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Fig. 13.6: Effects of DBS pulses (at 10 Hz) on a single GPi neuron in the GPi as
observed experimentally and reported by Dostrovsky et al. [36]. The larger vertical
line segments are stimulus artifacts, while the shorter line segments can be attributed
to neuronal spike activity. It can be seen that as stimulus energy increases from 8 to
80
μ
A, the neural activity becomes more sparse.
13.5.4 DBS Programming
The typical procedure for programming DBS apparatus postoperatively begins with
the determination of the “therapeutic window” of stimulation for each electrode
[5, 152]. That is, using monopolar stimulus, keeping the pulse width at 60
s and
the frequency at 130 Hz, the pulse amplitude is increased from 0 V at increments of
0.2-0.5 V. Furthermore, the therapeutic window or range for a particular electrode
is the set of amplitude values between the smallest therapeutic amplitude and the
onset of undesirable side effects such as rigidity and dystonia (sustained muscle
contractions). Next, the electrode with the largest therapeutic range is selected as
the stimulus electrode [152].
Over the months following implantation, DBS parameters are modified according
to the side effects and therapeutic results observed. Typically, the amplitude or fre-
quency is increased as the patient develops a tolerance to the stimulus effect. More-
over, it is believed that a higher impedance or displacement of the electrodes due to
glial tissue scarring is responsible for the diminishing effectiveness of DBS over the
first postoperative months [40, 108]. In addition, long-term physiological processes
μ
