HOCK - Chapter 1
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
HOCK - Chapter 1
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
HOCK - Chapter 1
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
HOCK - Chapter 1
More experience = bigger brain

Experiment
• 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
HOCK - Chapter 1
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
HOCK - Chapter 1
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
HOCK - Chapter 1
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
HOCK - Chapter 1
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
HOCK - Chapter 1
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)
HOCK - Chapter 1
More experience = bigger brain

Discussion and Criticisms
– Stress
– Impoverished rats had stressful life
– Completed another experiment to show stress
differences
HOCK - Chapter 1
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
HOCK - Chapter 1
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
Discussion Questions
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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?