Developmental Approaches to the Memory Process

In the last half of the nineteenth century, scientists in fields ranging from histology to psychiatry were proposing that memory and development were intimately linked to subtle changes in neural processes. Because synapses were not visible with the microscopic techniques available at the time, these connections between neurons became the focus of much speculation. Ramon y Cajal (1893) suggested that learning might involve the formation of new synaptic connections between neurons. Tanzi (1893), noting that the resistance to transmission between neurons might vary with the size of the connection, proposed that frequent use of a synapse might produce growth similar to that produced by exercising a muscle, thereby strengthening preexisting connections. Both theories assumed that the structural plasticity seen in development extended into adulthood, a concept that was not demonstrated until nearly a century later. Little theoretical or empirical progress was made along this line until Hebb (1949) suggested how experience could be represented in new or modified neural organizations. Rejecting the "one memory — one neuron" concept.