What Is LTP?

At present, long-term potentiation (LTP) of synaptic transmission is the most widely studied model for neuronal change that occurs during learning and that stores information in the brain. When Bliss and Lømo discovered the phenomenon of LTP 30 years ago, it must have been a very exciting moment (see Bliss and Lømo, 1996, for a detailed account). The finding was an important step in the long ongoing search for the neuronal basis of memory formation in the nervous system. Even though anatomists such as Exner showed changes in neuronal connections that were induced by exposure to rich environments as early as 1884 (Exner, 1884), it was by no means clear how exactly neurons change in order to store information. Exner and others (Hebb, 1949; Hinton, 1992; Jodar and Kaneto, 1995) proposed activity-dependent, selective plastic changes in the connections between neurons that could “freeze” the pattern of activity of the neurons and therefore preserve information. The theoretical basis for LTP existed for a long time, and when LTP was described by Bliss and Lømo in a full paper (Bliss and Lømo, 1973), researchers in the field were more than ready for the actual empirical evidence that neuronal network processes might be used in the brain.

The basic principle of every neuronal net is that connections between neurons can change in a defined, use-dependent way thereby storing information. Such a system has certain attributes such as pattern completion, parallel processing, and self-instructing learning properties, all of which are characteristics of activity in working brains (Hinton, 1992; Jodar and Kaneto, 1995).