1. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
History of Brain Studies
Studies were shown as early as 1785
Malacarne used pairs of dogs and birds
From each pair one was trained extensively while the other was not
Trained subjects showed more folds and fissures in Autopsied brains, believed to be more complex for this reason
Research stopped for an unknown reason

2. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
New Technology (1960)
Experiments at University of California
Measure brain activity with great magnification, noting brain enzymes and neurotransmitters
Mark Rosenzweig, Edward Bennett, and Marian Diamond used these techniques in 16 experiments over 10 years
Used rats in the experiments

3. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
Why Rats?
Convenient
Cerebral cortex is smooth,
- easy to measure
Small and inexpensive
Large litters
Inbred rats allow researchers to include genetics in experiments if desired

4. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
Experiment
AIM: Believed rats raised in a highly enriched environment will demonstrate differences in brain growth and chemistry vs non stimulated
3 rats chosen from each litter
Randomly chosen for one of 3 environments
12 rats in each condition for 16 experiments

5. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
The Three Environments
Standard colony cage
Several rats with adequate space and plenty of food/water
Impoverished environment
Slightly smaller cage in an isolated room with adequate food and water
Enriched environment
6-8 rats lived in large cage with many different objects to play with, a new set everyday

6. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
Results
The cerebral cortex was significantly heavier and thicker in the “enriched” rats
The cerebral cortex deals w/ experience, movement, memory, learning and all sensory input
Greater chemical activity of acetylcholinesterase

7. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
Results
Same number of neurons but neurons were larger
Ratio of RNA to DNA (important for cell growth) was larger in “enriched rats”
Synapses of enriched rats brains were 50%
larger than the impoverished rats

8. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
Results
Although differences were not large they were consistent and repeatable
“There can now be no doubt that many aspects of brain anatomy and brain chemistry are changed by experience.”
- M. R. Rosenzweig

9. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
Discussion and Criticisms
Handling
Enriched rats handled more
Solved this problem by handling impoverished rats in different experiment (no brain growth simply from handling)
Then ran enrichment experiment again handling rats equally this time (same results as before)

10. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
Discussion and Criticisms
Stress
Impoverished rats had stressful life
Completed another experiment to show stress differences

11. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
More Criticisms
- Tame lab mice used
To solve: Wild deer mice used in enrichment experiment showed similar gains as lab mice
Deer mice had larger cerebral cortex initially, coming from a natural setting
Greater brain mass
- Relevance to humans
Hard to compare even rats to rats let alone show how it is in humans

12. Rosenzweig Bennett & Diamond 1972 More experience = bigger brain
Recent Applications
Human autopsies
Blind people – less developed cortex in
corresponding area
Baby study
Early stress in life and mental illness
Early intervention

13. Discussion Questions Why were rats used?
How were the three environments different in this experiment?
How were the enriched rats brains different from the impoverish rats brains?
Why were deer mice used?
Why is this relevant to human brains?