State-of-the-art MEMS and microsystem tools for brain research

Mapping brain activity has received growing worldwide interest because it is expected to improve disease treatment and allow for the development of important neuromorphic computational methods.MEMS and microsystems are expected to continue to offer new and exciting solutions to meet the need for high-density,high-fidelity neural interfaces.Herein,the state-of-the-art in recording and stimulation tools for brain research is reviewed,and some of the most significant technology trends shaping the field of neurotechnology are discussed.

Dual color optogenetic control of neural populations using low-noise,multishank optoelectrodes

Optogenetics allows for optical manipulation of neuronal activity and has been increasingly combined with intracellular and extracellular electrophysiological recordings.Genetically-identified classes of neurons are optically manipulated,though the versatility of optogenetics would be increased if independent control of distinct neural populations could be achieved on a sufficient spatial and temporal resolution.We report a scalable multisite optoelectrode design that allows simultaneous optogenetic control of two spatially intermingled neuronal populations in vivo.We describe the design,fabrication,and assembly of low-noise,multisite/multicolor optoelectrodes.Each shank of the four-shank assembly is monolithically integrated with 8 recording sites and a dualcolor waveguide mixer with a 7×30μm cross-section,coupled to 405 nm and 635 nm injection laser diodes(ILDs)via gradient-index(GRIN)lenses to meet optical and thermal design requirements.To better understand noise on the recording channels generated during diode-based activation,we developed a lumped-circuit modeling approach for EMI coupling mechanisms and used it to limit artifacts to amplitudes under 100μV upto an optical output power of 450μW.We implanted the packaged devices into the CA1 pyramidal layer of awake mice,expressing Channelrhodopsin-2 in pyramidal cells and ChrimsonR in paravalbumin-expressing interneurons,and achieved optical excitation of each cell type using sub-mW illumination.We highlight the potential use of this technology for functional dissection of neural circuits.

Novel diamond shuttle to deliver flexible neural probe with reduced tissue compression

The ability to deliver flexible biosensors through the toughest membranes of the central and peripheral nervous system is an important challenge in neuroscience and neural engineering.Bioelectronic devices implanted through dura mater and thick epineurium would ideally create minimal compression and acute damage as they reach the neurons of interest.We demonstrate that a three-dimensional diamond shuttle can be easily made with a vertical support to deliver ultra-compliant polymer microelectrodes(4.5-µm thick)through dura mater and thick epineurium.The diamond shuttle has 54%less cross-sectional area than an equivalently stiff silicon shuttle,which we simulated will result in a 37%reduction in blood vessel damage.We also discovered that higher frequency oscillation of the shuttle(200Hz)significantly reduced tissue compression regardless of the insertion speed,while slow speeds also independently reduced tissue compression.Insertion and recording performance are demonstrated in rat and feline models,but the large design space of these tools are suitable for research in a variety of animal models and nervous system targets.