Wireless Performance of a Fully Passive Neurorecording Microsystem Embedded in Dispersive Human Head Phantom

This paper reports the wireless performance of a biocompatible fully passive microsystem implanted in phantom media simulating the dispersive dielectric properties of the human head, for potential application in recording cortical neuropotentials. Fully passive wireless operation is achieved by means of backscattering electromagnetic (EM) waves carrying 3rd order harmonic mixing products (2f(sub 0) plus or minus f(sub m)=4.4-4.9 GHZ) containing targeted neuropotential signals (fm approximately equal to 1-1000 Hz). The microsystem is enclosed in 4 micrometer thick parylene-C for biocompatibility and has a footprint of 4 millimeters x 12 millimeters x 500 micrometers. Preliminary testing of the microsystem implanted in the lossy biological simulating media results in signal-to-noise ratio's (SNR) near 22 (SNR approximately equal to 38 in free space) for millivolt level neuropotentials, demonstrating the potential for fully passive wireless microsystems in implantable medical applications

A color detection glove with haptic feedback for the visually disabled

The following paper describes the design and preliminary results of a compact color detecting and feedback system. The device is intended for use by those with vision-loss or disabilities who may benefit by a means of perceiving color. The device consists of a glove incorporating optical color sensors along with tactile switches affixed to the fingertips, a haptic feedback interface wrapped around the fore arm, and a microprocessor unit to control communication between sensing and feedback. The color data and finger selection is encoded to spatial and temporal parameters on tactors. The study extends on earlier investigations by Tapson et. al. that have successfully demonstrated the capability of accurately identifying colors through haptic feedback. To further extend the field, the present research attempts to characterize color information in a temporally and spatially continuous representation to more realistically map the features of color space, and allow higher resolution of color perception

Chronic multi-modal monitoring of neural activity in rodents and primates

We developed multi-modal systems comprising implantable carbon fiber (CF)-based electrodes to record synchronously chemical (e.g. dopamine) and electrical (e.g. local field potential, LFP) forms of activity in the brain. These systems were equipped with implantable micro-invasive probes and moveable silica-based CF probes capable of recording chronically from fixed locations, or from multiple depths along predetermined trajectories, respectively, spanning 48 spatially distinct sites in the caudate nucleus and the putamen. Electrochemical fast scan cyclic voltammetry (FSCV) was implemented in combination with standard electrophysiology to provide subsecond chemical and electrical recordings. The chronic stability of our micro-invasive probes, as tested previously in rodents and translated for use in nonhuman primate (NHP), was necessary to ensure functional recording from fixed locations in the brain without degradation in probe sensitivity over time. These systems were used to examine the relationship between dopamine and beta-band LFPs, prominent biomarkers of untreated Parkinson’s disease. We recorded dopamine and beta in rhesus monkeys performing oculomotor tasks in which reward valuation and movement control, key functions impaired in Parkinson’s disease, could be quantified. Highly stable measurements of dopamine and LFP neural signals were made over a period of months

Long-term dopamine neurochemical monitoring in primates

Many debilitating neuropsychiatric and neurodegenerative disorders are characterized by dopamine neurotransmitter dysregulation. Monitoring subsecond dopamine release accurately and for extended, clinically relevant timescales is a critical unmet need. Especially valuable has been the development of electrochemical fast-scan cyclic voltammetry implementing microsized carbon fiber probe implants to record fast millisecond changes in dopamine concentrations. Nevertheless, these well-established methods have only been applied in primates with acutely (few hours) implanted sensors. Neurochemical monitoring for long timescales is necessary to improve diagnostic and therapeutic procedures for a wide range of neurological disorders. Strategies for the chronic use of such sensors have recently been established successfully in rodents, but new infrastructures are needed to enable these strategies in primates. Here we report an integrated neurochemical recording platform for monitoring dopamine release from sensors chronically implanted in deep brain structures of nonhuman primates for over 100 days, together with results for behavior-related and stimulation-induced dopamine release. From these chronically implanted probes, we measured dopamine release from multiple sites in the striatum as induced by behavioral performance and reward-related stimuli, by direct stimulation, and by drug administration. We further developed algorithms to automate detection of dopamine. These algorithms could be used to track the effects of drugs on endogenous dopamine neurotransmission, as well as to evaluate the long-term performance of the chronically implanted sensors. Our chronic measurements demonstrate the feasibility of measuring subsecond dopamine release from deep brain circuits of awake, behaving primates in a longitudinally reproducible manner. Keywords: striatum; voltammetry; neurotransmitters; chronic implantsNational Institute of Neurological Diseases and Stroke (U.S.) (Grant R01 NS025529)National Institute of Neurological Diseases and Stroke (U.S.) (Grant F32 NS093897)United States. Army Research Office (Contract W911NF-16-1-0474)National Institute of Biomedical Imaging and Bioengineering (U.S.) (Grant R01 EB016101

Cellular-scale probes enable stable chronic subsecond monitoring of dopamine neurochemicals in a rodent model

Chemical signaling underlies both temporally phasic and extended activity in the brain. Phasic activity can be monitored by implanted sensors, but chronic recording of such chemical signals has been difficult because the capacity to measure them degrades over time. This degradation has been attributed to tissue damage progressively produced by the sensors and failure of the sensors themselves. We report methods that surmount these problems through the development of sensors having diameters as small as individual neuronal cell bodies (<10 mu m). These micro-invasive probes (mu IPs) markedly reduced expression of detectable markers of inflammation and tissue damage in a rodent test model. The chronically implanted mu IPs provided stable operation in monitoring sub-second fluctuations in stimulation-evoked dopamine in anesthetized rats for over a year. These findings demonstrate that monitoring of chemical activity patterns in the brain over at least year-long periods, long a goal of both basic and clinical neuroscience, is achievable

Cellular-scale probes enable stable chronic subsecond monitoring of dopamine neurochemicals in a rodent model

Helen Schwerdt et al. report micro-invasive probes capable of monitoring chemical signaling in the rat brain for over a year. The probes have diameters as small as single neuronal cell bodies and can monitor sub-second fluctuations in chemical signaling without significant induction of inflammation or tissue damage