Answer: The Silver Spring monkeys were experimental macaques who were the center of an animal rights debate in the 1980s.
The ethical and humane treatment of experimental animals should always be a concern for scientists who use animal models in research. All living animals need to be treated humanely, especially those that are considered to be "higher" on an evolutionary hierarchy, such as primates.
In 1981, a group of Philippine-born macaque monkeys were used in neuroscience research. The head researcher, a psychologist named Edward Taub, was interested in seeing if the adult brain was capable of neuroplasticity, the ability to remap connections after some kind of injury. It was known that inputs from the peripheral nervous system arrive into the brain via a series of afferent nerves that enter the spinal cord and ascend into the somatosensory cortex in the brain. However, it was unknown if the mapping of these bodily inputs are able to change in an adult after injury.
Dr. Taub and his fellow researchers performed the experiment on cortical remapping by surgically severing the afferent inputs. These monkeys, with deafferented limbs, could therefore no longer feel any sensations in their arms and hands. The monkeys acted towards the deafferented arm as if it were not their own: a lot of the time, they would chew at the arms or fingers, causing significant injury.
The monkeys generally compensated for their deafferented arm by using their intact arm instead. So, in order to see if the brain can remap inputs based on frequent use, Taub and collaborators restrained the intact arm. As it turns out, the monkeys are able to use their deafferented arm for doing everyday actions, even without any inputs to the brain.
The controversy began in 1981, when a graduate student began volunteering in Taub's research lab. He worked late at night, when he was able to take pictures of the lab and video taped monkey behavior. According to Taub, the graduate student neglected to care for the monkeys for an extended period of time before taking the photos and videos, causing the conditions to appear worse than they were on average.
As a result of the actions of the graduate student, the local police conducted the first ever raid of a federally-funded research laboratory. PETA was also involved, as they tipped off the media as to when the raid was happening. Taub was charged with 17 counts of animal cruelty.
The monkeys were confiscated and stored in the basement of a woman Lori Kennedy, who was the head of the local humane society. The animals disappeared from their cages, after which the police arrested Kennedy, informing her that charges against Taub could not go to court without the monkeys. Suddenly, the monkeys reappeared five days later, with Kennedy claiming ignorance.
Taub's research had been defunded as a result of the poor living conditions of the animals and the negative publicity of the case. Eventually, Taub went on to be a major player in stroke research, developing constraint induced therapy, a new approach to helping post-stroke patients recover use in their weakened limbs.
Scientifically, the researchers discovered that significant cortical remapping had occurred, as predicted by Taub and his collaborators. An 8 to 10 millimeter patch of cortex that would normally have received arm input now received somatosensory information from the face. There were also changes in thalamic connectivity, which is a brain area that processes ascending somatosensory inputs. These findings demonstrated that the brain was able to adjust its connections depending on the conditions.
The Animal Welfare Act of 1985 was put into place as a result of the Silver Spring monkey controversy.