Modeling subcortical white matter stimulation.
Melissa Dali, Jennifer S Goldman, Olivier Pantz, Alain Destexhe and
Objective. Intracranial electrical stimulation of subcortical
axonal tracts is particularly useful during brain surgery, where
mapping helps identify and excise dysfunctional tissue while
avoiding damage to functional structures. Stimulation parameters
are generally set empirically and consequences for the spatial
recruitment of axons within subcortical tracts are not well
identified. Approach. Computational modeling is employed to study
the effects of stimulation parameters on the recruitment of axons:
monophasic versus biphasic stimuli induced with monopolar versus
bipolar electrodes, oriented orthogonal or parallel to the tract,
for isotropic and anisotropic tracts. Main results. The area and
depth of axonal activation strongly depend on tissue conductivity
and electrode parameters. The largest activation area results from
biphasic stimulation with bipolar electrodes oriented orthogonal to
axonal fasciculi, for anisotropic and especially isotropic tracts.
For anisotropic tracts, the maximal activation depth is similar
regardless of whether a monopolar or bipolar electrode is employed.
For isotropic tracts, bipolar parallel and monopolar stimulation
activate axons deeper than orthogonal bipolar stimulation.
Attention is warranted during monophasic stimulation: a blockade of
action potentials immediately under cathodes and a propagation of
action potentials under anodes are found. Significance. Considering
the spatial patterns of blockade and activation present during
monophasic stimulation with both monopolar and bipolar electrodes,
biphasic stimulation is recommended to explore subcortical axon
responses during intraoperative mapping. Finally, the precise
effect of electrical stimulation depends on conductivity profiles
of tracts, and as such, should be explicitly considered for each
individual subject and tract undergoing intracranial mapping.
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