The Precedent in Biology
Before describing what PCM does, it is worth saying who else builds this way. The answer is: every mind we have ever observed in nature.
The brain does not store its knowledge in weights. It stores it as structure. The cortex is full of topographic maps that preserve geometry from one layer to the next. The primary visual cortex preserves the spatial arrangement of the retina; the somatosensory cortex preserves the topology of the body; the motor cortex preserves the layout of the muscles it controls. These are not pedagogical simplifications. Adjacent neurons in V1 actually respond to adjacent regions of the visual field. The shape of the cortex carries information that the firing rates by themselves do not.
The hippocampus is more striking still. Place cells fire when an animal occupies a particular location in its environment. Grid cells fire at the vertices of a triangular lattice that tiles whatever space the animal moves through. Together they form a coordinate system, a literal geometric representation of space, that the rest of the brain reads. The 2014 Nobel Prize in Physiology recognized this work because it changed how neuroscience thinks about representation itself.
In the last decade, the picture has generalized. The activity of large populations of neurons in many cortical areas traces out continuous low-dimensional structures, what the field now calls neural manifolds. The manifold is where the meaning lives. Two motor neurons can fire in different ways across two reaching motions, but the population trajectory on the manifold tells you which motion was being performed. The geometry, not the cells, is the signal.
We believe this is not coincidence. Geometry is what intelligence runs on, in the only working examples of intelligence we have. PCM is built on the same premise, applied to artificial substrate.