People with Parkinson’s disease are less likely to make certain kinds of mistakes – those that happen when we are “on autopilot”. The surprising finding helps support a new theory about the condition’s root causes in the brain.
Parkinson’s disease is a progressive condition causing slowness, difficulties in moving and tremors. It involves the death of brain cells, especially those that make the signalling molecule dopamine.
In 2010, Peter Redgrave at the University of Sheffield, UK, and colleagues proposed that many of the core symptoms are caused by loss of automatic movements, which are actions we can perform without thinking about them.
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Whenever we first carry out a movement it is under our conscious control, but after many repetitions, we start to be able to do it unthinkingly. Many everyday physical actions, from walking to reaching and grasping for objects, are at least partly automatic.
Tying shoelaces
Recent work has shown that some of the first brain cells to die in Parkinson’s are those that give automatic control. According to Redgrave, loss of these cells could explain why people with the condition are less facially expressive and start walking in a jerky or shuffling way – because they are having to think about every step. “Tying shoelaces is a nightmare for them because you do it so automatically,” he says.
Testing the theory isn’t easy. It might seem possible to look at whether people with Parkinson’s are worse at learning to automate new actions – but they’d be expected to do worse on physical tests anyway because of their condition.
Redgrave’s colleague Tom Stafford came up with a different approach. If the theory is correct, people with Parkinson’s should – counterintuitively – be less susceptible to errors that arise from automatic movements happening when they shouldn’t, sometimes called “action slips”.
Examples of these are when we tidy something away in the fridge that shouldn’t go there, or if we drive a certain route to work every weekday we might wrongly take that route on a Saturday trip to the gym. “Most of the time, that’s the right behaviour,” says Stafford.
Random mistakes like those can’t easily be measured, but action slips also happen when we are typing – for instance, people often type “thing” instead of “think” because “ing” is a common group of letters in English. The team designed a typing test that can distinguish between keyboard action slips and ordinary clumsy mistakes, by using software that knows the most common letter combinations.
Typing test
They asked 61 people, about half of whom had Parkinson’s, to type out sentences, then their software analysed any wrong key presses. Those with the condition made more clumsy mistakes but fewer action slips than the unaffected volunteers.
David Dexter of says as well as shedding light on the condition’s causes, the finding might be turned into a new test for those in its earliest stages. At the moment people tend to be diagnosed only once they have physical symptoms.
“There are quite a lot of drugs in early phases of development,” says Dexter. “We need to be ready to use them by being able to spot people who have early Parkinson’s.”
However, this study involved people who had already been diagnosed with the condition, so further work is needed to see if the typing test identifies people before diagnosis, says Dexter.
Another proposed way to identify Parkinson’s through typing is by analysing the rhythm of their keystrokes, which starts to synchronise with their hand tremor.
PsyArXiv
