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.