Biology subjects

Choi, I.

Publications and source records attributed to Choi, I..

At least 37 records · Page 2Linked to original sources

bioRxiv2022

Immediate neural network impact after the loss of a semantic hub

The human brain extracts meaning from the world using an extensive neural system for semantic knowledge. Whether such broadly distributed systems1-3 crucially depend on or can compensate for the loss of one of their highly interconnected hubs4-6 is controversial4. The strongest level of causal evidence for the role of a brain hub is to evaluate its acute network-level impact following disconnection and any rapid functional compensation that ensues. We report rare neurophysiological data from two patients who underwent awake intracranial recordings during a speech prediction task immediately before and after neurosurgical treatment that required disconnection of the left anterior temporal lobe (ATL), a crucial hub for semantic knowledge4-6. Informed by a predictive coding framework, we tested three sets of hypotheses including diaschisis causing disruption in interconnected sites7 and incomplete or complete compensation by other language-critical and speech processing sites8-10. Immediately after ATL disconnection, we observed highly specific neurophysiological alterations in the recorded fronto-temporal network, including abnormally magnified high gamma responses to the speech sounds in auditory cortex. We also observed evidence for rapid compensation, seen as focal increases in effective connectivity involving language-critical sites in the inferior frontal gyrus and speech processing sites in auditory cortex. However, compensation was incomplete, in part because after ATL disconnection speech prediction signals were depleted in auditory cortex. This study provides direct causal evidence for a semantic hub in the human brain and shows striking neural impact and a rapid attempt at compensation in a neural network after the loss of one of its hubs.

neuroscience↗

bioRxiv2022

Single-cell Transcriptomic Atlas of the Human Substantia Nigra in Parkinson's Disease

Parkinsons disease (PD) is a common and complex neurodegenerative disorder. Loss of neuromelanin-containing dopaminergic (DA) neurons in the substantia nigra (SN) is a hallmark of PD neuropathology; the etiology of PD remains unclear. Single-cell (-nucleus) RNA sequencing (sc or snRNAseq) has significantly advanced our understanding of neurodegenerative diseases including Alzheimers, but limited progress has been made in PD. Here we generated by far the largest snRNAseq data of high-quality 315,867 nuclei from the human SN including 9 healthy controls and 23 idiopathic PD cases across different Braak stages. Clustering analysis identified major brain cell types including DA neurons, excitatory neurons, inhibitory neurons, glial cells, endothelial, pericytes, fibroblast and T-cells in the human SN. By combining immunostaining and validating against the datasets from independent cohorts, we identified three molecularly distinct subtypes of DA-related neurons, including a RIT2-enriched population, in human aged SN. All DA neuron subtypes degenerated in PD, whereas the composition of non-neuronal cell clusters including major glial types showed little change. Our study delineated cell-type-specific PD-linked gene expression in the SN and their alterations in PD. Examination of cell-type-based transcriptomic changes suggests the complexity and diversity of molecular mechanisms of PD. Analysis of the remaining DA neurons of the three subtypes from PD demonstrated alterations of common gene sets associated with neuroprotection. Our findings highlight the heterogeneity of DA neurons in the human SN and suggest molecular basis for vulnerability and resilience of human DA neurons in PD. Our cohort thus provides a valuable resource for dissecting detailed mechanisms of DA neuron degeneration and identifying new neuroprotective strategies for PD.

neuroscience↗

bioRxiv2022

Location bias contributes to functionally selective responses of biased CXCR3 agonists

Some G protein-coupled receptor (GPCR) ligands act as "biased agonists" which preferentially activate specific signaling transducers over others. Although GPCRs are primarily found at the plasma membrane, GPCRs can traffic to and signal from many subcellular compartments. Here, we determine that differential subcellular signaling contributes to the biased signaling generated by three endogenous ligands of the chemokine GPCR CXCR3. The signaling profile of CXCR3 changed as it trafficked from the plasma membrane to endosomes in a ligand-specific manner. Endosomal signaling was critical for biased activation of G proteins, {beta}-arrestins, and ERK1/2. In CD8+ T cells, the chemokines promoted unique transcriptional responses predicted to regulate inflammatory pathways. In a mouse model of contact hypersensitivity, {beta}-arrestin-biased CXCR3-mediated inflammation was dependent on receptor internalization. Our work demonstrates that differential subcellular signaling is critical to the overall biased response observed at CXCR3, which has important implications for drugs targeting chemokine receptors and other GPCRs.

biochemistry↗

bioRxiv2021

Neural correlates of individual differences in speech-in-noise performance in a large cohort of cochlear implant users

ObjectivesUnderstanding speech in noise (SiN) is a complex task that recruits multiple cortical subsystems. Individuals vary in their ability to understand SiN. This cannot be explained by simple peripheral hearing profiles, but recent work by our group (Kim et al., 2021, Neuroimage) highlighted central neural factors underlying the variance in SiN ability in normal hearing (NH) subjects. The current study examined neural predictors of speech-in-noise ability in a large cohort of cochlear-implant (CI) users, with the long-term goal of developing a simple electrophysiological correlate that could be implemented in clinics. DesignWe recorded electroencephalography (EEG) in 114 post-lingually deafened CI users while they completed the California Consonant Test (CCT): a word-in-noise task. In many subjects, data were also collected on two other commonly used clinical measures of speech perception: a word-in-quiet task (Consonant-Nucleus-Consonant [CNC]) word and a sentence-in-noise task (AzBio sentences). Neural activity was assessed at a single vertex electrode (Cz), to maximize generalizability to clinical situations. The N1-P2 complex of event-related potentials (ERPs) at this location were included in multiple linear regression analyses, along with several other demographic and hearing factors as predictors of speech in noise performance. ResultsIn general, there was a good agreement between the scores on the three speech perception tasks. ERP amplitudes did not predict AzBio performance which was predicted by the duration of device use, low-frequency hearing thresholds, and age. However, ERP amplitudes were strong predictors for performance for both word recognition tasks: the CCT (which was conducted simultaneously with EEG recording), and the CNC (conducted offline). These correlations held even after accounting for known predictors of performance including residual low-frequency hearing thresholds. In CI-users, better performance was predicted by an increased cortical response to the target word, in contrast to previous reports in normal-hearing subjects in whom speech perception ability was accounted for by the ability to suppress noise. ConclusionsThese data indicate a neurophysiological correlate of speech-in-noise performance that can be relatively easily captured within the clinic, thereby revealing a richer profile of an individuals hearing performance than shown by psychoacoustic measures alone. These results also highlight important differences between sentence and word recognition measures of performance and suggest that individual differences in these measures may be underwritten by different mechanisms. Finally, the contrast with prior reports of NH listeners in the same task suggests CI-users performance may be explained by a different weighting of neural processes than NH listeners.

neuroscience↗

bioRxiv2021

Beta-arrestin-mediated Angiotensin II type 1 Receptor Activation Promotes Pulmonary Vascular Remodeling in Pulmonary Hypertension

ObjectivesThe goal of this study was to test whether a {beta}-arrestin-biased agonist of the angiotensin II (AngII) type 1 receptor (AT1R), which acts as a vasodilator while not blocking cellular proliferation, would have positive effects compared to a balanced agonist, angiotensin II (AngII), or an antagonist, losartan, in pulmonary arterial hypertension (PAH). BackgroundPAH is a disease of abnormal pulmonary vascular remodeling whose treatment has focused on targeting vasoactive substances, such as inhibiting endothelin signaling and promoting prostacyclin signaling. PAH medical therapies are thought to primarily act as vasodilators, although they may also have effects on pulmonary vascular remodeling. There are a number of reports that blocking AT1R signaling can be beneficial in preclinical models of PAH. The AT1R is a G protein-coupled receptor (GPCR) that promotes vasoconstriction through heterotrimeric G proteins but also signals via {beta}-arrestins, which promote cardioprotective effects and vasodilation. MethodsWe compared the effects of a {beta}-arrestin-biased AT1R agonist, TRV120023 (TRV023), to a balanced agonist (AngII) and an antagonist (losartan) in preclinical PAH models. ResultsIn acute infusion studies, AngII increased right ventricular (RV) pressures while TRV023 did not. However, with chronic infusion in monocrotaline (MCT) PAH rats, TRV023 failed to improve hemodynamics or survival compared to AngII, while losartan significantly improved survival. Both TRV023 and AngII enhanced proliferation and migration of pulmonary artery smooth muscle cells (PASMCs) from PAH patients, which was associated with the promotion of proliferative MAP kinase signaling. Conclusions{beta}-arrestin-mediated AT1R signaling promotes vascular remodeling and worsens PAH, and suggests that the primary benefit of current PAH therapies is through pulmonary vascular reverse remodeling and not vasodilation.

molecular biology↗

bioRxiv2020

Gated feedforward inhibition in the frontal cortex releases goal-directed action

Cortical circuits process sensory information and generate motor signals in animals performing perceptual tasks. However, it is still unclear how sensory inputs generate motor signals in the cortex to initiate goal-directed action. Here, we identified a visual-to-motor inhibitory circuit in the anterior cingulate cortex (ACC) that induced action initiation in mice performing visual Go/No-go tasks. Interestingly, higher activity in sensory neurons and faster suppression in motor neurons of the ACC predicted faster reaction times. Notably, optogenetic activation of visual inputs in the ACC evoked strong suppression of neighboring motor neurons by activating fast-spiking sensory neurons and drove task-relevant actions in mice via activating striatal neurons. Finally, the ACC network activity maintained low during spontaneous and perceptual actions and increased during action cancellation in response to the stop signals. Collectively, our data demonstrate that visual salience in the frontal cortex exerts gated feedforward inhibition to release goal-directed actions.

neuroscience↗

bioRxiv2020

Neurofeedback Training of Auditory Selective Attention Enhances Speech-in-noise Perception

Selective attention enhances cortical responses to attended sensory inputs while suppressing others, which can be an effective strategy for speech-in-noise (SiN) understanding. Here, we introduce a training paradigm designed to reinforce attentional modulation of auditory evoked responses. Subjects attended one of two speech streams while our EEG-based attention decoder provided online feedback. After four weeks of this neurofeedback training, subjects exhibited enhanced cortical response to target speech and improved performance during a SiN task. Such training effects were not found in the Placebo group that underwent attention training without neurofeedback. These results suggest an effective rehabilitation for SiN deficits.

neuroscience↗

bioRxiv2020

Biased agonists of the chemokine receptor CXCR3 differentially drive formation of Gαi:β-arrestin complexes

G-protein-coupled receptors (GPCRs), the largest family of cell surface receptors, signal through the proximal effectors G proteins and {beta}-arrestins to influence nearly every biological process. Classically, the G protein and {beta}-arrestin signaling pathways have largely been considered separable. Recently, direct interactions between G protein and {beta}-arrestin have been described and suggest a distinct GPCR signaling pathway. Within these newly described G:{beta}-arrestin complexes, Gi/o, but not other G protein subtypes, have been appreciated to directly interact with {beta}-arrestin, regardless of canonical GPCR G protein subtype coupling. However it is unclear how biased agonists differentially regulate this newly described Gi:{beta}-arrestin interaction, if at all. Here we report that endogenous ligands (chemokines) of the GPCR CXCR3, CXCL9, CXCL10, and CXCL11, along with two small molecule biased CXCR3 agonists, differentially promote the formation of Gi:{beta}-arrestin complexes. The ability of CXCR3 agonists to form Gi:{beta}-arrestin complexes does not correlate well with either G protein signaling or {beta}-arrestin recruitment. Conformational biosensors demonstrate that ligands that promoted Gi:{beta}-arrestin complex formation generated similar {beta}-arrestin conformations. We find these Gi:{beta}-arrestin complexes can associate with CXCR3, but not with ERK. These findings further support that Gi:{beta}-arrestin complex formation is a distinct GPCR signaling pathway and enhance our understanding of biased agonism.

biochemistry↗

bioRxiv2020

Identification of antiviral drug candidates against SARS-CoV-2 from FDA-approved drugs

COVID-19 is an emerging infectious disease and was recently declared as a pandemic by WHO. Currently, there is no vaccine or therapeutic available for this disease. Drug repositioning represents the only feasible option to address this global challenge and a panel of 48 FDA-approved drugs that have been pre-selected by an assay of SARS-CoV was screened to identify potential antiviral drug candidates against SARS-CoV-2 infection. We found a total of 24 drugs which exhibited antiviral efficacy (0.1 M < IC50 < 10 M) against SARS-CoV-2. In particular, two FDA-approved drugs - niclosamide and ciclesonide - were notable in some respects. These drugs will be tested in an appropriate animal model for their antiviral activities. In near future, these already FDA-approved drugs could be further developed following clinical trials in order to provide additional therapeutic options for patients with COVID-19.

microbiology↗

bioRxiv2020

Analysis of circulating-microRNA expression in lactating Holstein cows under summer heat stress

Korean peninsular weather is rapidly becoming subtropical due to global warming. In summer 2018, South Korea experienced the highest temperatures since the meteorological observations recorded in 1907. Heat stress has a negative effect on Holstein cows, the most popular breed of dairy cattle in South Korea, which is susceptible to heat. To examine physiological changes in dairy cows under heat stress conditions, we analyzed the profiles circulating microRNAs isolated from whole blood samples collected under heat stress and non-heat stress conditions using small RNA sequencing. We compared the expression profiles in lactating cows under heat stress and non-heat stress conditions to understand the regulation of biological processes in heat-stressed cows. Moreover, we measured several heat stress indicators, such as rectal temperature, milk yield, average daily gain, and progesterone concentration. All these assessments showed that pregnant cows were more susceptible to heat stress than non-pregnant cows. Particularly, progesterone concentrations known to have maternal warming effects were at similar levels in non-pregnant cows but significantly increased in pregnant cows under heat stress conditions. The differentially expressed miRNAs and their putative target genes were analyzed in pregnant cows. Interestingly, we found that differentially expressed miRNAs (bta-miR-146b, bta-miR-20b, bta-miR-29d-3p, bta-miR-1246) specifically targeted progesterone biosynthesis (StAR) and the function of corpus luteum-related genes (CCL11, XCL), suggesting that pregnant cows with elevated progesterone concentrations are more susceptible to heat stress. In addition, we found the differential expression of 11 miRNAs (bta-miR-19a, bta-miR-19b, bta-miR-30a-5p, and several from the bta-miR-2284 family) in both pregnant and non-pregnant cows under heat stress conditions. In target gene prediction and gene set enrichment analysis, these miRNAs were found to be associated with the cytoskeleton, cell junction, vasculogenesis, cell proliferation, ATP synthesis, oxidative stress, and immune responses involved in heat response. These miRNAs can be used as potential biomarkers for heat stress.

genomics↗

bioRxiv2020

ThiL is a valid antibacterial target that is essential for both thiamine biosynthesis and salvage pathway in Pseudomonas aeruginosa

Thiamine pyrophosphate (TPP) is an essential cofactor for various pivotal cellular processes in all living organisms, including bacteria. As thiamine biosynthesis occurs in bacteria but not humans, bacterial thiamine biosynthesis is an attractive target for antibiotic development. Among enzymes in the thiamine biosynthetic pathway, thiamine monophosphate kinase (ThiL) catalyzes the final step of the pathway, phosphorylating thiamine monophosphate (TMP) to produce TPP. In this work, we extensively investigated ThiL in Pseudomonas aeruginosa, a major pathogen of hospital-acquired infections. We demonstrated that thiL deletion abolishes not only thiamine biosynthesis but also thiamine salvage capability, showing growth defects of the {Delta}thiL mutant even in the presence of thiamine derivatives except TPP. Most importantly, the pathogenesis of the {Delta}thiL mutant was markedly attenuated compared to wild-type bacteria, with lower inflammatory cytokine induction and 103~104 times decreased bacterial load in an in vivo infection model where the intracellular TPP level is in the submicromolar range. In order to validate P. aeruginosa ThiL (PaThiL) as a new drug target, we further characterized its biochemical properties determining a Vmax of 4.0{+/-}0.2 nomol{middle dot}min-1 and KM values of 111{+/-}8 and 8.0{+/-}3.5M for ATP and TMP, respectively. A subsequent in vitro small molecule screening identified PaThiL inhibitors including WAY213613 that is a noncompetitive inhibitor with a Ki value of 13.4{+/-}2.3 M and a potential antibacterial activity against P. aeruginosa. This study proved that PaThiL is a new drug target against P. aeruginosa providing comprehensive biological and biochemical data that could facilitate to develop a new repertoire of antibiotics.

microbiology↗

bioRxiv2020

Screening of FDA-approved drugs using a MERS-CoV clinical isolate from South Korea identifies potential therapeutic options for COVID-19

Therapeutic options for coronavirus remain limited. To address this unmet medical need, we screened 5,406 compounds, including United States Food and Drug Administration (FDA)- approved drugs and bioactives, for activity against a South Korean Middle East respiratory syndrome coronavirus (MERS-CoV) clinical isolate. Among 221 identified hits, 54 had therapeutic indexes (TI) greater than 6. Time-of-addition studies with selected drugs demonstrated eight and four FDA-approved drugs acted on the early and late stages of the viral life cycle, respectively. Confirmed hits included several cardiotonic agents (TI>100), atovaquone, an anti-malarial (TI>34), and ciclosonide, an inhalable corticosteroid (TI>6). Furthermore, utilizing the severe acute respiratory syndrome CoV-2 (SARS-CoV-2), combinations of remedesivir with selected dugs were evaluated, which identified ciclosonide and nelfinavir to be additive and synergistic drugs in vitro, respectively. Together, we screened FDA-approved drugs using patient-derived MERS-CoV, triaged hits to discriminate between early and late viral life cycle inhibitors, confirmed selected drugs using SARS-CoV-2, and demonstrated the added value of selected medications in combination with remedesivir. Our results identify potential therapeutic options for MERS-CoV infections, and provide a basis to treat coronavirus disease 2019 (COVID-19) and other coronavirus-related illnesses.

microbiology↗

bioRxiv2019

Microglia Clear Neuron-released α-Synuclein via Selective Autophagy and Prevent Neurodegeneration

Microglia maintain brain homeostasis by removing neuron-derived components such as myelin and cell debris. The evidence linking microglia to neurodegenerative diseases is growing, however, the precise mechanisms remain poorly understood. Herein we report a neuroprotective role for microglia in the clearance of neuron-released -synuclein. Neuronal -synuclein activates microglia, which in turn engulf -synuclein into autophagosomes for degradation via selective autophagy (termed Synucleinphagy). Synucleinphagy is initiated by the interaction of -synuclein with Toll-like receptor 4 (TLR4), which induces transcriptional upregulation of p62/SQSTM1 through the NF-{kappa}B signaling pathway without causing TLR4 endocytosis. Induction of p62, an autophagy receptor, is necessary for the formation of -synuclein/ubiquitin-positive puncta that are degraded by autophagy. Finally, disruption of microglial autophagy in mice expressing human -synuclein promotes the accumulation of misfolded -synuclein and causes midbrain dopaminergic neuron degeneration. Our study thus identifies a novel neuroprotective function of microglia in the clearance of -synuclein via TLR4-NF-{kappa}B-p62 mediated Synucleinphagy.

neuroscience↗

bioRxiv2019

External and Internal Signal-to-noise Ratios Alter Timing and Location of Cortical Activities During Speech-in-noise Perception

Understanding speech in noise (SiN) is a complex task that recruits multiple cortical subsystems. There is a variance in individuals ability to understand SiN that cannot be explained by simple hearing profiles, which suggests that central factors may underlie the variance in SiN ability. Here, we elucidated a few cortical functions involved during a SiN task and their contributions to individual variance using both within- and across-subject approaches. Through our within-subject analysis of source-localized electroencephalography, we investigated how acoustic signal-to-noise ratio (SNR) alters cortical evoked responses to a target word across the speech recognition areas, finding stronger responses in left supramarginal gyrus (SMG, BA40 the dorsal lexicon area) with quieter noise. Through an individual differences approach, we found that listeners show different neural sensitivity to the background noise and target speech, reflected in the amplitude ratio of earlier auditory-cortical responses to speech and noise, named as an internal SNR. Listeners with better internal SNR showed better SiN performance. Further, we found that the post-speech time SMG activity explains a further amount of variance in SiN performance that is not accounted for by internal SNR. This result demonstrates that at least two cortical processes contribute to SiN performance independently: pre-target time processing to attenuate neural representation of background noise and post-target time processing to extract information from speech sounds.

neuroscience↗

bioRxiv2019

Causal links between parietal alpha activity and spatial auditory attention

Both visual and auditory spatial selective attention result in lateralized alpha (8-14 Hz) oscillatory power in parietal cortex: alpha increases in the hemisphere ipsilateral to attentional focus. Brain stimulation studies suggest a causal relationship between parietal alpha and suppression of the representation of contralateral visual space. However, there is no evidence that parietal alpha controls auditory spatial attention. Here, we performed high definition transcranial alternating current stimulation (HD-tACS) on human subjects performing an auditory task in which they attended either spatial or nonspatial features. Alpha (10 Hz) but not theta (6 Hz) HD-tACS of right parietal cortex interfered with attending left but not right auditory space. Parietal stimulation had no effect for nonspatial auditory attention. Moreover, performance in post-stimulation trials returned rapidly to baseline. These results demonstrate a causal, frequency-, hemispheric-, and task-specific effect of parietal alpha brain stimulation on top-down control of auditory spatial attention.

neuroscience↗

bioRxiv2019

Topographic specificity of alpha power during auditory spatial attention

Visual and somatosensory spatial attention both induce parietal alpha (7-14 Hz) oscillations whose topographical distribution depends on the direction of spatial attentional focus. In the auditory domain, contrasts of parietal alpha power for leftward and rightward attention reveal a qualitatively similar lateralization; however, it is not clear whether alpha lateralization changes monotonically with the direction of auditory attention as it does for visual spatial attention. In addition, most previous studies of alpha oscillation did not consider subject-specific differences in alpha frequency, but simply analyzed power in a fixed spectral band. Here, we recorded electroencephalography in human subjects when they directed attention to one of five azimuthal locations. After a cue indicating the direction of an upcoming target sequence of spoken syllables (yet before the target began), alpha power changed in a task specific manner. Subject-specific peak alpha frequencies differed consistently between frontocentral electrodes and parieto-occipital electrodes, suggesting multiple neural generators of task-related alpha. Parieto-occipital alpha increased over the hemisphere ipsilateral to attentional focus compared to the contralateral hemisphere, and changed systematically as the direction of attention shifted from far left to far right. These results showing that parietal alpha lateralization changes smoothly with the direction of auditory attention as in visual spatial attention provide further support to the growing evidence that the frontoparietal attention network is supramodal.

neuroscience↗

bioRxiv2019

Noncanonical scaffolding of Gαi and β-arrestin by G protein-coupled receptors

G-protein-coupled receptors (GPCRs) enable cells to sense and respond appropriately to hormonal and environmental signals, and are a target of ~30% of all FDA-approved medications. Canonically, each GPCR couples to distinct G proteins, such as Gs, Gi, Gq or G12/13, as well as {beta}-arrestins. These transducer proteins translate and integrate extracellular stimuli sensed by GPCRs into intracellular signals through what are broadly considered separable signalling pathways. However, the ability of G proteins to directly interact with {beta}-arrestins to integrate signalling has not previously been appreciated. Here we show a novel interaction between Gi protein family members and {beta}-arrestin. Gi:{beta}-arrestin complexes were formed by all GPCRs tested, regardless of their canonical G protein isoform coupling, and could bind both GPCRs as well as the extracellular signal-regulated kinase (ERK). This novel paradigm of Gi:{beta}-arrestin scaffolds enhances our understanding of GPCR signalling.

cell biology↗

bioRxiv2019

Non-Invasive Assays of Cochlear Synaptopathy -- Candidates and Considerations

Studies in multiple species, including in post-mortem human tissue, have shown that normal aging and/or acoustic overexposure can lead to a significant loss of afferent synapses innervating the cochlea. Hypothetically, this cochlear synaptopathy can lead to perceptual deficits in challenging environments and can contribute to central neural effects such as tinnitus. However, because cochlear synaptopathy can occur without any measurable changes in audiometric thresholds, synaptopathy can remain hidden from standard clinical diagnostics. To understand the perceptual sequelae of synaptopathy and to evaluate the efficacy of emerging therapies, sensitive and specific non-invasive measures at the individual patient level need to be established. Pioneering experiments in specific mice strains have helped identify many candidate assays. These include auditory brainstem responses, the middle-ear muscle reflex, envelope-following responses, and extended high-frequency audiograms. Unfortunately, because these non-invasive measures can be also affected by extraneous factors other than synaptopathy, their application and interpretation in humans is not straightforward. Here, we systematically examine six extraneous factors through a series of interrelated human experiments aimed at understanding their effects. Using strategies that may help mitigate the effects of such extraneous factors, we then show that these suprathreshold physiological assays exhibit across-individual correlations with each other indicative of contributions from a common physiological source consistent with cochlear synaptopathy. Finally, we discuss the application of these assays to two key outstanding questions, and discuss some barriers that still remain.

neuroscience↗