Patrick J. Rousche

Chronic recording capability of the Utah Intracortical Electrode Array in cat sensory cortex

The Utah Intracortical Electrode Array (UIEA) is an array of 100 penetrating silicon microelectrodes designed to focally electrically stimulate or record neurons residing in a single layer up to 1.5 mm beneath the surface of the cerebral cortex. Apart from its use as a unique tool to study parallel processing in the central nervous system, this array could form the platform for a cortical neuroprosthetic system. Although the UIEA has been used extensively in acute neural recording and stimulation experiments, its long-term performance in a chronic application has yet to be demonstrated. As an initial investigation into the feasibility of long-term cortical recording with an array of microelectrodes, we have hard-wired a subset of 11 electrodes of the UIEA to a percutaneous connector. This chronic UIEA assembly was then implanted into the cerebral cortices of ten cats for durations ranging from 2 to 13 months; over which time, both random and stimulus-evoked single and multiple unit action potentials were periodically recorded. On average, after a 6-month implant period, 60% of implanted arrays could still record some type of activity. Post-sacrifice dissections revealed a fibrous encapsulation of the UIEA. Although most implanted cortex was histologically normal, evidence of a chronic astroglial response was seen in a few cases. The results of the reported experiments indicate that the UIEA can be successfully used for limited times in a chronic recording application.

A neural interface for a cortical vision prosthesis

The development of a cortically based vision prosthesis has been hampered by a lack of basic experiments on phosphene psychophysics. This basic research has been hampered by the lack of a means to safely stimulate large numbers of cortical neurons. Recently, a number of laboratories have developed arrays of silicon microelectrodes that could enable such basic studies on phosphene psychophysics. This paper describes one such array, the Utah electrode array, and summarizes neurosurgical, physiological and histological experiments that suggest that such an array could be implanted safely in visual cortex. We also summarize a series of chronic behavioral experiments that show that modest levels of electrical currents passed into cortex via this array can evoke sensory percepts. Pending the successful outcome of biocompatibility studies using such arrays, high count arrays of penetrating microelectrodes similar to this design could provide a useful tool for studies of the psychophysics of phosphene perception in human volunteers. Such studies could provide a proof-of-concept for cortically based artificial vision.

A method for pneumatically inserting an array of penetrating electrodes into cortical tissue

The goal of this research was to find a practical means by which an array of 100 needle-shaped electrodes could be implanted into the cerebral cortex with minimal brain tissue trauma. It was found that insertion of these structures into cortical tissues could only be performed using high insertion speeds. A pneumatically actuated impact insertion system has been developed that is capable of inserting an electrode array into feline brain tissue at speeds from about 1 to 11 m/s. We found that a minimum array insertion speed of 8.3 m/s was necessary for a complete, safe insertion of all 100 electrodes in the array to a depth of 1.5 mm into feline cortex. The performance of the impact insertion system is discussed in terms of a simplified representation of cortical tissue.

Chronic intracortical microstimulation (ICMS) of cat sensory cortex using the Utah intracortical electrode array

In an effort to assess the safety and efficacy of focal intracortical microstimulation (ICMS) of cerebral cortex with an array of penetrating electrodes as might be applied to a neuroprosthetic device to aid the deaf or blind, we have chronically implanted three trained cats in primary auditory cortex with the 100-electrode Utah Intracortical Electrode Array (UIEA). Eleven of the 100 electrodes were hard-wired to a percutaneous connector for chronic access. Prior to implant, cats were trained to lever-press in response to pure tone auditory stimulation. After implant, this behavior was transferred to lever-presses in response to current injections via single electrodes of the implanted arrays. Psychometric function curves relating injected charge level to the probability of response were obtained for stimulation of 22 separate electrodes in the three implanted cats. The average threshold charge/phase required for electrical stimulus detection in each cat was, 8.5, 8.6, and 11.6 nC/phase respectively, with a maximum charge/phase of 26 nC/phase and a minimum of 1.5 nC/phase thresholds were tracked for varying time intervals, and seven electrodes from two cats were tracked for up to 100 days. Electrodes were stimulated for no more than a few minutes each day. Neural recordings taken from the same electrodes before and after multiple electrical stimulation sessions were very similar in signal/noise ratio and in the number of recordable units, suggesting that the range of electrical stimulation levels used did not damage neurons in the vicinity of the electrodes. Although a few early implants failed, we conclude that ICMS of cerebral cortex to evoke a behavioral response can be achieved with the penetrating UIEA. Further experiments in support of a sensory cortical prosthesis based on ICMS are warranted.

Optimizing recording capabilities of the Utah Intracortical Electrode Array

The Utah Intracortical Electrode Array is a unique silicon-based monolithic structure designed for use as a multichannel interface to the central nervous system. In this paper, we describe a series of acute experiments designed to determine the neural recording capabilities of this electrode array and the dependence of the signal-to-noise ratio (SNR) of the recordings on the electrode surface area (length of metallized tip). We found that both separable unit and multiunit cluster responses could be recorded. Additionally, high SNR recordings could be achieved for some electrodes (with electrode tip lengths of 30-220 microns), while recordings with signals substantially greater than the noise could be made from most of the electrodes provided that the proper electrode surface area was used. The demonstrated recording capabilities of the Utah Intracortical Electrode Array and its unique three-dimensional structure should form the basis for innovative physiological investigations into the functional organization of the cortex as well as for long term neuroprosthesis development.

Examination of the spatial and temporal distribution of sensory cortical activity using a 100-electrode array

This paper introduces improved techniques for multichannel extracellular electrophysiological recordings of neurons distributed across a single layer of topographically mapped cortex. We describe the electrode array, the surgical implant techniques, and the procedures for data collection and analysis. Neural events are acquired through an array of 25 or 100 microelectrodes with a 400-microm inter-electrode spacing. One advantage of the new methodology is that implantation is achieved through transdural penetration, thereby reducing the disruption of the cortical tissue. The overall cortical territory sampled by the 25-electrode array is 1.6 x 1.6 mm (2.56 mm2) and by the 100-electrode array 3.6 x 3.6 mm (12.96 mm2). Using a recording system with 100 channels available, neural activity is simultaneously acquired on all electrodes, amplified, digitized, and stored on computer. In our data, average peak-to-peak signal/noise ratio was 11.5 and off-line waveform analysis typically allowed the separation of at least one well-discriminated single-unit per channel. The reported technique permits analysis of cortical function with high temporal and spatial resolution. We use the technique to create an image of neural activity distributed across the whisker representation of rat somatosensory (barrel) cortex.

Rapid prototyping for neuroscience and neural engineering

Rapid prototyping (RP) is a useful method for designing and fabricating a wide variety of devices used for neuroscience research. The present study confirms the utility of using fused deposition modeling, a specific form of RP, to produce three devices commonly used for basic science experimentation. The accuracy and precision of the RP method varies according to the type and quality of the printer as well as the thermoplastic substrate. The printer was capable of creating device channels with a minimum diameter of 0.4 or 0.6mm depending on the orientation of fabrication. RP enabled the computer-aided design and fabrication of three custom devices including a cortical recording/stroke induction platform capable of monitoring electrophysiological function during ischemic challenge. In addition to the recording platform, two perfusion chambers and a cranial window device were replicated with sub-millimeter precision. The ability to repeatedly modify the design of each device with minimal effort and low turn-around time is helpful for oft-unpredictable experimental conditions. Results obtained from validation studies using both the cortical recording platform and perfusion chamber did not vary from previous results using traditional hand-fabricated or commercially available devices. Combined with computer-aided design, rapid prototyping is an excellent alternative for developing and fabricating custom devices for neuroscience research.

A System For Impact Insertion Of A 100 Electrode Array Into Cortical Tissue

ABSTRACI Complex silicon microelectrode arrays capable of having up to 100 electrodes per device are now a reality. By directly interfacing to the central nervous system, these devices could allow for restoration of sensory or motor functions at a level previously unobtainable. However, the structural complexity of these devices has mandated the development of a new insertion technology not necessary for simpler electrode designs. To meet this demand, a pneumatic momentum-transfer system has been developed. This portable system uses a sliding mass mechanism to achieve an impact insertion of a silicon structure consisting of 100 sharpened needles into cortical tissue. The system has successfully implanted these silicon electrode arrays in over 30 feline preparations. Preliminary histological evidence shows an expected inflammatory response with a small amount of bleeding, yet no significant long-term neural tissue damage due to the insertion procedure. These results suggest that impact insertion is a viable way to introduce complicated electrode structures into the central nervous system.

Chronic recordings of visually evoked responses using the utah intracortical electrode array

The Utah Intracortical Electrode Array is a three dimensional monolithic silicon-based 100-electrode device which has demonstrated acute cortical recording capabilities. In the following, we describe a series of visual conex chronic electrode array implants which demonstrate the recording abilities of these electrodes over longer periods of time. To date, we have successfully recorded visually evoked neural responses five months post-implant. Additionally, we have studied the effects of anesthetics on neural activity. The demonstrated long term recording capabilities of the Utah Array hold promise for future work in both the development of a recording neuroprosthetic device and chronic neurophysiological studies of the cortex.

A method for acute cerebral cortex recordings using the Utah Intracortical Electrode Array

The Utah Intracortical Electrode Array is a unique three-dimensional silicon-based device originally designed to be used as a chronic multichannel interface to the central nervous system. We describe herein a method that can be used in acute experiments that allows for direct and easy access to each of the 100 electrodes in the array. This technique has been employed successfully for acute recordings of stimulus correlated clusters of neural activity in the visual and auditory cortices of cats. Our data indicate that this recording method, and the unique 3D architecture of the electrode array makes it well suited for recording neural activity during acute neurophysiological experimentation.