If we start from this circuit: Input -> neuron_1 -> output ↓ ⋮ ↓ neuron_n And record neurons 1 to n simultaneously (where n could be very large). We can obtain a matrix of neural activity (neurons x time). 🧵2/5

A common approach to analysing this data would be to apply PCA (or another technique). Yielding a matrix of population activity (d x time). Where d < the number of neurons. A common interpretation of this would be that "the brain uses a low dimensional manifold to link this input-output". 🧵3/5

However, In this case, from the anatomy (circuit diagram above), we know that only neuron_1 is involved in the computation (transforming the input to the output). And the manifold we observe is misleading. 🧵4/5