Nam et al Critical review of using MEA Technology
Researchers from Biomedical departments in Korea and Gainesville, Florida have recently collaborated to create a critical review of Microelectrode Array Technology and its use in generating in vitro model systems within neuroscience. They described the limiting factors and variables which will influence the effectiveness and reliability of neural recordings using this technique.
Microelectrode Array Technology is widely used to characterize the electrical activity of neuronal networks in cultures, slices, and in vivo experiments. A wide variety of different electrode types and recording protocols are in use. An array typically consists of a precisely organised patterns of microelectrodes ( in the region of 10/20 micrometers in diameter so they are comparable to that of a neuron) within a cell culture dish; the microelectrodes are connected by conductor lines with spacing of usually 100/200um which transmit the signal picked up to the microelectrode to an extracellular amplifier. The MEA system will also include an analogue and digital signal processor.
Within the study Nam et al reviewed the different factors that influenced the quality and success of MEA experiments. MEA technology is a powerful tool for quantitative analysis of among many things neural network plasticity and synaptogenesis, providing very precise spatiotemporal information about neuronal activity. However this is extremely reliant on the configuration and interfacing between microelectrode and neuron. During in vitro studies dissociated neurons are usually cultured on a planar array, this creates a very unique coupling between neuron and electrode. They demonstrated the variation in spike shapes and size influenced by the cell geometry, size and age.
The authors distinguished six groups of spike shape response; firstly divided by polarity of the largest peak, positive or negative, then into monophasic, biphasic and triphasic waveforms. They then described the effect of electrode geometry on spike waveforms, comparing flat type MEA's, recessed MEA's and 3D tip type MEA's and elaborated on the potential advantages and disadvantaged of different MEA types for specific applications . They also described the changes that occur with maturation of the cultures; increased amplitude and increased phasing of the waveform.
Furthermore, a review is given about attempts which have been made to decrease the impedance of MEA and improve the cell to electrode interface, to decrease background noise and increase the quality of recordings. This included modification by nanomaterials and surface patterning to increase yield of cell-electrode coupling.
Nam et al have importantly described the key factors which need to be considered for optimisation of MEA systems which will allow researchers to develop these techniques and further explore problems of brain-machine interfacing.
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In Vitro Microelectrode Array Technology and Neural Recordings Yoonkey Nam & Bruce C. Wheeler
Critical Reviews in Biomedical Engineering, 39(1):45–62 (2011)
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