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A personal story: how emotion and cognitive load influence Parkinson’s tremor.

I love this video. Rene van Helsingen has made a beautiful and personal documentary, describing how his tremor and movements are influenced by emotion, stress, and cognitive load. He describes how jazz improvisation – his passion – increases his tremor under particular circumstances. Arousal and excitement, and particularly explicit thinking (cognitive load) worsen his tremor and prevent him from entering an effortless “flow”. He has also found a coping mechanism to deal with this problem: banning disturbing thoughts from his mind. This video is so rich in thoughts and ideas that everyone interested in movement disorders should watch it. This is what inspired me:

  1. Emotions and thoughts that have a negative valence increase tremor, but positive emotions (excitement when listening to a favorite piece of music) can do the same. Both have one thing in common: increased arousal. In the brain, arousal is associated with increased activity in the noradrenergic system. The noradrenergic system connects to several brain regions involved in movement. In Parkinson’s disease, it may disturb a delicate balance of functioning in these areas. Should we tune down the noradrenergic system in Parkinson’s disease? And can we do that without interfering with positive excitement?
  2. Dual tasking worsens the tremor. This is is well-known problem in people with Parkinson’s disease, who “stop walking when talking”. Many theories have been proposed to explain this problem. One theory holds that dopamine depletion in Parkinson’s disease leads to increased interference between emotional, cognitive, and motor circuits in the brain. For example, we have shown reduced focussing of brain activity in the striatum during dual tasks in Parkinson’s disease (link). In line with this idea, others have found increased connectivity between different brain circuits in Parkinson’s disease (link). Thus, when emotional, cognitive and motor networks are activated at the same time, they interfere with each other, resulting in impaired output (behavior). It is interesting that noradrenaline, which is released during stress, is thought to promote integration between brain networks (link). This could further aggravate the interference problem that is already present in Parkinson’s disease. A second theory poses that dual tasking involved continuous switching of attention between the different tasks (e.g., paying attention to the audience, to the written music, to the others musicians). Since switching is critically impaired in Parkinson’s disease (link), it takes more time. This could also lead to delays in movement. Rene van Helsdingen introduces a third theory, namely that dual tasking is more “dopamine-expensive” than performing a single task. Given that dopamine is already depleted in Parkinson’s disease, he tries to dose his brain activities such that the required dopamine matches the available dopamine. I love this explanation. As far as I know, it has not been tested in humans, simply because it is difficult to measure the release of dopamine in a task-based manner.
  3. Rene notices that his timing is impaired. This could of course be caused by slowing of movement in a dual task context. What is very interesting, is that Parkinson patients have a specific problem with certain forms of timing, but not all. That is, it has been found that patients with Parkinson’s disease (a disorder of the basal ganglia) have problems with detecting rhythms, patients with ataxia (a disorder of the cerebellum) have problems with detecting fixed intervals (link).
  4. More to come!



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