For decades, the leading model of memory storage held that individual synapses encoded specific experiences. Strengthen a synapse, and you strengthen a memory. The model was elegant, experimentally tractable, and, it now appears, incomplete.
A team at the Howard Hughes Medical Institute spent four years mapping every synaptic connection in a cubic millimetre of mouse cortex — roughly one million neurons and 150 million synapses. What they found was a level of redundancy and cross-linking that the dominant model had not predicted.
The implication is not that the synaptic model is wrong, but that memory may be distributed across patterns of connectivity in ways that make individual synapses less like storage units and more like letters in an alphabet.
