Connectionists: World wide VVTNS series (fifth season): Wednesday, January 22, 2025, at 11:00 am EST| Srdjan Ostojic, Ecole normale supérieure, Paris

[David Hansel]

[image: VVTNS.png]
https://www.wwtns.online
<https://streaklinks.com/A9c7PbbpKY7PxB6PaAJWGD3-/https%3A%2F%2Fwww.wwtns.online>
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on twitter: wwtns at TheoreticalWide

You are cordially invited to the lecture given by

Srdjan Ostojic

Ecole normale supérieure, Paris


 on the topic of

Structured Excitatory-Inhibitory Networks: a low-rank approach


The lecture will be held on zoom on Wednesday, January 22, 2025, at *11:00
am EST *
To receive the zoom link: https://www.wwtns.online/register-page


*Abstract: * Networks of excitatory and inhibitory (EI) neurons form a
canonical circuit in the brain. Classical theoretical analyses of dynamics
in EI networks have revealed key principles such as EI balance or
paradoxical responses to external inputs. These seminal results assume that
synaptic strengths depend on the type of neurons they connect but are
otherwise statistically independent. However, recent synaptic physiology
datasets have uncovered connectivity patterns that deviate significantly
from independent connection models. Simultaneously, studies of task-trained
recurrent networks have emphasized the role of connectivity structure in
implementing neural computations. Despite these findings, integrating
detailed connectivity structures into mean-field theories of EI networks
remains a substantial challenge. In this talk, I will outline a theoretical
approach to understanding dynamics in structured EI networks by employing a
low-rank approximation based on an analytical computation of the dominant
eigenvalues of the full connectivity matrix. I will illustrate this
approach by investigating the effects of pair-wise connectivity motifs on
linear dynamics in EI networks. Specifically, I will present recent results
demonstrating that an over-representation of chain motifs induces a strong
positive eigenvalue in inhibition-dominated networks, generating a
potential instability that challenges classical EI balance criteria.
Furthermore, by examining the effects of external input, we found that
chain motifs can, on their own, induce paradoxical responses, wherein an
increased input to inhibitory neurons leads to a counterintuitive decrease
in their activity through recurrent feedback mechanisms. Altogether, our
theoretical approach opens new avenues for relating recorded connectivity
structures with dynamics and computations in biological networks.

*About VVTNS : Launched as the World Wide  Theoretical Neuroscience Seminar
(WWTNS) in November 2020 and renamed in homage to Carl van Vreeswijk in
Memoriam (April 20, 2022), 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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