![](bg1.png)
Simultaneous Optical Stimulation and Electrophysiological Recordings
in Closed-loop Operation
Thoa Nguyen
1,3
, Ling Wang
1,3
, Henrique Cabral
1,4
, Georges Gielen
2,3
, Francesco Battaglia
1,4
and Carmen Bartic
1,3
1
NERF, Leuven, Belgium
2
Imec, Leuven, Belgium
3
Katholieke Universiteit Leuven, Leuven, Belgium
4
Radboud Universiteit Nijmengen, Nijmengen, Netherlands
1 INTRODUCTION
Closed-loop brain computer interfaces are rapidly
progressing due to their application in funda-
mental neuroscience and prosthetics implemented
(Hatsopoulos and Donoghue, 2009; Lebedev and
Nicolelis, 2006). The integration of optical stim-
ulation and electrophysiological recordings, on one
hand, brings the advantage of cell-type selectivity. On
the other hand, it provides an alternative solution to
the stimulation-induced artifacts, a challenge in elec-
trical stimulation (Zhang et al., 2009; Zhang and Oert-
ner, 2007; Wininger et al., 2009).
In this contribution, we describe a prototype al-
lowing simultaneous optical stimulation and electro-
physiological recordings in a closed-loop manner.
The prototype is implemented with online spike de-
tection and classification for selective cell-type stim-
ulation.
2 METHODS
2.1 System Architecture
The implemented system is based on commercial off-
the-shelf electronics with three functional parts: (1)
data acquisition, (2) LED stimulation, and (3) control
software (see Fig. 1).
The acquisition circuitry measures the brain activ-
ity collected on 32 channels with respect to the skull
reference electrode. The on-board amplifier (Intan
chip - RHA2132) amplifies and then multiplexes the
signal before delivering it to the analog-to-digital con-
verter (AD7980). The filters integrated in the ampli-
fier are set by external resistors to record the broad-
band signal, i.e. 0.2 - 5000 Hz. The acquisition head-
stage is digitally interfaced with the digital I/O board
(Data acquisition card (DAQ) - PCI 6259M).
The fiber-coupled LED light source (Thorlab) is
controlled by TTL voltage pulses. The pulses are de-
livered from the analog output of the DAQ card with
pre-defined amplitude and duration.
Our custom developed software controls the ac-
quisition, triggers the stimulation, and analyzes the
recorded signals. The software is implemented on
LabVIEW platform and integrates signal processing
code written in Matlab. Data from the headstage are
transferred to the computer’s memory through a high-
speed acquisition loop. In parallel to that, a consumer
loop stores and analyzes the data.
A data processing sequence for spike detection
and classification is defined for the real-time execu-
tion. The implemented spike detection recognizes
possible spikes by an adaptive threshold-based algo-
rithm (Quiroga et al., 2004) applied to the band-pass
filtered data (300 - 5000 Hz). Next, the detected
signals are correlated with previously extracted tem-
plates, which were defined offline from a baseline
recording period at the beginning of the session. In
this first prototype, we employed a simplest form of
template matching, i.e. a dot-product, and assigned
the spikes to the cluster resulting in the maximum cor-
related value.
2.2 Microdrive with Optical Fibers
A microdrive is built based on a previous design
(Kloosterman et al., 2009) (see Fig. 1). It hosts two
separate tetrode bundles with 12 recording tetrodes
(Wilson and McNaughton, 1993) and one optic fiber
each, allowing recording and optically stimulating
neural activity from two different brain regions. Each
tetrode consists of a twisted bundle of four or eight
polyimide-insulated microwires, fused and cut to cre-
ate a blunt tip.
Nguyen T., Wang L., Cabral H., Gielen G., Battaglia F. and Bartic C..
Simultaneous Optical Stimulation and Electrophysiological Recordings in Closed-loop Operation.
Copyright
c
2013 SCITEPRESS (Science and Technology Publications, Lda.)