[CTN] CTN seminar: Dr. Paul Cisek, 3:30 Nov 20, PAS 2464

[Bryan Tripp]

Hi everyone,

The next CTN seminar will be next Friday (not Tuesday!) the 20th at 3:30,
in PAS 2464. Paul Cisek is visiting from University of Montreal. The title
and abstract follow.

Please let me know if you would like to meet with Paul and/or join us for
dinner after the talk.

Regards,
Bryan

The neural dynamics of dynamic decisions

During natural behavior, animals must continuously make decisions in a
rapidly changing environment. Recent studies suggest that in such
conditions, the brain simultaneously represents multiple potential actions
that compete against each other within the same sensorimotor control
circuits involved in execution. Here, I present analyses of neural spiking
activity recorded from the cerebral cortex of monkeys, while they decided
between two reaching movements based on a changing stimulus indicating
which is more likely to be rewarded. We represent the state of the system
as an evolving trajectory in a very high-dimensional space where each axis
corresponds to the activity of one neuron, and use dimensionality reduction
to project this to a 9-dimensional space capturing most of the variance in
the data. We find that during the process of deliberation, the neural state
evolves upon a roughly two-dimensional “decision manifold” defined by
orthogonal components related to sensory evidence and the growing urge to
respond. The moment of commitment occurs when the neural state falls off
the edge of this manifold into one of two orthogonal attractors that lead
to the initiation of the movements. We find qualitatively different
decision manifolds in different brain regions. For example, the manifold in
premotor cortex is significantly curved while in primary motor cortex it is
remarkably linear. We conjecture that the premotor cortex implements a
non-linear recurrent attractor system in which the decision is made, and
this is read-out by the primary motor cortex to initiate the chosen action.
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