Micro-electrode Arrays

Neural EngineeringDept. of Biomedical Engineering

Kyung Hee University

Multi-electrode Array

• Multi-electrode arrays or microelectrode arrays are devices that contain multiple plates or shanks through which neural signals are measured or delivered.

• Two general classes of MEAs: implantable MEAs and non-implantable MEAs.

Multi-Electrode ArraysAllow simultaneous recording from many locations.Problem: does that mean from many neurons?The answer is no. Much signal processingneeded to separate sources.

History I• First implantable arrays were microwire

arrays developed in the 1950s.• In 1972, first experiment involved the use

of an array to record from cultured cells: used 2x15 array of gold electrodes plated with platinum black, each spaced 100um.

• In 1977, an independent study by G. Gross exploring the electrophysiology of snail ganglia.

• In 1982, studies neural activity of spinal cord neurons.

History II• Before the 1990’s, significant entry

barriers for new laboratories.• Lately with commercial MEA hardware and

software, many other laboratories use MEAs to undertake research.

In Vitro Arrays• The standard type of in vitro MEA in a pattern of

8x8 or 6x10 electrodes.• Electrodes are composed of indium tin oxide or

titanium with their diameters between 10 and 30 um.

• Normally used for single-cell cultures or acute brain slices.

• Spatial resolution is one of the key advantages of MEAs.

• High-density MEA has a grid pattern of 256 electrodes that cover an area of 2.8x2.8mm^2

In Vitro MEA

IrOx: Iridium Oxcide

In Vivo Arrays I• Three major categories of implantable MEAs are

microwire, silicon-based, and flexible microelectrode arrays.

• Microwire MEAs are largely made of stainless steel or tungsten.

• Silicon-based microelectrode arrays include two specific models: the Michigan and Utah arrays.– Michigan arrays allow a higher density of sensors for

implantation as well as a higher spatial resolution than microwire MEAs. They also allow signals to be obtained along the length of the shank, rather than just at the ends of the shanks.

In Vivo MEAs

Michigan MEAs

In Vivo Arrays II– Utah arrays are 3-D, consisting of 100 conductive

silicon needles. However, in a Utah array signals are only received from the tips of each electrode, which limits the amount of information that can be obtained at one time. Furthermore, Utah arrays are manufactured with set dimensions and parameters while the Michigan array allows for more design freedom.

• Flexible arrays, made with polyimide, parylene, or benzocyclobutene, provide an advantage over rigid microelectrode arrays because they provide a closer mechanical match

Utah MEAs

3-D Microelectrode Array(Univ. of Michigan)

Advantages of MEAs• In general, the major strengths of in vitro arrays

when compared to more traditional methods such as patch clamping include,– Allowing the placement of multiple electrodes at once

rather than individually – The ability to set up controls within the same

experimental setup (by using one electrode as a control and others as experimental)

– The ability to select different recordings sites within the array

– The ability to simultaneously receive data from multiple sites

Disadvantages of MEAs• In vitro MEAs are less suited for recording and

stimulating single cells due to their low spatial resolution compared to patch clamp and dynamic clamp systems

• The complexity of signals an MEA electrode could effectively transmit to other cells is limited compared to the capabilities of dynamic clamps.

• There are also several biological responses to implantation of a microelectrode array, particularly in regards to chronic implantation. Most notable among these effects are neuronal cell loss, glial scarring, and a drop in the number of functioning electrodes

Cell Damages due to MEAs

In Vitro Applications• MEAs can be used to study pharmacological effects on

dissociated neuronal cultures in a more simple, controlled environment

• MEAs have been used to interface neuronal networks with non-biological systems as a controller– For example, a neural-computer interface can be created using

MEAs. Dissociated rat cortical neurons were integrated into a closed stimulus-response feedback loop to control an animal in a virtual environment

In Vivo Applications• Deep brain stimulators, cochlear implants, and cardiac

pacemakers.• Deep brain stimulation (DBS) has been effective at

treating movement disorders such as Parkinson’s disease

• implants have helped many to improve their hearing by assisting stimulation of the auditory nerve.

• 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.

Bionic Eyes

Second Sight

• http://www.youtube.com/watch?v=VupYRCq59NI

• http://www.youtube.com/watch?v=tbv2hebWdlM

Cochlear Implant

Deep Brain Stimulation

Neurally Controlled Animat

• http://www.youtube.com/watch?v=E8l3_kAUe0w

Electrode setup

- Drill hole in cranium under anesthesia- Install and seal “recording chamber”- Allow animal to wake up and heal- Because there are no pain receptors

in brain, electrodes can thenbe inserted & moved in chamberwith no discomfort to animal.

Recording setup- Connect electrodes to amplifier& noise suppression board.- Sample & record.- Label & store data.

Brain Computer Interface

Directional control

Neural Interface Neural Signals Signal Processing Algorithms/Command Extraction

Sensors

Control Command

Robot Hand

Environmental Feedback

The Brain-Controlled Robot Hand

BMI Monkey

• https://www.youtube.com/watch?reload=9&v=MeSkcF6nuoQ

NeuroRobotics

http://www.youtube.com/watch?v=AYTf6qAwe98

Monkey controls robotic arm with BCIhttp://www.youtube.com/watch?v=gnWSah4RD2E