Corticospinal state variability and hemispheric asymmetries in motivational tendencies

This transcranial magnetic stimulation (TMS) study examined interrelations between asymmetrical hemispheric differences in the degree of variability of corticospinal excitability levels and motivational tendencies. The relative standard deviation in motor evoked potentials (MEP) to single pulse TMS over the left and right primary motor cortex, and approach- and avoidance-related motivational tendencies were investigated in sixty right-handed healthy volunteers. Results showed that subjects exhibited significantly higher state variability in the left as compared to the right frontal cortex and subjects displayed a dominant pattern of approach versus avoidance related motivational tendencies. Differences in left-right corticospinal state variability and approach-avoidance related motivation were significantly correlated and are consistent with the frontal lateralization model of motivational direction. This study demonstrates that MEP variability may provide an additional means for studying non-stationary properties of corticospinal excitability in relation to hemispheric asymmetries and motivational tendencies.