Connectionists: REMINDER: World wide VVTNS series: Wednesday, February 7 2024 at 11am (ET), Nicholas Priebe | The University of Texas at Austin

[David Hansel]

[image: VVTNS.png]
https://www.wwtns.online - on twitter: wwtns at TheoreticalWide

You are cordially invited to the lecture  given by

Nicholas Priebe

The University of Texas at Austin

on the topic of

*"The origins of variable responses in neocortical neurons"*

The lecture will be held on zoom on *February 7, 2024*, at *11:00 am ET *

Register on our website - https://www.wwtns.online  -to receive the zoom
link


*Abstract:*  I will discuss a collaborative project studying the origins of
variable responses in neocortical neurons.  The spiking responses of
neocortical neurons are remarkably variable. Distinct patterns are observed
when the same stimulus is presented in the sensory areas or when the same
action is executed in motor areas. This is quantified across trials by
measuring the Fano factor of the neuronal spike counts, which is generally
near 1, consistent with spiking times following a noisy Poisson process.
 The two candidate sources for noise are the synaptic drive that converges
on individual neurons or intrinsic transducing processes within neurons. To
parse the relative contributions of these noise sources, we made whole-cell
intracellular recordings from cortical slices and used in the whole cell
dynamic clamp configuration while using dynamic clamp to injecting
excitatory and inhibitory conductances previously recorded in vivo from
visual cortical neurons (Tan et al. 2011).  By controlling the conductance
directly, we can test whether intrinsic processes contribute to poisson
firing. We found that repeated injections of the same excitatory and
inhibitory conductance evoked stereotypical spike trains, resulting in fano
factors near 0.2. Varying the amplitude of both excitatory and inhibitory
conductances changed the firing rate of recorded neurons but not the Fano
factor. These records indicate that intrinsic processes do not contribute
substantially to the Poisson spiking of cortical cells. Next, to test
whether differences in network input are responsible for Poisson spike
patterns, we examined spike trains evoked by injecting excitatory and
inhibitory conductances recorded from different presentations of the same
visual stimulus. These records exhibited different behaviors depending on
whether the injected conductances were from visually-driven or spontaneous
epochs: during visually-driven epochs, spiking responses were Poisson (Fano
factor near 1); during spontaneous epochs spiking responses were
super-Poisson (fano factors above 1).  Both of these observations are
consistent with the quenching of variability by sensory stimulation or
motor behavior (Churchland et al. 2010).  We also found that excitatory
conductances, in the absence of inhibition, are sufficient to generate
spike trains with Poisson statistics. Our results indicate that the Poisson
spiking emerges not from intrinsic sources but from differences in the
synaptic drive across trials, the nature of this synaptic drive can alter
the nature of variability, and that that excitatory input alone is
sufficient to generate Poisson spiking.

*About VVTNS : Created as the World Wide Neuroscience Seminar (WWTNS) in
November 2020 and renamed in homage to Carl van Vreeswijk in Memoriam
(April 20, 2022), its aim is to be a platform to exchange ideas among
theoreticians. Speakers have the occasion to talk about theoretical aspects
of their work which cannot be discussed in a setting where the majority of
the audience consists of experimentalists. The seminars, **held on
Wednesdays at 11 am ET,**  are 45-50 min long followed by a discussion. The
talks are recorded with authorization of the speaker and are available to
everybody on our YouTube channel.*

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-- 
'Life is good ..' (Carl van Vreeswijk, 1962-2022)
---------------------------------------
David Hansel
Directeur de Recherche  au CNRS
Co-Group leader
Cerebral Dynamics Plasticity and Learning lab., CNRS
45 rue des Saints Pères 75270 Paris Cedex 06
Tel (Cell):   +33 607508403



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