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

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

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

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

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

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

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

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

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)

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

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

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

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?