A. Ramon y Cajal (1893)

• Learning and experiencing involve formation of new synaptic connections
• Brain as a neural net

B. Donald Hebb (1949) The organization of Behavior

• Experience represented by new or modified nural connections
• "Hebbian synapse"

• Synapses that are repeatedly activated become stronger and more efficient
• Possible mechanism of how information is stored

C. Diamond, Rosenzweig & Greenough (1960’s)

• Learning and experience can have direct physical effects on brain structure.
• Two types of information storage (Greenough):

1.  Experience-Expectant

• Organism is developmentally prepared to learn
• Critical Period

2.  Experience-Dependent

• Development is dependent on experience

A. Hebb’s Rats

1. Allowed "Free-run" of his house
2. Out-preformed lab rats on all learning tests
3. Enriched experience

B. Effects of the enriched environment

1. Bennett (1964) found "enriched rats" to have a heavier thicker cortex than "Isolated rats"
2. EC/IC Paradigm

• Developed by Rosenzweig, Diamond and Greenough late 1960’s
• Three conditions enriched

1. Enriched Condition (EC)
2. Social Condition (SC)
3. Impoverished Condition (IC)

    3.  Results

1. EC rats have larger neurons
2. 25% more synapses per neuron
3. 20% more dendrite per neuron
4. Increased acetycholine

• SC show many of the same effects of EC, but are still significantly lower than EC
• Blind Rats show same increases
• EC rats respond better to stress