A theory of memory based on the networks of associations that connect different bits of information. Each piece of information within a network is called a node, which may be in the form of images, smells, memories, emotions, etc. For example, the word dog may be linked associatively with characteristics such as barking, makes the house untidy or even with the emotion of fear, which may be based on an idiosyncratic episodic memory of being bitten by a dog in childhood. According to spreading-activation theory, activating one node in a network triggers activation in closely related nodes, i.e. it spreads activation to related information stored in memory. This spreading activation does not have to start with a word, but may be triggered by a thought, an image or even a smell.