Field evoked potentials in the globus pallidus of non-human primates

Stimulation-induced field evoked potentials (fEPs) have been described in the basal ganglia output nuclei of patients with Parkinson's disease and dystonia. The aim of this study was to ascertain whether fEPs were inducible in the external (GPe) and internal (GPi) segments of the globus pallidus in normal non-human primates (NHPs). Microelectrode recording and stimulation was performed in the GPe and GPi of 2 healthy NHPs. Stimulus response curves of the fEP response to changing pulse width and amplitude examined strength-duration relationships and allowed for calculation of fEP chronaxie in the GPe and GPi. Traditional localization techniques were also used, including comparison of neuronal firing rates, optic tract activation, and internal capsule activation. Notable differences were seen in the fEPs found in GPe compared to the fEPs found in GPi. The GPe fEP had a smaller chronaxie time and larger positive deflection amplitude compared to GPi. In addition, an earlier negative deflection was identified in both nuclei and a late negative deflection was observed in the GPe in contrast to reported fEPs in patients with movement disorders. fEPs proved valuable as an ancillary method in localizing the GPe and GPi in NHPs and may be useful in the operating room during human GPi deep brain stimulation or pallidotomy procedures.