I think you shall think another way if you want to come closer to the answer.
If you look at this page
under Biosynthesis and regulation close to the bottom of the page.
You will see that dopamine and adrenaline(=epinephrine), is closely related.
Epinephrine is the International Nonproprietary Name and the US Adopted Name.
Adrenaline is the British Approved Name and the European Pharmacopoeia name.
So you can get healed of everything that can remove adrenaline, as that is the reason that you have tremor and stiffness due to fight, flight and freeze instinctive stress response. Your dopamine is used up too quickly in the production of adrenaline.
So that is why sport helps, because you use up all the adrenaline if you for ½-2 hours get sweaty, and you use your instinct responses flight and fight in the right way by "acting" and you feel calm after this.
But that will not remove the reasons to why you are producing too much adrenaline, so the next day you are back into much adrenaline.
The reason is that you in your lifetime have had some sort of trauma (psychologically or physically), you may not even remember it or you think that "everybody has this experience".
When you go around in your daily day a lot of things reminds you about what happened or you have developed a general worried mind.
So that is why you freeze in the middle of the street, why your tremor is bigger when you are shopping or doing new things.
And there, of course, is the embarrassment when eating soup with strangers.
All these add up and in the end, as you get older and more fragile (might not be the best word) in any way end you have tremor/freeze all the time.
I am coaching people and it is not with psychotherapy but other methods. I have two Parkinson persons improving big time. The one the neurologist now is in doubt if he had the Parkinson after all.
the other has now reduced his dopamine with more than 50% and he is stepping out of pills fast now.
You will not find a lot of studies as no doctor until now believe us. But you will find a lot about stress and Parkinson and you can google old YouTube clip where you see people with shell shock where you are in no doubt that it is severe Parkinson's.
The reason why meditation, yoga, mindfulness, and Qi Gong helps is due to you training your brain to stay in peace not producing adrenaline, but you need persistent work to be better in this way.
I could talk for hours about this so please feel free to ask me questions.
I am a biologist as well as a coach and therapist so I explain everything g from a viewpoint of biology.
You can find my youtube channel where I have started posting about Michael that will soon be free of medicine.
will he stop having tremor forever? No, but while reducing traumas and learning him to stay calm in more and more situations, in the end, it will only be in a few occasions that he show his sign of stress - the tremor.
We have worked through old traumas, worries about work, performance anxiety, embarrassment and a lot of other stuff, and now he is fully aware of why he one day have the tremor.