Decoding reach-to-grasp from EEG using classifiers trained with data from the contralateral limb.

Fundamental to human movement is the ability to interact with objects in our environment. How one reaches an object depends on the object's shape and intended interaction afforded by the object, e.g., grasp and transport. Extensive research has revealed that the motor intention of reach-to-grasp can be decoded from cortical activities using EEG signals. The goal of the present study is to determine the extent to which information encoded in the EEG signals is shared between two limbs to enable cross-hand decoding. We performed an experiment in which human subjects (n = 10) were tasked to interact with a novel object with multiple affordances using either right or left hands. The object had two vertical handles attached to a horizontal base. A visual cue instructs what action (lift or touch) and whether the left or right handle should be used for each trial. EEG was recorded and processed from bilateral frontal-central-parietal regions (30 channels). We trained LDA classifiers using data from trials performed by one limb and tested the classification accuracy using data from trials performed by the contralateral limb. We found that the type of hand-object interaction can be decoded with approximately 59 and 69% peak accuracy in the planning and execution stages, respectively. Interestingly, the decoding accuracy of the reaching directions was dependent on how EEG channels in the testing dataset were spatially mirrored, and whether directions were labeled in the extrinsic (object-centered) or intrinsic (body-centered) coordinates.

Learning acquisition of consistent leader-follower relationships depends on implicit haptic interactions.

Are leaders made or born? Leader-follower roles have been well characterized in social science, but they remain somewhat obscure in sensory-motor coordination. Furthermore, it is unknown how and why leader-follower relationships are acquired, including innate versus acquired controversies. We developed a novel asymmetrical coordination task in which two participants (dyad) need to collaborate in transporting a simulated beam while maintaining its horizontal attitude. This experimental paradigm was implemented by twin robotic manipulanda, simulated beam dynamics, haptic interactions, and a projection screen. Clear leader-follower relationships were learned only when strong haptic feedback was introduced. This phenomenon occurred despite participants not being informed that they were interacting with each other and the large number of equally-valid alternative dyadic coordination strategies. We demonstrate the emergence of consistent leader-follower relationships in sensory-motor coordination, and further show that haptic interaction is essential for dyadic co-adaptation. These results provide insights into neural mechanisms responsible for the formation of leader-follower relationships in our society.

Distinct adaptation processes underlie multidigit force coordination for dexterous manipulation.

The human sensorimotor system can adapt to various changes in the environmental dynamics by updating motor commands to improve performance after repeated exposure to the same task. However, the characteristics and mechanisms of the adaptation process remain unknown for dexterous manipulation, a unique motor task in which the body physically interacts with the environment with multiple effectors, i.e., digits, in parallel. We addressed this gap by using robotic manipulanda to investigate the changes in the digit force coordination following mechanical perturbation of an object held by tripod grasps. As the participants gradually adapted to lifting the object under perturbations, we quantified two components of digit force coordination. One is the direction-specific manipulation moment that directly counteracts the perturbation, whereas the other one is the direction-independent internal moment that supports the stability and stiffness of the grasp. We found that trial-to-trial improvement of task performance was associated with increased manipulation moment and a gradual decrease of the internal moment. These two moments were characterized by different rates of adaptation. We also examined how these two force coordination components respond to changes in perturbation directions. Importantly, we found that the manipulation moment was sensitive to the extent of repetitive exposure to the previous context that has an opposite perturbation direction, whereas the internal moment did not. However, the internal moment was sensitive to whether the postchange perturbation direction was previously experienced. Our results reveal, for the first time, that two distinct processes underlie the adaptation of multidigit force coordination for dexterous manipulation.NEW & NOTEWORTHY Changes in digit force coordination in multidigit object manipulation were quantified with a novel experimental design in which human participants adapted to mechanical perturbations applied to the object. Our results show that the adaptation of digit force coordination can be characterized by two distinct components that operate at different timescales. We further show that these two components respond to changes in perturbation direction differently.

Bio-inspired design of a self-aligning, lightweight, and highly-compliant cable-driven knee exoskeleton.

Powered knee exoskeletons have shown potential for mobility restoration and power augmentation. However, the benefits of exoskeletons are partially offset by some design challenges that still limit their positive effects on people. Among them, joint misalignment is a critical aspect mostly because the human knee joint movement is not a fixed-axis rotation. In addition, remarkable mass and stiffness are also limitations. Aiming to minimize joint misalignment, this paper proposes a bio-inspired knee exoskeleton with a joint design that mimics the human knee joint. Moreover, to accomplish a lightweight and high compliance design, a high stiffness cable-tension amplification mechanism is leveraged. Simulation results indicate our design can reduce 49.3 and 71.9% maximum total misalignment for walking and deep squatting activities, respectively. Experiments indicate that the exoskeleton has high compliance (0.4 and 0.1 Nm backdrive torque under unpowered and zero-torque modes, respectively), high control bandwidth (44 Hz), and high control accuracy (1.1 Nm root mean square tracking error, corresponding to 7.3% of the peak torque). This work demonstrates performance improvement compared with state-of-the-art exoskeletons.

Age-Dependent Upper Limb Myoelectric Control Capability in Typically Developing Children.

Research in EMG-based control of prostheses has mainly utilized adult subjects who have fully developed neuromuscular control. Little is known about children's ability to generate consistent EMG signals necessary to control artificial limbs with multiple degrees of freedom. As a first step to address this gap, experiments were designed to validate and benchmark two experimental protocols that quantify the ability to coordinate forearm muscle contractions in typically developing children. Non-disabled, healthy adults and children participated in our experiments that aimed to measure an individual's ability to use myoelectric control interfaces. In the first experiment, participants performed 8 repetitions of 16 different hand/wrist movements. Using offline classification analysis based on Support Vector Machine, we quantified their ability to consistently produce distinguishable muscle contraction patterns. We demonstrated that children had a smaller number of highly independent movements (can be classified with >90% accuracy) than adults did. The second experiment measured participants' ability to control the position of a cursor on a 1-DoF virtual slide using proportional EMG control with three different visuomotor gain levels. We found that children had higher failure rates and slower average target acquisitions than adults did, primarily due to longer correction times that did not improve over repetitive practice. We also found that the performance in both experiments was age-dependent in children. The results of this study provide novel insights into the technical and empirical basis to better understand neuromuscular development in children with upper-limb loss.

Molecular mapping for fruit-related traits, and joint identification of candidate genes and selective sweeps for seed size in melon.

Melon is a popular fruit vegetable crop worldwide with diverse morphological variation. We report a high-density genetic map of melon and nine major QTLs with physical region ranging from 43.47 kb to 1.89 Mb. Importantly, two seed-related trait QTLs were repeatedly detected in two environments, and the mapping region was narrowed to 522 kb according to a regional linkage analysis. A total of 40 annotated genes were screened for nonsynonymous variations, of which EVM0009818, involved in cytokinin-activated signaling, was differentially expressed in the young fruits of parents based on RNA-seq. Selective sweep analysis identified 152 sweep signals for seed size, including the two seed-related QTLs and nine homologs that have been verified to regulate seed size in Arabidopsis or rice. This work illustrates the power of a joint analysis combining resequencing-based genetic map for QTL mapping and a combination of KASP genotyping and RNA-seq analysis to facilitate QTL fine mapping.

Inter-personal motor interaction is facilitated by hand pairing.

The extent to which hand dominance may influence how each agent contributes to inter-personal coordination remains unknown. In the present study, right-handed human participants performed object balancing tasks either in dyadic conditions with each agent using one hand (left or right), or in bimanual conditions where each agent performed the task individually with both hands. We found that object load was shared between two hands more asymmetrically in dyadic than single-agent conditions. However, hand dominance did not influence how two hands shared the object load. In contrast, hand dominance was a major factor in modulating hand vertical movement speed. Furthermore, the magnitude of internal force produced by two hands against each other correlated with the synchrony between the two hands' movement in dyads. This finding supports the important role of internal force in haptic communication. Importantly, both internal force and movement synchrony were affected by hand dominance of the paired participants. Overall, these results demonstrate, for the first time, that pairing of one dominant and one non-dominant hand may promote asymmetrical roles within a dyad during joint physical interactions. This appears to enable the agent using the dominant hand to actively maintain effective haptic communication and task performance.

Fine-mapping and identification of a candidate gene controlling seed coat color in melon (Cucumis melo L. var. chinensis Pangalo).

KEY MESSAGE: MELO3C019554 encoding a homeobox protein (PHD transcription factor) is a candidate gene that involved in the formation of seed coat color in melon. Seed coat color is related to flavonoid content which is closely related to seed dormancy. According to the genetic analysis of a six-generation population derived from two parents (IC2508 with a yellow seed coat and IC2518 with a brown seed coat), we discovered that the yellow seed coat trait in melon is controlled by a single dominant gene, named CmBS-1. Bulked segregant analysis sequencing (BSA-Seq) revealed that the gene is located at 11,860,000-15,890,000 bp (4.03 Mb) on Chr 6. The F2 population was genotyped using insertion-deletions (InDels), from which cleaved amplified polymorphic sequence (dCAPS) markers were derived to construct a genetic map. The gene was then fine-mapped to a 233.98 kb region containing 12 genes. Based on gene sequence analysis with two parents, we found that the MELO3C019554 gene encoding a homeobox protein (PHD transcription factor) had a nonsynonymous single nucleotide polymorphism (SNP) mutation in the coding sequence (CDS), and the SNP mutation resulted in the conversion of an amino acid (A → T) at residue 534. In addition, MELO3C019554 exhibited lower relative expression levels in the yellow seed coat than in the brown seed coat. Furthermore, we found that MELO3C019554 is related to 12 flavonoid metabolites. Thus, we predicted that MELO3C019554 is a candidate gene controlling seed coat color in melon. The study lays a foundation for further cloning projects and functional analysis of this gene, as well as marker-assisted selection breeding.

Comprehensive Analysis of Transcriptome and Metabolome Reveals the Flavonoid Metabolic Pathway Is Associated with Fruit Peel Coloration of Melon.

The peel color is an important external quality of melon fruit. To explore the mechanisms of melon peel color formation, we performed an integrated analysis of transcriptome and metabolome with three different fruit peel samples (grey-green 'W', dark-green 'B', and yellow 'H'). A total of 40 differentially expressed flavonoids were identified. Integrated transcriptomic and metabolomic analyses revealed that flavonoid biosynthesis was associated with the fruit peel coloration of melon. Twelve differentially expressed genes regulated flavonoids synthesis. Among them, nine (two 4CL, F3H, three F3'H, IFS, FNS, and FLS) up-regulated genes were involved in the accumulation of flavones, flavanones, flavonols, and isoflavones, and three (2 ANS and UFGT) down-regulated genes were involved in the accumulation of anthocyanins. This study laid a foundation to understand the molecular mechanisms of melon peel coloration by exploring valuable genes and metabolites.

QTLs and candidate genes analyses for fruit size under domestication and differentiation in melon (Cucumis melo L.) based on high resolution maps.

BACKGROUND: Melon is a very important horticultural crop produced worldwide with high phenotypic diversity. Fruit size is among the most important domestication and differentiation traits in melon. The molecular mechanisms of fruit size in melon are largely unknown. RESULTS: Two high-density genetic maps were constructed by whole-genome resequencing with two F2 segregating populations (WAP and MAP) derived from two crosses (cultivated agrestis × wild agrestis and cultivated melo × cultivated agrestis). We obtained 1,871,671 and 1,976,589 high quality SNPs that show differences between parents in WAP and MAP. A total of 5138 and 5839 recombination events generated 954 bins in WAP and 1027 bins in MAP with the average size of 321.3 Kb and 301.4 Kb respectively. All bins were mapped onto 12 linkage groups in WAP and MAP. The total lengths of two linkage maps were 904.4 cM (WAP) and 874.5 cM (MAP), covering 86.6% and 87.4% of the melon genome. Two loci for fruit size were identified on chromosome 11 in WAP and chromosome 5 in MAP, respectively. An auxin response factor and a YABBY transcription factor were inferred to be the candidate genes for both loci. CONCLUSION: The high-resolution genetic maps and QTLs analyses for fruit size described here will provide a better understanding the genetic basis of domestication and differentiation, and provide a valuable tool for map-based cloning and molecular marker assisted breeding.

Dimensionality analysis of forearm muscle activation for myoelectric control in transradial amputees.

Establishing a natural communication interface between the user and the terminal device is one of the central challenges of hand neuroprosthetics research. Surface electromyography (EMG) is the most common source of neural signals for interpreting a user's intent in these interfaces. However, how the capacity of EMG generation is affected by various clinical parameters remains largely unknown. In this study, we examined the EMG activity of forearm muscles recorded from 11 transradially amputated subjects who performed a wide range of movements. EMG recordings from 40 able-bodied subjects were also analyzed to provide comparative benchmarks. By using non-negative matrix factorization, we extracted the synergistic EMG patterns for each subject to estimate the dimensionality of muscle control, under the framework of motor synergies. We found that amputees exhibited less than four synergies (with substantial variability related to the length of remaining limb and age), whereas able-bodied subjects commonly demonstrate five or more synergies. The results of this study provide novel insight into the muscle synergy framework and the design of natural myoelectric control interfaces.

Transcriptomic and metabolomic analyses reveal that melatonin promotes melon root development under copper stress by inhibiting jasmonic acid biosynthesis.

Melatonin has been shown to alleviate the effects of abiotic stress and to regulate plant development. Copper, a common heavy metal and soil pollutant, can suppress plant growth and development. In this work, we explored the protective effects of exogenous melatonin on lateral root formation in response to copper stress using melon seeds subjected to three germination treatments: CK1 (control), CK2 (300 µmol/L CuSO4), and MT3 (300 µmol/L melatonin + 300 µmol/L CuSO4). Melatonin pretreatment increased the antioxidant enzyme activities and root vigor, and decreased the proline and malondialdehyde (MDA) contents in the roots of copper-stressed melon seedlings. We then used transcriptomic and metabolomic analyses to explore the mechanisms by which exogenous melatonin protects against copper stress. There were 70 significant differentially expressed genes (DEGs) (28 upregulated, 42 downregulated) and 318 significantly differentially expressed metabolites (DEMs) (168 upregulated, 150 downregulated) between the MT3 and CK2 treatments. Melatonin pretreatment altered the expression of genes related to redox and cell wall formation processes. In addition, we found that members of the AP2/ERF, BBR/BPC, GRAS, and HD-ZIP transcription factor families may have vital roles in lateral root development. Melatonin also increased the level of Glutathione (GSH), which chelates excess Cu2+. The combined transcriptomic and metabolomic analysis revealed DEGs and DEMs involved in jasmonic acid (JA) biosynthesis, including four lipoxygenase-related genes and two metabolites (linoleic acid and lecithin) related to melatonin's alleviation effect on copper toxicity. This research elucidated the molecular mechanisms of melatonin's protective effects in copper-stressed melon.

A comprehensive genome variation map of melon identifies multiple domestication events and loci influencing agronomic traits.

Melon is an economically important fruit crop that has been cultivated for thousands of years; however, the genetic basis and history of its domestication still remain largely unknown. Here we report a comprehensive map of the genomic variation in melon derived from the resequencing of 1,175 accessions, which represent the global diversity of the species. Our results suggest that three independent domestication events occurred in melon, two in India and one in Africa. We detected two independent sets of domestication sweeps, resulting in diverse characteristics of the two subspecies melo and agrestis during melon breeding. Genome-wide association studies for 16 agronomic traits identified 208 loci significantly associated with fruit mass, quality and morphological characters. This study sheds light on the domestication history of melon and provides a valuable resource for genomics-assisted breeding of this important crop.

A High-Quality Melon Genome Assembly Provides Insights into Genetic Basis of Fruit Trait Improvement.

Accurate reference genomes have become indispensable tools for characterization of genetic and functional variations. Here we generated a high-quality assembly of the melon Payzawat using a combination of short-read sequencing, single-molecule real-time sequencing, Hi-C, and a high-density genetic map. The final 12 chromosome-level scaffolds cover ∼94.13% of the estimated genome (398.57 Mb). Compared with the published DHL92 genome, our assembly exhibits a 157-fold increase in contig length and remarkable improvements in the assembly of centromeres and telomeres. Six genes within STHQF12.4 on pseudochromosome 12, identified from whole-genome comparison between Payzawat and DHL92, may explain a considerable proportion of the skin thickness. In addition, our population study showed that melon domesticated at multiple times from whole-genome perspective and melons in China are introduced from different routes. Selective sweeps underlying the genes related to desirable traits, haplotypes of alleles associated with agronomic traits, and the variants from resequencing data enable efficient breeding.

Inter-Limb Transfer of Grasp Force Perception With Closed-Loop Hand Prosthesis.

Sensory feedback of grasp forces provides important information about physical interactions between the hand and objects, enabling both reactive and anticipatory neural control mechanisms. The numerous studies have shown artificial sensory feedback of various forms improves force control during grasping tasks by prosthetic hand users through a closed-feedback loop. However, little is known about how perceptual information is transferred between an intact limb and a closed-loop prosthetic limb, and the extent to which training inter-limb transfer may improve myoelectric prosthetic control. We addressed these gaps by using a contralateral force-matching task in which able-bodied participants were asked to generate grasp forces with their native hand, and then match it using the contralateral hand or a soft-synergy prosthetic hand worn on the contralateral arm that was coupled with a mechanotactile feedback device. We found that absolute matching error and matching time were greater when using the prosthetic system than the native hand. However, with contralateral specific training, subjects were able to produce similar relative matching error with the prosthetic system and the native hand, especially at the untrained force level. These findings suggest that an association can be established between the perception produced by the prosthetic limb and the contralateral intact limb, and provide novel insights about potential applications to training and design of the closed-loop prosthesis.

A Physics-based Virtual Reality Environment to Quantify Functional Performance of Upper-limb Prostheses.

Usability of upper-limb prostheses remains to be a challenge due to the complexity of hand-object interactions in activities of daily living. Functional evaluation is critical for the optimization of prosthesis performance during device design and parameter tuning phase. Therefore, we implemented a low-cost physics-based virtual reality environment (VRE) capable of simulating wide range of object grasping and manipulation tasks to enable human-in-the-loop optimization. Importantly, our novel VRE can assess user performance quantitatively using movement kinematics and interaction forces. We present a preliminary experiment to validate our VRE. Four able-bodied subjects performed object transfer tasks with a simulated myoelectric one DoF soft-synergy prosthetic hand, while wearing braces to restrain different levels of wrist motion. We found that the task completion time was similar across conditions, however limited wrist pronation led to more shoulder compensatory motion whereas challenging object orientation caused more torso compensatory motion.

On the Role of Physical Interaction on Performance of Object Manipulation by Dyads.

Human physical interactions can be intrapersonal, e.g., manipulating an object bimanually, or interpersonal, e.g., transporting an object with another person. In both cases, one or two agents are required to coordinate their limbs to attain the task goal. We investigated the physical coordination of two hands during an object-balancing task performed either bimanually by one agent or jointly by two agents. The task consisted of a series of static (holding) and dynamic (moving) phases, initiated by auditory cues. We found that task performance of dyads was not affected by different pairings of dominant and non-dominant hands. However, the spatial configuration of the two agents (side-by-side vs. face-to-face) appears to play an important role, such that dyads performed better side-by-side than face-to-face. Furthermore, we demonstrated that only individuals with worse solo performance can benefit from interpersonal coordination through physical couplings, whereas the better individuals do not. The present work extends ongoing investigations on human-human physical interactions by providing new insights about factors that influence dyadic performance. Our findings could potentially impact several areas, including robotic-assisted therapies, sensorimotor learning and human performance augmentation.

Genome-wide identification of Hami melon miRNAs with putative roles during fruit development.

MicroRNAs represent a family of small endogenous, non-coding RNAs that play critical regulatory roles in plant growth, development, and environmental stress responses. Hami melon is famous for its attractive flavor and excellent nutritional value, however, the mechanisms underlying the fruit development and ripening remains largely unknown. Here, we performed small RNA sequencing to investigate the roles of miRNAs during Hami melon fruit development. Two batches of flesh samples were collected at four fruit development stages. Small RNA sequencing yielded a total of 54,553,424 raw reads from eight libraries. 113 conserved miRNAs belonging to 30 miRNA families and nine novel miRNAs comprising nine miRNA families were identified. The expression of 42 conserved miRNAs and three Hami melon-specific miRNAs significantly changed during fruit development. Furthermore, 484 and 124 melon genes were predicted as putative targets of 29 conserved and nine Hami melon-specific miRNA families, respectively. GO enrichment analysis were performed on target genes, "transcription, DNA-dependent", "rRNA processing", "oxidation reduction", "signal transduction", "regulation of transcription, DNA-dependent", and "metabolic process" were the over-represented biological process terms. Cleavage sites of six target genes were validated using 5' RACE. Our results present a comprehensive set of identification and characterization of Hami melon fruit miRNAs and their potential targets, which provide valuable basis towards understanding the regulatory mechanisms in programmed process of normal Hami fruit development and ripening. Specific miRNAs could be selected for further research and applications in breeding practices.

Improving Fine Control of Grasping Force during Hand-Object Interactions for a Soft Synergy-Inspired Myoelectric Prosthetic Hand.

The concept of postural synergies of the human hand has been shown to potentially reduce complexity in the neuromuscular control of grasping. By merging this concept with soft robotics approaches, a multi degrees of freedom soft-synergy prosthetic hand [SoftHand-Pro (SHP)] was created. The mechanical innovation of the SHP enables adaptive and robust functional grasps with simple and intuitive myoelectric control from only two surface electromyogram (sEMG) channels. However, the current myoelectric controller has very limited capability for fine control of grasp forces. We addressed this challenge by designing a hybrid-gain myoelectric controller that switches control gains based on the sensorimotor state of the SHP. This controller was tested against a conventional single-gain (SG) controller, as well as against native hand in able-bodied subjects. We used the following tasks to evaluate the performance of grasp force control: (1) pick and place objects with different size, weight, and fragility levels using power or precision grasp and (2) squeezing objects with different stiffness. Sensory feedback of the grasp forces was provided to the user through a non-invasive, mechanotactile haptic feedback device mounted on the upper arm. We demonstrated that the novel hybrid controller enabled superior task completion speed and fine force control over SG controller in object pick-and-place tasks. We also found that the performance of the hybrid controller qualitatively agrees with the performance of native human hands.

Transcriptome profiling of Cucumis melo fruit development and ripening.

Hami melon (Cucumis melo) is the most important melon crop grown in the north-western provinces of China. In order to elucidate the genetic and molecular basis of developmental changes related to size, flesh, sugar and sour content, we performed a transcriptome profiling of its fruit development. Over 155 000 000 clean reads were mapped to MELONOMICS genome, yielding a total of 23 299 expressed genes. Of these, 554 genes were specifically expressed in flowers, and 3260 genes in fruit flesh tissues. The 7892 differentially expressed genes (DEGs) were related to fruit development and mediated diverse metabolic processes and pathways; 83 DEGs and 13 DEGs were possibly associated with sucrose and citric acid accumulation, respectively. The quantitative real-time PCR results showed that six out of eight selected candidate genes displayed expression trends similar to our DEGs. This study profiled the gene expression related to different growing stages of flower and fruit at the whole transcriptome level to provide an insight into the regulatory mechanism underlying Hami melon fruit development.