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 the remaining 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 used to 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 muscles. By contrast, in amputees, imagined dorsiflexion and plantarflexion enhanced the map area and volume of the hand muscles. In the forearm muscle maps, both groups displayed a similar pattern of isodirectional coupling during both motor imagery tasks. Imagined dorsiflexion facilitated MEP amplitudes of the extensor and inhibited the flexor muscles of the upper limb. This pattern was reversed during imagined plantarflexion.


CONCLUSIONS
We argue that there exists an inhibitory relationship between the foot and hand motor cortices that ceases to exist after leg amputation.


CONCLUSIONS
The understanding of these functional mechanisms may shed light on the motor network underlying interlimb coordination.
Marconi
Barbara
B
European Brain Research Institute (EBRI), Foundation Rita Levi-Montalcini, 00143 Rome, Italy. b.marconi@hsantalucia.it
Koch
Giacomo
G
Pecchioli
Cristiano
C
Cavallari
Paolo
P
Caltagirone
Carlo
C
D000328:Adult; D000674:Amputees / Q000523:psychology*; D000704:Analysis of Variance; D001931:Brain Mapping; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D005528:Foot; D006225:Hand / Q000294:innervation* / Q000503:physiopathology; D006801:Humans; D007092:Imagination; D035002:Lower Extremity; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D010591:Phantom Limb / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation