In-vivo Test: In-vivo animal experiment in a rat is performed to
verify the efficacy of the proposed stimulator for seizure suppression
application. Fig. 8(a) shows the experimental environment for the test.
The PC updates the stimulation parameters to the FPGA through the UART
interface, followed by the SPI interface from FPGA to the stimulation
IC. While stimulation pulses are applied to the rat, the commercial RHS
recording platform (from intan technologies) records the ECoG signals,
which is transmitted to the PC. As shown in Fig. 8(b), a
micro-fabricated graphene electrode, which shows the impedance
characteristics of Fig. 9, is directly attached to the somatosensory
and/or motor cortical area of the
brain
for the experiment. Bicuculline is used to mimic seizure and is injected
into the brain’s somatosensory and motor cortex at a concentration of
15mM. Fig. 10(a) shows the entire waveform of bicuculline-induced
seizure, which is suppressed through stimulation. Stimulation is
performed with a frequency of 5 Hz, which is the most effective for
seizure inhibition. Stimulation is continued for 40 seconds with the
amplitude of 50µA and the pulse width of 10µs. Fig. 10(b-e) shows the
waveforms when epilepsy, stimulation, inter-period of seizure
to
stop, and suppression occurs, respectively. After 40 seconds
stimulation, it takes 14 seconds to suppress the seizure.
A performance summary and comparison with other neural stimulators are
presented in Table I. This work achieves high compliance per supply
voltage through a low-cost standard CMOS technology. The 64-channel
stimulator can be independently configured with a high resolution of 8
bits. In addition, for the feasibility verification, an animal test is
peformed.
Conclusions: We present a 64-channel implantable current mode
stimulator IC with a passive charge balancing scheme for seizure
suppression. The proposed stimulator uses passive CB with a bootstrapped
switch, demonstrating sub-nC charge-balanced operation. The regulated
cascode driver satisfies a high compliance voltage ratio of 0.98 per
supply voltage in 0.18 mm standard CMOS technology. The amplitude, pulse
width, and activated channel of the stimulation waveform are variably
adjusted with the SPI interface. In-vivo test shows the feasibility of
seizure suppression through a 5Hz stimulation frequency with 50µA
current amplitude and 10µs pulse width.