One question I keep coming back to in olfaction is deceptively simple: before odors reach the downstream classifier-like layers of the brain, what should the early circuit do to the raw receptor responses?
Olfactory receptor neurons (ORNs) already transform chemical mixtures into neural activity. But their responses can be redundant, correlated, and strongly shaped by nuisance variables such as total concentration. A good preprocessing circuit should keep the useful relationships between odors while making the representation more efficient for downstream computation.
This is where similarity matching becomes a useful lens.