Differential excitation of the inner capsule by hemispheric and trans-hemispheric electrical stimulation: Clinical and mathematical evidence

Lorena Vega Zelaya, Jesús Pastor


Objective: To evaluate the differences in inner capsule (IC) excitability for trans-hemispheric and hemispheric trans-cranial electrical stimulation (thTES and hTES).

Methods: We performed thTES and hTES in the intact motor systems of 18 patients. We measured motor evoked potential (MEP) voltage thresholds (Vth, V) at the extensor digitorum and tibialis anterior, latencies (ms) and thresholds of movement (Vth_mov, V). We developed an analytical 2D model of the electric field ( ) of the brain.

Results: The stimulation pattern was similar for both methods, although the thTES Vth was lower; however, the Vth_mov was higher for hTES. Latency for upper limb muscles was lower for thTES. The mathematical model predicted excitability onset at a more caudal region for thTES. The model correctly predicted that excitability in lower limbs during hTES should be lower.

Conclusions: Clinical and analytical results showed that excitability with small step voltages occurs in relatively small length increments of the IC. In addition, the  induced by hTES is more cranial than that induced by thTES and is also a less perturbing technique for surgeons.


analytical model, corticospinal tract, intraoperative neurophysiological monitoring, motor evoked potentials, semioval centre.

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DOI: http://dx.doi.org/10.18103/imr.v4i6.726


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