Strong and weak principles of neural dimension reduction

TL;DR

This paper discusses the conceptual distinction between weak and strong principles of neural dimension reduction, emphasizing their different implications for understanding neural circuit function and interpretation of high-dimensional neural data.

Contribution

It introduces a framework distinguishing weak and strong principles of neural dimension reduction and analyzes their implications for interpreting neural data and circuit function.

Findings

Weak principle treats dimension reduction as a data analysis tool.

Strong principle suggests dimension reduction reveals neural circuit operations.

Evidence supports both principles coexisting in brain function.

Abstract

If spikes are the medium, what is the message? Answering that question is driving the development of large-scale, single neuron resolution recordings from behaving animals, on the scale of thousands of neurons. But these data are inherently high-dimensional, with as many dimensions as neurons - so how do we make sense of them? For many the answer is to reduce the number of dimensions. Here I argue we can distinguish weak and strong principles of neural dimension reduction. The weak principle is that dimension reduction is a convenient tool for making sense of complex neural data. The strong principle is that dimension reduction shows us how neural circuits actually operate and compute. Elucidating these principles is crucial, for which we subscribe to provides radically different interpretations of the same neural activity data. I show how we could make either the weak or strong principles appear to be true based on innocuous looking decisions about how we use dimension reduction on our data. To counteract these confounds, I outline the experimental evidence for the strong principle that do not come from dimension reduction; but also show there are a number of neural phenomena that the strong principle fails to address. To reconcile these conflicting data, I suggest that the brain has both principles at play.