K Jensen, TC Kao, M Tripodi, and G Hennequin

#### Abstract

A common problem in neuroscience is to elucidate the collective neural
representations of behaviorally important variables such as head direction,
spatial location, upcoming movements, or mental spatial transformations.
Often, these latent variables are internal constructs not directly accessible
to the experimenter. Here, we propose a new probabilistic latent variable
model to simultaneously identify the latent state and the way each neuron
contributes to its representation in an unsupervised way. In contrast to
previous models which assume Euclidean latent spaces, we embrace the fact
that latent states often belong to symmetric manifolds such as spheres, tori,
or rotation groups of various dimensions. We therefore propose the manifold
Gaussian process latent variable model (mGPLVM), where neural responses arise
from (i) a shared latent variable living on a specific manifold, and (ii) a
set of non-parametric tuning curves determining how each neuron contributes
to the representation. Cross-validated comparisons of models with different
topologies can be used to distinguish between candidate manifolds, and
variational inference enables quantification of uncertainty. We demonstrate
the validity of the approach on several synthetic datasets, as well as on
calcium recordings from the ellipsoid body of *Drosophila melanogaster* and
extracellular recordings from the mouse anteriodorsal thalamic nucleus. These
circuits are both known to encode head direction, and mGPLVM correctly
recovers the ring topology expected from neural populations representing a
single angular variable.