Elsevier

Brain Stimulation

Volume 5, Issue 3, July 2012, Pages 369-377
Brain Stimulation

Original Article
Current steering to activate targeted neural pathways during deep brain stimulation of the subthalamic region

https://doi.org/10.1016/j.brs.2011.05.002Get rights and content

Deep brain stimulation (DBS) has steadily evolved into an established surgical therapy for numerous neurological disorders, most notably Parkinson's disease (PD). Traditional DBS technology relies on voltage-controlled stimulation with a single source; however, recent engineering advances are providing current-controlled devices with multiple independent sources. These new stimulators deliver constant current to the brain tissue, irrespective of impedance changes that occur around the electrode, and enable more specific steering of current towards targeted regions of interest. In this study, we examined the impact of current steering between multiple electrode contacts to directly activate three distinct neural populations in the subthalamic region commonly stimulated for the treatment of PD: projection neurons of the subthalamic nucleus (STN), globus pallidus internus (GPi) fibers of the lenticular fasiculus, and internal capsule (IC) fibers of passage. We used three-dimensional finite element electric field models, along with detailed multicompartment cable models of the three neural populations to determine their activations using a wide range of stimulation parameter settings. Our results indicate that selective activation of neural populations largely depends on the location of the active electrode(s). Greater activation of the GPi and STN populations (without activating any side effect related IC fibers) was achieved by current steering with multiple independent sources, compared to a single current source. Despite this potential advantage, it remains to be seen if these theoretical predictions result in a measurable clinical effect that outweighs the added complexity of the expanded stimulation parameter search space generated by the more flexible technology.

Section snippets

Materials and methods

Predictions of neural activation in response to DBS were performed using a detailed computational model of STN DBS that included three major components: (1) three-dimensional representation of the DBS electrode within the subthalamic nucleus, (2) three-dimensional reconstructions of STN, GPi, and IC populations, and (3) finite element models of the electric fields generated by a wide range of stimulation settings. The number of active cathodic and/or anodic contacts, as well as the current

Results

This study was undertaken with the basic assumption that optimal therapeutic benefit from DBS is achieved when activation of target neural populations is maximized, and the activation of side effect neural populations is minimized. Within the context of this theoretical study, our target neural population was composed of STN projection neurons and GPi fibers of passage. The IC fibers of passage were defined as the deleterious side effect neural population. Our results outline the impact of

Discussion

The goal of this study was to evaluate the ability of current steering technology to improve DBS activation selectivity in targeted neural populations. We used a highly detailed electric field model coupled to three-dimensional neuron models with anatomically realistic geometries and membrane dynamics. We focused on activation of three different neural populations (STN projection neurons, GPi fibers of the lenticular fasciculus, and IC fibers of passage), and quantified their activation by

Conclusion

Although typical clinical practice with traditional DBS technology tends to focus on monopolar stimulation, we found that DBS devices capable of current steering between contacts opens up additional opportunities to achieve an improved balance between activation of target and side effect neural populations. This study demonstrated that increased selective activation was possible by using a current-controlled device with independent sources. Future studies are needed to explicitly define the

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      Given a more advanced lead design with a larger channel count in three dimensions, it may be possible to perform selective stimulation of various fiber tracts emanating from or impinging on the STN. It has been shown by earlier modeling studies that, compared to bipolar current steering, monopolar two- electrode current steering may stimulate a greater fraction of the STN projection neurons simultaneously with axons of the internal globus pallidus (Chaturvedi et al., 2012) while avoiding the axons of the internal capsule. On the other hand, the same authors showed that unbalanced bipolar current steering may be able to stimulate a greater fraction of only STN projection neurons in comparison to monopolar current steering (Chaturvedi et al., 2012).

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    This work was supported by the National Institutes of Health (R01 NS059736) and Boston Scientific Neuromodulation Corporation.

    Paid consultancy for A.C. and C.C.M. (Intelect Medical Inc.); A.C., T.J.F., and C.C.M. (Boston Scientific Neuromodulation Corp.)

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