Breakdown of inhibitory effects induced by foot motor imagery on hand motor area in lower-limb amputees

Objective:Amputation of a limb induces plastic changes in motor cortex that modify the relationships between the missing limb and theremaining body part representations. We used motor imagery to explore the interactions between a missing lower limb and the hand/forearm cortical representations.Methods:Eight right leg amputees and nine healthy subjects participated in the study. Focal transcranial magnetic stimulation was usedto map out the hand/forearm muscle maps at rest and during imagined ankle dorsiflexion and plantarflexion.Results:In healthy subjects, both motor imagery tasks strongly inhibited the map volume and contracted the map area of the hand mus-cles. By contrast, in amputees, imagined dorsiflexion and plantarflexion enhanced the map area and volume of the hand muscles. In theforearm muscle maps, both groups displayed a similar pattern of isodirectional coupling during both motor imagery tasks. Imagineddorsiflexion facilitated MEP amplitudes of the extensor and inhibited the flexor muscles of the upper limb. This pattern was reversedduring imagined plantarflexion.Conclusions:We argue that there exists an inhibitory relationship between the foot and hand motor cortices that ceases to exist after legamputation.Significance:The understanding of these functional mechanisms may shed light on the motor network underlying interlimbcoordination