MR-compatible device for monitoring hand tracing and writing tasks in fMRI with an application to healthy subjects

Monitoring devices enable control of the correct execution of a given task during functional magnetic resonance imaging (fMRI) acquisitions and analysis of behavioral features that can influence brain activation patterns. In this report, we describe and validate a low-cost device for monitoring hand tracing and writing tasks during fMRI. The subject holds a light-emitting pen whose light spot is recorded by a fixed camera aligned with the tracing plane. Pen trajectories are extracted by a blob detection algorithm through Laplacian of Gaussian filtering applied to the camera recordings. Following phantom and in vivo experiments which demonstrated MR compatibility, the device was applied to monitor the particular case of the task of continuous and self-paced writing of an "8" figure in 10 healthy subjects. They underwent fMRI examinations during the task under three conditions: spontaneous frequency and figure size, "low" frequency and "small" figure size. The task recordings were analyzed with a dedicated algorithm that computed both frequency and area of the figures "8" writing. The device was judged comfortable by all subjects. fMRI data analysis showed that task frequency influenced the activation within primary sensory motor and premotor frontal cortices, while figure size interfered with the activation in posterior parietal cortex. Both frequency and size parameters modulated activation in the inferior cerebellum.