Oscillatory dynamics of response competition in human sensorimotor cortex

Neurophysiological studies in non-human primates have provided evidence for simultaneous activation of competing responses in the (pre)motor cortex. Human evidence, however, is limited, partly because experimental approaches have often mapped competing responses to paired effectors represented in opposite hemispheres, which restricts the analysis to between-hemisphere comparisons and allows simultaneous execution. A demonstration of competition between different movement plans in the motor cortex is more compelling when simultaneous execution of the alternative responses is ruled out and they are represented in one motor cortex. Therefore, in the current MEG study we have used a unimanual Eriksen flanker paradigm with alternative responses assigned to flexion and extension of the right index finger, activating different direction-sensitive neurons within the finger representation area of the same motor cortex. Results showed that for stimuli eliciting response competition the pre-response motor cortex beta-band (17-29 Hz) power decreased stronger than for stimuli that did not induce response competition. Furthermore, response competition elicited an additional pre-response mid-frontal high-gamma band (60-90 Hz) power increase. Finally, larger gamma-band effect sizes correlated with greater behavioral response delay induced by response competition. Taken together, our results provide evidence for co-activation of competing responses in the human brain, consistent with evidence from non-human primates.