[Abstract Title]. - Society for Neuroscience

Title: Effect of tissue capacitance and dispersion in an inhomogeneous model of deep brain
stimulation
Authors: *P. F. GRANT, M. M. LOWERY;
Univ. Col. Dublin, Dublin 4, Ireland
Abstract: Deep Brain Stimulation (DBS) has been shown to be highly effective for suppressing
the symptoms of Parkinson's Disease. Despite its widespread use, the mechanisms of action of
DBS remain unknown, and the region of tissue activated is unclear. In this study, a threedimensional,
inhomogeneous, finite element model of the head was constructed to examine the
time-dependent distribution of the electric field in the vicinity of the subthalamic nucleus during
DBS. Typical DBS stimuli, approximating square waves, carry energy through a wide range of
frequency components. Many biological tissues have frequency-dependent conductivities and
permittivities, caused by alpha dispersions in water molecules. For example, the relative
permittivity of white matter at 100 Hz is over twenty times that reported in the literature at 1
kHz. It is likely that the broad spectral nature of the stimulus pulse, coupled with the frequency
dependent material properties will have a significant effect on the magnitude of the electric field
in the region of neural tissue close to the electrode. Most bioelectric models of DBS to date have
assumed that tissues are purely resistive. To properly quantify the capacitive effects in the tissue,
it is necessary to incorporate the effect of dispersion. In this study a new model has been
developed to examine the effect of both tissue capacitance and dispersion over a wide range of
frequencies. Using this model, the electric potentials in the region of neural tissue close to the
stimulating electrode were calculated for varying capacitive and dispersive material properties.
The electric potential observed in the region of neural tissue close to the electrode during
current-controlled stimulation was found to be sensitive to variations in the frequency at which
material properties were estimated. The peak magnitude of the electric potential at a point 5 mm
posterior to the stimulating electrode where material properties were estimated at 1 kHz, was
over 2.5 times that observed when material properties were estimated at 100 Hz. Furthermore,
results indicate a further effect on both the magnitude and shape of the electric potential
observed when dispersive material properties are incorporated. It is, therefore, concluded that
inclusion of the frequency-dependent material properties is necessary for accurate computation
of the temporal electric field in the vicinity of DBS electrodes.
Disclosures: P.F. Grant, None; M.M. Lowery, None.
Poster
247. Parkinson's Disease Interventions: Animal and Clinical Models
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 247.15/S10