Microelectrode array
[citation needed] The size and shape of a recorded signal depend upon several factors: the nature of the medium in which the cell or cells are located (e.g. the medium's electrical conductivity, capacitance, and homogeneity); the nature of contact between the cells and the MEA electrode (e.g. area of contact and tightness); the nature of the MEA electrode itself (e.g. its geometry, impedance, and noise); the analog signal processing (e.g. the system's gain, bandwidth, and behavior outside of cutoff frequencies); and the data sampling properties (e.g. sampling rate and digital signal processing).
Myocytes harvested from embryonic chicks were dissociated and cultured onto the MEAs, and signals up to 1 mV high in amplitude were recorded.
Electrodes are typically composed of indium tin oxide, platinum black or titanium nitride and have diameters between 10 and 30 μm.
[3] One challenge among in vitro MEAs has been imaging them with microscopes that use high power lenses, requiring low working distances on the order of micrometers.
[3][11] Another challege among in vitro MEAs has been the rigidity of the glass substrate, which does not replicate the soft, flexible nature of biological tissues, thus impacting cellular behavior and experimental outcomes.
[12] To address this limitation, flexible and stretchable microelectrode arrays have been developed to better simulate the mechanical properties of living tissues.
[3] Increased spatial resolution is provided by CMOS-based high-density microelectrode arrays featuring thousands of electrodes along with integrated readout and stimulation circuits on compact chips of the size of a thumbnail.
The perforated MEA design applies negative pressure to openings in the substrate so that tissue slices can be positioned on the electrodes to enhance contact and recorded signals.
Microwire MEAs are largely made of stainless steel or tungsten and they can be used to estimate the position of individual recorded neurons by triangulation.
This ion flux through the cellular membrane generates a sharp change in voltage in the extracellular environment, which is what the MEA electrodes ultimately detect.
Implantable arrays allow signals to be obtained from individual neurons enabling information such as position or velocity of motor movement that can be used to control a prosthetic device.
The short term response occurs within hours of implantation and begins with an increased population of astrocytes and glial cells surrounding the device.
[28] Immunohistochemical markers showed a surprising presence of hyperphosphorylated tau, an indicator of Alzheimer's disease, near the electrode recording site.
The phagocytosis of electrode material also brings into question the issue of a biocompatibility response, which research suggests has been minor and becomes almost nonexistent after 12 weeks in vivo.
For example, the capacity of such networks to extract spatial[33] and temporal[34] features of various input signals, dynamics of synchronization,[35] sensitivity to neuromodulation[36][37][38] and kinetics of learning using closed loop regimes.
[39][40] Finally, combining MEA technology with confocal microscopy allows for studying relationships between network activity and synaptic remodeling.
Dissociated rat cortical neurons were integrated into a closed stimulus-response feedback loop to control an animat in a virtual environment.
[41] A closed-loop stimulus-response system has also been constructed using an MEA by Potter, Mandhavan, and DeMarse,[42] and by Mark Hammond, Kevin Warwick, and Ben Whalley in the University of Reading.
About 300,000 dissociated rat neurons were plated on an MEA, which was connected to motors and ultrasound sensors on a robot, and was conditioned to avoid obstacles when sensed.
[33] This "Braitenberg vehicle" was used to demonstrate the indeterminacy of reverse neuro-engineering showing that even in a simple setup with practically unlimited access to every piece of relevant information,[44] it was impossible to deduce with certainty the specific neural coding scheme that was used to drive the robots behavior.
Research suggests that MEAs may provide insight into processes such as memory formation and perception and may also hold therapeutic value for conditions such as epilepsy, depression, and obsessive-compulsive disorder [citation needed].
MEAs provide the high resolution necessary to record time varying signals, giving them the ability to be used to both control and obtain feedback from prosthetic devices, as was shown by Kevin Warwick, Mark Gasson and Peter Kyberd.
[9] A biannual scientific user meeting is held in Reutlingen, organized by the Natural and Medical Sciences Institute (NMI) at the University of Tübingen.
The meetings offer a comprehensive overview of all aspects related to new developments and current applications of Microelectrode Arrays in basic and applied neuroscience as well as in industrial drug discovery, safety pharmacology and neurotechnology.
[50][51][52][53] MEART consisted of rat cortical neurons grown in vitro on an MEA in Atlanta, a pneumatic robot arm capable of drawing with pens on paper in Perth, and software to govern communications between the two.
