Table 1.

Globus pallidus internus microelectrode recording lead location based on recordings and stimulation

Position of lead	Recordings and effects of stimulation
Anterior	MER often reveals reduction/absence of the GPi or kinesthestic cells (lack of somatotopy/evoked potentials)
	Long GPi MER run lengths in addition to long runs of striatum
	Absence of capsular side effects of fosphenes during macrostimulation
Posterior	Posterior tracks often yield motor side effects (i.e. tonic muscle contractions) due to stimulation of capsular fibers. Thresholds for such side effects are often narrow and may widen with dorsal contacts (depending on entry point/angle)
	Visual evoked potentials might be more clearly identified with posterior tracks; however, there may be a gap between the inferior border and optic tract (due to shape of GPi tapering superiorly on the posterior aspect)
Lateral	MER demonstrating a large segment of GPe and a small segment of GPi, a large lamina between them (border cells)
	Absence of optic tract/phosphenes and/or capsular side effects during MER and macrostimulation
Medial	MER typically reveals large segment of GPi and a small segment of GPe
	Loud visual evoked potentials in optic tract testing
	Low threshold for capsular side effects (i.e. muscle contractions) across all contacts (depending on angles)
Dorsal	Lack of side effects during macrostimulation
Ventral	Low thresholds for phosphenes during optic tract testing
	Lower thresholds for capsular side effects (i.e. muscle contractions)

GPe Globus pallidus externus, GPi globus pallidus internus, MER microelectrode recording