From OpenCog

See also: ImportanceDiffusionAgent

The ImportanceSpreadingAgent takes the amount of excess importance that an atom has and spreads it along the HebbianLinks, with more importance being spread along HebbianLinks with higher TruthValues. This excess importance is defined as the amount of STI above the importance spreading threshold and this is usually greater than the attentional focus boundary to ensure that importance spreading doesn’t remove atoms from the attentional focus. This transfer of importance can then result in these destination atoms being elevated into the attentional focus, increasing their chances of being used in inference and other cognitive processes.