Single-trial dynamics of neural activity in parietal cortex during decision-making

Summary

Date: 
May 3, 2017 - 1:00pm - 2:00pm
Location: 
Northwest 243
About the Speaker
Name: 
Jonathan Pillow (Princeton University)

Neural firing rates in the macaque lateral intraparietal (LIP) cortex
exhibit gradual "ramping" that is commonly believed to reflect the
accumulation of sensory evidence during decision-making. However, ramping that
appears in trial-averaged responses does not necessarily indicate that the
spike rate ramps on single trials; a ramping average rate could also arise from
instantaneous steps that occur at different times on each trial. In this talk,
I will describe an approach to this problem based on explicit statistical
latent-dynamical models of spike trains. We analyzed LIP spike responses using
spike train models with: (1) ramping "accumulation-to-bound"
dynamics; and (2) discrete "stepping" or "switching"
dynamics. Surprisingly, we found that a majority of choice-selective neurons in
LIP are better explained by a model with stepping dynamics. We show that the
stepping model provides an accurate description of LIP spike trains, allows for
accurate decoding of decisions, and reveals latent structure that is hidden by
conventional stimulus-aligned analyses. Finally, I will discuss more recent
insights into the coding of decisions using simultaneous multi-neuron recording
in areas MT and LIP during decision formation.