Conceptual hypometria? An evaluation of conceptual mapping of space in Parkinson's disease

When interacting with objects in their environment, patients with Parkinson's disease (PD) often make hypometric movements (e.g., micrographia). The purpose of this study was to learn if patients with PD, in the absence of overt actions or environmental stimuli, have egocentric (body-centered) conceptual (representational) hypometria. Actions can take place in either proximal or distal peri-personal space. Normally, the right hemisphere has a distal and the right a proximal attentional bias. We also want to learn if a patient with onset of disease in the right hemisphere would have a greater conceptual action hypometria than individuals with left hemispheric onset. Seventeen subjects with PD and 15 age-matched controls were given a questionnaire evaluating subjective perception of personal action space. The questionnaire asked individuals to rate, using a 0-5 scale, the distances between their body and hand when performing the various actions that take place in peri-personal space. When compared to control participants, participants with PD, and especially those with predominant left sided symptoms (right greater than left hemispheric dysfunction) had hypometric mental perceptions for actions that normally occur in far peri-personal space. Individuals with PD appear to demonstrate a conceptual hypometria, suggesting that there is a perturbation of their interactive representational maps and these maps appear to be more disordered by right than left hemisphere dysfunction. However, it is also possible that when making action distance computations, participants used covert actions and it was the hypometric covert actions that induced the computational hypometria.