The Hebb Rule for Synaptic Plasticity: Algorithms and Implementations

In 1949 Donald Hebb published "The Organization of Behavior," in which he introduced several hypotheses about the neural substrate of learning and memory, including the Hebb learning rule or Hebb synapse. At that time very little was known about neural mechanisms of plasticity at the molecular and cellular levels. The primary data on which Hebb formulated his hypotheses was Golgi material, provided mainly by Lorente de No, and psychological evidence for short-term and long-term memory traces. Hebb's hypotheses were an attempt to understand the development and the organization of behavior based on the antamomical and physiological data available to him, though they did not constitute a model for learning or memory in a formal sense. Some 40 years later we now have solid physiological evidence, verified in several laboratories, that long-term potentiation (LTP) in some parts of the mammalian hippocampus follows the Hebb rule (Kelso et al., 1986; Levy rt al., 1983; McNaughton et al., 1978; Wigstrom and Gustafsson, 1985; McNaughton and Morris, 1987; Brown et id., 1988; see Chapter 14 in this volume). However, Hebb was primarily concerned with cerebral cortex, not the hippocampus. The relevance of Hebbian plasticity in the hippocampus to Hebb's original motivation for making the hypothesis is not obvious, although LTP may well be found under somewhat different circumstances in cerebral cortex (Artola and Singer, 1987; Komatsu et nl., 1988). The Hebb rule and variations on it have also served as the starting point for the study of information storage in simplified "neural network"