Passive Sensorimotor System Boosts Brain-fMRI Accuracy

An experimental device allowing passive sensorimotor testing of brain-surgery patients shows promise in enhancing functional magnetic resonance imaging (fMRI) accuracy.

The experiment, whose results were published online on July 21 in the American Journal of Neuroradiology, was aimed at helping neurological patients who have difficulty doing standard fMRI sensorimotor tasks. The effort was led by Alexandra J. Golby, MD, of the Harvard Medical School and the Department of Neurosurgery at Brigham and Women's Hospital.

fMRI of the motor cortex helps the presurgical evaluation of patients with brain tumors. But sometimes lesion-related neurologic render patients unable to do the sensorimotor tasks - such as finger tapping and hand clenching - that fMRI depend on, the authors said. Moreover, patients attempting to compensate for this diminished ability may introduce head-motion artifacts in the fMRI results.

The study enlisted 10 healthy volunteers (five women averaging 26.9 years) and six neurosurgery patients (four women, average age 41 years). Healthy controls performed a series of four passive and six active hand-movement tasks while undergoingblood oxygen level-dependent (BOLD) echo-planar MR imaging.

Four of the six patients had preoperative motor deficits, which included hand weakness. Diagnoses included oligoastrocytoma, glioblastoma, and recurrent glioma without anaplastic features. A custom-built, MR imaging-compatible, pneumatically driven finger-moving device - which researchers called a “manipulandum” - was used for all passive tasks.

Golby and colleagues found the passive device activated the primary motor cortex, primary somatosensory cortex, and supplementary motor area in the healthy as well as the control patients, and it reduced head motion compared with active tasks. The device reduced head movement in patients more than it did with the healthy controls. An added advantage, the researchers found, was the ability to more precisely control subject performance through standardized tasks, thereby equalizing performance across patients.

“The development of passive tasks can extend the advantages of preoperative fMRI to the subset of neurosurgical candidates with pre-existing deficits,” the researchers concluded.