29/01/2016 07:39 GMT | Updated 28/01/2017 05:12 GMT

Flagship Monkey Research 'Success Story' Owes Everything to Human - Not Monkey - Investigations

Why experiments on monkeys weren't the key to Parkinson's disease treatment


People who defend animal experiments often cite specific examples of 'success' in an attempt to prove the general scientific validity of testing on animals. This tendency is especially prevalent for experiments involving monkeys, as this type of research is particularly controversial and opposed by the majority of people.

One of the claimed 'flagships' of monkey research is deep brain stimulation for the treatment of tremors related to Parkinson's disease. Deep brain stimulation is used for people with Parkinson's who do not respond well to other therapies. It involves implanting an electrode into the brain, to stimulate very specific deep-brain areas resulting in control of tremors. Though not without its limitations and problems, and while not a cure, this technique has proved to be an effective treatment for tens of thousands of people.

In most patients, the specific target of the implanted electrode is a part of the basal ganglia called the subthalamic nucleus. Supporters of research involving monkeys have insisted for some years that deep brain stimulation of the subthalamic nucleus could not have been developed without the use of monkeys.

This debate came to a head for Cruelty Free International recently. In response to a paper we had published, outlining the fundamental genetic reasons why monkeys are not, and can never be, good 'models' to research human biology and diseases, key deep brain stimulation monkey researchers complained about our statement that:

"Deep-brain stimulation of [Parkinson's disease] patients, often claimed to have been developed through [non-human primate] experiments, was actually discovered serendipitously in a human patient and arguably owes nothing to NHPs for its advancement."

They claimed that: "...the treatment of [Parkinson's disease] by delivering [deep brain stimulation] to the [subthalamic nucleus] owes everything to the research in non-human primates..."

Cruelty Free International has recently published a second response to their letter, in which we highlight the evidence that - in contrast to this claim - human clinical research is the foundation to deep brain stimulation, and not experiments on monkeys:

  • The subthalamic nucleus was linked to movement disorders in humans in the 1920s, as a result of both clinical and post mortem studies, long before similar observations were made in monkeys.
  • The basal ganglia were being operated on in patients in the 1940s to alleviate movement disorders, belying claims that the discovery of the role of the basal ganglia in these conditions was due to monkey experiments.
  • During electrode-based surgical procedures used since the 1960s, it was noted that the stimulation of particular brain structures could suppress the symptoms of movement disorders, including Parkinson's disease.
  • Human deep brain stimulation was used from the late 1970s in various parts of the brain, including the basal ganglia, to control tremor.
  • The monkey 'model' of Parkinson's was not reported until 1983.

What appears to have happened is that experiments on monkeys in the 1980s reignited interest in the subthalamic nucleus as a potential site for deep brain stimulation for Parkinson's. It is clear, however, that this could have just as easily been shown in humans, and indeed human research was clearly pointing in that direction already.

It is therefore disingenuous to suggest that deep brain stimulation of the subthalamic nucleus would not have occurred had experiments on monkeys not been permitted. Far from this treatment 'owing everything' to non-human primate research, it 'stands on the shoulders of giants' in the form of decades of human-based investigations. It 'owes everything' to everything but research on monkeys.

Many claimed successes of animal experiments fail to stand up to analysis, just like subthalamic nucleus deep brain stimulation. In any case, these examples of the 'success' of animal based discoveries--whether shown to be 'true' or not--cannot be used as a justification for the continued use of animals. They MUST be viewed in the context of all the times tests on animals failed or misled researchers.

The value of any practice, whether it be animal research or otherwise, must be justified based on systematic and comprehensive review and analysis. That is science. A broken watch is still correct twice a day!