Abstract
An intraoperative electrode (microelectrode) is used in the deep brain stimulation (DBS) technique to pinpoint the brain target and to choose the best parameters for the electrical stimulus. However, when the intraoperative electrode is replaced with the chronic one (macroelectrode), the observed effects do not always coincide with predictions. To investigate the causes of such discrepancies, a 3D model of the basal ganglia has been considered and realistic models of both intraoperative and chronic electrodes have been developed and numerically solved. Results of simulations of the electric potential (V) and the activating function (AF) along neuronal fibers show that the different geometries and sizes of the two electrodes do not change the distributions and polarities of these functions, but rather the amplitudes. This effect is similar to the one produced by the presence of different tissue layers (edema or glial tissue) in the peri-electrode space. Conversely, an inaccurate positioning of the chronic electrode with respect to the intraoperative one (electric centers not coincident) may induce a completely different electric stimulation in some groups of fibers.
Highlights
Deep brain stimulation (DBS) is an effective symptomatic treatment for several movement disorders, such as Parkinson’s disease (PD), essential tremor (ET), and dystonia (Okun et al, 2012)
The brain nuclei mostly chosen as the stimulation targets are the Subthalamic Nucleus (STN) for the PD, and the Globus Pallidus (Gp) and Ventral Intermediate (VIM) nucleus for the ET (Limousin and Martinez-Torres, 2008; Benabid et al, 2009; Chopra et al, 2013; Lozano and Hallett, 2013; Okun and Zeilman, 2014)
The electrode performances in the different studied conditions have been compared in terms of impedance and suitable electric quantities (V and activating function (AF)) inside the brain nuclei along lines representative of neuronal fibers connecting the STN and the Gp, in order to identify www.frontiersin.org which parameters mainly affect the stimulation characteristics and can be used to interpret the clinically observed discrepancies between intraoperative and chronic stimulation
Summary
Deep brain stimulation (DBS) is an effective symptomatic treatment for several movement disorders, such as Parkinson’s disease (PD), essential tremor (ET), and dystonia (Okun et al, 2012). It is an invasive stimulation technique, where a biphasic pulsed electric stimulus is delivered by implanted electrodes to the basal ganglia, the brain region associated with the control of voluntary motor movements. The dosimetric computation can be performed by numerically solving the electromagnetic problem inside realistic brain models, stimulated by simplified or realistic electrodes (McIntyre and Grill, 2002; Butson and McIntyre, 2006; Bossetti et al, 2008; Grant and Lowery, 2010; Joucla et al, 2012a,b; Wongsarnpigoon and Grill, 2012; Paffi et al, 2013b). The extracellular electrical stimulation must be coupled with neuronal models (Giannì et al, 2005; Miocinovic et al, 2006; Paffi et al, 2013a) to obtain the actual neuronal response (Joucla et al, 2014)
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