here, here, and here). In my review of Erik Scherder's book Laat je hersenen niet zitten I summarized the benefits of walking as he describes them. Daily moderately intensive physical activity, for at least half an hour, not only contributes to a better physical health but also to keeping your brain healthy. It helps to improve cognitive functioning and delays and often decreases brain related diseases. Scherder quotes research which shows that the benefits of physical activity have mainly been demonstrated for people who have not yet been affected by brain disorders and diseases. For people who do already have these kinds of problems there is much less evidence, in some cases because little relevant research has been done, in other cases because the findings of studies which have been done are varied and inconclusive.
One chapter in Norman Doidge's book The brain’s way of healing describes the fascinating case of a Parkinson's disease (PD) patient, John Pepper, who began to get symptoms of PD since 1968 and who was diagnosed with PD in 1992. In 2008, he wrote Doidge a letter in which he explained how he had taught himself to consciously control movements, which are normally controlled by the autonomous, unconscious, nervous system. Due to this he had been able to reverse all of the main symptoms of the disease and he was now no longer recognizable as a PD patient. He had been able to improve his way of walking by walking a lot and at a steady pace. As he was walking, he always paid close attention to his movements and corrected them whenever he noticed that he did not move well. He walked 15 miles per week, in three five mile sessions. First, he improved his way of walking; after that he trained away the tremor, which is so characteristic for PD. He now wasn't on medication anymore. In his letter he wrote that he had written a book about his healing which was, unfortunately, not taken very seriously by many in the medical profession.
After Doidge had read Pepper's book he went to South Africa to visit Pepper and to thoroughly study his case. He found out that doctors who had heard about his case, rejected it, saying that PD symptoms are not reversible and that therefore Pepper could not have been a real PD patient. This, however might be a case of circular reasoning. Doidge traced Pepper's complete disease history and spoke to the doctor who had make the original diagnosis. On the basis of this investigation, he concluded that Pepper was actually a real PD patient. Doidge also learned that, while its symptoms had disappeared, the disease itself had not, at least not completely. When Pepper had become ill on several occasions and had not been able to walk during that time, the symptoms reappeared. When, after that, he started walking again, after some time, the symptoms disappeared again. It is not clear how these effects have happened. Yet, some research with animals suggests that Pepper's claim of having walked away his symptoms is credible. Before we take a look at this research, here is a brief description of PD.
With PD, cells of the substantia nigra (black matter) slowly die. These cells produce dopamine and transport this neurotransmitter to the striatum, which is a part of the basal ganglia. The standard treatment of PD is the prescription of medication which compensates the lack of stimulation by dopamine in the basal ganglia through a substance which resembles dopamine, levodopa. This treatment often succeeds in suppressing the symptoms but has some serious disadvantages. One disadvantage is that the medication can lead to new movement problems. A second disadvantage is that in some cases it can lead to hallucinations as a side effect. A third disadvantage is that its effectiveness tends to wear off after some years so that its dose has to be increased which, in turn, increases the risk of the other two disadvantages.
After this very brief summary of PD, let's return to the research which appears to support Pepper's story. Researcher Jennifer Tillerson chemically induced PD symptoms in rodents and found that when these animals did moderate treadmill exercise for mine days after being given the chemicals, they retained their capacity to move well. The dopamine producing system in the substantia nigra had been better preserved than in the animals who didn't exercise. Research by Michael Zigmond and his team supports these findings. Rats and monkeys with chemically induced PD symptoms suffered less loss of dopamine producing cells by a combination of running and an enriched environment. Their research also showed that the level of GDNF (a substance which makes neurons grow and survive) increased. Normally, GDNF levels decrease in PD patients. It is also known that physical activity stimulates the BDNF level, which help neurons make connections.
Researchers Tillerson, Miller, and Zigmond discovered another interesting thing. They induced PD symptoms in animals on one side of their body. Then, they used Edward Taub's constraint induced therapy. This means that they put their good limbs in a cast, so they were forced to only use their affected limbs. When, after 7 days, they removed the cast, the movement problems had completely disappeared. The researchers found that animals with a 20% loss of dopamine soon lose 60% of their dopamine when they are unable to move. decreased physical activity is not only a symptom of PD but also a cause.
I end my description of Pepper's case, here. The chapter in Doidge's book contains many more interesting details, so I recommend you read it. I hope that there will soon be much more research into the effects of movement on PD!