Simultaneous multisite recording using multi-electrode arrays (MEAs) in cultured neurons, brain slices, and organoids is an emerging technique in the field of network electrophysiology. Indeed, deciphering neural network function in health and disease requires recording from many active neurons simultaneously. Over the past 40 years, great efforts have been made by both scientists and companies, to advance this technique. The MEA technique has been widely applied to many regions of the brain, retina, heart, and muscle at the network level. However, while electrophysiological approaches have improved rapidly for 2D cultures, only in the past several years have advances been made to overcome limitations posed by the three-dimensionality of brain organoids.
Brain organoids have become widely used to study the human brain in vitro. As pluripotent stem cell-derived structures recapitulating physiological cell types and architecture, brain organoids bridge the gap between relatively simple 2D human cell cultures and non-human animal models. This allows for high complexity and physiological relevance in a controlled in vitro setting, opening the door for a variety of applications including development and disease modeling and high-throughput screening. While technologies such as single-cell sequencing have led to significant advances in brain organoid characterization and understanding, improved functional analysis (especially electrophysiology) is needed to realize the full potential of brain organoids. Parallel to recent advances in optical Ca(2+) imaging, an emerging approach consists of adopting complementary-metal-oxide-semiconductor (CMOS) technology to realize MEA devices.
This novel MEA platform allows nowadays to record from several thousands of single neurons at sub-millisecond temporal resolution, shedding light on the mechanisms underlying brain functions and dysfunctions at the network level that remained largely unknown due to the technical difficulties.
Usually, cell-based assays analyze cells placed in plastic dishes or acute slices on the interface or submerged chamber. Standard approaches provide for extracting information from cells through optical systems or sensors embedded in the plastic substrate (e.g. passive microelectrode array "MEA" technology). In these systems, the information acquired from the cells travels on limited bandwidth across long distances (compared to the cell's size) before reaching a CPU on a paired machine where this information will be processed. Long distances affect the quality of the information and bandwidth issues limit the quantity of information that can be transmitted to a few frames per second through imaging or a few sensors in an MEA. However, cells¿ behaviors arise from complex collective interactions between large populations of cells. Then a change in paradigm is required to gain insights into cell network processing and the mechanisms of neuronal network functions in physiological and pathological conditions.
This unique technology will be mainly applied to solve specific open questions in the field of neuroscience in physiological conditions and in systems mimicking neurodevelopmental and neurodegenerative disorders.
The in-vitro and the ex-vivo fields are constantly evolving to better model human brain physiologic and pathology. On one hand, the rise of human-derived stem cell technology and the progression toward more in vivo-like human models raise new challenges in identifying reliable and efficient readout technology. On the other hand, the development of murine models harboring human mutations linked to either neurodevelopmental or neurodegenerative diseases pushes to unravel the complexity of the neuronal networks and of their interplay with the whole organism.
In this context the development of innovative products - like the 3D CMOS chip ¿ which, with respect to conventional electrodes, maximizes the potential of the dense information acquired from both advanced in-vitro models such as human-derived organoids or spheroids and acute mouse brain slices.
These MEAs, based on high-density microelectrode array technology, allow studying the physiological and pathological functional activity of neuronal cultures. They are a versatile tool to investigate in detail the mechanisms of neuronal signal processing and to improve the quality and reliability of drug screenings or toxicological assays.
In addition, HD-MEAs can record both spiking activity and field potential propagations (EPSP, Population Spikes) over different regions in brain tissue preparations at unprecedented spatial and temporal resolutions, and resolve signals from dendritic compartments or somatic layers within sub-areas of the circuitry
With respect to the AIMS of this proposal the 3Brain MEA offers a number of advantages:
Advantages of using 3Brain technology on neuronal cultures (AIM1 and AIM2):
- Label-free functional monitoring of large networks with single-cell spiking activity resolution
- Tracking of signal propagation among cells for functional connectivity studies
- Kinetic functional assay to follow culture development over weeks and months
- The improved statistical significance of the calculated network activity parameters
Advantages of 3Brain technology with brain slices (AIM3 and AIM4):
- Large brain region monitoring of spontaneous activity patterns and precise mapping of activity propagation over multiple circuits
- Precise electrical stimulation capability
- Automated LTP/LTD protocols for plasticity studies.
Advantages of 3Brain technology with Brain Organoids (AIM1 and AIM2):
- Label-free functional monitoring of whole organoids with single-cell spiking activity resolution
- Improved statistical significance measuring from thousands of neurons simultaneously
- Multiple sample recordings: 3Brain¿s HD-MEAs has a sensing area of up to 25mm², allowing to record of multiple organoids in a single experiment.
Moreover, the 3Brain MEA can be implemented with the CorePlate technology to transform the standard plastic dishes used by researchers for many years to study cell networks into an intelligent device. Each well now integrates a semiconductor processing core, namely a BioSPU (BioSignalProcessing Unit), that pairs with the cell processing network. The BioSPU core pre-processes cell data in-situ, efficiently, with neither speed nor band limits and with the best quality output.