Cognitive processing speed has been found to be slower in those with manifest and premanifest Huntington’s disease (Maroof, Gross & Brandt, 2011) compared to controls. However, the most commonly employed measures of cognitive processing speed, such as the Stroop Test, Symbol Digit Modalities Test and Trail Making, all rely on motor responses, either written or verbal. Given that motor deficits are a feature of HD, even during the premanifest stage (Biglan, et al., 2009), it is important to understand whether poor performance on these tests are purely due to cognitive processing speed issues, or if they are confounded by motor response speed. This is particularly interesting in premanifest HD, as these patients do not have motor problems that would lead to a clinical diagnosis of manifest disease, but may have slowed motor responses (Tabrizi, et al., 2013).Aims
The aim of this study is to explore how much of the variance in traditional cognitive processing tasks can be accounted for by motor speed in HD participants.Methods
This is a retrospective study using data from cognitive processing speed tasks collected as part of the Enroll HD study at the Cambridge Site; including the Stroop Test, Symbol Digit Modalities Task and Trail Making, combined with data from a simple speeded hand tapping task carried out as part of participants routine clinic visit, which provides a marker of motor speed. Statistical analysis was used to explore the relationship between performance on cognitive processing tasks and tapping speed at different stages of disease with particular emphasis on patients either side of the clinical diagnosis.Conclusions
Understanding the contribution of motor speed to participants’ scores on measures of cognitive processing speed provides a more in depth understanding of why people with HD experience a worsening of performance and impacts the way in which data on these tasks is interpreted.