Interlimb co-ordination of force and movement-related cortical potentials.

The question we asked in this study was how the cerebral hemispheres are coordinated when the two hands simultaneously generate force at the same level. Interlimb co-ordination of contractions at 20% of the maximal level was investigated during bilateral (BL) and unilateral (UL) handgrip in eight male right-handed subjects. The accuracy as determined by the force error was larger during BL than during UL for the left hand only. The movement-related cortical potential (MRCP) of C3 (left precentral cortex) was studied during UL right and BL handgrip and the C4 (right precentral cortex) during UL left and BL handgrip. At the phase of the readiness potential (-1.0 to -0.6 s prior to the force onset), similar levels of correlation in the C3 (C4) MRCP amplitudes (P < 0.05) between UL right (UL left) and BL handgrip were observed. At the phase of the negative slope (-0.6 to -0.2 s) and the motor potential (-0.2 to -0.05 s), C3 revealed almost the same levels of correlation as for the readiness potential, whereas in C4 a marked decrease was noted. Accordingly, from this study the force error and movement-related cortical potentials would indicate that the left dominant hemisphere is specialized not only for unilateral contractions but also for bilateral contractions.