The quest to find a standard test to detect Parkinson’s disease has been an ongoing one. Despite many efforts, we still do not have one, but could a language test be the answer?
Do I have Parkinson’s disease? Ideally, I would have a yes or no answer, based on a simple test.
About 100, 000 people in the Netherlands are currently diagnosed with Parkinson’s disease (Stichting Parkinson Nederland, 2016). This number is believed to grow even larger in the next few years, as the population is ageing.
There is presently no standard diagnostic test that can be used to detect the disease. So far, tests of motor functions can be used, but do not provide any conclusive evidence. Usually, a positive response to the administration of medication (commonly levodopa) is considered as one of the ways to identify Parkinson’s disease. Sometimes, an MRI scan may be used to rule out any alternative explanations.
In an ideal world, a simple blood test could be the answer. Research on biomarkers is extensive (Chahine, Stern, Chen-Plotkin, 2014), but unfortunately does not provide a solution yet. Research is expensive and time consuming. We will therefore have to be patient before any progress is made in terms of diagnosis.
However, coming from a completely different area, cognitive psychologists have made some interesting discoveries about Parkinson’s disease. In one study by Peran and colleagues (2003), Parkinson’s patients completed a verb or noun generation task. In this task, participants were presented with either a verb or a noun. They were then asked to provide a semantically related verb or noun. For instance, in reaction to the word “drink”, participants could answer with the word “eat” if they needed to generate a verb, or with the word “water” if they needed to answer with a noun. The Parkinson’s patients did not have any memory problems, as assessed by the Mini-Mental State Examination. In addition, a control group of healthy aged matched adults also completed the word generation task. The results show that Parkinson’s patients had more difficulty in generating verbs compared to nouns. This difference was not found in the control group.
How are these results explained? According to embodied cognition, the processing of verbs is closely connected to our motor behaviour. In fact, the theory claims that in order to understand the meaning of a verb, activation in our motor areas is necessary. Several studies have indeed shown that the motor and premotor areas are activated when we are presented with action verbs (Hauk, Johnsrude, & Pulvermüller, 2004; Vigliocco, Warren, Siri, Arciuli, Scott, & Wise, 2006). There is indeed a connection between action verb processing and motor area activation. However, an important remaining question was whether the motor activation was absolutely necessary for action verb processing. One symptom in Parkinson’s disease is a difficulty in initiating movement. Based on this, the finding that these patients have difficulties processing action words may be quite consistent with the embodied cognition theory. From this we can conclude that the motor areas are perhaps not crucial, but at least helpful for action word processing.
Returning to the initial issue of diagnosis, Cardona et al. (2013), suggest that this difficulty in verb processing could serve as a cognitive marker used in the diagnosis of early Parkinson’s disease. It remains unclear, however, whether this finding is unique to Parkinson’s disease. Further research is certainly necessary. But these results point to a low cost method of detecting Parkinson’s disease that could be used in association to neurological tests. It is not perfect, but it is a step in the right direction.