Timing of transcranial direct current stimulation at M1 does not affect motor sequence learning.

Administering anodal transcranial direct current stimulation (tDCS) at the primary motor cortex (M1) at various temporal loci relative to motor training is reported to affect subsequent performance gains. Stimulation administered in conjunction with motor training appears to offer the most robust benefit that emerges during offline epochs. This conclusion is made, however, based on between-experiment comparisons that involved varied methodologies. The present experiment addressed this shortcoming by administering the same 15-minute dose of anodal tDCS at M1 before, during, or after practice of a serial reaction time task (SRTT). It was anticipated that exogenous stimulation during practice with a novel SRTT would facilitate offline gains. Ninety participants were randomly assigned to one of four groups: tDCS before practice, tDCS during practice, tDCS after practice, or no tDCS. Each participant was exposed to 15 min of 2 mA of tDCS and motor training of an eight-element SRTT. The anode was placed at the right M1 with the cathode at the left M1, and the left hand was used to execute the SRTT. Test blocks were administered 1 and 24 h after practice concluded. The results revealed significant offline gain for all conditions at the 1-hour and 24-hour test blocks. Importantly, exposure to anodal tDCS at M1 at any point before, during, or after motor training failed to change the trajectory of skill development as compared to the no-stimulation control condition. These data add to the growing body of evidence questioning the efficacy of a single bout of exogenous stimulation as an adjunct to motor training for fostering skill learning.

Memory consolidation of sequence learning and dynamic adaptation during wakefulness.

Motor learning involves acquiring new movement sequences and adapting motor commands to novel conditions. Labile motor memories, acquired through sequence learning and dynamic adaptation, undergo a consolidation process during wakefulness after initial training. This process stabilizes the new memories, leading to long-term memory formation. However, it remains unclear if the consolidation processes underlying sequence learning and dynamic adaptation are independent and if distinct neural regions underpin memory consolidation associated with sequence learning and dynamic adaptation. Here, we first demonstrated that the initially labile memories formed during sequence learning and dynamic adaptation were stabilized against interference through time-dependent consolidation processes occurring during wakefulness. Furthermore, we found that sequence learning memory was not disrupted when immediately followed by dynamic adaptation and vice versa, indicating distinct mechanisms for sequence learning and dynamic adaptation consolidation. Finally, by applying patterned transcranial magnetic stimulation to selectively disrupt the activity in the primary motor (M1) or sensory (S1) cortices immediately after sequence learning or dynamic adaptation, we found that sequence learning consolidation depended on M1 but not S1, while dynamic adaptation consolidation relied on S1 but not M1. For the first time in a single experimental framework, this study revealed distinct neural underpinnings for sequence learning and dynamic adaptation consolidation during wakefulness, with significant implications for motor skill enhancement and rehabilitation.

Effects of transcranial direct current stimulation over human motor cortex on cognitive-motor and sensory-motor functions.

The primary motor cortex (M1) is broadly acknowledged for its crucial role in executing voluntary movements. Yet, its contributions to cognitive and sensory functions remain largely unexplored. Transcranial direct current stimulation (tDCS) is a noninvasive neurostimulation method that can modify brain activity, thereby enabling the establishment of a causal link between M1 activity and behavior. This study aimed to investigate the online effects of tDCS over M1 on cognitive-motor and sensory-motor functions. Sixty-four healthy participants underwent either anodal or sham tDCS while concurrently performing a set of standardized robotic tasks. These tasks provided sensitive and objective assessments of brain functions, including action selection, inhibitory control, cognitive control of visuomotor skills, proprioceptive sense, and bimanual coordination. Our results revealed that anodal tDCS applied to M1 enhances decision-making capacity in selecting appropriate motor actions and avoiding distractors compared to sham stimulation, suggesting improved action selection and inhibitory control capabilities. Furthermore, anodal tDCS reduces the movement time required to accomplish bimanual movements, suggesting enhanced bimanual performance. However, we found no impact of anodal tDCS on cognitive control of visuomotor skills and proprioceptive sense. This study suggests that augmenting M1 activity via anodal tDCS influences cognitive-motor and sensory-motor functions in a task-dependent manner.

C3 in the 10-20 system may not be the best target for the motor hand area.

The C3 region in the international 10-20 system for electroencephalography (EEG) recording is assumed to represent the right motor hand area. Therefore, in the absence of transcranial magnetic stimulation (TMS) or a neuronavigational system, neuromodulation methods, such as transcranial direct current stimulation, target C3 or C4, based on the international 10-20 system, to influence the cortical excitability of the right and left hand, respectively. The purpose of this study is to compare the peak-to-peak motor evoked potential (MEP) amplitudes of the right first dorsal interosseus (FDI) muscle after single-pulse TMS at C3 and C1 in the 10-20 system and at the region between C3 and C1 (i.e., C3h in the 10-5 system). Using an intensity of 110% of the resting motor threshold, 15 individual MEPs from each of C3, C3h, C1, and hotspots were randomly recorded from FDI for sixteen right-handed undergraduate students. Average MEPs were greatest at C3h and C1, with both being larger than those recorded at C3. These data are congruent with recent findings using topographic analysis of individual MRIs that revealed poor correspondence between C3/C4 and the respective hand knob. Implications for the use of scalp locations determined using the 10-20 system for localizing the hand area are highlighted.

Integrated crop-livestock systems result in less nitrate leaching than ungrazed crop systems in North Florida.

Integrated crop-livestock systems provide an array of benefits to agricultural systems, including a reduction in nitrogen (N) leaching. A farm approach to integrate crops and livestock is the adoption of grazed cover crops. Moreover, the addition of perennial grasses into crop rotations may improve soil organic matter and decrease N leaching. However, the effect of grazing intensity in such systems is not fully understood. This 3-year study investigated short-term effects of cover crop planting (cover and no cover), cropping system (no grazing, integrated crop-livestock [ICL], and sod-based rotation [SBR]), grazing intensity (heavy, moderate, and light grazing), and cool-season N fertilization (0, 34, and 90 kg N ha-1 ) on NO3 -N and NH4 -N concentration in leachate, and cumulative N leaching by using 1.5-m deep drain gauges. The ICL was a cool-season cover crop-cotton (Gossypium hirsutum L.) rotation, whereas SBR was a cool-season cover crop-bahiagrass (Paspalum notatum Flüggé) rotation. There was a treatment × year × season for cumulative N leaching (p = 0.035). Further contrast analysis indicated that cover crops decreased cumulative N leaching compared to no cover (18 vs. 32 kg N ha-1 season-1 ). Nitrogen leaching was lesser for grazed compared to nongrazed systems (14 vs. 30 kg N ha-1 season-1 ). Treatments containing bahiagrass had lesser NO3 -N concentration in leachate (7 vs. 11 mg L-1 ) and cumulative N leaching (8 vs. 20 kg N ha-1 season-1 ) compared to ICL systems. Adding cover crops can reduce cumulative N leaching in crop-livestock systems; moreover, warm-season perennial forages can further enhance this benefit.

Effects of Grass-Based Crop Rotation, Nematicide, and Irrigation on the Nematode Community in Cotton.

Plant-parasitic and free-living nematodes - bacterivores, fungivores, omnivores, predators - comprise the nematode community. Nematicide application and crop rotation are important tools to manage plant-parasitic nematodes, but effects on free-living nematodes and nematode ecological indices need further study. The nematicide fluopyram was recently introduced in cotton (Gossypium hirsutum) production and its effects on the nematode community need assessment. This research was conducted in 2017 and 2018 at a long-term field site in Quincy, FL where perennial grass/sod-based (bahiagrass, Paspalum notatum) and conventional cotton rotations were established in 2000. The objective of this research was to evaluate the effects of fluopyram nematicide, crop rotation phase, and irrigation on free-living nematodes and nematode ecological indices based on three soil sampling dates each season. We did not observe consistent effects of crop rotation phase on free-living nematodes or nematode ecological indices. Only omnivores were consistently negatively impacted by fluopyram. Nematode ecological indices reflected this negative effect by exhibiting a degraded/ stressed environmental condition relative to untreated plots. Free-living nematodes were not negatively impacted by nematicide when sod-based rotation was used.

Genomic regions associated with resistance to soybean rust (Phakopsora pachyrhizi) under field conditions in soybean germplasm accessions from Japan, Indonesia and Vietnam.

KEY MESSAGE: Eight soybean genomic regions, including six never before reported, were found to be associated with resistance to soybean rust (Phakopsora pachyrhizi) in the southeastern USA. Soybean rust caused by Phakopsora pachyrhizi is one of the most important foliar diseases of soybean [Glycine max (L.) Merr.]. Although seven Rpp resistance gene loci have been reported, extensive pathotype variation in and among fungal populations increases the importance of identifying additional genes and loci associated with rust resistance. One hundred and ninety-one soybean plant introductions from Japan, Indonesia and Vietnam, and 65 plant introductions from other countries were screened for resistance to P. pachyrhizi under field conditions in the southeastern USA between 2008 and 2015. The results indicated that 84, 69, and 49% of the accessions from southern Japan, Vietnam or central Indonesia, respectively, had negative BLUP values, indicating less disease than the panel mean. A genome-wide association analysis using SoySNP50K Infinium BeadChip data identified eight genomic regions on seven chromosomes associated with SBR resistance, including previously unreported regions of Chromosomes 1, 4, 6, 9, 13, and 15, in addition to the locations of the Rpp3 and Rpp6 loci. The six unreported genomic regions might contain novel Rpp loci. The identification of additional sources of rust resistance and associated genomic regions will further efforts to develop soybean cultivars with broad and durable resistance to soybean rust in the southern USA.

Differences in motor unit recruitment patterns and low frequency oscillation of discharge rates between unilateral and bilateral isometric muscle contractions.

INTRODUCTION: Distinct cortical activities contribute to unilateral and bilateral motor control. However, it remains largely unknown whether the behavior of motor neurons differs between unilateral and bilateral isometric force generation. Here, we first investigated motor units (MUs) recruitment patterns during unilateral and bilateral force generation. Considering that the force control is primarily regulated by low-frequency synaptic inputs to motor neurons, we also examined the relation between MU discharge rate and force output during unilateral and bilateral muscle contractions. METHODS: Using advanced electromyography (EMG) sensor arrays and spike-triggered averaging techniques, we examined a large population of MUs in the right first dorsal interosseous (FDI) muscle during unilateral and bilateral force tracking tasks. Using the principal component analysis, we analyzed the first common component (FCC) of MU discharge rate to describe the force fluctuations during unilateral and bilateral contractions. RESULTS: We found that MU discharge rate decreased during bilateral compared with unilateral contractions. MU recruitment threshold increased, while the amplitude and duration of MU action potential (MUAP) remained unchanged during bilateral compared with unilateral contractions. We found that the coefficients of variation (CV) for the force and FCC signal increased during bilateral compared with unilateral contractions. Notably, the FCC signal captured a great amount of MU discharge variability, and its CV correlated with the CV of the force signal. CONCLUSION: Our findings suggest that MU recruitment patterns are altered during bilateral compared with unilateral isometric force generation, likely related to changes at the low-frequency portion of the synaptic drive.

The decay and consolidation of effector-independent motor memories.

Learning a motor adaptation task produces intrinsically unstable or transient motor memories. Despite the presence of effector-independent motor memories following the learning of novel environmental dynamics, it remains largely unknown how those memory traces decay in different contexts and whether an "offline" consolidation period protects memories against decay. Here, we exploit inter-effector transfer to address these questions. We found that newly acquired motor memories formed with one effector could be partially retrieved by the untrained effector to enhance its performance when the decay occurred with the passage of time or "washout" trials on which error feedback was provided. The decay of motor memories was slower following "error-free" trials, on which errors were artificially clamped to zero or removed, compared with "washout" trials. However, effector-independent memory components were abolished following movements made in the absence of task errors, resulting in no transfer gains. The brain can stabilize motor memories during daytime wakefulness. We found that 6 h of wakeful resting increased the resistance of effector-independent memories to decay. Collectively, our results suggest that the decay of effector-independent motor memories is context-dependent, and offline processing preserves those memories against decay, leading to improvements of the subsequent inter-effector transfer.

A multi-representation approach to the contextual interference effect: effects of sequence length and practice.

The present study investigated the long-term benefit of Random-Practice (RP) over Blocked-Practice (BP) within the contextual interference (CI) effect for motor learning. We addressed the extent to which motor sequence length and practice amount factors moderate the CI effect given that previous reports, often in applied research, have reported no long-term advantage from RP. Based on predictions arising from the Cognitive framework of Sequential Motor Behavior (C-SMB) and using the Discrete Sequence Production (DSP) task, two experiments were conducted to compare limited and extended practice amounts of 4- and 7-key sequences under RP and BP schedules. Twenty-four-hour delayed retention performance confirmed the C-SMB prediction that the CI-effect occurs only with short sequences that receive little practice. The benefit of RP with limited practice was associated with overnight motor memory consolidation. Further testing with single-stimulus as well as novel and unstructured (i.e., random) sequences indicated that limited practice under RP schedules enhances both reaction and chunking modes of sequence execution with the latter mode benefitting from the development of implicit and explicit forms of sequence representation. In the case of 7-key sequences, extended practice with RP and BP schedules provided for equivalent development of sequence representations. Higher explicit awareness of sequence structures was associated with faster completion of practiced but also of novel and unstructured sequences.

Exercising the Sleepy-ing Brain: Exercise, Sleep, and Sleep Loss on Memory.

We examine the novel hypothesis that physical exercise and sleep have synergistic effects on memory. Exercise can trigger mechanisms that can create an optimal brain state during sleep to facilitate memory processing. The possibility that exercise could counteract the deleterious effects of sleep deprivation on memory by protecting neuroplasticity also is discussed.

The Interactions Between Primary Somatosensory and Motor Cortex during Human Grasping Behaviors.

Afferent inputs to the primary somatosensory cortex (S1) are differentially processed during precision and power grip in humans. However, it remains unclear how S1 interacts with the primary motor cortex (M1) during these two grasping behaviors. To address this question, we measured short-latency afferent inhibition (SAI), reflecting S1-M1 interactions via thalamo-cortical pathways, using paired-pulse transcranial magnetic stimulation (TMS) during precision and power grip. The TMS coil over the hand representation of M1 was oriented in the posterior-anterior (PA) and anterior-posterior (AP) direction to activate distinct sets of corticospinal neurons. We found that SAI increased during precision compared with power grip when AP, but not PA, currents were applied. Notably, SAI tested in the AP direction were similar during two-digit than five-digit precision grip. The M1 receives movement information from S1 through direct cortico-cortical pathways, so intra-hemispheric S1-M1 interactions using dual-site TMS were also evaluated. Stimulation of S1 attenuated M1 excitability (S1-M1 inhibition) during precision and power grip, while the S1-M1 inhibition ratio remained similar across tasks. Taken together,our findings suggest that distinct neural mechanisms for S1-M1 interactions mediate precision and power grip, presumably by modulating neural activity along thalamo-cortical pathways.

Improving online and offline gain from repetitive practice using anodal tDCS at dorsal premotor cortex.

Administering anodal transcranial direct current stimulation at the left dorsal premotor cortex (PMd) but not right PMd throughout the repetitive practice of three novel motor sequences resulted in improved offline performance usually only observed after interleaved practice. This gain only emerged following overnight sleep. These data are consistent with the proposed proprietary role of left PMd for motor sequence learning and the more recent claim that PMd is central to sleep-related consolidation of novel skill memory.

Exposure to Sleep, Rest, or Exercise Impacts Skill Memory Consolidation but so Too Can a Challenging Practice Schedule.

When discussing procedural learning, it is now routine to consider both online and offline influences for skill acquisition. This is because it is commonly assumed that the evolution of a novel skill memory continues well after practice is over. Indeed, factors impacting offline contributions to skill memory development such as sleep and exercise have garnered considerable research interest in recent years. This is partly because of their capacity to foster postpractice consolidation, a process that has been identified as critical to moving a skill memory from a labile to more stable or elaborate form. While uncovering the potency of non-practice factors to facilitate consolidation is undoubtedly important, the present opinion is designed to remind the reader that a practice schedule, organized to challenge the learner, can, in and of itself, be effective in supporting consolidation resulting in significant gains in long-term skill retention.

Prefrontal Cortex Activation During Motor Sequence Learning Under Interleaved and Repetitive Practice: A Two-Channel Near-Infrared Spectroscopy Study.

Training under high interference conditions through interleaved practice (IP) results in performance suppression during training but enhances long-term performance relative to repetitive practice (RP) involving low interference. Previous neuroimaging work addressing this contextual interference effect of motor learning has relied heavily on the blood-oxygen-level-dependent (BOLD) response using functional magnetic resonance imaging (fMRI) methodology resulting in mixed reports of prefrontal cortex (PFC) recruitment under IP and RP conditions. We sought to clarify these equivocal findings by imaging bilateral PFC recruitment using functional near-infrared spectroscopy (fNIRS) while discrete key pressing sequences were trained under IP and RP schedules and subsequently tested following a 24-h delay. An advantage of fNIRS over the fMRI BOLD response is that the former measures oxygenated and deoxygenated hemoglobin changes independently allowing for assessment of cortical hemodynamics even when there is neurovascular decoupling. Despite slower sequence performance durations under IP, bilateral PFC oxygenated and deoxygenated hemoglobin values did not differ between practice conditions. During test, however, slower performance from those previously trained under RP coincided with hemispheric asymmetry in PFC recruitment. Specifically, following RP, test deoxygenated hemoglobin values were significantly lower in the right PFC. The present findings contrast with previous behavioral demonstrations of increased cognitive demand under IP to illustrate a more complex involvement of the PFC in the contextual interference effect. IP and RP incur similar levels of bilateral PFC recruitment, but the processes underlying the recruitment are dissimilar. PFC recruitment during IP supports action reconstruction and memory elaboration while RP relies on PFC recruitment to maintain task variation information in working memory from trial to trial. While PFC recruitment under RP serves to enhance immediate performance, it does not support long-term performance.

Peanut disease epidemiology under dynamic microclimate conditions and management practices in North Florida.

Diverse field characteristics, weather patterns, and management practices can result in variable microclimates. The objective was to relate in-field microclimate conditions with peanut diseases and yield and determine the effect of irrigation and fungicides within these environments. Irrigation did not have a major impact on disease and yield. Stem rot (Athelia rolfsii) and early (Passalora arachidicola) and late (Nothopassalora personata) leaf spot were most affected by changes in environmental patterns across seasons. Average non-treated stem rot was 12.9% in 2017 which dropped considerably in 2018 to 0.2% but emerged again in 2019 to 3.2%. Stem rot incidence varied across the field, and the response to fungicides depended on management zone. Leaf spot defoliation in non-treated plots was severe in 2019 reaching an average of 73% at 126 days after planting but only reached 15% in 2017 and 35% in 2019 at the same stage. A low-input fungicide schedule was able to reduce foliar disease in all zones and seasons, but the microclimatic conditions in the low-lying area favored leaf spot in 2017 and 2018 although not in the dryer 2019 season. Seasonal differences in disease and plant growth affected the level of protection against average yield loss using a standard low-input program which in 2017 (527 kg/ha) was not as great as 2018 (2,235 kg/ha) or 2019 (1,763 kg/ha). Disease prediction models built on dynamic environmental factors in the context of multiple pathogens and natural field conditions could be developed to improve within-season management decisions for more efficient fungicide inputs.

Improving consolidation by applying anodal transcranial direct current stimulation at primary motor cortex during repetitive practice.

Engagement of primary motor cortex (M1) is important for successful consolidation of motor skills. Recruitment of M1 has been reported to be more extensive during interleaved compared to repetitive practice and this differential recruitment has been proposed to contribute to the long-term retention benefit associated with interleaved practice. The present study administered anodal direct current stimulation (tDCS) during repetitive practice in an attempt to increase M1 activity throughout repetitive practice with the goal to improve the retention performance of individuals exposed to this training format. Fifty-four participants were assigned to one of three experimental groups that included: interleaved-sham, repetitive-sham, and repetitive-anodal tDCS. Real or sham stimulation at M1 was administered during practice of three motor sequences for approximately 20-min. Performance in the absence of any stimulation was evaluated prior to practice, immediately after practice as well as at 6-hr, and 24-h after practice was complete. As expected, for the sham conditions, interleaved as opposed repetitive practice resulted in superior offline gain. This was manifest as more rapid stabilization of performance after 6-h as well as an enhancement in performance with a period of overnight sleep. Administration of anodal stimulation at M1 during repetitive practice improved offline gains assessed at both 6-h and 24-h tests compared to the repetitive practice sham group. These data are consistent with the claims that reduced activation at M1 during repetitive practice impedes offline gain relative to interleaved practice and that M1 plays an important role in early consolidation of novel motor skills even in the context of the simultaneous acquisition of multiple new skills. Moreover, these findings highlight a possible role for M1 during sleep-related consolidation, possibly as part of a network including the dorsal premotor region, which supports delayed performance enhancement.

Improvement in trunk kinematics after treadmill-based reactive balance training among older adults is strongly associated with trunk kinematics before training.

Reactive balance training (RBT) is an emerging fall prevention exercise intervention for older adults. To better understand factors that influence improvements after RBT, the goal of this study was to identify key factors that strongly associate with training-induced improvements in reactive balance. This study is a secondary analysis of data from a prior study. Twenty-eight residents of senior housing facilities participated, including 14 RBT participants and 14 Tai Chi participants (controls). Before and one week after training, participants completed balance and mobility tests and a reactive balance test. Reactive balance was operationalized as the maximum trunk angle in response to standardized trip-like perturbations on a treadmill. Bivariate (Pearson) correlation was used to identify participant characteristics before RBT and measures of performance during RBT that associated with training-induced changes in maximum trunk angle. Maximum trunk angle before reactive balance training exhibited the strongest association with training-induced changes in maximum trunk angle among RBT participants (r2 = 0.84; p < .001), but not among Tai Chi participants (r2 = 0.17; p = .138). Measures of performance during RBT, based upon perturbation speed, also associated with RBT-induced improvements in maximum trunk angle. These results help clarify the characteristics of individuals who can benefit from RBT, and support the use of treadmill perturbation speed as a surrogate measure of training-induced improvements in trunk kinematics.

Sixty-One Years Following Registration, Phorate Applied In-Furrow at Planting Suppresses Development of Late Leaf Spot on Peanut.

Late and early leaf spot are caused by Nothopassalora personata and Passalora arachidicola, respectively, and are damaging diseases of peanut (Arachis hypogaea L.) capable of defoliation and yield loss. Management of these diseases is most effective through the integration of tactics that reduce starting inoculum and prevent infection. The insecticide phorate was first registered in 1959 and has been used in peanut production for decades in-furrow at planting to suppress thrips. Phorate further provides significant suppression of Tomato spotted wilt virus infection beyond suppression of its thrips vector alone by activating defense-related responses in the peanut plant. From six experiments conducted from 2017 to 2019 in Blackville, SC, Reddick, FL, and Quincy, FL, significantly less leaf spot defoliation was exhibited on peanuts treated with phorate in-furrow at planting (26%) compared with nontreated checks (48%). In-season fungicides were excluded from five of the experiments, whereas the 2018 Quincy, FL, experiment included eight applications on a 15-day interval. Across individual experiments, significant suppression of defoliation caused by late leaf spot was observed from 64 to 147 days after planting. Although more variable within location-years, pod yield following phorate treatment was overall significantly greater than for nontreated peanut (2,330 compared with 2,030 kg/ha; P = 0.0794). The consistent defoliation suppression potential was estimated to confer an average potential net economic yield savings of $90 to $120 per hectare under analogous leaf spot defoliation. To our knowledge, these are the first data in the 61 years since its registration demonstrating significant suppression of leaf spot on peanut following application of phorate in-furrow at planting. Results support phorate use in peanut as an effective and economical tactic to incorporate to manage late and early leaf spot infections and development of fungicide resistance.