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Estimation of the Spatial Extent of Activation in Thalamic Deep Brain Stimulation
John Doe 1, Scott E. Baker 2, Janice M. Holson 3 , Scott Adams 3 , and Wyatt M. Watson
1 Department of Biomedical Engineering, Duke University, Durham, NC
2 Department of Neurology, Cleveland Clinic Foundation, Cleveland, OH
3 Department of Neurosurgery, Cleveland Clinic Foundation, Cleveland, OH
Successful treatment of movement disorders with deep brain stimulation (DBS) requires accurate
electrode placement within the target brain area and the selection of appropriate stimulus
parameters. The objectives of this research are first to quantify the effects of varying voltage and
electrode positions (active contact on the DBS lead) on the responses to DBS, and second, to use
these data to determine the spatial extent of neuronal activation during DBS.
Nine subjects with essential tremor and DBS of the ventral intermediate nucleus of the thalamus,
at least 3 months postimplant, were tested. Tremor amplitude and side-effect intensity were
recorded at 5 to 10 voltages for each of the four electrode contacts in monopolar configuration
with 90µs pulse width and 160 Hz frequency.
In all subjects, the most ventral contact required the lowest voltage to elicit side effects, which
invariably were paresthesias, while the most dorsal contact required the highest voltage to elicit
side effects. The contact that required the least voltage for maximal tremor suppression varied
across subjects. This variation could represent either a difference in the electrode location
relative to the site of tremor suppression or anatomical variation in the site of tremor suppression
itself.
Stimulus (voltage) - Response (side effect intensity or tremor power) curves generated from the
empirical data and the threshold (V th) - distance (r) relationship, defined as V th = V o + kr 2 (V
o is the offset, k is the slope), were used to estimate the distance from the electrode to the
anatomical targets that either caused SE or alleviated tremor. Model-based studies with r = 4 mm
and k = 0.2 V/mm 2 indicated that in the presence of 10 percent noise, r and k were estimated
with a mean error of 0.32 mm and 0.02 V/mm 2, respectively. These results indicate that the
stimulus-response data can be used to estimate the distance to the neuronal elements responsible
for the effects of DBS and, thus, can determine the spatial extent of stimulation.
Understanding the effects of contact configuration on the clinical response to DBS and
quantifying the spread of activation may improve electrode targeting and the techniques of
stimulus parameter adjustment.
This work was supported by NIH R01-NS-40894 and NIH T32-GM07535.