Optimized activation of the primary sensorimotor cortex for clinical functional MR imaging

BACKGROUND AND PURPOSE: One application of functional MR imaging is to iden tify the primary sensorimotor cortex (M1 and S1) around the central sulcus before brain surgery. However, it has been shown that undesirable coactivat ion of nonprimary motor areas, such as the supplementary motor area and the premotor area, can interfere with the identification of the primary motor cortex, especially in patients with distorted anatomic landmarks. We theref ore sought to design a simple functional MR imaging paradigm for selective activation of the primary sensorimotor cortex. Methods: Different paradigms using finger tapping for motor activation were examined and compared with respect to the distribution of activated voxels in primary and nonprimary cortical areas. Studies were conducted in 14 hea lthy volunteers using a blood oxygen level-dependent multislice echo-planar imaging sequence. RESULTS: The most selective activation of the primary sensorimotor cortex w as obtained with a paradigm combining right-sided finger tapping as the act ivation condition with left-sided finger tapping as the control condition. Analysis of the signal time course of primary and nonprimary areas revealed that the highly selective primary motor activation was due to it being res tricted to contralateral finger movements, as opposed to the nonprimary mot or areas, which were activated by ipsilateral, contralateral, and bilateral finger movements alike. CONCLUSION: When performing functional MR imaging to determine the location of the primary sensorimotor cortex, one should compare unilateral voluntar y movements as the activation condition with contralateral movements as the control condition to accentuate activation of the primary motor area and t o suppress undesirable coactivation of nonprimary motor areas.