Biology subjects

Yun, R.

Publications and source records attributed to Yun, R..

11 recordsLinked to original sources

bioRxiv2025

Silent Speech Recognition with Wearable Magnetometers

Next-generation human-computer interaction (HCI) is moving towards more seamless, intuitive, and personal modes of communication, redefining how we interact with technology and one another. Within this landscape, silent speech recognition (SSR) offers a powerful new interaction paradigm, enabling hands-free, private interaction while supporting individuals with speech impairments and enabling communication in noisy or sensitive environments. Recent advances in miniaturized sensors and artificial intelligence (AI) have accelerated the development of more sophisticated wearable SSR systems, driven by growing demand for effortless and accessible communication. Although electrophysiological (ExG) modalities, particularly electromyography (EMG), have dominated early efforts in developing wearable SSR, critical challenges remain. Limited generalizability across users, sensor-skin interface issues, and difficulties with the comfort of use are all current roadblocks to reliable, high-fidelity signals in a wearable form factor. We propose that magnetometers offer a promising alternative to ExG and have the potential to unlock more robust, generalizable, and user-friendly SSR systems. We demonstrate that magnetometers embedded in a headphone form factor achieve a per-user SSR accuracy of 86%, significantly outperforming previously reported state-of-the-art wearable headphones combining ExG and inertial measurement units (IMUs). In addition, we show that wearable magnetometry enables generalization across individuals for SSR. Extending beyond headphones, we also introduce a necklace form factor with magnetometers that is capable of decoding both silent and overt speech in ambient conditions, further showcasing the versatility of magnetometers across different wearable designs in real-world conditions.

neuroscience↗

bioRxiv2024

Generalizable gesture recognition usingmagnetomyography

The progression of human-computer interfaces into immersive and touchless realities requires new ways of interacting with machines that are correspondingly intuitive and seamless. Among these are gesture-based systems that use natural hand movements to interact with and control digital devices. Today, these systems are most commonly implemented through the use of cameras or inertial sensors, which have drawbacks in environments that are poorly lit, in conditions where the hands are obscured, or for applications that require fine motor control. More recent studies have advocated for the use of surface electromyography (sEMG) to capture gesture information by sensing electrical activity generated by muscle contraction. While promising demonstrations have been shown, studies have also outlined limitations in sEMG when it comes to generalization across a population, largely due to physiological differences between individuals. Magnetomyography (MMG) is an alternative modality for measuring the same motor signals at the muscle, but is impervious to distortions caused by tissue, hair, and moisture; this indicates potential for lower variability caused by physiological differences and changes in skin conductivity, making MMG a promising generalizable solution for gesture control. To test this theory, we developed wristbands with magnetic sensors and implemented a signal processing pipeline for gesture classification. Using this system, we measured MMG across 30 participants performing a gesture task consisting of nine discrete gestures. We demonstrate average single-participant classification accuracy of 95.4%, rivaling state-of-the-art accuracy with sEMG. In addition, we achieved higher cross-session and cross-participant accuracy compared to sEMG studies. Given that these results were obtained with a non-ideal recording system, we anticipate significantly better results with better sensors. Together, these findings suggest that MMG can provide higher performance for control systems based on gesture recognition by overcoming limitations of existing techniques.

neuroscience↗

bioRxiv2024

Cholinergic feedback for context-specific modulation of sensory representations

The brains ability to prioritize behaviorally relevant sensory information is crucial for adaptive behavior, yet the underlying mechanisms remain unclear. Here, we investigated the role of basal forebrain cholinergic neurons in modulating olfactory bulb (OB) circuits in mice. Calcium imaging of cholinergic feedback axons in OB revealed that their activity is strongly correlated with orofacial movements, with little responses to passively experienced odor stimuli. However, when mice engaged in an odor discrimination task, OB cholinergic axons rapidly shifted their response patterns from movement-correlated activity to odor-aligned responses. Notably, these odor responses during olfactory task engagement were absent in cholinergic axons projecting to the dorsal cortex. The level of odor responses correlated with task performance. Inactivation of OB-projecting cholinergic neurons during task engagement impaired performance and reduced odor responses in OB granule cells. Thus, the cholinergic system dynamically modulates sensory processing in a modality-specific and context-dependent manner, providing a mechanism for a flexible and adaptive sensory prioritization.

neuroscience↗

bioRxiv2024

Magnetomyography: A novel modality for non-invasive muscle sensing

The measurement of magnetic fields generated by skeletal muscle activity, called magnetomyography (MMG), has seen renewed interest from the academic community in recent years. Although studies have demonstrated complex models of MMG and experiments classifying between different movements using MMG, there has yet to be time frequency analysis of MMG as well as concurrent recordings of MMG and its electrical counterpart, surface electromyography (sEMG). Here, we aim to better understand MMG in the context of sEMG by simultaneously recording both modalities during various muscle contraction tasks. We found that, similar to sEMG, MMG shows highly linearly correlated power to the degree of muscle contraction, has a unimodal distribution in spectral power, and can detect changes in muscle fatigue via changes in the spectral distribution. One main difference we found was that MMG typically has more high frequency content compared to sEMG, even when accounting for the filtering induced by the size of the sEMG electrodes. We additionally demonstrate empirically the decrease in MMG power due to distance from the arm and show MMG decreases slower than the inverse square law and can be measured up to 50 mm from the surface of the skin. Finally, we were able to capture MMG with non-OPM sensors showing that sensor technology has made great strides towards enabling MMG applications.

neuroscience↗

bioRxiv2024

Aedes albopictus is not an arbovirus aficionado - Impacts of sylvatic flavivirus infection in vectors and hosts on mosquito engorgement on non-human primates

The contact structure between vertebrate hosts and arthropod vectors plays a key role in the spread of arthropod-borne viruses (arboviruses); thus, it is important to determine whether arbovirus infection of either host or vector alters vector feeding behavior. Here we leveraged a study of the replication dynamics of two arboviruses isolated from their ancestral cycles in paleotropical forests, sylvatic dengue-2 (DENV-2) and Zika (ZIKV), in one non-human primate (NHP) species from the paleotropics (cynomolgus macaques, Macaca fascicularis) and one from the neotropics (squirrel monkeys, Saimiri boliviensis) to test the effect of both vector and host infection with each virus on completion of blood feeding (engorgement) of the mosquito Aedes albopictus. Although mosquitoes were starved and given no choice of hosts, engorgement rates varied dramatically, from 0% to 100%. While neither vector nor host infection systematically affected engorgement, NHP species and body temperature at the time of feeding did. We also interrogated the effect of repeated mosquito bites on cytokine expression and found that epidermal growth factor (EGF) and macrophage migration inhibitory factor (MIF) concentrations were dynamically associated with exposure to mosquito bites. This study highlights the importance of incorporating individual-level heterogeneity of vector biting in arbovirus transmission models.

systems biology↗

bioRxiv2023

Dehydration induced AePer50 regulates midgut infection in Aedes aegypti

In the face of climate change, mosquitoes will experience evolving climates including longer periods of drought. An important physiological response to dry environments is the protection against water loss or dehydration, here defined as desiccation tolerance. Various environmental factors including temperature are known to alter interactions between the mosquito, Aedes aegypti, and the arboviruses it transmits, but little is known about how low humidity impacts arboviral infection. Here, we report that a gene upregulated in response to desiccation is important for controlling midgut infection. We have identified two genetically diverse lines of Ae. aegypti with marked differences in desiccation tolerance. To understand if the genetic basis underlying desiccation tolerance is the same between the contrasting lines, we compared gene expression profiles between desiccant treated and non-desiccant treated individuals in both the desiccation tolerant and susceptible lines by RNAseq. Gene expression analysis demonstrates that different genes are differentially expressed in response to desiccation stress between desiccation tolerant and susceptible lines. The most highly expressed transcript under desiccation stress in the desiccation susceptible line encodes a peritrophin protein, AePer50. Peritrophins play a crucial role in peritrophic matrix formation after a bloodmeal. Gene silencing of AePer50 by RNAi demonstrates that expression of AePer50 is required for survival of the desiccation susceptible line under desiccation stress, but not for the desiccation tolerant line. Moreover, the knockdown of AePer50 results in higher infection rates and viral replication rates of ZIKV and higher infection rates of CHIKV. Finally, following a bloodmeal, the desiccation susceptible line develops a thicker peritrophic matrix than the desiccation tolerant line. Together these results provide a functional link between the protection against desiccation and midgut infection which has important implications in predicting how climate change will impact mosquito-borne viruses.

microbiology↗

bioRxiv2023

Immunologically mediated trade-offs shaping transmission of sylvatic dengue and Zika viruses in native and novel non-human primate hosts

Mosquito-borne dengue (DENV) and Zika (ZIKV) viruses originated in Old World sylvatic cycles involving monkey hosts, spilled over into human transmission, and were translocated to the Americas, creating potential for spillback into neotropical sylvatic cycles. Studies of the trade-offs that shape within-host dynamics and transmission of these viruses are lacking, hampering efforts to predict spillover and spillback. We exposed native (cynomolgus macaque) or novel (squirrel monkey) hosts to mosquitoes infected with either sylvatic DENV or ZIKV and monitored viremia, natural killer cells, transmission to mosquitoes, cytokines, and neutralizing antibody titers. Unexpectedly, DENV transmission from both host species occurred only when serum viremia was undetectable or near the limit of detection. ZIKV replicated in squirrel monkeys to much higher titers than DENV and was transmitted more efficiently but stimulated lower neutralizing antibody titers. Increasing ZIKV viremia led to greater instantaneous transmission and shorter duration of infection, consistent with a replication-clearance trade-off.

microbiology↗

bioRxiv2022

Paired stimulation for spike-timing dependent plasticity quantified with single neuron responses in primate motor cortex

Spike-timing dependent plasticity (STDP) is an extensively studied topic. Previous studies have demonstrated stimulus induced targeted STDP both in vitro and in vivo, but a more consistent and robust method is required. We hypothesized there were two reasons contributing to the inconsistent results previously reported: 1. the measure of connectivity is poorly understood, and 2. the timing of stimulation is static or has low temporal specificity. To test our hypotheses, we applied paired stimulation to the primary motor cortex of awake primates. Single unit responses to stimulation were used as measures of connectivity, and we applied inter-stimulus intervals (ISIs) from {+/-}0.1 to {+/-}50 ms with sub-millisecond intervals. The excitatory single unit response resulted in very consistent changes after conditioning that was dependent on the ISI. Negative ISIs resulted in depression similar to classic STDP, but positive ISI also often resulted in depression. Normalizing the ISIs to the timing of the excitatory response revealed that potentiation only occurred if the second stimulus arrived before the response. Stimuli occurring around the time of the response often resulted in depression as strong as negative ISIs. We additionally tracked the changes in cortico-cortical evoked potentials (CCEPs), a commonly used measure of connectivity in plasticity experiments. CCEP changes showed a similar but more variable dependence to ISI. These results show that the classic STDP curve may be more difficult to induce due to interactions between excitatory and inhibitory circuitry, and that CCEPs may not be the ideal measure of changes in strength of connectivity.

neuroscience↗

bioRxiv2022

Local field potentials and single unit dynamics in motor cortex of unconstrained macaques during different behavioral states

Different sleep states have been shown to be vital for a variety of brain function, including learning, memory, and skill consolidation. However, our understanding of neural dynamics during sleep and the role of prominent LFP frequency bands remain incomplete. To elucidate such dynamics and changes between different behavioral states we collected multichannel LFP and spike data in primary motor cortex of unconstrained macaques for up to 24 hours using the Neurochip3. Each 8 second bin of time was classified into awake and moving (Move), awake and at rest (Rest), REM sleep (REM), or non-REM sleep (NREM) by using dimensionality reduction and clustering on the average spectral density and the acceleration of the head. LFP power showed high delta during NREM, high theta during REM, and high beta when the animal was awake. Cross-frequency phase-amplitude coupling typically showed higher coupling for deeper sleep between all pairs of frequency bands. Two notable exceptions were high delta-high gamma and theta-high gamma coupling during Move, and high theta-beta coupling during REM. Sorted single units showed decreased firing rate with deeper sleep, though with higher "bursty" patterns during NREM compared to other states. Spike-LFP synchrony showed high delta synchrony during Move, and higher coupling with all other frequency bands with deeper sleep. These results altogether are consistent with previous findings showing reactivation of cortical circuitry during sleep, which may be moderated by delta band LFP.

neuroscience↗

bioRxiv2022

Responses of cortical neurons to intracortical microstimulation in awake primates

Intracortical microstimulation (ICMS) is commonly used in many experimental and clinical paradigms; however, its effects on the activation of neurons are still not completely understood. To document the responses of cortical neurons in non-human primates to stimulation, we recorded single unit activity while delivering single-pulse stimulation via Utah arrays implanted in primary motor cortex of three macaque monkeys. Stimuli between 5-50 A delivered to single channels reliably evoked spikes in neurons recorded throughout the array with delays of up to 12 milliseconds. ICMS pulses also induced a period of inhibition lasting up to 150 ms that typically followed the initial excitatory response. Higher current amplitudes led to a greater probability of evoking a spike and extended the duration of inhibition. The likelihood of evoking a spike in a neuron was dependent on the spontaneous firing rate as well as the delay between its most recent spike time and stimulus onset. Tonic repetitive stimulation between 2 and 20 Hz often modulated both the probability of evoking spikes and the duration of inhibition, although high frequency stimulation in particular was more likely to change both responses. On a trial-by-trial basis, whether a stimulus evoked a spike did not affect the subsequent inhibitory response; however, their changes over time were frequently positively or negatively correlated. Our results document the complex dynamics of cortical neural responses to electrical stimulation that need to be considered when utilizing ICMS for scientific and clinical applications. Significance statementIntracortical microstimulation (ICMS) is commonly used to probe the cortex, and previous studies have characterized the responses of single neurons to ICMS. However, these studies typically explored the averaged effects of ICMS throughout each experimental session, rather than by a trial-by-trial basis for each stimulation pulse. By shifting the approach, we explored the dependence of neural responses to ICMS on the spontaneous neural activity as well as the dynamics of responses over time due to repetitive stimulation. Our results highlight how the responses of neurons to ICMS are likely the result of interactions between local excitatory and inhibitory cortical circuits. These results will help inform the design of ICMS for both basic research and clinically relevant stimulation protocols.

neuroscience↗

bioRxiv2020

Emergence of Zika virus: Role of founder effects, drift and mutational reversions in spread to the Americas

Summary ParagraphMosquito-borne viruses have recently spread globally, with major impacts on human health. Zika virus (ZIKV) emerged from obscurity in 2013 to spread from Asia to the South Pacific and the Americas, where millions of people were infected. For the first time, severe clinical manifestations, including Guillain Barre syndrome and defects to the fetuses of pregnant women, were detected. Phylogenetic studies have shown that ZIKV evolved in Africa and later spread to Asia, and that the Asian lineage is responsible for the recent epidemics. However, the reasons for the sudden emergence of ZIKV remain incompletely understood. Accumulating evidence on other arboviruses like chikungunya and West Nile suggest the likelihood that viral mutations could be determinants of change in ZIKV transmission efficiency responsible for efficient spread. Using evolutionary analyses, we determined that four mutations, which occurred just before ZIKV introduction to the Americas, represent direct reversions of previous mutations that accompanied spread many decades ago from ZIKVs native Africa to Asia and early circulation there. Experimental infections of mosquitoes, human cells, and mice using ZIKV strains with and without these mutations demonstrated that the original mutations reduced fitness for urban transmission, while the reversions restored fitness, increasing epidemic risk. Overall, our findings include the three newly identified, transmission-adaptive ZIKV mutations, and demonstration that these and one identified previously restored fitness for epidemic transmission soon before introduction into the America. The initial mutations may have followed founder effects and/or drift when the virus was introduced into Asia, or could be related to changes on host or vector utilization within Asia.

microbiology↗