Title: Sensory prosthetics - clinical and scientific utility of a vestibular implant
Objective: To determine if a vestibular prosthesis could improve function in subjects with severe vestibular damage and could be used it as a scientific tool to investigate central vestibular processing. Background: Damage to the vestibular labyrinth is common and usually permanent. We therefore developed and tested a vestibular implant (VI) that is designed to mimic the information normally provided by the vestibular labyrinth to determine if we can reduce vestibular-mediated deficits and study temporal integration of sensory cues in the brain. Design/Methods: Monkeys had electrodes implanted in the semicircular canals of one ear and then severe bilateral vestibular damage was induced with aminoglycosides. Eye movements, perception, and balance were tested before and after vestibular damage and with the VI activated, which supplied head motion information to the brain via electrical stimulation delivered by the implanted electrodes. Humans also had electrode implantation (done in conjunction with a cochlear implant, CI) and they were tested on a temporal binding psychophysical task Results: Stimulation provided by VI in vestibulopathic monkeys improved their balance, perception of spatial orientation, and eye movement responses. Timing experiments in humans using CI and VI stimuli showed that unlike past experiments that used motion to generate the vestibular signal, CI and VI signals were received by the cerebral cortex with the same latency and were perceived as simultaneous, but this timing perception was highly sensitive to adaption. Conclusions: VI improves oculomotor, postural, and perceptual behavior in vestibulopathic monkeys and could prove to be an effective way to improve these functions in patients with permanent labyrinthine damage. Timing experiments show that when novel stimuli are used, the brain synthesizes them in accordance with their arrival at the cortex, but that experience can rapidly recalibrate this timing relationship, which may be why normal stimuli that are experienced habitually lack this characteristic. more »« less
According to the National Institute of Deafness and other Communication Disorders 2012 report, the number of cochlear implant (CI) users is steadily increasing from 324,000 CI users worldwide. The cochlea, located in the inner ear, is a snail-like structure that exhibits a tonotopic geometry where acoustic waves are filtered spatially according to frequency. Throughout the cochlea, there exist hair cells that transduce sensed acoustic waves into an electrical signal that is carried by the auditory nerve to ultimately reach the auditory cortex of the brain. A cochlear implant bridges the gap if non-functional hair cells are present. Conventional CIs directly inject an electrical current into surrounding tissue via an implanted electrode array and exploit the frequency-to-place mapping of the cochlea. However, the current is dispersed in perilymph, a conductive bodily fluid within the cochlea, causing a spread of excitation. Magnetic fields are more impervious to the effects of the cochlear environment due to the material properties of perilymph and surrounding tissue, demonstrating potential to improve precision. As an alternative to conventional CI electrodes, the development and miniaturization of microcoils intended for micromagnetic stimulation of intracochlear neural elements is described. As a step toward realizing a microcoil array sized for cochlear implantation, human-sized coils were prototyped via aerosol jet printing. The batch reproducible aerosol jet printed microcoils have a diameter of 1800 μm, trace width and trace spacing of 112.5 μm, 12 μm thickness, and inductance values of approximately 15.5 nH. Modelling results indicate that the coils have a combined depolarization–hyperpolarization region that spans 1.5 mm and produce a more restrictive spread of activation when compared with conventional CI.
Boundy-Singer, Zoe M; Ziemba, Corey M; Goris, Robbe_L T
(, Proceedings of the National Academy of Sciences)
Perception is fallible. Humans know this, and so do some nonhuman animals like macaque monkeys. When monkeys report more confidence in a perceptual decision, that decision is more likely to be correct. It is not known how neural circuits in the primate brain assess the quality of perceptual decisions. Here, we test two hypotheses. First, that decision confidence is related to the structure of population activity in the sensory cortex. And second, that this relation differs from the one between sensory activity and decision content. We trained macaque monkeys to judge the orientation of ambiguous stimuli and additionally report their confidence in these judgments. We recorded population activity in the primary visual cortex and used decoders to expose the relationship between this activity and the choice-confidence reports. Our analysis validated both hypotheses and suggests that perceptual decisions arise from a neural computation downstream of visual cortex that estimates the most likely interpretation of a sensory response, while decision confidence instead reflects a computation that evaluates whether this sensory response will produce a reliable decision. Our work establishes a direct link between neural population activity in the sensory cortex and the metacognitive ability to introspect about the quality of perceptual decisions.
Riis, Thomas S; Feldman, Daniel A; Kwon, Sarah S; Vonesh, Lily C; Koppelmans, Vincent; Brown, Jefferson R; Solzbacher, Daniela; Kubanek, Jan; Mickey, Brian J
(, Biological Psychiatry)
BACKGROUND: Severe forms of depression have been linked to excessive subcallosal cingulate cortex (SCC) ac- tivity. Stimulation of the SCC with surgically implanted electrodes can alleviate depression, but current noninvasive techniques cannot directly and selectively modulate deep targets. We developed a new noninvasive neuromodulation approach that can deliver low-intensity focused ultrasonic waves to the SCC. METHODS: Twenty-two individuals with treatment-resistant depression participated in a randomized, double-blind, sham-controlled study. Ultrasonic stimulation was delivered to the bilateral SCC during concurrent functional magnetic resonance imaging to quantify target engagement. Mood state was measured with the Sadness subscale of the Positive and Negative Affect Schedule before and after 40 minutes of real or sham SCC stimulation. Change in depression severity was measured with the 6-item Hamilton Depression Rating Scale at 24 hours and 7 days. RESULTS: Functional magnetic resonance imaging demonstrated a target-speci c decrease in SCC activity during stimulation (p = .028, n = 16). In 7 of 16 participants, SCC neuromodulation was detectable at the individual participant level with a single 10-minute scan (p , .05, small-volume correction). Mood and depression scores improved more with real than with sham stimulation. In the per-protocol sample (n = 19), real stimulation was superior to sham for 6-item Hamilton Depression Rating Scale scores at 24 hours and for Sadness scores (both p , .05, d . 1). Nonsigni cant trends were found in the intent-to-treat sample. CONCLUSIONS: This small pilot study indicates that ultrasonic stimulation modulates SCC activity and can rapidly reduce depressive symptoms. The capability to noninvasively and selectively target deep brain areas creates new possibilities for the future development of circuit-directed therapeutics and for the analysis of deep-brain circuit function in humans.
Letner, Joseph G.; Patel, Paras R.; Hsieh, Jung-Chien; Smith Flores, Israel M.; della Valle, Elena; Walker, Logan A.; Weiland, James D.; Chestek, Cynthia A.; Cai, Dawen
(, Journal of Neural Engineering)
Abstract Objective.Characterizing the relationship between neuron spiking and the signals that electrodes record is vital to defining the neural circuits driving brain function and informing clinical brain-machine interface design. However, high electrode biocompatibility and precisely localizing neurons around the electrodes are critical to defining this relationship.Approach.Here, we demonstrate consistent localization of the recording site tips of subcellular-scale (6.8µm diameter) carbon fiber electrodes and the positions of surrounding neurons. We implanted male rats with carbon fiber electrode arrays for 6 or 12+ weeks targeting layer V motor cortex. After explanting the arrays, we immunostained the implant site and localized putative recording site tips with subcellular-cellular resolution. We then 3D segmented neuron somata within a 50µm radius from implanted tips to measure neuron positions and health and compare to healthy cortex with symmetric stereotaxic coordinates.Main results.Immunostaining of astrocyte, microglia, and neuron markers confirmed that overall tissue health was indicative of high biocompatibility near the tips. While neurons near implanted carbon fibers were stretched, their number and distribution were similar to hypothetical fibers placed in healthy contralateral brain. Such similar neuron distributions suggest that these minimally invasive electrodes demonstrate the potential to sample naturalistic neural populations. This motivated the prediction of spikes produced by nearby neurons using a simple point source model fit using recorded electrophysiology and the mean positions of the nearest neurons observed in histology. Comparing spike amplitudes suggests that the radius at which single units can be distinguished from others is near the fourth closest neuron (30.7 ± 4.6µm, ± S) in layer V motor cortex.Significance.Collectively, these data and simulations provide the first direct evidence that neuron placement in the immediate vicinity of the recording site influences how many spike clusters can be reliably identified by spike sorting.
Lim, J.; Wang, P.T.; Shaw, S.J.; Armacost, M.; Gong, H.; Liu, C.Y.; Heydari, P.; Do, A.H.; Nenadic, Z.
(, Seventh International BCI Meeting, Abstract Book)
Introduction:Current brain-computer interfaces (BCIs) primarily rely on visual feedback. However, visual feedback may not be sufficient for applications such as movement restoration, where somatosensory feedback plays a crucial role. For electrocorticography (ECoG)-based BCIs, somatosensory feedback can be elicited by cortical surface electro-stimulation [1]. However, simultaneous cortical stimulation and recording is challenging due to stimulation artifacts. Depending on the orientation of stimulating electrodes, their distance to the recording site, and the stimulation intensity, these artifacts may overwhelm the neural signals of interest and saturate the recording bioamplifiers, making it impossible to recover the underlying information [2]. To understand how these factors affect artifact propagation, we performed a preliminary characterization of ECoG signals during cortical stimulation.Materials/Methods/ResultsECoG electrodes were implanted in a 39-year old epilepsy patient as shown in Fig. 1. Pairs of adjacent electrodes were stimulated as a part of language cortical mapping. For each stimulating pair, a charge-balanced biphasic square pulse train of current at 50 Hz was delivered for five seconds at 2, 4, 6, 8 and 10 mA. ECoG signals were recorded at 512 Hz. The signals were then high-pass filtered (≥1.5 Hz, zero phase), and the 5-second stimulation epochs were segmented. Within each epoch, artifact-induced peaks were detected for each electrode, except the stimulating pair, where signals were clipped due to amplifier saturation. These peaks were phase-locked across electrodes and were 20 ms apart, thus matching the pulse train frequency. The response was characterized by calculating the median peak within the 5-second epochs. Fig. 1 shows a representative response of the right temporal grid (RTG), with the stimulation channel at RTG electrodes 14 and 15. It also shows a hypothetical amplifier saturation contour of an implantable, bi-directional, ECoG-based BCI prototype [2], assuming the supply voltage of 2.2 V and a gain of 66 dB. Finally, we quantify the worstcase scenario by calculating the largest distance between the saturation contour and the midpoint of each stimulating channel.Discussion:Our results indicate that artifact propagation follows a dipole potential distribution with the extent of the saturation region (the interior of the white contour) proportional to the stimulation amplitude. In general, the artifacts propagated farthest when a 10 mA current was applied with the saturation regions extending from 17 to 32 mm away from the midpoint of the dipole. Consistent with the electric dipole model, this maximum spread happened along the direction of the dipole moment. An exception occurred at stimulation channel RTG11-16, for which an additional saturation contour emerged away from the dipole contour (not shown), extending the saturation region to 41 mm. Also, the worst-case scenario was observed at 6 mA stimulation amplitude. This departure could be a sign of a nonlinear, switch-like behavior, wherein additional conduction pathways could become engaged in response to sufficiently high stimulation.Significance:While ECoG stimulation is routinely performed in the clinical setting, quantitative studies of the resulting signals are lacking. Our preliminary study demonstrates that stimulation artifacts largely obey dipole distributions, suggesting that the dipole model could be used to predict artifact propagation. Further studies are necessary to ascertain whether these results hold across other subjects and combinations of stimulation/recording grids. Once completed, these studies will reveal practical design constraints for future implantable bi-directional ECoG-based BCIs. These include parameters such as the distances between and relative orientations of the stimulating and recording electrodes, the choice of the stimulating electrodes, the optimal placement of the reference electrode, and the maximum stimulation amplitude. These findings would also have important implications for the design of custom, low-power bioamplifiers for implantable bi-directional ECoG-based BCIs.References:[1] Hiremath, S. V., et al. "Human perception of electrical stimulation on the surface of somatosensory cortex." PloS one 12.5 (2017): e0176020.[2] Rouse, A. G., et al. "A chronic generalized bi-directional brain-machine interface." Journal of Neural Engineering 8.3 (2011): 036018
Haburcakova, C., Merfeld, D., Gong, W., Guinand, N., Perez, Fornos A., Thompson, L.A., Guyot, J.P., and Lewis, R.F. Sensory prosthetics - clinical and scientific utility of a vestibular implant. Retrieved from https://par.nsf.gov/biblio/10048831. Neurology 88.16
Haburcakova, C., Merfeld, D., Gong, W., Guinand, N., Perez, Fornos A., Thompson, L.A., Guyot, J.P., & Lewis, R.F. Sensory prosthetics - clinical and scientific utility of a vestibular implant. Neurology, 88 (16). Retrieved from https://par.nsf.gov/biblio/10048831.
Haburcakova, C., Merfeld, D., Gong, W., Guinand, N., Perez, Fornos A., Thompson, L.A., Guyot, J.P., and Lewis, R.F.
"Sensory prosthetics - clinical and scientific utility of a vestibular implant". Neurology 88 (16). Country unknown/Code not available. https://par.nsf.gov/biblio/10048831.
@article{osti_10048831,
place = {Country unknown/Code not available},
title = {Sensory prosthetics - clinical and scientific utility of a vestibular implant},
url = {https://par.nsf.gov/biblio/10048831},
abstractNote = {Objective: To determine if a vestibular prosthesis could improve function in subjects with severe vestibular damage and could be used it as a scientific tool to investigate central vestibular processing. Background: Damage to the vestibular labyrinth is common and usually permanent. We therefore developed and tested a vestibular implant (VI) that is designed to mimic the information normally provided by the vestibular labyrinth to determine if we can reduce vestibular-mediated deficits and study temporal integration of sensory cues in the brain. Design/Methods: Monkeys had electrodes implanted in the semicircular canals of one ear and then severe bilateral vestibular damage was induced with aminoglycosides. Eye movements, perception, and balance were tested before and after vestibular damage and with the VI activated, which supplied head motion information to the brain via electrical stimulation delivered by the implanted electrodes. Humans also had electrode implantation (done in conjunction with a cochlear implant, CI) and they were tested on a temporal binding psychophysical task Results: Stimulation provided by VI in vestibulopathic monkeys improved their balance, perception of spatial orientation, and eye movement responses. Timing experiments in humans using CI and VI stimuli showed that unlike past experiments that used motion to generate the vestibular signal, CI and VI signals were received by the cerebral cortex with the same latency and were perceived as simultaneous, but this timing perception was highly sensitive to adaption. Conclusions: VI improves oculomotor, postural, and perceptual behavior in vestibulopathic monkeys and could prove to be an effective way to improve these functions in patients with permanent labyrinthine damage. Timing experiments show that when novel stimuli are used, the brain synthesizes them in accordance with their arrival at the cortex, but that experience can rapidly recalibrate this timing relationship, which may be why normal stimuli that are experienced habitually lack this characteristic.},
journal = {Neurology},
volume = {88},
number = {16},
author = {Haburcakova, C. and Merfeld, D. and Gong, W. and Guinand, N. and Perez, Fornos A. and Thompson, L.A. and Guyot, J.P. and Lewis, R.F.},
}
Warning: Leaving National Science Foundation Website
You are now leaving the National Science Foundation website to go to a non-government website.
Website:
NSF takes no responsibility for and exercises no control over the views expressed or the accuracy of
the information contained on this site. Also be aware that NSF's privacy policy does not apply to this site.
An official website of the United States government
