Functional overlap between hand and forearm motor cortical representations during motor cognitive tasks

Objective:The aim of this study was to verify whether motor imagery (MI) and observation of a movement (MO) enhanced corticalrepresentations of the hand/forearm muscles not primarily involved in the task. We also explored the existence of functional overlapsin the upper-limb cortical representations during the aforementioned tasks.Methods:Focal transcranial magnetic stimulation (TMS) was used to map out the cortical representation of the opponens pollicis (OP,target muscle) and other hand and forearm muscles at rest and during MI and MO.Results:The MI and MO tasks induced similar changes in the area and volume of both the OP and synergic muscles. No significantchanges were observed in the cortical excitability of the remaining muscles. The superimposition of different muscle maps revealed exten-sive functional overlaps in the hand/forearm cortical territories.Conclusions:This study demonstrates that neither the MI nor MO changes single muscle motor responses and that the hand/forearmmuscle maps extensively overlap during motor cognitive tasks.Significance:The data reported in this study support the notion that the basic unit of cortical output is not the mere activation of a givenmuscle. This flexible organization may have important implications in motor learning and plasticity