Floating Microelectrode Arrays

Our lab has been using chronically implanted Floating Microelectrode Arrays from Microprobes to record neural data from 13 Rhesus macaques over the past 15 years. Such a preparation allows the recording of both spike and local field potential activity in a “plug-and-play” fashion for months to years following surgical implantation. Because data can be recorded simultaneously from many electrodes (currently we use 512) in a single session, the data for an experimental study can be recorded in a few daily or weekly sessions. Data for a number of different studies therefore can be collected from a single monkey. Though spike recordings gradually decline over months and years (as with any implanted microelectrode array), microstimulation continues to be effective. We have collected data productively from individual macaques for as long as 10 years after implantation. Key for our studies has been that electrodes can be as long as 10 mm, and can be of varied lengths on a single FMA. This allows electrodes to sample down the banks of sulci in the cerebral cortex (which is not possible with other arrays for which electrode length is limited to 2 mm). In addition, multiple FMAs can be implanted to follow the curvature of sulci at the hemispheric surface (e.g. the macaque arcuate sulcus), and the cortical surface can be “tiled” with multiple arrays to sample widely within a cortical region.

I use FMAs exclusively in all of the labs in which I’ve done chronic multielectrode array recordings in cortex: my lab during postdoctoral training, 3 collaborating labs, and my own lab. The ability to individually define the electrode depths allows us to implant a wide range of brain areas. We routinely put in at least 10 arrays and have put in over 20 in a single surgery. The arrays go in easily and with a good plan it’s possible to implant lots of areas. We almost never have an array fail, they are surprisingly durable. The recordings have been very stable for us with our highest number of single units coming 3-12 months after implant but we get still get lots of units for years after implant.

We are currently using the 36 channel FMAs in combination with TDT technologies to record from a sensory-motor network in non-human primates. These arrays provide a great signal to noise ratio, and a very good yield of SUA & LFPs per array. Crucially, you can customize the electrodes per array in terms of materials, length and impedance. The last has allowed us to perform microstimulation & recording experiments using these arrays. The recordings are stable across several months. During the first months the signal quality is at its best. The arrays work equally fine in cortical areas that lie within the cortical surface, as well as deeper cortical areas like the cingulate. Good targeting of the desired area and electrode length estimation are crucial to record from the desired area. The Microprobes team is great in helping with the customization of the design, troubleshooting with mapping and urgent orders. It has been a pleasure and a great learning experience to work with them.

Microprobes for Life Science has been my preferred array vendor for almost eight years. Our group relies on floating microelectrode arrays implanted in many cortical areas. In our experience, every single MLS floating array has yielded amazing data for over two years each. One hundred percent of implantations have been successful, largely because of the geometry of the arrays (which have longer ground/reference electrodes, to anchor the arrays in place) and because of the MLS-provided instructions for surgical implantation, which encourage a gradual, slow introduction of the electrodes into the brain parenchyma. MLS has been highly responsive to our requests, including creating minimalist titanium cases for array connectors, which obviate the use of acrylic and allow tissue healing more effectively. We have tried alternative arrays, and none are as reliable as those from Microprobes.

I have been using FMAs for over 15 years now. During this time, I have also used microelectrode arrays from other companies. I have found that FMAs are the easiest to implant (in particular the cable management) and have the best longevity to isolate single neurons, with arrays that work for many years. Different electrode technologies are best suited to address different questions, and I find that FMAs provide the best compromise between electrode density and cortical coverage to study questions related to multi-region interactions.