5.8.12- The role animal models have played in understanding human brain development and function

Pavlov’s Dogs


Pavlov had observed that an unconditioned stimulus causes an unconditioned response, i.e. food causes salivation. This is not learned and is, therefore, unconditioned.

What Pavlov discovered was that if a neutral stimulus, such as a bell is rung just before the food is given for a few occasions, the dog will salivate every time the bell is rung, even if no food is presented. In this case, the dog has learned that the bell signals food. The food is, therefore, a conditioned stimulus and it prompts a conditioned response.

US -> UR

US + CS -> UR

Eventually, CS -> CR

Hubel & Wiesel


  • Hubel & Wiesel investigated the critical
  • They used monkeys and kittens in their studies
  • Their work permanently blinded some animals and can be argued to be unethical.





Hubel & Wiesel’s Method:


  1. Raise monkeys from birth in three groups for 6 months


  1. Group 1 are the control (no blindfold), Group 2 are blindfolded  in both eyes, Group 3 are blindfolded in one eye (monocular deprivation)
  2. Test the monkeys to see whether they can see using each eye
  3. Test the sensitivity of retinal cells
  4. Test the activity of nerves in the visual cortex in response to stimuli


The results:


  • Monkeys in Group 2 (both eyes blindfolded) had impaired vision
  • Monkeys in Group 3 (monocular deprivation) were blind in the deprived eye
  • Retinal cells were responsive in all groups
  • Cortical activity was reduced in parts of the brain that process information from the deprived eye
  • Adults undergoing the same tests showed no difference between groups. All could

The Conclusion:

There is a critical window for visual neural development, which requires stimulus from the eye. If this window is missed the monkey is blind, because of events happening in the brain, not the eye.

You need to know about these experiments because they all use animals