Connectionists: New recording on the VVTNS YouTube channel: David Clark, Kempner Institute at Harvard University | Computation Through Neuronal-Synaptic Dynamics

[David Hansel]

[image: VVTNS.png]

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New on the VVTNS YouTube Channel
https://www.wwtns.online/past-seminars-2025-2026

*Computation Through Neuronal-Synaptic Dynamics*

lecture delivered on January 14, 2026  by

David Clark

Kempner Institute at Harvard University


*Abstract: *Computations in neural circuits are often construed as being
implemented through the coordinated dynamics of neurons. In this picture,
the role of synaptic connectivity is to sculpt neuronal dynamics to
implement computations of interest. Of course, synapses are not static but
change on a variety of timescales, including fast timescales comparable to
those of neurons. Thus, a more accurate view of computation in neural
circuits may involve the coupled dynamics of neurons and synapses. This
form of computation is closer to what is implemented by Transformers via an
equivalence between ongoing synaptic plasticity and self-attention. I  will
first describe a nonlinear recurrent neural-network model with ongoing
Hebbian dynamics of “fast” synapses atop unstructured “slow” synapses. I
will then describe two computations implemented through neuronal-synaptic
dynamics, which can be studied in this model using techniques including
dynamical mean-field theory and random-matrix theory. First, there exists a
novel phase termed “freezable chaos” in which a stable fixed point of
neuronal dynamics is continuously destabilized by synaptic dynamics. This
allows for the creation of a stable fixed point at any neuronal state
visited by the network by halting synaptic plasticity. Second, I will
describe an effect termed “persistent oscillations” in which, following
stimulation by a periodic signal, a plastic network continues to
autonomously reproduce a similar signal for a duration exceeding any
intrinsic timescale in the system. Thus, ongoing Hebbian plasticity can
provide a dynamic form of working memory, complementing the static form
provided by freezable chaos. Ongoing experimental work suggests that this
effect is realized in cortical organoids. Overall, this line of work
suggests that synapses should be promoted to first-class dynamical degrees
of freedom in our conceptual understanding of neural-circuit function.

*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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