IEEE Solid-States Circuits Magazine - Fall 2023 - 43

rate as a potential predictor of seizures.
Medtronic's investigational Percept PC
and Summit employ spectral analysis
and a linear discriminant function with
a limited number of channels (four to
six) for stimulation regulation [10].
Newronika's AlphaDBS (with CE mark
approval) utilizes simple biomarkers
of targeted movement disorders
to adjust the stimulation parameters.
The investigational Picostim DyNeuMo
Mk-1 device is a cranial system that incorporates
three-axis accelerometers
for inertial sensing and closed-loop
motion-adaptive neurostimulation [Figure
1(a)] [11].
In addition, we see an array of
neurotech startups in the BCI space,
as shown in Figure 1(b). For instance,
Blackrock Neurotech and Paradromics
develop devices that consist of small
silicon-based structures with multiple
microelectrodes that can be inserted
into specific brain regions, such as
the motor cortex. Since the first human
implantation of Blackrock's Utah
array in 2005, over 30 patients have
participated in ongoing clinical trials,
utilizing one or more implants to control
prosthetic devices [1]. Paradromics
develops electrode arrays with thousands
of channels, enabling advanced
capabilities for high-resolution recording
and stimulation of neural activity.
The Neuralink devices consist
of thin and flexible electrode arrays
with over 1,000 channels, capable
of recording and stimulating electrical
activity at the level of individual
neurons. Precision Neuroscience develops
a flexible surface implant to record
ECoG activity, while Synchron's
stentrode is a minimally invasive tubular
metallic mesh with embedded
electrodes that adheres to cerebral
blood vessel walls to record population-level
neural activity [Figure 1(b)].
The Drive for Higher
Channel Counts
Notably, there is a shift toward the
development of neural interfaces
with substantially greater electrode
counts than those typically found in
commercial systems. Major contributors
to this trend include Neuropixels,
Neuralink, and Paradromics. The
imec's Neuropixels probe prioritizes
fundamental neuroscience research
and the measurement of large-scale
brain activity, which explains its relatively
high power consumption and
lack of neuromodulation capability
[12]. In contrast, Neuralink and Paradromics
strive to develop fully implantable
BCIs with potential clinical
applications, although specific neurological
indications have not yet
been defined. Achieving this goal
requires significant miniaturization
and power reduction of neural interface
circuits compared to the existing
designs [13], [14], integration of
closed-loop control strategies, and
addressing electrode safety and reliability
concerns in chronic settings.
These advancements are essential
for enabling the future clinical application
of these systems.
Closed-Loop Versus
Open-Loop Stimulation
While current therapeutic applications
of neurostimulation predominantly
employ the open-loop
approach, the most promising potential
lies in the development of
closed-loop or bidirectional technologies
for optimal patient outcomes.
For instance, deep-brain stimulation
(DBS) has gained FDA approval as a
therapy for essential tremor, Parkinson's
disease (PD), epilepsy, OCD,
and dystonia [15]. However, the
conventional open-loop DBS in PD
leads to persistent side effects, such
as gait and speech impairments, as
well as psychiatric complications.
These issues primarily arise from
the continuous delivery of high-frequency
(~130 Hz) stimulation, disregarding
the dynamically varying
clinical state of the patients.
In a pioneering study [16], electrophysiological
biomarkers of PD,
NeuroPace RNS
AspireSR VNS
Medtronic Percept PC
AlphaDBS
DyNeuMo
Flexible Leods
(x2)
Electrodes
(x4)
Implantable
Generator
(a)
Blackrock Neurotech
Synchron
Paradromics
Neuralink
Precision Neuroscience
(b)
FIGURE 1: (a) Closed-loop neuromodulation devices (commercially available and investigational) for epilepsy and movement disorders.
(b) Examples of neurotech startups and companies building invasive neural devices for BCI and neuromodulation.
IEEE SOLID-STATE CIRCUITS MAGAZINE
FALL 2023
43

IEEE Solid-States Circuits Magazine - Fall 2023

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