Objective
Recording of local field potentials (LFPs) during deep brain
stimulation (DBS) is necessary to investigate the instantaneous brain
response to stimulation, minimize time delays for closed-loop
neurostimulation and maximise the available neural data. To our knowledge,
existing recording systems lack the ability to provide artefact-free
high-frequency (>100 Hz) LFP recordings during DBS in real time
primarily because of the contamination of the neural signals of interest by
the stimulation artefacts.
Approach
To solve this problem, we designed and developed a novel, low-noise
and versatile analog front-end (AFE) that uses a high-order (8th) analog
Chebyshev notch filter to suppress the artefacts originating from the
stimulation frequency. After defining the system requirements for concurrent
LFP recording and DBS artefact suppression, we assessed the performance of
the realised AFE by conducting both in vitro and in
vivo experiments using unipolar and bipolar DBS (monophasic
pulses, amplitude ranging from 3 to 6 V peak-to-peak, frequency 140 Hz and
pulse width 100 μs). A full performance comparison
between the proposed AFE and an identical AFE, equipped with an 8th order
analog Bessel notch filter, was also conducted.
Main results
A high-performance, 4 nV (Hz)−1 AFE that is capable of recording nV-scale
signals was designed in accordance with the imposed specifications. Under
both in vitro and in vivo experimental
conditions, the proposed AFE provided real-time, low-noise and artefact-free
LFP recordings (in the frequency range 0.5–250 Hz) during
stimulation. Its sensing and stimulation artefact suppression capabilities
outperformed the capabilities of the AFE equipped with the Bessel notch
filter.
Significance
The designed AFE can precisely record LFP signals, in and without the
presence of either unipolar or bipolar DBS, which renders it as a functional
and practical AFE architecture to be utilised in a wide range of
applications and environments. This work paves the way for the development
of externalized research tools for closed-loop neuromodulation that use low-
and higher-frequency LFPs as control signals.