Nice writeup of Keith Murray, our UROP who works with Jaedong and Akhilan!

# Author: ilafiete

## Long overdue: hierarchical latent inference in neural circuits

I realize I didn’t announce Rylan’s work on neural circuits performing hierarchical latent inference when it appeared in NeurIPS last December! Here’s a brief summary:

Often we must make decisions between two alternatives, but which of the two is more likely to result in a payoff might change over time. The International Brain Laboratory trains animals in a setting where the payoff balance between the two switches discretely, and the switches are uncued. To make a good decision, animals must infer the unknown balance of payoff probabilities, by accumulating information over multiple trials. In addition, each trial requires integration of evidence. Rylan showed how a neural circuit can perform this latent hierarchical inference task, by training RNNs. The RNN finds solutions that are not Bayesian but rather simple linear filters over time. It also uses the same coupled activity subspace to integrate evidence both within-trial and across-trials, albeit with different time-constants.

We also introduce a new method for network “distillation”, RADD: training a small network based on the hidden states of a bigger network to achieve a highly compact network that can solve the same latent inference problem (when the small network trained directly on the problem cannot do so). Next up: comparison of model predictions with neural data.

## Congrats to Rylan and Aaditya for grad school decisions

Rylan accepted Stanford CS and Aaditya accepted UCL/Gatsby, after making a clean sweep. Congrats to both! Both are also beginning summer (2021) internships @ DeepMind.

## NSF Grad Fellowship Award: Akhilan

Congratulations to Akhilan for his selection as an NSF Graduate Fellow!

## Welcome, Dounia!

Thrilled to have Dounia Mulders join the group. Dounia comes from an applied math/engineering background from Louvain, and is interested in modeling pain.

## Congrats Akhilan and Aaditya — 2021 Hertz finalists!

Very proud that Akhilan and Aaditya are both finalists for the Hertz Foundation Fellowship!

## Welcome, Sarthak and Akhilan!

Delighted and excited to have Sarthak join the lab as a postdoc, and Akhilan as a Ph.D. student. Read more about them in their bios (coming soon)!

## Circuit inference biased in strongly recurrent networks and a possible solution

Abhranil’s new paper is out! Congrats Abhranil.

We show that connectivity inference from activity in strongly recurrent networks will be systematically biased regardless of data volume and even given access to every neuron in the network. But measuring activity far-out-of equilibrium after a simple low-dimensional suppressive input could ameliorate the bias.

## Memories from patterns: a review

“Memory from patterns: Attractor and integrator networks in the brain”, with Mikail, is submitted. Comments and suggestions are welcomed!

The theory of how complex patterns emerge from simple interactions and constituents is one of the big ideas in biology, explaining animal coats and morphogenesis.

The same principles can produce dynamical states for computation in the brain, in the form of attractor networks. We review how attractor networks generate states for robust representation, integration, and memory.

Our review covers the conceptual ideas, the theory, and the potential utility of continuous and discrete attractor networks, then focuses on the empirical evidence that the brain computes using these structures. Finally, we discuss modern developments in combining the concepts of modularity and attractors, and list future challenges.

We hope the review provides a vista of a field of systems neuroscience driven by theoretical ideas, where theory and experiment have come together fruitfully and harmoniously.

## What are the main sources of homing error in young and aging humans?

Matthias and Ingmar’s paper is out in Nature Communications!

Homing, or determining the straight path back to “home” after a winding outbound journey, is a critical but error-prone computation.

What are the main causes of human homing error, and how do they change with age?

We put humans into immersive VR, measured homing errors along winding paths, and modeled the time-resolved process of error accumulation with a Langevin-type diffusion equation.

We found that forgetful integration, biases in velocity estimation or integration, and reporting or readout errors do not limit homing ability; rather, the bottleneck is an accumulation of unbiased random error.

The random error accumulates with movement but not time, suggesting it is related to velocity sensing rather than integration.

Aging humans do worse; their diminished performance is not from new sources of error but an increase in the unbiased error already limiting young subjects.