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

Outline

• Introduction

Problem Definition

• Paper Summery

Main Contribution

Technical Evaluation

Major Findings

Strength and Weakness

• Conclusion

Problem Definition

How Brain Works…!?

Understanding the circuit-level functional organization of the brain hasimportant 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)

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].

Main ContributionDevelopment 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 isintegrated to a commercial 6 x 6 MEAof each 1 mm long microelectrode .

Shape & Dimension of optrodematched with intracortical electrode.

Optrode is mechanically strongenough to penetrate through the duramatter.

Tapered ends of optical fiber areshaped to minimize neuronal damageduring insertion.

Optrode-MEA: Optical Electrode integrated with Micro-Electrode Array

Main Contribution (Cont…)

Capability of Optrode-MEA to optically modulate at one corticalsite while recording from an ensemble of neurons that define thelocal circuit in the vicinity of stimulus site.

Ability to control the excitation volume of brain by controlling theemitted optical power from optrode and its distribution within thebrain tissue.

Demonstrated successfully for potential use in future chronic in-vivo experiments for freely moving animals.

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. Thepower is significantly enhanced at the light stimulation frequency and itsharmonics. (Left)

• LFP power around the pulse stimulation frequency as a function of estimatedlight intensity at the recording electrode site. (Right)

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).

Technical Evaluation

Design & fabrication of Optrode described clearly.

Verification of single optrode as in vivo electrophysiologicalrecording tool was demonstrated.

Experiments with two freely moving rats for up to 2 and 8 monthsrespectively to demonstrate successful use in chronic application.

Detail analysis of the experimental results with differentconditions proved the successful demonstration of such device.

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.

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

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.

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 largeranatomical workspace.

• Correlation between neural activity and behaviour is not explicitlyunderstandable.

• A significant cortical depression was found to be present. The reasonfor such depression is still unclear.

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].

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.

Thank you

Q&A