Self-paced frequency of a simple motor task and brain activation. An fMRI study in healthy subjects using an on-line monitor device.

Application of fMRI to clinical neurology implies the selection of a simple task and control of the task performance. The capability to objectively monitor variables related to task execution is, therefore, important and could improve accuracy of clinical fMRI studies. We assessed the influence of different self-paced frequencies of a simple motor task on brain activation in healthy subjects. A device was developed to measure the force exerted by a subject in pressing an air-filled rubber bulb with the last four fingers of the dominant hand. The task frequency was determined by analysis of the force signal. Nine healthy subjects performed twice the task with self-paced slow (0.35+/-0.09 Hz), intermediate (0.58+/-0.21 Hz) or fast (0.98+/-0.32 Hz) frequency. The device revealed impaired task execution in 1 subject. The coefficient of variation of frequency was 8.7% for slow, 12.2% for intermediate and 15.8% for fast paced task. No significant differences were found comparing the activation maps obtained at slow, intermediate and fast frequencies in the contralateral sensorimotor cortex and ipsilateral cerebellum. Cluster reproducibility was good for location (standard deviation<or=7.3 mm), but poor for signal intensity (coefficient of variation 0-176.8%) and extent (coefficient of variation 1.9-140.6%). In conclusion, self-paced frequency variations of a simple motor task in the 0.2-2 Hz range are not a relevant source of the variability of the fMRI results in healthy subjects. Use of the device for evaluation of the neurologically impaired patients might broaden the clinical applications of fMRI.