From the perspective of Parkinson's Disease as a dysregulation of the Nervous System, in which people with PD are stuck in the freeze (playing dead) stress response, see

the hands and fingers, and their use or lack thereof, have key roles either in the rate of degeneration or in progressive symptom reduction. Indeed, if you've ever seen one of those grotesque renderings of how the human body is actually represented by the proportion of brain power devoted to each body part (a homunculus), the hands come out as absolutely massive - hands and neurology are very strongly linked!

If no interventions are put in place to remedy the situation, the hands of people with PD become stiffer, with fingers more curled up and eventually the ability to pick things up, grasp or push and pull is lost. One of the major contributing factors in this degeneration is the states of stress people with PD are locked into, fight-or-flight and especially freeze (playing dead). Under chronic stress the use and senses of our hands become inhibited, as the body draws its energies inwards to protect vital organs: while we can survive the loss of a limb or two to a lion, we can't survive having our guts ripped open, so our fingers are de-prioritized from the brain and body's resources. When unnaturally stressed too frequently or for extended time, due to the pressures of modern life for example, this loss of dexterity and proprioception (sense of relative position and effort needed to move) in our hands, and loss of senses of touch, can become permanent. The nerve fibre connections responsible become harder to fire up as the networks of motor and sensing neurons continue to atrophy.  Indeed, the diminishing of the range of movement of the hands is one of the very first signs of PD: one the earliest symptoms which become obvious in people developing PD manifests as handwriting getting smaller and smaller.

This lack of ability to use the hands can have knock-on negative effects for the senses and muscles in other parts of the body too, since it also inhibits self-touch. In particular, it may become more difficult to touch/compress/hold pain points of the body, thus amplifying these pains and problems, since touching pain points is a natural pain relieving mechanism and down regulate excited states of the Nervous System. Self-touch lets our Nervous System know we have heeded the internal alarm and have paid attention. Indeed, in his book on Dystonia, Dr Joaquin Farias emphasises the importance of touching the affected muscles.

Conversely, the use of our hands for complex tasks is "stress interrupting", so using our hands in specific ways can be calming on the Nervous System. This is especially true when using the hands for tasks which require use of other senses, such as hand-eye-co-ordination or clapping along to music, which bring into play other parts of the brain. Indeed, those practices which we now know can delay the progression and aid symptom reduction in people with PD all appear to involve the hands intimately. Riding bicycles, unlike walking, involves the handle bars and the breaks, while walking with poles and sticks seems to increase the benefit of that exercise. Tai-Chi, Yoga, Qi Gong, Gyrokinetics all also focus heavily on hand shaping and on the hands leading movements. Ballet involves the expression of the hands. Then there is boxing exercise, which is proving one of the most beneficial forms for PD, which could not be more hands focused.

Therefore hand exercises and finger stimulation are critically important for preventing the ravishes of neuronal atrophy in PD, and also to strengthen "para-sympathetic tone", enhancing the ability to maintain a relaxed state, so important for people affected by the disease. Indeed, the story of Chris Lacey is intriguing, with reports he is now free from PD symptoms after intensive carving of chess pieces as a hobby.

The importance of hands and fingers is hence profound for those of us who have been diagnosed with chronic disease.

In a previous article, I explained how PD is far from a problem with the mobilization (movement) circuits of the Nervous System alone, but also involves strong inhibition of the Social Engagement circuits, 

See the groundbreaking work of Dr Stephen Porges to understand more about this aspect of our Nervous System and its role in wellness and disease, based on the fact that mammals have a more evolved part of the Nervous System specifically designed for purposes of Social Engagement and Social Co-operation.

Social Engagement involves mainly the Cranial Nerves and their use in social functions such as making sounds and vocal calls for communication, and in facial expressiveness for transmitting emotional states to each other. Dysregulation of this Social Engagement part of our NS seems now to be a principal underlying cause in many chronic conditions, especially in PD, where loss of voice and loss of facial expression are major symptoms. See

for more about this in the context of PD.

However, I believe there is something unique about the Social Engagement system in humans, even amongst mammals: our hands. We humans also use hands for expressing our emotions in very significant ways too. Indeed, we can communicate very profoundly like this: we have even developed sign languages, so we can and do literally talk with our hands. 

We can also hush each other with hands without making sound ourselves - meaning we can communicate that serious danger (e.g. a lion!) is present requiring everyone in the social group to keep quiet to avoid attracting attention, in such a way that we don't attract attention ourselves.

Orienting is also an important part of the Cranial Nerve function for threat/safety evaluation, including the ability to turn eyes or ears to the source of potential threat. But with our hands we can also, naturally, orient each other to potential threats which we individually may have detected, within social groups - pointing a finger in direction of danger, for example, or signalling to the group to stop in its tracks. 

We can also make very distinct sounds and a wide range of "calls to action" directly with our hands: clapping, clicking fingers, whistling through the fingers, not to mention beating drums, etc.

I have just communicated all this to you through my hands too, because I typed these words with my fingers!

So, uniquely, our hands are incredibly important parts of our Social Engagement Nervous System programming and thus survival abilities under stress. This is why I suggest a lot of hand work is highly beneficial in chronic conditions, and conversely why the hands and fingers appear to be problem points in conditions like Parkinson's Disease, in which inhibition of social communication skills is an inherent part of degeneration. 

I have done a lot of hand/finger stimulation and experimented to optimize such exercises, in the spirit of Curiosity and Play. I've personally found significant benefit in pursuing this line of research. Indeed, I have managed to recover a lot of my independence and quality of life through hand and finger therapy, and I know just how much of a major part it has played in my own progressive symptom reduction.

I therefore encourage everyone with PD to do as much hand and finger stimulation as possible, through games and play and self-discovery. By doing nothing, the only thing that will happen is that out situation will rapidly become worse, because we will lose the use of our hands quicker and consign ourselves to increased suffering. By applying neuroplasticity techniques (persistent use and expanding ranges of movement), we can delay the worse ravishes of the disease or even, like in my own case, continuously push the symptoms back and recover some independence. I feel this is an important message for those newly diagnosed, in particular.