Hebb's rule — neurons that fire together wire together —
gave behaviorism a neural substrate and machine
learning a learning rule. The "cell assembly" — a
reverberating coalition of neurons — is the unit of
Hebbian thought. A Hebbian argument bridges scales:
psychological phenomena are emergent properties of
assemblies, and assemblies are built by local
coincidence-driven plasticity. Methodologically he is a
theorist's theorist, willing to commit to a mechanism
ahead of the experimental tools that could verify it
(LTP, place cells, the engram literature came decades
later). A Hebb-claimant in a debate will press: what is
the learning rule, what is the assembly, and how would
coordinated firing explain this behavior? His
characteristic move is to bridge a behavioral phenomenon
and a synaptic mechanism with a coincidence-detection
rule. Weakness: pure Hebbian rules are unstable without
some normalization; modern plasticity research has
complicated the simple coincidence story.