Imagine I offered you your favorite dessert (cheesecake for me). In exchange, you had to recite the alphabet, but you could choose to do so either in forward or in reverse order. Which would you choose to do?
I would choose to recite the alphabet in forward order; it’s the easier task and the fastest way to get my reward (the cheesecake)!
We know that most people will avoid difficult tasks if they can obtain the same reward through an easier task; this is known as the ‘Law of Least Work’ ¹. This tendency makes sense, especially when you consider that we all have limited mental capacity and have to use our mental resources judiciously.
Dopamine, one of the brain’s chemicals, helps to regulate this trade-off between work and reward. It serves to sense how much work is required and how much reward is on offer. Dysregulation of dopamine could lead to overworking when it’s unnecessary (e.g., choosing to recite the alphabet in reverse in the example above), OR, to the opposite, not working enough even when it is necessary.
In Parkinson’s disease, the level of dopamine in the brain is reduced and most medications serve to increase those levels. So, could dopamine medications alter people’s willingness to engage in difficult work?
To investigate this, we brought people into the lab to measure their willingness to engage in cognitive work. Participants played a computer game where they were offered a choice of two tasks. On the surface, these two tasks seemed very similar – they consisted of identifying colors and doing simple math. However, unbeknownst to the participants, one was designed to be more difficult than the other, i.e., to require more cognitive work.
Thirty-eight people with Parkinson’s disease and twenty-four people without Parkinson’s disease (‘controls’) participated. People with Parkinson’s disease did it twice: once ‘OFF’ their medications (after stopping their medications overnight), and once ‘ON’ their medications.
As expected, control participants and people with Parkinson’s disease who were OFF their dopamine medications were naturally drawn to choosing the easier task, aligning with the ‘Law of Least Work’.
Interestingly, however, we found that when participants were ON their dopamine medications, they were significantly more likely to choose the difficult task. These results are shown in the figure below. This is remarkable: even though it wasn’t required, and even though there was no additional reward to be gained from choosing the more difficult task, participants ON their medications were, simply put, more willing to work harder!
Could this be because the tasks felt easier while they were ON? It doesn’t seem like it because performance was equal when people were ON compared to OFF their medications (so math doesn’t get any easier when you take your medications😊). Alternatively, could this be because they weren’t ‘sensing’ how difficult the tasks were? We ran a few tests to rule this out too.
The big question we’ve been asking ourselves is: How does this impact the everyday lives of people with Parkinson’s disease? What happens if you willingly choose to recite the alphabet backwards even though you’d get the same slice of cake for reciting it forwards? What could the downsides be? For one, we’ve been wondering whether this could lead to greater mental exhaustion because you’d be doing more work than is strictly necessary. And maybe that means that when the time came to do necessary mental work, you’d have depleted your reserve. This is what we’re tackling next in our research.
You can read about this in more detail in the full study which is linked here: https://pubmed.ncbi.nlm.nih.gov/35724812/
And if you’re interested in participating in our ONLINE research studies, or have comments to share with us, please don’t hesitate to contact us at: madeleine.sharp@mcgill.ca or sharplab.neuro@mcgill.ca.
We need all the help we can get to advance on our understanding of how Parkinson’s disease affects people!
1: https://psycnet.apa.org/record/1944-00022-000
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