Name: optrode array for simultaneous optogenetic modulation and electrical neural recording
Uploaded: 2022-09-01T13:00:00
Description: Watch this Scientific Journal Video about Optrode Array for Simultaneous Optogenetic Modulation and Electrical Neural Recording at JoVE.com

This research was supported by Convergent Technology R&#38;D Program for Human Augmentation through the National Research Foundation of Korea (NRF), funded by the Ministry of Science and ICT (NRF-2019M3C1B8090805), and supported by a National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (no. 2019R1A2C1088909). We thank Seung-Hee Lee&#39;s laboratory at the Department of Biological Sciences, KAIST, Daejeon, Korea, for kindly providing the transgenic mice.

The animal care and surgical procedures were approved by the Institutional Animal Care and Use Committee (IACUC) at the Ewha Womans University (no. 20-029).
1. Preparation of an optrode array (Figure 1 and Figure 2)
<ol>
	<li>Attach optical fibers with the microlens array.
	<ol>
		<li>Remove the passivation coating of the optical fiber and cut it into 5 mm-long pieces using a precis...

The feasibility of the system for simultaneous optogenetic stimulation and electrophysiological recording was verified (Figure 6). The big spikes during light stimulation are photoelectric artifacts occurring at the same time as the light stimulation (Figure 6A). This is clear in the zoomed view of the waveform in the red dashed rectangle (Figure 6A). As shown in Figure 6A, the photoelectrical artifacts...

Recording and controlling neural activity is essential for understanding how the brain functions in a neural network and at cellular levels. Conventional electrophysiological recording methods include the patch clamp1,2,3,4 using a micropipette and extracellular recording using microneural electrodes5,6,7,8. As a neuromodulation method, electrical stimulation has been frequently used to directly stimulate a focal brain region through direct or indirect depolarization of neuronal cells. However, the electrical method cannot distinguish neuronal cell types for recording or stimulation because the electrical currents spread in all directions.
As an emerging technology, optogenetics has ushered in a new era in understanding how the nervous system works9,10,11,12,13,14,15,16. The essence of optogenetic techniques is to use light to control the activity of light-sensitive opsin proteins expressed by genetically modified cells. Thus, optogenetics enables the sophisticated modulation or monitoring of genetically selected cells in complicated neural circuits14,17. The wider use of the optogenetic approach has necessitated simultaneous neural recording to directly confirm optical neuromodulation. Therefore, an integrated device with light control and recording functions would be extremely valuable16,18,19,20,21,22,23,24,25.
There are limitations of conventional, laser-based optogenetic stimulation, which requires a bulky and expensive light delivery system26,27,28,29,30. Therefore, some research groups employed &#181;LED-based silicon probes to minimize the size of the light delivery system31,32,33,34. However, there is a risk of thermal brain damage caused by direct contact with &#181;LEDs due to the low energy conversion efficiency of LEDs. Light waveguides, such as optical fibers, SU-8, and silicon oxynitride (SiON), have been applied to avoid thermal damage30,35,36,37,38,39. However, this strategy also has a drawback due to its low coupling efficiency between light sources and the waveguides.
The microlens array was previously introduced to enhance the light coupling efficiency between LEDs and optical fibers40. An optrode system was developed based on microelectromechanical systems (MEMS) technologies for optical stimulation and electrical recording on a microscale40. The microlens array between an LED and optical fibers increased the light efficiency by 3.13 dB. As shown in Figure 1, a 2x2 optical fiber array is aligned on the 4x4 microlens array, and the LED is positioned below the microlens array. The 2x2 optical fibers are mounted instead of 4x4 to reduce brain damage. A tungsten electrode array is positioned adjacent to the optrode array using silicon via holes for electrophysiological recording (Figure 1B).
The system consists of a top disposable part and detachable bottom parts. The top disposable part, which includes the optical fiber array, microlens array, and the tungsten electrode array, is designed to be permanently implanted into the brain for in vivo experiments. The bottom part includes an LED light source and an external power supply line, which is easily removable and reusable for another animal experiment. An attachable plastic cover protects the disposable part when the detachable part is removed.
The feasibility of the system is verified by implantation into the brains of transgenic mice expressing channelrhodopsin-2 (ChR2) in Ca2+/calmodulin-dependent protein kinase II-positive neurons (CaMKII&#945;::ChR2 mouse). Recording electrodes were used to record the neural activities from individual neurons during optical stimulation of the neurons.

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optrode array for simultaneous optogenetic modulation and electrical neural recording

During the last decade, optogenetics has become an essential tool for the investigation of neural signaling due to its unique capability of selective neural modulation or monitoring. As specific types of neuronal cells can be genetically modified to express opsin proteins, optogenetics enables optical stimulation or inhibition of the selected neurons. There have been several technological advances in the optical system for optogenetics. Recently, it was proposed to combine the optical waveguide for light delivery with electrophysiological recording to simultaneously monitor the neural responses to optogenetic stimulation or inhibition. In this study, an implantable optrode array (2x2 optical fibers) was developed with embedded multichannel electrodes. 
A light-emitting diode (LED) was employed as a light source, and a microfabricated microlens array was integrated to provide sufficient light power at the tip of the optical fibers. The optrode array system comprises the disposable part and the reusable part. The disposable part has optical fibers and electrodes, while the reusable part has the LED and electronic circuitry for light control and neural signal processing. The novel design of the implantable optrode array system is introduced in the accompanying video in addition to the procedure of the optrode implantation surgery, optogenetic light stimulation, and the electrophysiological neural recording. The results of in vivo experiments successfully showed time-locked neural spikes evoked by the light stimuli from hippocampal excitatory neurons of mice.

The optrode system is successfully fabricated to provide sufficient light power to activate the target neurons. The fine alignment of the tungsten electrodes is achieved through the microfabricated silicon via the holes. The measured light intensity is 3.6 mW/mm2 at the optical fiber tip when 50 mA current is applied. The microlens increased the light efficiency by 3.13 dB. Due to the microlens array, which enhances the light coupling, the applied current is approximately half of the current required to achiev...

Watch this Scientific Journal Video about Optrode Array for Simultaneous Optogenetic Modulation and Electrical Neural Recording at JoVE.com

Optrode Array for Simultaneous Optogenetic Modulation and Electrical Neural Recording

Here, we present the fabrication method of an optrode system with optical fibers for light delivery and an electrode array for neural recording. In vivo experiments with transgenic mice expressing channelrhodopsin-2 show the feasibility of the system for simultaneous optogenetic stimulation and electrophysiological recording.

During the last decade, optogenetics has become an essential tool for the investigation of neural signaling due to its unique capability of selective ...

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