
pre-constructed attribute diagrams


==============