Neuroplasticity Research: Lost Story of Silver Spring Monkeys

science of neuroplasticity


Neuroplasticity is a fascinating Hydra-like trick of the brain. In Greek mythology, Hydra was a many-headed lake-monster that would grow two heads when one was cut.

The brain does something similar. The brain cells can recast themselves into new roles after a trauma from illness or injury, and deal with the new circumstances in a way that almost seems magical and mythical.

Neuroplasticity is the brain’s capacity to redesign itself by creating very new nerve networks. It enables the brain cells to grow new roots, take up new roles, and make up for its functional frailty after any brain damage.

This redesigning starts with sprouting of new nerve endings by the unharmed nerve fibers (axons). These new sprigs then reconnect to the neurons whose connections were cut off. Meanwhile, the intact axons also grow new nerve endings. Now, these virgin sprouts from the two sources weave together, and lay down a grid of fresh neural pathways that carry out newly assigned missions.

For instance, when one-half of the brain globe (the cerebral hemisphere) gets wrecked, the other side may gradually take control over some of its duties via its extraordinary capacity of neuroplasticity.

17 Monkeys That Rebuilt The Science of Brain Plasticity

Let’s start out on a journey to the unknown story of neuroplasticity, and how 17 monkeys rebuilt the science of brain plasticity. This broke the world of brain science and gave birth to the biggest society of animal lovers on earth, so tighten your seat-belts.

Prologue: The Doctor Who Split Brains

The science of neuroplasticity has its earliest roots in the 1950s, when the American neuropsychologist and neurobiologist Roger W. Sperry started working on split-brains.

For sake of science, Sperry split apart the two halves of the brains of his lab monkeys and studied their behaviors. His monkeys showed that each half of their brains could still learn new things. But each half did not share its learning  with the other half.

Sperry later located some human patients whose brains have been similarly split into two halves — to treat them of their severe epilepsy. He found an identical pattern in these patients. Each of their brain hemisphere had its own world of consciousness and was entirely independent of the other with regard to learning and retention.

Finally, in the winter of 1981, the Karolinska Institutet, Sweden, chose Sperry to receive one-half of that year’s Nobel Prize in Physiology or Medicine for his two decades of work on split-brains.

Threshold: The Silver Spring Monkeys

In the summer of the same year, 1981, Alexander Pacheco went to work as an unpaid volunteer at the Institute for Behavioral Research (IBR) in Silver Spring, Maryland. This was a federally funded research facility. And the scientist who ran it was Dr Edward Taub — a psychologist and researcher who loved doing animal experiments, and had a record of securing nearly 15 federal grants for eighteen years of his work with monkeys.

The 23-year-old Pacheco, son of a doctor who wanted to be a Catholic priest, walked into a place that was an animal hell on earth.

Sixteen macaques and one rhesus were kept jammed into small, rusty wire-cages roughly 18 inches wide. Many kept their arms hanging out. The air in the lab stank foul with urine, feces, and rotting flesh of these monkeys.

Pacheco soon discovered that in 9 of these seventeen animals, the scientists had cut off the sensory nerves leading from their arms to their brains, a process called deafferentation. This made one or two of their arms go limp and useless.

But Taub, the 50-year-old lead scientist, wanted these monkeys to start using their impaired limbs again. Since the monkeys couldn’t do it, Taub kept devising novel ways to make them move those arms — using torture, hunger, and electric shocks.

In one experiment, the monkeys sat imprisoned inside a dark refrigerator, motionless, until they started receiving electric shocks. The shocks kept coming in bursts and never stopped till they could finally move their crippled arms.

In another, the scientists strapped the monkeys with packing tape at their waists, necks, ankles, and wrists into a chair made of metal pipes. Then, for pain, they latched pliers onto their skin at various places, including their testicles.

When the monkeys couldn’t move their disabled limbs, as further punishment, Taub let them go hungry for days on end.

The repeated trauma and the incessant hunger made these monkeys go so deranged that they gnawed off thirty-nine of their own fingers. Dried blood from those fingers caked the cage wires and lab floor.

“Several had bitten off their own fingers and had festering stubs, which they extended towards me as I discreetly took fruit from my pockets. With these pitiful limbs they searched through the foul mess of their waste pans for something to eat,” Pacheco later wrote in an article in Peter Singer’s book In Defense of Animals.

Aghast, he started secretly photographing these maimed monkeys and logging details of the torturous experiments. And, at night, he stole in veterinarians and primatologists as eye witnesses to tour the lab.

Then he went to the police with all his evidence.

On September 11, 1981, in an unprecedented move, the Montgomery County police raided the laboratory and seized the monkeys. They criminally charged and arrested Taub for animal cruelty and failing to provide adequate veterinary care.

The monkeys were released from the lab, but had nowhere to go. The county Humane Society, which first agreed to take them in, backtracked on its words. The respite for the mutilated monkeys came as Lori Lehner, a 23-year-old animal lover who was also a Humane Society member. Lori housed them in the basement of her Rockville home. She pampered them with food, toys, mirrors, and love. While there, the monkeys became hooked to daily television shows.

Explosion: Meteoric Rise of The Saviors

This was the first ever animal research case against a scientist on American grounds, and later became the first such case to reach the US Supreme Court.

The case launched an animal rights movement that spread like a wild-fire and drew support from all over the country. Several celebrities and politicians joined the campaign for the release of the monkeys. Finally, the macaques were rescued and spared further research.

Just an year before he walked into IBR, Pacheco had met Washington DC’s first female poundmaster Ingrid Newkirk while volunteering at the local dog pound. Together they started an animal rights society with about 20 members. In fact, Pacheco had gone into the lab as a mole for their act to make public the realities of animal atrocities.

Now, it was through this society that Pacheco and his friends were fighting this high-profile case for the rights of the Silver Spring monkeys. And it was precisely this battle that transformed their fledgling outfit into an internationally known organization.

We know them as People for the Ethical Treatment of Animals, or PETA.

Born in 1980, PETA today is a nonprofit corporation with 300 employees generating $67 million in annual revenue. It is the world’s largest animal rights organization with 6.5 million members and supporters from across the world.

Today, anyone can mail an envelope with nothing more than “PETA” written on it from anywhere within US, and the letter will still reach one of its offices.

Pacheco, who never completed his political science and environmental studies major from George Washington University, served as the chairman of PETA for 20 years before leaving in 2000. Under him, PETA forced many of the world’s largest corporations — General Motors, Exxon, Amway, L’Oréal, Revlon, Mobil Oil, and Benetton — to end various inhumane practices against animals.

As for Taub, he was convicted on six counts of misdemeanor. All of the six charges, however, were overturned — five during a second trial, by jury, and the sixth on appeal in 1983. He had to pay $3,500 as fine.

The National Institutes of Health (NIH) suspended the remaining $200,000 for Taub’s experiments. But after the courts cleared Taub, the NIH reversed its decision not to fund him.

Fragments: The Last Gift From The Monkeys

The case of the Silver Spring monkeys lasted a decade.

During these 10 years, several of the macaques grew old and lived out their last hours. Finally, in July 1991, the US Supreme Court rejected PETA’s application for the custody of the remaining monkeys.

Days later, to save them from further suffering, the last of the monkeys were killed.

But before that, the neuroscientists from the National Institute for Mental Health approached William Raub, the deputy director of NIH, where the monkeys lived by then. They argued since the animals would be going for mercy deaths, they wanted to examine their brains in one last experiment — for sake of science. They wanted to see what happened to their brain after the area called  somatosensory cortex stopped receiving any sensation from their limbs.

Raub agreed to the procedure, but on condition that the scientists finished up within four hours, and euthanized the animals before the anesthesia wore off.

So, in 1991, three deafferented monkeys — Augustus, Domition and Big Boya — were drugged into deep coma by a group of scientists led by Dr. Tim P. Pons. Then they opened their skulls to place tiny electrodes into the brain areas that normally felt sensations from their paralyzed hands.

The researchers then stimulated points on the face, limbs and torso of each animal and watched those micro-electrodes pick up signals. When they touched their limbs and trunk, there was no response. But when they touched their faces, the electrodes recorded bursts of electrical impulses coming from brain.

This broke the entire field of brain science, and stunned the neuroscientists everywhere.

The brain region that originally processed sensations from the fingers, hands, and arms of these monkeys had changed its job. After not receiving any signals for some twelve years from those body parts, this brain region was now processing signals from their faces.

This was contrary to everything known to mankind up to that point. Until then, the neuroscientists believed that brain parts that stop receiving signals from a body part will eventually die out. Either the brain did what it was supposed to do, or it shut shop.

But that’s not what had happened in those monkey brains. What had happened was “cortical remapping.”

The non-used brain area in the monkeys had reorganized itself to carry out new functions — to a degree 10 times greater than previously thought.

This was a direct evidence of the brain’s massive reorganization capacity — its neuroplasticity.

This ushered in a new era of brain science. Away from the old model, the brain was now an ever-growing and ever-changing organ. The words Pons used to explain the moment — “It’s absolute dynamite.”


Epilogue: Touched By The Finger of God

Taub originally wanted to find techniques that would help stroke survivors regain use of their paralyzed limbs.

After the case, and after receiving death threats for 5 years, Taub finally received a grant by the University of Alabama-Birmingham. There he developed a new form of physiotherapy for brain stroke patients with non-functional limbs.

Based on neuroplasticity, Taub named it Constraint-Induced Movement Therapy. The CI therapy or CIMT involves tying up the good arm in a sling or splint, and exercising the affected arm intensively for six hours each day for 2 to 3 weeks. As a result of this, the brain grows new neural pathways, so that it could now make the affected wrist and hand move.

In simple words, CI therapy changes the brain so the patient can reclaim use of the affected limb.

Taub carried out a number of neuro-imaging and transcranial magnetic stimulation studies to show that CIMT can produce a massive use-dependent cortical reorganization. He showed, with CIMT,  the brain increases its area of control over the affected limb.

Over 600 papers have appeared in various publications on the effects of CI therapy. The NIH funded a multi-center clinical trial for stroke rehabilitation by Taub’s therapy. The American Stroke Association endorsed CI therapy for impaired upper limbs of stroke survivors.

In 2015, a team of Cochrane researchers searched the medical literature and identified 42 CIMT studies involving 1453 participants. They concluded: CIMT appeared to be more effective at improving arm movement than active physiotherapy treatments or no treatment.

In 2003, the Society of Neuroscience named Taub’s CI therapy research as one of the top 10 Translational Neuroscience Accomplishments of the 20th century.

Final Facts

Some of those horrifying pictures that Pacheco took are still floating around on the internet. Anyone can find them by Googling ‘Silver Spring monkeys.’

Animal experimenters have used macaque monkeys to study brains for over 70 years, because the functioning parts of their brains resemble much of that of humans. A 2014 research at Oxford University showed 11 of the 12 components of the human brain’s vlFC had a corresponding area in the macaque brain. A 2017 study found macaques can evaluate memories just like humans.

As of 1981, by one count, 41 Nobel Prizes for Physiology or Medicine had been awarded in this century for research based on animals.

[Scientists have shown that early childhood stress is long-lasting, even if the children later move to a more positive environment. Read here.]

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Author Bio: Sandip Roy is psychology writer, happiness researcher, and medical doctor. Founder of Happiness India Project, and chief editor of its blog. He writes popular-science articles on positive psychology and related topics.

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