This summarizes a document reviewing an integrated device for combined optical neuromodulation and electrical recording for chronic in-vivo applications. The device consists of an optical fiber integrated with a microelectrode array (MEA), called an optrode-MEA, that allows for simultaneous optical stimulation and electrophysiological recording. The summary is: [1] The optrode-MEA was developed to allow for optical stimulation at one cortical site while recording neural activity from surrounding neurons to study local circuit dynamics. [2] Experiments in freely moving rats demonstrated the device could successfully record neural signals over months, mapping spatially and temporally resolved neuronal responses. [3] Analysis of recorded signals under different stimulation conditions proved the

1. Review on
Integrated Device for Combined Optical
Neuromodulation and Electrical Recording
for Chronic In-Vivo Applications
By
Md. Kafiul Islam
A0080155M
Supervisor: Dr. Zhi Yang

2. Outline
• Introduction
 Problem Definition
• Paper Summery
 Main Contribution
 Technical Evaluation
 Major Findings
 Strength and Weakness
• Conclusion

3. Problem Definition
How Brain Works…!?
Understanding the circuit-level functional organization of the brain has
important implication for both basic and clinical neuroscience.
Understanding of local neural circuit dynamics
– Simultaneous stimulation and recording (with high spatiotemporal resolution)
– Both single-unit activities and local field potential recording
– In-vivo experiments for freely moving or behaving animals
Electrical & Magnetic Stimulation (Conventional)
– Lacks selective neuromodulation (e.g. due to complex patterns of current flow
in electrical micro-stimulation)

4. Problem Definition (Cont…)
Optogenetics (Recent)
 Combined genetics and optics
 More selective modulation
 Less instrumental interference
 Technically scalable
Conventional Optogenetics:
 Recording optically evoked signals is limited to individual electrodes adhesively
attached in parallel to optical fiber [12-16] (not integrated, inappropriate for chronic
experiments in freely moving animals)
 Can only sample one recording site at a time as an optical fiber is mechanically
attached to an electrode [26]. ( local neural activity unknown)
 Loose confinement of etched optical waveguide results in low spatial resolution
where multi-shank silicon probes combined with a bare optical fiber [9, 27].

5. Main Contribution
Development of Optrode-MEA to use in chronic in-vivo neural experiments of freely
moving animals for simultaneous optical stimulation and electrophysiological
recording
 Single localized optical fiber is
integrated to a commercial 6 x 6 MEA
of each 1 mm long microelectrode .
 Shape & Dimension of optrode
matched with intracortical electrode.
 Optrode is mechanically strong
enough to penetrate through the dura
matter.
 Tapered ends of optical fiber are
shaped to minimize neuronal damage
during insertion.
Optrode-MEA: Optical Electrode integrated
with Micro-Electrode Array

6. Main Contribution (Cont…)
 Capability of Optrode-MEA to optically modulate at one cortical
site while recording from an ensemble of neurons that define the
local circuit in the vicinity of stimulus site.
 Ability to control the excitation volume of brain by controlling the
emitted optical power from optrode and its distribution within the
brain tissue.
 Demonstrated successfully for potential use in future chronic in-
vivo experiments for freely moving animals.

7. Some Results and Observation
Representative examples of light activation of LFP under a pulse train of
473 nm, 8 Hz and 20 ms pulse duration.
• Power spectrogram and power density plot of optically modulated LFP. The
power is significantly enhanced at the light stimulation frequency and its
harmonics. (Left)
• LFP power around the pulse stimulation frequency as a function of estimated
light intensity at the recording electrode site. (Right)

8. Some Results and Observation (Cont…)
Spatially and temporally resolved neuronal activities from a large
cortical area
– The mapping of averaged (N = 100) spike waveforms on each input channel
obtained from a sample recording session (Left).
– Pulse-triggered LFPs at various locations show both proximal and distal
field potential in response to the 1 ms pulse stimulation (Right).

9. Technical Evaluation
 Design & fabrication of Optrode described clearly.
 Verification of single optrode as in vivo electrophysiological
recording tool was demonstrated.
 Experiments with two freely moving rats for up to 2 and 8 months
respectively to demonstrate successful use in chronic application.
 Detail analysis of the experimental results with different
conditions proved the successful demonstration of such device.

10. Major Findings
 Total volume of excitation decided primarily by the optical power
distribution
 Different stimulation frequencies might give a new dimension
how the neural network actually responds to optogenetic
excitation.
 Diversity in neural responses represents the complicated
dynamics of the photo-modulated cortical network.
 No obvious signature of tissue-array interaction or damage found.

11. Strengths
• The design and fabrication of the device was described in detail
and clearly. The unique design of optrode to use it for in-vivo
chronic application in freely moving animals was also obvious.
• The experiment paradigms were also clearly described and
demonstrated
• The analysis made on the recorded signals relating to different
stimulations was

12. Strengths (Cont…)
• Allows monitoring of the spread of activity in a network of
neurons in response to the local stimulation.
• The capability of recording the full-spectrum neural signals
offers opportunity to study the dynamics of neuromudulation
by focusing on the power of particular frequency bands.
• The ability to control the excitation volume by controlling the
emitted light power and its distribution within the brain.

13. Weakness
• The skull-anchored optrode-MEA might have less chance of stable
recording from the same single units in comparison with epi-cortical
‘floating’ MEA [6]. Moreover, skull mounted device takes larger
anatomical workspace.
• Correlation between neural activity and behaviour is not explicitly
understandable.
• A significant cortical depression was found to be present. The reason
for such depression is still unclear.

14. Weakness (Cont…)
• How to handle the photo-induced artifacts for high scale
experiments is unclear.
• No point on the motion artifacts that could be severe for freely
moving animals.
• Not possible to accurate identification of current sinks and
sources over space and time as no. of recording channels is small
[7].

15. Conclusion
• Overall a nice presentation of the paper.
• New dimension of information for neural local circuit dynamics.
• Future work can be extension of stimulation sites and recording
channels to allow more neurons and a more global network to
study.
• Investigation with particular behavior/task can be incorporated to
study correlation of neural response with behavior or motor
function.

16. Thank you
Q&A