Ms Steps Research Articles

Multispecies Discrimination of Seals (Pinnipeds) using Hidden Markov Models (HMMs)

Hidden Markov Models (HMMs) were developed and implemented for the discrimination of 5 available Seals (Pinnipeds), namely the Bearded Seal (Erignathus barbatus), Harp Seal (Pagophilus groenlandicus), Leopard Seal (Hydrurga leptonyx), Ross Seal (Ommatophoca rossii), and Weddell Seal (Leptonychotes weddellii). The main objectives of the experiments were to study the impact of the frame size and step size and number of states for feature extraction and acoustic models on classification accuracy. Based on the experiments using Mel-Frequency Cepstral Coefficients (MFCCs) extracted from the vocalizations (15 ms frame size and 4 ms step size), HMMs containing 20 states with single underlying Gaussian Mixture Model (GMM) produced discrimination of 95.77%. From the results, the framework could be applied to analysis for other marine mammals for both classification and detection of vocalizations and species.

Real-time imaging of individual electropores proves their longevity in cells

With over 50 years of electroporation research, the nature of cell membrane permeabilization remains elusive. The lifetime of electropores in molecular models is limited to nano- or microseconds, whereas the permeabilization of electroporated cells can last minutes. This study aimed at resolving a longstanding debate on whether the prolonged permeabilization is due to the formation of long-lived pores in cells. We developed a method for dynamic monitoring and conductance measurements of individual electropores. This was accomplished by time-lapse total internal reflection fluorescence (TIRF) imaging in HEK cells loaded with CAL-520 dye and placed on an indium tin oxide (ITO) surface. Applying a 1-ms, 0 to −400 mV pulse between the patch pipette and ITO evoked focal Ca2+ transients that identified individual electropores. Some transients disappeared in milliseconds but others persisted for over a minute. Persistent transients (“Ca2+ plumes”) faded over time to a stable or a randomly fluctuating level that could include periods of full quiescence. Single pore conductance, measured by 0 to −50 mV, 50 ms steps at 30 and 60 s after the electroporation, ranged from 80 to 200 pS. These experiments proved electropore longevity in cells, in stark contrast to molecular simulations and many findings in lipid bilayers.

BASIC AND SUPERORDINATE IMAGE CATEGORIZATION. INFLUENCE OF THE CONGRUENCE DEGREE AND TEMPORAL PARAMETERS OF PREVIOUS STIMULUS PRESENTATION

The influence of temporal characteristics of mask presentation on performance in basic and superordinate image categorization tasks was investigated in young healthy subjects using a forward masking model. The masks could be congruent, noncongruent, or semantically neutral to the stimulus images. In the first series of experiments, the influence of stimulus onset asynchrony (SOA, the time interval between the onset of the mask and the onset of the stimulus) was studied. SOA varied from 100 to 350 ms in steps of 50 ms, whereas mask duration remained unchanged and equaled 100 ms. In the second series, the influence of mask duration was investigated. It varied from 100 to 250 ms in steps of 50 ms, while SOA remained constant at 250 ms. It was found that superordinate categorization was performed faster. This could be due to the fact that superordinate categorization involves a low-frequency information of stimulus description that is rapidly transmitted through the magnocellular visual pathway. The basic categorization was more sensitive to the temporal properties of the mask and its category. Changes in SOA had a stronger effect than those in mask duration. Assuming that SOA changes affect the early perceptual phase of stimulus processing, the sensitivity of this phase to irrelevant information seems to be reflected in the stronger influence of SOA changes on basic categorization compared to superordinate categorization.

A novel workflow for advanced mapping of repolarization dispersion from endocardial unipolar electrograms in patients with coved-type brugada syndrome

Abstract Funding Acknowledgements Type of funding sources: None. Background Accentuation of the action potential notch in the epicardium causes the prolongation of the epicardial action potentials in the right ventricular outflow tract (RVOT) and is the basis for arrhythmogenesis in patients affected by Brugada syndrome (BrS). Activation-recovery interval (ARI) approximates the action potential duration and may be used to study repolarization dispersion in BrS. Purpose Our aim was to investigate repolarization dispersion within the RVOT in spontaneous coved-type ECG BrS patients and in controls, evaluating also the relation between repolarization dispersion and conduction abnormalities to better define the electro-anatomical substrate of the disease. Methods BrS probands (n=13) and control subjects (n=4) underwent endocardial mapping of RV with the CARTO 3 system. BrS patients were also studied with programmed ventricular stimulation (PVS). Data was exported from the CARTO system and converted into MatLab format using OpenEP. A specific region of interest (ROI) including the sub-pulmonary RVOT and entire RV free wall was then selected using Paraview. With an automated algorithm, we measured ARI and ARIc (corrected using the "Bazett formula") for each point of the ROI, which were then interpolated to obtain ARI maps. We also acquired right ventricular activation time (RVAT) and maps for the assessment of slow conduction zones. By dividing RVAT color scale in 5 ms steps (isoSteps), isochronal activation areas were identified in the ROI. Results Out of the 13 BrS subjects, 4 had VT or VF inducible during PVS (PVS+) while 9 did not (PVS-). One patient had appropriate ICD shocks during follow-up. BrS patients had higher mean ARI and ARIc compared to controls (288.5±22.2 vs 251.5±8.4 ms, p<0.001; 312.0±30.4 vs 281.8±10.3 ms, p=0.023). ARI was found to be higher in PVS+ than in PVS- patients (294.8±27.1 vs 285.8±20.1 ms, p=0.5), as well as ARIc (327.7±49.9 vs 304.6±16.4 ms, p=0.49) although these differences were not significant. BrS patients showed a longer RVAT (106.0±21.4 vs 74.5±5.5 ms, p=0.003), and increased zones of crowding, as expressed by isochronal steps (13.85±2.94 vs 9.25±1.26, p=0.01). Notably, a strong correlation was found between ARIc and RVAT (Pearson R coefficient = 0.83, p<0.05), independently from the results of PVS (PVS+ R=0.99, p=0.01; PVS- R=0.83, p=0.06). Conclusions We introduced a novel workflow for the electrical substrate characterisation of subjects with BrS phenotype. Our preliminary data show the presence of repolarization dispersion along with conduction slowing in the RVOT of BrS patients compared to controls. In our population, repolarization dispersion and impairment of RVOT conduction were strongly related especially in inducible BrS patients.

“Lab of the Future”─Today: Fully Automated System for High-Throughput Mass Spectrometry Analysis of Biotherapeutics

Here we describe a state-of-the-art, integrated, multi-instrument automated system designed to execute methods involved in mass spectrometry characterization of biotherapeutics. The system includes liquid and microplate handling robotics and utilities, integrated LC-MS, along with data analysis software, to perform sample purification, preparation, and analysis as a seamless integrated unit. The automated process begins with tip-based purification of target proteins from expression cell-line supernatants, which is initiated once the samples are loaded onto the automated system and the metadata are retrieved from our corporate data aggregation system. Subsequently, the purified protein samples are prepared for MS, including deglycosylation and reduction steps for intact and reduced mass analysis, and proteolytic digestions, desalting, and buffer exchange via centrifugation for peptide map analysis. The prepared samples are then loaded into the LC-MS instrumentation for data acquisition. The acquired raw data are initially stored on a local area network storage system that is monitored by watcher scripts that then upload the raw MS data to a network of cloud-based servers. The raw MS data are processed with the appropriately configured analysis workflows such as database search for peptide mapping or charge deconvolution for undigested proteins. The results are verified and formatted for expert curation directly in the cloud. Finally, the curated results are appended to sample metadata in the corporate data aggregation system to accompany the biotherapeutic cell lines in subsequent processes.

Voltage sensor current, SR Ca2+ release, and Ca2+ channel current during trains of action potential-like depolarizations of skeletal muscle fibers.

In skeletal muscle, CaV 1.1 serves as the voltage sensor for both excitation-contraction coupling (ECC) and L-type Ca2+ channel activation. We have recently adapted the technique of action potential (AP) voltage clamp (APVC) to monitor the current generated by the movement of intramembrane voltage sensors (IQ ) during single imposed transverse tubular AP-like depolarization waveforms (IQAP ). We now extend this procedure to monitoring IQAP , and Ca2+ currents during trains of tubular AP-like waveforms in adult murine skeletal muscle fibers, and compare them with the trajectories of APs and AP-induced Ca2+ release measured in other fibers using field stimulation and optical probes. The AP waveform remains relatively constant during brief trains (<1 sec) for propagating APs in non-V clamped fibers. Trains of 10 AP-like depolarizations at 10 Hz (900 ms), 50 Hz (180 ms), or 100 Hz (90 ms) did not alter IQAP amplitude or kinetics, consistent with previous findings in isolated muscle fibers where negligible charge immobilization occurred during 100 ms step depolarizations. Using field stimulation, Ca2+ release did exhibit a considerable decline from pulse to pulse during the train, also consistent with previous findings, indicating that the decline of Ca2+ release during a short train of APs is not correlated to modification of charge movement. Ca2+ currents during single or 10 Hz trains of AP-like depolarizations were hardly detectable, were minimal during 50 Hz trains, and became more evident during 100 Hz trains in some fibers. Our results verify predictions on the behavior of the ECC machinery in response to AP-like depolarizations and provide a direct demonstration that Ca2+ currents elicited by single AP-like waveforms are negligible, but can become more prominent in some fibers during short high-frequency train stimulation that elicits maximal isometric force.

Multispecies discrimination of seals (pinnipeds) using hidden Markov models (HMMs)

Hidden Markov models (HMMs) were developed and implemented for the discrimination of five available Seals (Pinnipeds), namely, the Bearded Seal (Erignathus Barbatus), Harp Seal (Pagophilus Groenlandicus), Leopard Seal (Hydrurga Leptonyx), Ross Seal (Ommatophoca Rossii), and Weddell Seal (Leptonychotes Weddellii). The main objectives of the experiments were to study the impact of the frame size and step size and number of states for feature extraction and acoustic models on classification accuracy. Based on the experimentation using Mel-Frequency Cepstral Coefficients (MFCCs) extracted from the vocalizations (15 ms frame size and 4 ms step size), HMMs containing 20 states with single underlying Gaussian mixture model (GMM) produced discrimination of 95.77%. From the results, the framework could be applied to analysis for other marine mammals for both classification and detection of vocalizations and species.

Threshold Determination Method for Detecting the Gazing Areas on a PC Screen While Silent Reading Japanese Texts

This study aims to develop a method that can detect the areas of Japanese texts that are difficult to read on a PC screen by analyzing eye movements. An effective method for detecting the areas of text that are difficult to read is to create a heatmap and consider the areas where the eye stays for longer than a fixation duration threshold (threshold). Usually, the threshold is determined through a 50 ms step search. However, since the eye stay time (fixation duration) for difficult‐to‐read text is longer than the fixation duration when reading smoothly, it is expected that steps that last longer than 50 ms are more effective at detecting the threshold. Furthermore, there are individual differences in the speed at which we comprehend text. In this study, we proposed a method that considers both the efficient search and individual differences among each subject. The experimental results showed that the threshold determined by the proposed method is more useful than the thresholds of 1000 and 800 ms that were used in a previous study, as well as the usual fixation duration of 250 ms. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

How Good Does This Sound? Examining Listeners’ Second Language Proficiency and Their Perception of Category Goodness in Their Native Language

Language learners often transfer the sounds and prosody of their native language into their second language, but this influence can also flow in the opposite direction, with the second language influencing the first. Among other variables, language proficiency is known to affect the degree and directionality of cross-linguistic influence. However, little is known about how second language learning affects listeners’ perception of their native language. To begin addressing this gap, we examined the relationship between learners’ second language proficiency and their category goodness ratings in their native language. Thirty-nine English-speaking learners of Spanish listened to English words that began with voiced and voiceless stop consonants and were asked to rate how well the word represented the intended word on a 5-point scale. To create a voicing continuum, we manipulated the voice onset time of the word-initial stop in each target item from 125 ms of prevoicing to 100 ms of aspiration, in 25 ms steps. Proficiency did not affect the perception of voiced targets, but both proficiency and L2 stop production affected the perception of voiceless targets.

Nanopore tweezers measurements of RecQ conformational changes reveal the energy landscape of helicase motion.

Helicases are essential for nearly all nucleic acid processes across the tree of life, yet detailed understanding of how they couple ATP hydrolysis to translocation and unwinding remains incomplete because their small (∼300 picometer), fast (∼1 ms) steps are difficult to resolve. Here, we use Nanopore Tweezers to observe single Escherichia coli RecQ helicases as they translocate on and unwind DNA at ultrahigh spatiotemporal resolution. Nanopore Tweezers simultaneously resolve individual steps of RecQ along the DNA and conformational changes of the helicase associated with stepping. Our data reveal the mechanochemical coupling between physical domain motions and chemical reactions that together produce directed motion of the helicase along DNA. Nanopore Tweezers measurements are performed under either assisting or opposing force applied directly on RecQ, shedding light on how RecQ responds to such forces in vivo. Determining the rates of translocation and physical conformational changes under a wide range of assisting and opposing forces reveals the underlying dynamic energy landscape that drives RecQ motion. We show that RecQ has a highly asymmetric energy landscape that enables RecQ to maintain velocity when encountering molecular roadblocks such as bound proteins and DNA secondary structures. This energy landscape also provides a mechanistic basis making RecQ an ‘active helicase,’ capable of unwinding dsDNA as fast as it translocates on ssDNA. Such an energy landscape may be a general strategy for molecular motors to maintain consistent velocity despite opposing loads or roadblocks.

The natural frequencies of the resting human brain: An MEG-based atlas

Brain oscillations are considered to play a pivotal role in neural communication. However, detailed information regarding the typical oscillatory patterns of individual brain regions is surprisingly scarce. In this study we applied a multivariate data-driven approach to create an atlas of the natural frequencies of the resting human brain on a voxel-by-voxel basis. We analysed resting-state magnetoencephalography (MEG) data from 128 healthy adult volunteers obtained from the Open MEG Archive (OMEGA). Spectral power was computed in source space in 500 ms steps for 82 frequency bins logarithmically spaced from 1.7 to 99.5 Hz. We then applied k-means clustering to detect characteristic spectral profiles and to eventually identify the natural frequency of each voxel. Our results provided empirical confirmation of the canonical frequency bands and revealed a region-specific organisation of intrinsic oscillatory activity, following both a medial-to-lateral and a posterior-to-anterior gradient of increasing frequency. In particular, medial fronto-temporal regions were characterised by slow rhythms (delta/theta). Posterior regions presented natural frequencies in the alpha band, although with differentiated generators in the precuneus and in sensory-specific cortices (i.e., visual and auditory). Somatomotor regions were distinguished by the mu rhythm, while the lateral prefrontal cortex was characterised by oscillations in the high beta range (>20 Hz). Importantly, the brain map of natural frequencies was highly replicable in two independent subsamples of individuals. To the best of our knowledge, this is the most comprehensive atlas of ongoing oscillatory activity performed to date. Critically, the identification of natural frequencies is a fundamental step towards a better understanding of the functional architecture of the human brain.

Optimal saturation recovery time for minimizing the underestimation of arterial input function in quantitative cardiac perfusion MRI.

PurposeThe purpose of this study was to determine an optimal saturation‐recovery time (TS) for minimizing the underestimation of arterial input function (AIF) in quantitative cardiac perfusion MRI without multiple gadolinium injections per subject.MethodsWe scanned 18 subjects (mean age = 59 ± 14 years, 9/9 males/females) to acquire resting perfusion data and 1 additional subject (age = 38 years, male) to obtain stress‐rest perfusion data using a 5‐fold accelerated pulse sequence with radial k‐space sampling and applied k‐space weighted image contrast (KWIC) filters on the same k‐space data to retrospectively reconstruct five AIF images with effective TS ranging from 10 to 21.2 ms (2.8 ms steps). Undersampled images were reconstructed using a compressed sensing framework with temporal‐total‐variation and temporal‐principal‐component as 2 orthogonal sparsifying transforms. The image processing steps included, same motion correction across five different AIF images, signal normalization by the proton‐density‐weighted‐image, signal‐to‐T1 conversion using a Bloch equation, T1‐to‐gadolinium‐concentration conversion assuming fast water exchange, T2* correction to the AIF, and gadolinium‐concentration to myocardial blood flow (MBF) conversion based on a Fermi model.ResultsAmong five TS values, the shortest TS (10 ms) produced significantly (P < 0.05) higher peak AIF and lower resting MBF (13.73 mM, 0.73 mL g−1 min−1) than 12.8 ms (11.24 mM, 0.89 mL g−1 min−1), 15.6 ms (9.56 mM, 1.05 mL g−1 min−1), 18.4 ms (8.55 mM, 1.17 mL g−1 min−1), and 21.2 ms (7.95 mM, 1.27 mL g−1 min−1). Similarly, shorter TS reduced underestimation of AIF (or overestimation of MBF) for both during stress and at rest, but this effect was canceled in myocardial‐perfusion‐reserve (MPR).ConclusionThis study demonstrates that TS of 10 ms reduces the underestimation of AIF and, hence, the overestimation of MBF compared with longer TS values (12.8‐21.2 ms).

Motivational salience, not valence, modulates time perception.

It has been argued that cognitive processes such as attention and memory are influenced by motivational salience (high or low predictability of an outcome) rather than valance or value (gain or loss). However, whether this holds for subjective time perception remains unclear. To investigate this, a two-phase study was conducted. First, in a value learning task, a set of neutral faces was imbued with different levels of motivational salience (high or low) crossed with two levels of value (gain, loss). Thus, a specific face could acquire, for example, high motivational salience and low value by repeatedly signaling an 80% chance of losing points. Faces with these learned associations were then presented as an oddball for a varying duration (300-700 ms in steps of 50 ms) in a sequence of standard stimuli previously seen but predictive of no outcome (each presented for 500 ms). Participants assessed whether the oddball was longer or shorter than the duration of the standard stimuli. The results show that an oddball associated with a high predictable outcome (80% chance of gain or loss) was perceived to last longer than an oddball associated with a low predictable outcome (20% chance of gain or loss). The present study supports previous studies by showing that a high motivational outcome, rather than valance/value, changes cognitive engagement with a stimulus. Attention may play an essential role in this interaction by modulating subjective expansion of time. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Acquiring Italian stop consonants: A challenge for Mandarin Chinese-speaking learners

The acquisition of Italian stop consonants by Mandarin Chinese-speaking learners has hardly been investigated. This study was designed to fill this gap. To investigate Chinese learners’ acquisition patterns of Italian voiced and voiceless stops, a perception experiment and a production experiment were conducted. Twenty Mandarin Chinese-speaking undergraduate students majoring in Italian, five native Italian and five native Mandarin speakers served as participants in the perception experiment; and an equal number of participants with the same language backgrounds served as participants in the production experiment. In the perception experiment, the participants had to identify the stimuli in three continua (i.e. bilabial, alveolar and velar) where voice onset time (VOT) values ranged from −50 ms to 90 ms in 10 ms steps. In the production experiment, data were collected from a reading task in which the participants were asked to read the target words with word-initial stops in carrier-sentences; the VOT and closure durations were measured. The results show that, in perception, Chinese learners have difficulty differentiating between Italian voiced and voiceless stops; in production, Italian voiced rather than voiceless stops represent a challenge for Chinese learners. The results are in line with the predictions made by the Perceptual Assimilation Model-L2 (PAM-L2) and the Speech Learning Model (SLM), as well as with most other studies focusing on the acquisition of stops of ‘true-voice languages’ by Chinese learners.

Multi-modal imaging of the auditory-larynx motor network for voicing perception

Voicing is one of the most important characteristics of phonetic speech sounds. Despite its importance, voicing perception mechanisms remain largely unknown. To explore auditory-motor networks associated with voicing perception, we firstly examined the brain regions that showed common activities for voicing production and perception using functional magnetic resonance imaging. Results indicated that the auditory and speech motor areas were activated with the operculum parietale 4 (OP4) during both voicing production and perception. Secondly, we used a magnetoencephalography and examined the dynamical functional connectivity of the auditory-motor networks during a perceptual categorization task of /da/-/ta/ continuum stimuli varying in voice onset time (VOT) from 0 to 40 ms in 10 ms steps. Significant functional connectivities from the auditory cortical regions to the larynx motor area via OP4 were observed only when perceiving the stimulus with VOT 30 ms. In addition, regional activity analysis showed that the neural representation of VOT in the auditory cortical regions was mostly correlated with categorical perception of voicing but did not reflect the perception of stimulus with VOT 30 ms. We suggest that the larynx motor area, which is considered to play a crucial role in voicing production, contributes to categorical perception of voicing by complementing the temporal processing in the auditory cortical regions.

Detection and Recognition of Asynchronous Auditory/Visual Speech: Effects of Age, Hearing Loss, and Talker Accent.

This investigation examined age-related differences in auditory-visual (AV) integration as reflected on perceptual judgments of temporally misaligned AV English sentences spoken by native English and native Spanish talkers. In the detection task, it was expected that slowed auditory temporal processing of older participants, relative to younger participants, would be manifest as a shift in the range over which participants would judge asynchronous stimuli as synchronous (referred to as the “AV simultaneity window”). The older participants were also expected to exhibit greater declines in speech recognition for asynchronous AV stimuli than younger participants. Talker accent was hypothesized to influence listener performance, with older listeners exhibiting a greater narrowing of the AV simultaneity window and much poorer recognition of asynchronous AV foreign-accented speech compared to younger listeners. Participant groups included younger and older participants with normal hearing and older participants with hearing loss. Stimuli were video recordings of sentences produced by native English and native Spanish talkers. The video recordings were altered in 50 ms steps by delaying either the audio or video onset. Participants performed a detection task in which they judged whether the sentences were synchronous or asynchronous, and performed a recognition task for multiple synchronous and asynchronous conditions. Both the detection and recognition tasks were conducted at the individualized signal-to-noise ratio (SNR) corresponding to approximately 70% correct speech recognition performance for synchronous AV sentences. Older listeners with and without hearing loss generally showed wider AV simultaneity windows than younger listeners, possibly reflecting slowed auditory temporal processing in auditory lead conditions and reduced sensitivity to asynchrony in auditory lag conditions. However, older and younger listeners were affected similarly by misalignment of auditory and visual signal onsets on the speech recognition task. This suggests that older listeners are negatively impacted by temporal misalignments for speech recognition, even when they do not notice that the stimuli are asynchronous. Overall, the findings show that when listener performance is equated for simultaneous AV speech signals, age effects are apparent in detection judgments but not in recognition of asynchronous speech.

Multispecies discrimination of whales (cetaceans) using Hidden Markov Models (HMMS)

Hidden Markov Models (HMMs) were developed and implemented for the discrimination of 11 available Whales (Cetaceans). The primarily aims of the experiments were to explore the impact frame size and step size, feature vector size, and number of states for feature extraction and acoustic models on classification accuracy. Through the experiments using Mel-Frequency Cepstral Coefficients (MFCCs) extracted from the vocalizations (7 ms frame size and 6 ms step size), HMMs containing 4 states with single underlying Gaussian Mixture Model (GMM) yielded high classification accuracies ranging from 82.72% (9 classes) to 100.00% (1–3 classes), including discrimination of 84.11% (11 classes). From the results, the framework could be applied to the analysis of other marine mammals for the automatic classification and detection of vocalizations and species.

Good test-retest reliability of a paired-pulse transcranial magnetic stimulation protocol to measure short-interval intracortical facilitation.

Transcranial magnetic stimulation (TMS) is used frequently to study human physiology, including the indirect-wave (I-wave) circuits generating short-interval intracortical facilitation (SICF). Growing evidence implicates SICF in plasticity and motor learning, suggesting that SICF is likely of functional relevance in both health and disease. To date, test-retest reliability has not been established for measures of SICF: given the clear potential of SICF to be used as a diagnostic tool, it is critical to establish the reliability of the paired-pulse TMS protocol to measure SICF. We investigated the test-retest reliability of SICF measured using paired-pulse TMS. SICF was measured in two sessions in 20 young adults using single- and paired-pulse TMS. Single-pulse TMS was set at an intensity that elicited MEPs of 1mV (SI1mV) and paired-pulse TMS was set with the first stimulus at SI1mV, the second stimulus (S2) 90% of resting motor threshold (RMT), and a total of 20 interstimulus intervals (ISI; 1.1-4.9ms with a 0.2ms step). Large intraclass correlation coefficients (ICC) indicate good test-retest reliability between sessions for all SICF peaks (ICCs ranging from 0.73 to 0.79). The ISI at which SICF was maximal within individuals was consistent at all three peaks across both experimental sessions. Results showed good test-retest reliability of SICF at all three peaks when using a standard paired-pulse protocol to measure SICF. This finding suggests that paired-pulse TMS can be used to reliably probe the excitability of the interneuronal circuits that generate SICF. This provides a strong platform for future research to investigate the functional role of I-wave circuitry, including the role of I-wave circuitry in motor control decline in healthy older adults and individuals with movement disorders.

Direct Observation of Vesicle Transport on the Synaptic Ribbon Provides Evidence That Vesicles Are Mobilized and Prepared Rapidly for Release.

Synaptic ribbons are thought to provide vesicles for continuous release in some retinal nonspiking neurons, yet recent studies indicate that genetic removal of the ribbon has little effect on release kinetics. To investigate vesicle replenishment at synaptic ribbons, we used total internal reflection fluorescence microscopy to image synaptic vesicles and ribbons in retinal bipolar cells of goldfish (Carassius auratus) of both sexes. Analysis of vesicles released by trains of 30 ms depolarizations revealed that most releasable vesicles reside within 300 nm of the ribbon center. A single 30 ms step to 0 mV was sufficient to deplete the membrane-proximal vesicle pool, while triggering rapid stepwise movements of distal vesicles along the ribbon and toward the plasma membrane. Replenishment only becomes rate-limiting for recovery from paired-pulse depression for interstimulus intervals shorter than 250 ms. For longer interstimulus intervals, vesicle movement down the ribbon is fast enough to replenish released vesicles, but newly arrived vesicles are not release-ready. Notably, the rates of vesicle resupply and maturation of newcomers are among the fastest measured optically at any synapse. Lastly, our data show that the delay in vesicle departure increases and vesicle speed decreases with multiple stimuli. Our results support a role for ribbons in the supply of vesicles for release, provide direct measurements of vesicle movement down the ribbon, and suggest that multiple factors contribute to paired-pulse depression.SIGNIFICANCE STATEMENT Synaptic ribbons are macromolecular scaffolds that tether synaptic vesicles close to release sites in nonspiking neurons of the retina and cochlea. Because these neurons release neurotransmitter continuously, synaptic ribbons are assumed to act as platforms for supplying vesicles rapidly in the face of prolonged stimulation. Yet, ribbon synapses suffer from profound paired-pulse depression, which takes seconds to subside. We investigated the mechanistic origin of this phenomenon by directly imaging triggered vesicle movement and release at ribbon sites in retinal bipolar cells, and find that, although ribbon synapses deliver and prime vesicles faster than most conventional synapses, both vesicle absence and vesicle priming contribute to the long recovery from paired-pulse depression.

Modulation of soleus H-reflex excitability following cervical transspinal conditioning stimulation in humans

The aim of this study was to establish the effects of transcutaneous spinal cord (transspinal) stimulation over the cervical region on soleus H-reflex excitability in healthy subjects while at rest. Reflex effects were established at subthreshold and suprathreshold cervical transspinal conditioning stimulation intensities of the extensor carpi radialis transspinal evoked potential. Twenty soleus H-reflexes at 0.125 Hz were recorded randomly under control conditions and following transspinal conditioning stimulation at conditioning-test intervals that ranged from 0 to 55 ms and tested in increment of 5 ms steps and at 100 ms. Cervical transspinal stimulation at suprathreshold and not at subthreshold intensities produced short, medium, and long-latency soleus H-reflex facilitation. The observed facilitatory reflex effects are consistent with activation of excitatory components of long propriospinal neurons. We propose the use of cervical transspinal stimulation to potentiate excitatory neuronal interactions between arms and legs in neurological disorders.