Fractal Dimension Studies of the Brain Shape in Aging and Neurodegenerative Diseases

The fractal dimension is a morphometric measure that has been used to investigate the changes of brain shape complexity in aging and neurodegenerative diseases. This chapter reviews fractal dimension studies in aging and neurodegenerative disorders in the literature. Research has shown that the fractal dimension of the left cerebral hemisphere increases until adolescence and then decreases with aging, while the fractal dimension of the right hemisphere continues to increase until adulthood. Studies in neurodegenerative diseases demonstrated a decline in the fractal dimension of the gray matter and white matter in Alzheimer's disease, amyotrophic lateral sclerosis, and spinocerebellar ataxia. In multiple sclerosis, the white matter fractal dimension decreases, but conversely, the fractal dimension of the gray matter increases at specific stages of disease. There is also a decline in the gray matter fractal dimension in frontotemporal dementia and multiple system atrophy of the cerebellar type and in the white matter fractal dimension in epilepsy and stroke. Region-specific changes in fractal dimension have also been found in Huntington's disease and Parkinson's disease. Associations were found between the fractal dimension and clinical scores, showing the potential of the fractal dimension as a marker to monitor brain shape changes in normal or pathological processes and predict cognitive or motor function.

Motor Control Changes after Utilizing Upper Extremity Myoelectric Powered Wearable Orthotics in Persons with Acute SCI

Following spinal cord injury (SCI), upper extremity (UE) weakness may impede one's ability to carry out activities of daily living (ADLs). Such a limitation drastically lowers a person's level of independence. Additionally, therapy and the field of assistive technology continue to place a strong premium on the restoration of UE motor function in patients with SCI. The main objective of this study was to assess the benefits of an UE myoelectric-powered wearable orthosis (MPWO) produced by MyoMo, Inc. (Boston, MA) on improving UE motor function in order to enhance ADLs and quality of life in individuals with subacute SCI. A 43-year-old man with subacute incomplete SCI (iSCI), American Spinal Injury Association (ASIA) Impairment Scale (AIS) C grade received 18 sessions (over a period of six weeks) of UE mobility therapy utilizing the MPWO. The MPWO was used to enhance active range of motion (AROM) of the hand and elbow, and associated muscle activations. After training with the MPWO, hand and elbow AROM and muscle activations were enhanced. These preliminary findings imply that UE-MPWO device-assisted rehabilitation may increase participants' UE activities, leading to improved function.Clinical Relevance- These preliminary findings from a person with iSCI in the subacute phase indicate that training with UE-MPWO assistive devices may enhance UE use during ADLs for people with muscle weakness but still having some residual voluntary muscle activation ability.

Combination of GWAS and FST-based approaches identified loci associated with economic traits in sugarcane

Sugarcane is a globally important plant for both sugar and biofuel production. Although conventional breeding has played an important role in increasing the productivity of sugarcane, it takes a long time to achieve breeding goals such as high yield and resistant to diseases. Molecular breeding, including marker-assisted breeding and genomic selection, can accelerate genetic improvement by selecting elites at the seedling stage with DNA markers. However, only a few DNA markers associated with important traits were identified in sugarcane. The purpose of this study was to identify DNA markers associated with sugar content, stalk diameter, and sugarcane top borer resistance. The sugarcane samples with trait records were genotyped using the restriction site-associated DNA sequencing (RADseq) technology. Using F_ST analysis and genome-wide association study (GWAS), a total of 9, 23 and 9 DNA variants (single nucleotide polymorphisms (SNPs)/insertions and deletions (indels)) were associated with sugar content, stalk diameter, and sugarcane top borer resistance, respectively. The identified genetic variants were on different chromosomes, suggesting that these traits are complex and determined by multiple genetic factors. These DNA markers identified by both approaches have the potential to be used in selecting elite clones at the seeding stage in our sugarcane breeding program to accelerate genetic improvement. Certainly, it is essential to verify the reliability of the identified DNA markers associated with traits before they are used in molecular breeding in other populations.

Bilateral transfer of motor performance as a function of motor imagery training: a systematic review and meta-analysis

Objective

The objective of this review was to evaluate the efficacy of mental imagery training (MIT) in promoting bilateral transfer (BT) of motor performance for healthy subjects.

Data sources

We searched 6 online-databases (Jul-Dec 2022) using terms: "mental practice," "motor imagery training," "motor imagery practice," "mental training," "movement imagery," "cognitive training," "bilateral transfer," "interlimb transfer," "cross education," "motor learning," "strength," "force" and "motor performance."

Study selection and data extraction

We selected randomized-controlled studies that examined the effect of MIT on BT. Two reviewers independently determined if each study met the inclusion criteria for the review. Disagreements were resolved through discussion and, if necessary, by a third reviewer. A total of 9 articles out of 728 initially identified studies were chosen for the meta-analysis.

Data synthesis

The meta-analysis included 14 studies for the comparison between MIT and no-exercise control (CTR) and 15 studies for the comparison between MIT and physical training (PT).

Results

MIT showed significant benefit in inducing BT compared to CTR (ES = 0.78, 95% CI = 0.57-0.98). The effect of MIT on BT was similar to that of PT (ES = -0.02, 95% CI = -0.15-0.17). Subgroup analyses showed that internal MIT (IMIT) was more effective (ES = 2.17, 95% CI = 1.57-2.76) than external MIT (EMIT) (ES = 0.95, 95% CI = 0.74-1.17), and mixed-task (ES = 1.68, 95% CI = 1.26-2.11) was more effective than mirror-task (ES = 0.46, 95% CI = 0.14-0.78) and normal-task (ES = 0.56, 95% CI = 0.23-0.90). No significant difference was found between transfer from dominant limb (DL) to non-dominant limb (NDL) (ES = 0.67, 95% CI = 0.37-0.97) and NDL to DL (ES = 0.87, 95% CI = 0.59-1.15).

Conclusion

This review concludes that MIT can serve as a valuable alternative or supplement to PT in facilitating BT effects. Notably, IMIT is preferable to EMIT, and interventions incorporating tasks that have access to both intrinsic and extrinsic coordinates (mixed-task) are preferred over those that involve only one of the two coordinates (mirror-task or normal-task). These findings have implications for rehabilitation of patients such as stroke survivors.

Aging-induced alterations in EEG spectral power associated with graded force motor tasks

BACKGROUND

It has been demonstrated that in young and healthy individuals, there is a strong association between the amplitude of EEG-derived motor activity-related cortical potential or EEG spectral power (ESP) and voluntary muscle force. This association suggests that the motor-related ESP may serve as an index of central nervous system function in controlling voluntary muscle activation Therefore, it may potentially be used as an objective marker to track changes in functional neuroplasticity due to neurological disorders, aging, and following rehabilitation therapies. To this end, the relationship between the band-specific ESP-combined spectral power of EEG oscillatory and aperiodic (noise) components-and voluntary elbow flexion (EF) force has been analyzed in elder and young individuals.

METHODS

20 young (22.6 ± 0.87 year) and 28 elderly (74.79 ± 1.37 year) participants performed EF contractions at 20%, 50%, and 80% of maximum voluntary contraction (MVC) while high-density EEG signals were recorded. Both the absolute and relative ESPs were computed for the EEG frequency bands of interest.

RESULTS

The MVC force generated by the elderly was foreseeably lower than that of the young participants. Compared to young, the elderly cohort's (1) total ESP was significantly lower for the high (80% MVC) force task; (2) relative ESP in beta band was significantly elevated for the low and moderate (20% MVC and 50% MVC) force tasks; (3) absolute ESP failed to have a positive trend with force for EEG frequency bands of interest; and (4) beta-band relative ESP did not exhibit a significant decrease with increasing force levels.

CONCLUSIONS

As opposed to young subjects, the beta-band relative ESP in elderly did not significantly decrease with increasing EF force values. This observation suggests the use of beta-band relative ESP as a potential biomarker for age-related motor control degeneration.

Elderly may benefit more from motor imagery training in gaining muscle strength than young adults: A systematic review and meta-analysis

Objective

The current review was aimed to determine the effectiveness of mental imagery training (MIT) on the enhancement of maximum voluntary muscle contraction (MVC) force for healthy young and old adults.

Data sources

Six electronic databases were searched from July 2021 to March 2022. Search terms included: "motor imagery training," "motor imagery practice," "mental practice," "mental training," "movement imagery," "cognitive training," "strength," "force," "muscle strength," "performance," "enhancement," "improvement," "development," and "healthy adults."

Study selection and data extraction

Randomized controlled trials of MIT in enhancing muscle strength with healthy adults were selected. The decision on whether a study met the inclusion criteria of the review was made by two reviewers independently. Any disagreements between the two reviewers were first resolved by discussion between the two reviewers. If consensus could not be reached, then it would be arbitrated by a third reviewer.

Data synthesis

Twenty-five studies including both internal MIT and external MIT were included in meta-analysis for determining the efficacy of MIT on enhancing muscle strength and 22 internal MIT were used for subgroup analysis for examining dose-response relationship of MIT on MVC.

Results

MIT demonstrated significant benefit on enhancing muscle strength when compared with no exercise, Effect Size (ES), 1.10, 95% confidence interval (CI), 0.89-1.30, favoring MIT, but was inferior to physical training (PT), ES, 0.38, 95% CI, 0.15-0.62, favoring PT. Subgroup analysis demonstrated that MIT was more effective for older adults (ES, 2.17, 95% CI, 1.57-2.76) than young adults (ES, 0.95, 95% CI, 0.74-1.17), p = 0.0002, and for small finger muscles (ES, 1.64, 95% CI, 1.06-2.22) than large upper extremity muscles (ES, 0.86, 95% CI, 0.56-1.16), p = 0.02. No significant difference was found in the comparison of small finger muscles and large lower extremity muscles, p = 0.19 although the ES of the former (ES, 1.64, 95% CI, 1.06-2.22) was greater than that of the later (ES, 1.20, 95%, 0.88-1.52).

Conclusion

This review demonstrates that MIT has better estimated effects on enhancing MVC force compared to no exercise, but is inferior to PT. The combination of MIT and PT is equivalent to PT alone in enhancing muscle strength. The subgroup group analysis further suggests that older adults and small finger muscles may benefit more from MIT than young adults and larger muscles.

Safety and effects of a therapeutic 15 Hz rTMS protocol administered at different suprathreshold intensities in able-bodied individuals

High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) remains a promising strategy for neurorehabilitation. The stimulation intensity (SI) influences the aftereffects observed. Here, we examined whether single sessions of a 15 Hz rTMS protocol, administered at suprathreshold SI, can be safely administered to able-bodied (AB) individuals. Six right-handed men were included in this pilot study. HF-rTMS was delivered over the right M1, in 10 trains of 75 biphasic stimuli at 15 Hz, at 105-120% of the individual resting motor threshold (RMT). To assess safety, electromyography (EMG) was monitored to control for signs of spread of excitation and brief EMG burst (BEB) after stimulation. Additionally, TMS side effects questionnaires and the numeric rating scale (NRS) were administered during each session. We assessed corticospinal excitability (CSE) and motor performance changes with measures of resting (rMEP) and active (aMEP) motor evoked potential and grip strength and box and blocks test (BBT) scores, respectively. Overall, the sessions were tolerated and feasible without any pain development. However, EMG analysis during 15 Hz rTMS administration revealed increased BEB frequency with SI. Statistical models revealed an increase of CSE at rest (rMEP) but not during active muscle contraction (aMEP). No linear relationship was observed between 15 Hz rTMS SI and rMEP increase. No significant changes were highlighted for motor performance measures. Although feasible and tolerable by the AB individuals tested, the results demonstrate that when administered at suprathreshold intensities (≥ 105% RMT) the 15 Hz rTMS protocol reveals signs of persistent excitation, suggesting that safety precautions and close monitoring of participants should be performed when testing such combinations of high-intensity and high-frequency stimulation protocols. The results also give insight into the nonlinear existent relationship between the SI and HF-rTMS effects on CSE.NEW & NOTEWORTHY The results of this pilot study show the effects of a therapeutically promising 15 Hz repetitive transcranial magnetic stimulation (rTMS) protocol, administered at different suprathreshold intensities in able-bodied individuals. Although tolerable and feasible with a neuromodulatory potential, 15 Hz rTMS might result in persistent excitability that needs to be closely monitored if administered at suprathreshold stimulation intensity. These results reaffirm the importance of feasibility studies, especially in translational animal-to-human research.

High-Frequency rTMS Combined with Task-Specific Hand Motor Training Modulates Corticospinal Plasticity in Motor Complete Spinal Cord Injury: A case report

Since its first use in spinal cord injury (SCI) in the early 2000s [1], high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) demonstrated a capacity to modulate corticospinal excitability (CSE) and motor performance. Studies focused on individuals with incomplete SCI. Here, we examined the feasibility of a 15-day therapeutic stimulation protocol combining HF-rTMS with task-specific motor training targeting the weaker hand in an individual with early chronic complete SCI. In this case report, we present evidence of progressive increase of CSE at rest and during muscle activation, and decreased cortical inhibition, associated with a trend toward improvement in pinch function of the weaker hand. These promising findings need to be confirmed in a larger population. Clinical Relevance- These preliminary results are promising and demonstrate the importance of a large number of training session repetitions to induce consistent changes relevant to the recovery after a complete SCI.

Stimulation Parameters Used During Repetitive Transcranial Magnetic Stimulation for Motor Recovery and Corticospinal Excitability Modulation in SCI: A Scoping Review

There is a growing interest in non-invasive stimulation interventions as treatment strategies to improve functional outcomes and recovery after spinal cord injury (SCI). Repetitive transcranial magnetic stimulation (rTMS) is a neuromodulatory intervention which has the potential to reinforce the residual spinal and supraspinal pathways and induce plasticity. Recent reviews have highlighted the therapeutic potential and the beneficial effects of rTMS on motor function, spasticity, and corticospinal excitability modulation in SCI individuals. For this scoping review, we focus on the stimulation parameters used in 20 rTMS protocols. We extracted the rTMS parameters from 16 published rTMS studies involving SCI individuals and were able to infer preliminary associations between specific parameters and the effects observed. Future investigations will need to consider timing, intervention duration and dosage (in terms of number of sessions and number of pulses) that may depend on the stage, the level, and the severity of the injury. There is a need for more real vs. sham rTMS studies, reporting similar designs with sufficient information for replication, to achieve a significant level of evidence regarding the use of rTMS in SCI.

EEG-Based Spectral Analysis Showing Brainwave Changes Related to Modulating Progressive Fatigue During a Prolonged Intermittent Motor Task

Repeatedly performing a submaximal motor task for a prolonged period of time leads to muscle fatigue comprising a central and peripheral component, which demands a gradually increasing effort. However, the brain contribution to the enhancement of effort to cope with progressing fatigue lacks a complete understanding. The intermittent motor tasks (IMTs) closely resemble many activities of daily living (ADL), thus remaining physiologically relevant to study fatigue. The scope of this study is therefore to investigate the EEG-based brain activation patterns in healthy subjects performing IMT until self-perceived exhaustion. Fourteen participants (median age 51.5 years; age range 26−72 years; 6 males) repeated elbow flexion contractions at 40% maximum voluntary contraction by following visual cues displayed on an oscilloscope screen until subjective exhaustion. Each contraction lasted ≈5 s with a 2-s rest between trials. The force, EEG, and surface EMG (from elbow joint muscles) data were simultaneously collected. After preprocessing, we selected a subset of trials at the beginning, middle, and end of the study session representing brain activities germane to mild, moderate, and severe fatigue conditions, respectively, to compare and contrast the changes in the EEG time-frequency (TF) characteristics across the conditions. The outcome of channel- and source-level TF analyses reveals that the theta, alpha, and beta power spectral densities vary in proportion to fatigue levels in cortical motor areas. We observed a statistically significant change in the band-specific spectral power in relation to the graded fatigue from both the steady- and post-contraction EEG data. The findings would enhance our understanding on the etiology and physiology of voluntary motor-action-related fatigue and provide pointers to counteract the perception of muscle weakness and lack of motor endurance associated with ADL. The study outcome would help rationalize why certain patients experience exacerbated fatigue while carrying out mundane tasks, evaluate how clinical conditions such as neurological disorders and cancer treatment alter neural mechanisms underlying fatigue in future studies, and develop therapeutic strategies for restoring the patients' ability to participate in ADL by mitigating the central and muscle fatigue.

Global-local consistency benefits memory-guided tracking of a moving target

INTRODUCTION

Previous findings have demonstrated that several Gestalt principles do facilitate VSTM performance in change detection tasks. However, few studies have investigated the role of and time-course of global-local consistency in motion perception.

METHODS

Participants were required to track a moving target surrounded by three different backgrounds: blank, inconsistent, or consistent. Global-local objects were be bound to move together (covariation). During the PMT, participants had to follow the moving target with their eyes and react as fast as possible when the target had just vanished behind the obstruction or would arrive at a predetermined point of interception. Variable error (VE) and constant error (CE) of estimated time-to-contact (TTC) and gain of smooth pursuit eye movements were calculated in various conditions and analyzed qualitatively.

RESULTS

Experiment 1 established the basic finding that VSTM performance could benefit from global-local consistency. Experiment 2 extended this finding by eye-tracking device. Both in visible phase and in occluded phase, CEs were smaller for the target in a consistent background than for the target in an inconsistent background and for the target in a blank background, with both differences significant (ps < .05). However, the difference in VE among three conditions was not significant. At early stage (100-250 ms), later stage (2750-3000 ms), and termination stage (5750-6000 ms) of smooth pursuit, the velocity gains were higher in the trials with consistent backgrounds than in the trials with inconsistent backgrounds and blank backgrounds (ps < .001). With the exception of 100-250 ms phase, the means did not differ between the inconsistent background and the blank background trials (ps > .1).

CONCLUSIONS

Global-local consistency could be activated within the first few hundred milliseconds to prioritize the deployment of attention and eye movement to component target. Meanwhile, it also removes ambiguity from motion tracking and TTC estimation under some unpredictable conditions, leading to the consistency advantage during smooth-pursuit termination phase. Global-local consistency may act as an important information source to TTC estimation and oculomotor response in PMT.

Ultrasound-guided superficial serratus plane block for persistent post-mastectomy pain: four case reports

BACKGROUND

Persistent post-mastectomy pain (PPMP) is common after surgery. Although multiple modalities have been used to treat this type of pain, including medications, physical therapy, exercise interventions, cognitive-behavioral psychology, psychosocial interventions, and interventional approaches, managing PPMP may be still a challenge for breast cancer survivors. Currently, serratus plane block (SPB) as a novel regional anesthetic technique shows promising results for controlling chronic pain.

METHODS

We report four cases of patients with PPMP that were treated using superficial serratus plane block (SSPB) at our clinic. A retrospective review of effect of pain relief was collected through postprocedure interviews.

RESULTS

We found that two of our patients were successfully treated with SSPB for pain after treatment for breast cancer. The third patient had an intercostobrachial nerve block that produced incomplete pain relief but had adequate pain relief with a SSPB. However, the fourth patient reported no pain relief after SSPB.

CONCLUSION

These cases illustrate that the patients with PPMP could benefit from SSPB. Particularly, we find patients with a subjective sense of "tightness" relating to reconstructive surgeries may be a good candidate for SSPB. Further studies are warranted to evaluate this block for PPMP, as it is low risk and relatively simple to perform.

Altered Modulation of the Movement-Related Beta Desynchronization with Force in Stroke - a Pilot Study

Conventional therapy improves motor recovery after stroke. However, 50% of stroke survivors still suffer from a significant level of long-term upper extremity impairment. Identifying a specific biomarker whose magnitude scales with the level of force could help in the development of more effective, novel, highly targeted rehabilitation therapies such as brain stimulation or neurofeedback. Four chronic stroke participants were enrolled in this pilot study to find such a neural marker using an Independent Component Analysis (ICA)-based source analysis approach, and investigate how it has been affected by the injury. Beta band desynchronization in the ipsilesional primary motor cortex was found to be most robustly scaling with force. This activity modulation with force was found to be significantly reduced, and to plateau at higher force than that of the contralesional (unaffected) side. A rehabilitation therapy that would target such a neuromarker could have the potential to strengthen the brain-to-muscle drive and improve motor learning and recovery.Clinical Relevance- This study identifies a neural marker that scales with motor output and shows how this modulation has been affected by stroke.

The Rehabilitation Effects of Myoelectric Powered Wearable Orthotics on Improving Upper Extremity Function in Persons with SCI

Upper extremity (UE) weakness and/or paralysis following spinal cord injury (SCI) can lead to a limited capacity to perform activities of daily living (ADL). Such disability significantly reduces an individual's level of independence. Further, restoration of UE motor function in people with SCI remains a high priority in rehabilitation and the field of assistive technology. The overall goal of this study was to evaluate the effects of a myoelectric-powered wearable orthosis (MPWO) manufactured by MyoMo, Inc. (Boston, MA) for UE movement assistance on ameliorating UE motor function in order to improve ADL and quality of life in people with SCI. Two male participants with chronic incomplete SCI (iSCI), a 75- and a 31-year-old with AIS D and B, respectively, underwent 18 sessions (over 6 weeks) of UE movement rehabilitation using the MPWO. Handgrip strength, active range of motion (AROM) of the hand, response time to initiate a movement, and muscles activations were examined before and after the rehabilitation training using the MPWO. The response time to initiate UE movements decreased, and handgrip strength and AROM improved after training with the MPWO. These preliminary data suggest that rehabilitation with the use of the UE-MPWO device could enhance the participants' UE activities that led to improved function.Clinical Relevance- These preliminary results from two individuals with iSCI suggest that training with UE-MPWO assistive devices may improve UE utilization during ADL for individuals with muscle weakness or paralysis but still possessing residual voluntary muscle activation capabilities.

Graph-theoretical analysis of EEG functional connectivity during balance perturbation in traumatic brain injury: A pilot study

Traumatic brain injury (TBI) often results in balance impairment, increasing the risk of falls, and the chances of further injuries. However, the underlying neural mechanisms of postural control after TBI are not well understood. To this end, we conducted a pilot study to explore the neural mechanisms of unpredictable balance perturbations in 17 chronic TBI participants and 15 matched healthy controls (HC) using the EEG, MRI, and diffusion tensor imaging (DTI) data. As quantitative measures of the functional integration and segregation of the brain networks during the postural task, we computed the global graph-theoretic network measures (global efficiency and modularity) of brain functional connectivity derived from source-space EEG in different frequency bands. We observed that the TBI group showed a lower balance performance as measured by the center of pressure displacement during the task, and the Berg Balance Scale (BBS). They also showed reduced brain activation and connectivity during the balance task. Furthermore, the decrease in brain network segregation in alpha-band from baseline to task was smaller in TBI than HC. The DTI findings revealed widespread structural damage. In terms of the neural correlates, we observed a distinct role played by different frequency bands: theta-band modularity during the task was negatively correlated with the BBS in the TBI group; lower beta-band network connectivity was associated with the reduction in white matter structural integrity. Our future studies will focus on how postural training will modulate the functional brain networks in TBI.

Altered Cortical and Postural Response to Balance Perturbation in Traumatic Brain Injury - An EEG Pilot Study

30-60% of traumatic brain injury (TBI) patients suffer from long-term balance deficit. Even though motor preparation and execution are altered and slowed in TBI, their relative contribution and importance to posture instability remain poorly understood. This study investigates the impaired cortical dynamics and neuromuscular response in TBI in response to balance perturbation and its relation to balance deficit. 12 TBI and 6 healthy control (HC) participants took the Berg Balance Scale (BBS) test and participated in a balance perturbation task where they were subjected to random anterior/posterior translation, while brain (EEG), muscle (EMG) activities, and center of pressure (COP) were continuously recorded. Using independent component analysis (ICA), the component most responsible for the N1 component of the perturbation evoked potential (PEP) was selected and its amplitude and latency were extracted. Balance task performance was measured by computing the COP displacement during the task. TBI had a significantly lower BBS, larger COP displacement and lower N1 amplitude compared to the HC group. No group differences was found for N1 latency and muscle activity onset delay to the perturbation. BBS was correlated with the COP displacement and N1 amplitude, and COP displacement was correlated with N1 latency. TBI balance deficit may be associated with more impaired than delayed cortical response to balance perturbation.

Effects of Tai Chi Chuan on Inhibitory Control in Elderly Women: An fNIRS Study

Background

Inhibitory control is a sub-ability of executive function and plays an important role in the entire cognitive process. However, declines in inhibitory control during aging significantly impair the quality of life of elderly people. Investigating methods to delay the decline of inhibitory control has become a focal point in current research. Tai Chi Chuan (TCC) is one effective method used to delay cognitive declines in older adults. However, the specific effects of TCC on inhibitory control and the mechanisms through which TCC may improve cognition in older adults have not been comprehensively investigated.

Objective

The study explores possible neurological mechanisms related to the effects of TCC interventions on inhibitory control in older people using a functional near-infrared spectroscopy (fNIRS) technique and reaction times (RTs).

Methods

A total of 26 healthy, elderly people who had not received TCC training completed all study procedures. The subjects were randomized to either the TCC group or the control group. Subjects in the TCC group were taught TCC by a certified instructor and trained for 8 weeks. The control group continued to perform general daily activities. The Flanker task was administered to every participant to evaluate inhibitory control pre- and post-intervention. While participants were performing the Flanker task, fNIRS data were collected.

Results

Post-intervention, significant differences for incongruent flankers were found only for the TCC intervention group. Faster RTs were observed for the incongruent flankers in the TCC group than in the control group (p < 0.05). Analysis of the fNIRS data revealed an increase in oxy-Hb in the prefrontal cortex during the incongruent flankers after the TCC exercise intervention.

Conclusion

The TCC intervention significantly improved inhibitory control in older adults, suggesting that TCC is an effective, suitable exercise for improving executive function and neurological health in elderly people.

Clinical Trial Registration

Chinese Clinical Trial Register, ChiCTR1900028457.

Mobility and Cognitive Improvements Resulted from Overground Robotic Exoskeleton Gait-Training in Persons with MS

Multiple sclerosis (MS) is a non-traumatic, immune-mediated neurodegenerative disease of the central nervous system (CNS), affecting more than 2 million individuals globally and approximately one million in the United States [1], [2]. This autoimmune inflammatory disease of the CNS featuring both neuroinflammatory and neurodegenerative aspects [3], often results in mobility and cognitive impairment. Rehabilitation has been suggested as the best [4], and perhaps, one of few methods for restoring function in MS [5]. The goal of the present investigation is to examine the effects of 4 weeks of supervised, over-ground gait training using a robotic exoskeleton (RE) compared with a control condition (conventional gait therapy, CGT) in persons with MS with ambulatory and cognition disabilities. Four subjects (mean age=50 years, three females) with relapsing-remitting MS (RRMS) participated in this study and completed a total of eight sessions (1-hour/session) gait training in a standard therapy gym either using a RE supervised by an RE training physical therapist (PT) or with the CGT supervised by a PT. Outcome measures (walking speed and temporal-spatial parameters) were measured on a level surface without RE using an instrumented walkway, for both groups, pre- and post-intervention. The two participants in the RE group were also tested in the same testing environment, while wearing a RE pre- and post-intervention. Cognitive processing speed was assessed using the Symbol Digit Modalities Test (SDMT) pre- and post-intervention. Subjects in the RE group tested without a RE increased average walking speed, stride length, and step length with decreased stride width and step time bilaterally after the 8-session of RE training. The two participants in the CGT group only had modest improvements in walking performance. Furthermore, while the CGT group had no improvements in the processing speed (SDMT scores), an average of 80% improvement in the processing speed was noted in the RE group.

Fractal dimension brain morphometry: a novel approach to quantify white matter in traumatic brain injury

Traumatic brain injury (TBI) is the main cause of disability in people younger than 35 in the United States. The mechanisms of TBI are complex resulting in both focal and diffuse brain damage. Fractal dimension (FD) is a measure that can characterize morphometric complexity and variability of brain structure especially white matter (WM) structure and may provide novel insights into the injuries evident following TBI. FD-based brain morphometry may provide information on WM structural changes after TBI that is more sensitive to subtle structural changes post injury compared to conventional MRI measurements. Anatomical and diffusion tensor imaging (DTI) data were obtained using a 3 T MRI scanner in subjects with moderate to severe TBI and in healthy controls (HC). Whole brain WM volume, grey matter volume, cortical thickness, cortical area, FD and DTI metrics were evaluated globally and for the left and right hemispheres separately. A neuropsychological test battery sensitive to cognitive impairment associated with traumatic brain injury was performed. TBI group showed lower structural complexity (FD) bilaterally (p < 0.05). No significant difference in either grey matter volume, cortical thickness or cortical area was observed in any of the brain regions between TBI and healthy controls. No significant differences in whole brain WM volume or DTI metrics between TBI and HC groups were observed. Behavioral data analysis revealed that WM FD accounted for a significant amount of variance in executive functioning and processing speed beyond demographic and DTI variables. FD therefore, may serve as a sensitive marker of injury and may play a role in outcome prediction in TBI.

Enhanced dielectric permittivity and suppressed electrical conductivity in polyvinylidene fluoride nanocomposites filled with 4,4'-oxydiphenol-functionalized graphene

Plastic film capacitors suffer from low charge storage capacity due to the low dielectric constant of the polymer (<10). We have devised a polyvinylidene fluoride (PVDF) composite film filled with small graphene oxide (GO) sheets that have aromatic molecules attached to their surfaces. The use of 4,4'-oxydiphenol molecules to functionalize graphene sheets is found to have a remarkable effect on enhancing the dielectric permittivity as well as reducing the electrical conductivity of the nanocomposite. When under an electric field, these molecules with an angled molecular geometry act as aligned electric dipoles to largely enhance the dielectric permittivity of the composite, reaching a level two orders of magnitude higher than that of the counterpart filled with blank graphene sheets. Also, the aromatic molecules on the graphene surface act as resistive barriers that block charge transfer between interconnected graphene sheets. As a consequence, the electric conductivity of the composite can be decreased by two orders of magnitude. The PVDF composite filled with functionalized graphene shows a percolation threshold of 13 wt% and a high dielectric constant of 1091 at 100 Hz at this point.

Quantitative analysis of grey matter degeneration in FTD patients using fractal dimension analysis

Fractal dimension (FD) is a quantitative parameter that can characterizes the complexity of human brain tissue. Extensive grey matter (GM) pathology has been previously identified in Frontotemporal dementia (FTD) and its variants. The aim of the present study was to investigate the GM morphometric abnormalities in the behavioral variant FTD (bvFTD) and primary progressive aphasia (PPA) using FD analysis. Twenty-seven bvFTD, 12 PPA and 20 controls were studied. SPM8 was used to segment the brain into GM tissue. Then the FD values were estimated for the GM skeleton, surface and general structure in patients and controls using our previously published algorithm. We found that patients with bvFTD had significant reduction in FD values of skeleton and general structure when compared to controls. In PPA, more significant decrease in FD was noted in the whole brain and left hemisphere skeleton along with left hemisphere general structure. Only the right hemisphere skeleton had a significant correlation with total score of Frontal Systems Behavior Scale (FrSBe). The results showed that the variants of FTD are associated with disease specific morphometric complexity patterns. These results indicate that FD can be used as a biomarker for the structural changes associated with neurodegenerative diseases.

Design of a low-cost MRI compatible plantarflexion force measurement device

Investigating the neural correlates of ankles' joint rotation is critical to better understand the underlying deficit in balance or posture control in the clinical population. This work describes the design and characteristics of a low-cost MRI compatible isometric plantarflexion force measurement device. The device is fully adjustable to the particular height and shoe size of participants. Each individual force sensor has an operational linear range up to 80-100kg amounting to a force range up to 180kg when combining the two sensors, which is well above the maximal force for the majority of the population. Preliminary neuroimaging tests suggest that performing submaximal ankle plantar flexions on the device induce minimal motion artifacts on fMRI signal that are within an acceptable range.

Unsupervised Stochastic Strategies for Robust Detection of Muscle Activation Onsets in Surface Electromyogram

Surface electromyographic (sEMG) data impart valuable information concerning muscle function and neuromuscular diseases especially under human movement conditions. However, they are subject to trial-wise and subject-wise variations, which would pose challenges for investigators engaged in precisely estimating the onset of muscle activation. To this end, we posited two unsupervised statistical approaches- scree-plot elbow detection (SPE) heavily relying on the threshold choice and the more robust profile likelihood maximization (PLM) that obviates parameter tuning-for accurately detecting muscle activation onsets (MAOs). The performance of these algorithms was evaluated using the sEMG dataset provided in the article by Tenan et al. and the simulated sEMG created as explained therein. These sEMG signals are reported to have been collected from the biceps brachii and vastus lateralis of 18 participants while performing a biceps curl or knee extension, respectively. The acquired sEMG signals were first preconditioned with the Teager-Kaiser energy operator, and then, either supplied to the SPE or to the PLM or to a state-of-the-art algorithm. The mean and median errors, between the MAO time in milliseconds estimated by each of the algorithms and the gold standard onset time, were computed. The outcome of a PLM variant, namely, PLM-Laplacian, has been found to have good agreement with the gold standard, i.e., an absolute median error of 9 and 21 ms in the simulated and the actual sEMG data, respectively; whereas, the errors produced by the other algorithms are statistically significantly larger than that incurred by the PLM-Laplacian according to Wilcoxon rank-sum test. In addition, the advocated approach does not necessitate parameter settings, lending itself to be flexible and adaptable to any application, which is a unique advantage over several other methods. Research is underway to further validate this technique by imposing various experimental conditions.

The level of effort, rather than muscle exercise intensity determines strength gain following a six-week training

AIM

This study investigated the effect of voluntary motor effort during a low-intensity (30% maximal voluntary contraction [MVC]) muscle exercise training program on increasing muscle strength.

MATERIALS AND METHODS

Eighteen young and healthy individuals were randomly assigned to one of three groups: high mental effort (HME), low mental effort (LME), or a no-training control (CTRL) group. Training lasted for 6weeks (15min/day, 5days/week). The participants' right-elbow flexor muscle strength was measured before and after the training program.

KEY FINDINGS

After training, the HME group gained 20.47±8.33% (P=0.01) strength while the LME and CTRL groups had negligible strength changes (1.89±0.96% and -3.27±2.61%, respectively; P>0.05) despite muscle contraction intensity (30% MVC) sustained during training was the same for the HME and LME groups. These results suggest that the level of effort involved in resistance exercise training plays a critical role in determining the amount of strength augmentation.

SIGNIFICANCE

The finding that high effort combined with low-level physical exercise training can significantly increase muscle strength has rehabilitation applications as many patients and frail older adults have difficulties in participating in high-intensity exercise training such as lifting heavy weights. High effort plus low-level muscle exercise might serve as a safe training regimen for effective muscle strengthening in vulnerable populations.

The effect of motor overflow on bimanual asymmetric force coordination

Motor overflow, typically described in the context of unimanual movements, refers to the natural tendency for a 'resting' limb to move during movement of the opposite limb and is thought to be influenced by inter-hemispheric interactions and intra-cortical networks within the 'resting' hemisphere. It is currently unknown, however, how motor overflow contributes to asymmetric force coordination task accuracy, referred to as bimanual interference, as there is need to generate unequal forces and corticospinal output for each limb. Here, we assessed motor overflow via motor evoked potentials (MEPs) and the regulation of motor overflow via inter-hemispheric inhibition (IHI) and short-intra-cortical inhibition (SICI) using transcranial magnetic stimulation in the presence of unimanual and bimanual isometric force production. All outcomes were measured in the left first dorsal interosseous (test hand) muscle, which maintained 30% maximal voluntary contraction (MVC), while the right hand (conditioning hand) was maintained at rest, 10, 30, or 70% of its MVC. We have found that as higher forces are generated with the conditioning hand, MEP amplitudes at the active test hand decreased and inter-hemispheric inhibition increased, suggesting reduced motor overflow in the presence of bimanual asymmetric forces. Furthermore, we found that subjects with less motor overflow (i.e., reduced MEP amplitudes in the test hemisphere) demonstrated poorer accuracy in maintaining 30% MVC across all conditions. These findings suggest that motor overflow may serve as an adaptive substrate to support bimanual asymmetric force coordination.

Baduanjin Mind-Body Intervention Improves the Executive Control Function

This study aims at comparing the effects of the Baduanjin mind-body (BMB) intervention with a conventional relaxation training program on enhancing the executive function. The study also attempts to explore the neural substrates underlying the cognitive effect of BMB intervention using near-infrared spectroscopy (NIRS) technique. Forty-two healthy college students were randomly allocated into either the Baduanjin intervention group or relaxation training (control) group. Training lasted for 8 weeks (90 min/day, 5 days/week). Each participant was administered the shortened Profile of Mood States to evaluate their mood status and the flanker task to evaluate executive function before and after training. While performing the flanker task, the NIRS data were collected from each participant. After training, individuals who have participated in BMB exercise showed a significant reduction in depressive mood compared with the same measure before the intervention. However, participants in the control group showed no such reduction. The before vs. after measurement difference in the flanker task incongruent trails was significant only for the Baduanjin intervention group. Interestingly, an increase in oxygenated hemoglobin in the left prefrontal cortex was observed during the Incongruent Trails test only after the BMB exercise intervention. These findings implicate that Baduanjin is an effective and easy-to-administering mind-body exercise for improving executive function and perhaps brain self-regulation in a young and healthy population.

Brain Functional Connectivity Is Different during Voluntary Concentric and Eccentric Muscle Contraction

Previous studies report greater activation in the cortical motor network in controlling eccentric contraction (EC) than concentric contraction (CC) of human skeletal muscles despite lower activation level of the muscle associated with EC. It is unknown, however, whether the strength of functional coupling between the primary motor cortex (M1) and other involved areas in the brain differs as voluntary movements are controlled by a network of regions in the primary, secondary and association cortices. Examining fMRI-based functional connectivity (FC) offers an opportunity to measure strength of such coupling. To address the question, we examined functional MRI (fMRI) data acquired during EC and CC (20 contractions each with similar movement distance and speed) of the right first dorsal interosseous (FDI) muscle in 11 young (20-32 years) and healthy individuals and estimated FC between the M1 and a number of cortical regions in the motor control network. The major findings from the mechanical and fMRI-based FC analysis were that (1) no significant differences were seen in movement distance, speed and stability between the EC and CC; (2) significantly stronger mean FC was found for CC than EC. Our finding provides novel insights for a better understanding of the control mechanisms underlying voluntary movements produced by EC and CC. The finding is potentially helpful for guiding the development of targeted sport training and/or therapeutic programs for performance enhancement and injury prevention.

Motor effort training with low exercise intensity improves muscle strength and descending command in aging

This study explored the effect of high mental effort training (MET) and conventional strength training (CST) on increasing voluntary muscle strength and brain signal associated with producing maximal muscle force in healthy aging. Twenty-seven older adults (age: 75 ± 7.9 yr, 8 women) were assigned into 1 of 3 groups: MET group-trained with low-intensity (30% maximal voluntary contraction [MVC]) physical exercise combined with MET, CST group-trained with high-intensity muscle contractions, or control (CTRL) group-no training of any kind. MET and CST lasted for 12 weeks (5 sessions/week). The participants' elbow flexion strength of the right arm, electromyography (EMG), and motor activity-related cortical potential (MRCP) directly related to the strength production were measured before and after training. The CST group had the highest strength gain (17.6%, P <0.001), the MET group also had significant strength gain (13.8%, P <0.001), which was not statistically different from that of the CST group even though the exercise intensity for the MET group was only at 30% MVC level. The CTRL group did not have significant strength changes. Surprisingly, only the MET group demonstrated a significant augmentation in the MRCP (29.3%, P <0.001); the MRCP increase in CST group was at boarder-line significance level (12.11%, P = 0.061) and that for CTRL group was only 4.9% (P = 0.539). These results suggest that high mental effort training combined with low-intensity physical exercise is an effective method for voluntary muscle strengthening and this approach is especially beneficial for those who are physically weak and have difficulty undergoing conventional strength training.

Post-exercise depression following submaximal and maximal isometric voluntary contraction

It is well known that corticomotor excitability is altered during the post-exercise depression following fatigue within the primary motor cortex (M1). However, it is currently unknown whether corticomotor reorganization following muscle fatigue differs between magnitudes of force and whether corticomotor reorganization occurs measured with transcranial magnetic stimulation (TMS). Fifteen young healthy adults (age 23.8±1.4, 8 females) participated in a within-subjects, repeated measures design study, where they underwent three testing sessions separated by one-week each. Subjects performed separate sessions of each: low-force isometric contraction (30% maximal voluntary contraction [MVC]), high-force isometric contraction (95% MVC) of the first dorsal interosseous (FDI) muscle until self-perceived exhaustion, as well as one session of a 30-min rest as a control. We examined changes in corticomotor map area, excitability and location of the FDI representation in and around M1 using TMS. The main finding was that following low-force, but not high-force fatigue (HFF) corticomotor map area and excitability reduced [by 3cm(2) (t(14)=-2.94, p=0.01) and 56% respectively t(14)=-4.01, p<0.001)]. Additionally, the region of corticomotor excitability shifted posteriorly (6.4±2.5mm) (t(14)=-6.33, p=.019). Corticomotor output became less excitable particularly in regions adjoining M1. Overall, post-exercise depression is present in low-force, but not for HFF. Further, low-force fatigue (LFF) results in a posterior shift in corticomotor output. These changes may be indicative of increased sensory feedback from the somatosensory cortex during the recovery phase of fatigue.

Reproducibility of transcranial magnetic stimulation metrics in the study of proximal upper limb muscles

OBJECTIVE

Reproducibility of transcranial magnetic stimulation (TMS) metrics is essential in accurately tracking recovery and disease. However, majority of evidence pertains to reproducibility of metrics for distal upper limb muscles. We investigate for the first time, reliability of corticospinal physiology for a large proximal muscle - the biceps brachii and relate how varying statistical analyses can influence interpretations.

METHODS

14 young right-handed healthy participants completed two sessions assessing resting motor threshold (RMT), motor evoked potentials (MEPs), motor map and intra-cortical inhibition (ICI) from the left biceps brachii. Analyses included paired t-tests, Pearson's, intra-class (ICC) and concordance correlation coefficients (CCC) and Bland-Altman plots.

RESULTS

Unlike paired t-tests, ICC, CCC and Pearson's were >0.6 indicating good reliability for RMTs, MEP intensities and locations of map; however values were <0.3 for MEP responses and ICI.

CONCLUSIONS

Corticospinal physiology, defining excitability and output in terms of intensity of the TMS device, and spatial loci are the most reliable metrics for the biceps. MEPs and variables based on MEPs are less reliable since biceps receives fewer cortico-motor-neuronal projections. Statistical tests of agreement and associations are more powerful reliability indices than inferential tests.

SIGNIFICANCE

Reliable metrics of proximal muscles when translated to a larger number of participants would serve to sensitively track and prognosticate function in neurological disorders such as stroke where proximal recovery precedes distal.

Weakening of Corticomuscular Signal Coupling During Voluntary Motor Action in Aging

BACKGROUND

Aging is associated with muscle weakness and impairment in performing skilled motor tasks. Still, little is known about whether the link or functional coupling or connection between the central and peripheral systems during voluntary motor performance is compromised in the elderly subjects. The purposes of this study were to estimate functional corticomuscular connection (CMC) strength in the elderly subjects by calculating EEG-EMG coherence during voluntary motor performance, determine the relationship between the CMC and voluntary muscle force, and compare these between the old and the young subjects.

METHODS

Maximal voluntary contraction (MVC) of elbow flexion (EF) and EFs at three submaximal (20%, 50%, and 80% MVC) levels were performed in 28 healthy older (74.96±1.32 years) and 20 young (22.60±0.90 years) individuals, while EEG and EMG from biceps brachii, brachioradialis, and triceps brachii muscles were recorded simultaneously.

RESULTS

Compared with the young, older individuals exhibited significantly weakened CMC at all force levels tested. There was a proportional relationship between the CMC and EF force and high-positive correlation between the CMC and EF strength in both groups.

CONCLUSIONS

Weakened CMC in aging may be a major factor contributing to age-related muscle weakness, and the linear relationship between the CMC and voluntary muscle force suggests dependence of force output on translation of the descending command to muscle electrical signal.

Hemispheric activation during planning and execution phases in reaching post stroke: a consort study

Enhanced activation in the non-lesion hemisphere in stroke patients was widely observed during movement of the affected upper limb, but its functional role related to motor planning and execution is still unknown.This study was to characterize the activation in the non-lesion hemisphere during movement planning and execution by localizing sources of high-density electroencephalography (EEG) signal and estimating the source strength (current density [A/m]).Ten individuals with chronic stroke and shoulder/elbow coordination deficits and 5 healthy controls participated in the study.EEG (64 channels) was recorded from scalp electrodes while the subjects performed a reach task involving shoulder flexion and elbow extension of the affected (patients) or dominant (controls) upper extremity. Sources of the EEG were obtained and analyzed at 17 time points across movement preparation and execution phases. A 3-layer boundary element model was overlaid and used to identify the brain activation sources. A distributed current density model, low-resolution electromagnetic tomography (LORETA) L1 norm method, was applied to the data pre-processed by independent component analysis.Subjects with stroke had stronger source strength in the sensorimotor cortices during the movement compared with the controls. Their contralesional/lesional activation ratio (CTLR) for the primary motor cortices was significantly higher than that of the controls during the movement-planning phase, but not during the execution phase. The CTLR was higher in planning than in the execution phase in the stroke group.Excessive contralesional motor cortical activation appears to be more related to movement preparation rather than execution in chronic stroke.

Evidence of significant central fatigue in patients with cancer-related fatigue during repetitive elbow flexions till perceived exhaustion

OBJECTIVE

To investigate whether fatigue induced by an intermittent motor task in patients with cancer-related fatigue (CRF) is more central or peripheral.

METHODS

Ten patients with CRF who were off chemo and radiation therapies and 14 age-matched healthy controls were enrolled. Participants completed a Brief Fatigue Inventory (BFI) and performed a fatigue task consisting of intermittent elbow-flexion contractions at submaximal (40% maximal voluntary contraction) intensity till self-perceived exhaustion. Twitch force was elicited by an electrical stimulation applied to the biceps brachii muscle. The relative degree of peripheral (muscle) vs. central contribution to fatigue induced by the intermittent motor task (IMT) was assessed using twitch force ratio (TF ratio) defined as post IMT twitch force to pre IMT twitch force. The total number of trials (intermittent contractions) and total duration of all trials performed by each subject were also quantified.

RESULTS

BFI scores were higher (p < 0.001) in CRF than controls, indicating greater feeling of fatigue in CRF patients than controls. A significantly smaller number of trials and shorter total duration of the trials (p < 0.05) were observed in CRF than control participants. The TF ratio (0.81 ± 0.05) in CRF was higher (p < 0.05) compared with that of controls (0.62 ± 0.05), suggesting CRF patients experienced a significantly lower degree of muscle (peripheral) fatigue at the time of perceived exhaustion.

CONCLUSION

Consistent with prior findings for fatigue under submaximal sustained contraction, our results indicate that motor fatigue in CRF is more of central than peripheral origin during IMT. Significant central fatigue in CRF patients limits their ability to prolong motor performance.

Aging interferes central control mechanism for eccentric muscle contraction

Previous studies report greater activation in the cortical motor network in controlling eccentric contraction (EC) than concentric contraction (CC) despite lower muscle activation level associated with EC vs. CC in healthy, young individuals. It is unknown, however, whether elderly people exhibiting increased difficulties in performing EC than CC possess this unique cortical control mechanism for EC movements. To address this question, we examined functional magnetic resonance imaging (fMRI) data acquired during EC and CC of the first dorsal interosseous (FDI) muscle in 11 young (20–32 years) and 9 old (67–73 years) individuals. During the fMRI experiment, all subjects performed 20 CC and 20 EC of the right FDI with the same angular distance and velocity. The major findings from the behavioral and fMRI data analysis were that (1) movement stability was poorer in EC than CC in the old but not the young group; (2) similar to previous electrophysiological and fMRI reports, the EC resulted in significantly stronger activation in the motor control network consisting of primary, secondary and association motor cortices than CC in the young and old groups; (3) the biased stronger activation towards EC was significantly greater in the old than the young group especially in the secondary and association cortices such as supplementary and premotor motor areas and anterior cingulate cortex; and (4) in the primary motor and sensory cortices, the biased activation towards EC was significantly greater in the young than the old group. Greater activation in higher-order cortical fields for controlling EC movement by elderly adults may reflect activities in these regions to compensate for aging-related impairments in the ability to control complex EC movements. Our finding is useful for potentially guiding the development of targeted therapies to counteract age-related movement deficits and to prevent injury.

Myoelectrical manifestation of fatigue less prominent in patients with cancer related fatigue

PURPOSE

A lack of fatigue-related muscle contractile property changes at time of perceived physical exhaustion and greater central than peripheral fatigue detected by twitch interpolation technique have recently been reported in cancer survivors with fatigue symptoms. Based on these observations, it was hypothesized that compared to healthy people, myoelectrical manifestation of fatigue in the performing muscles would be less significant in these individuals while sustaining a prolonged motor task to self-perceived exhaustion (SPE) since their central fatigue was more prominent. The purpose of this study was to test this hypothesis by examining electromyographic (EMG) signal changes during fatiguing muscle performance.

METHODS

Twelve individuals who had advanced solid cancer and cancer-related fatigue (CRF), and 12 age- and gender-matched healthy controls performed a sustained elbow flexion at 30% maximal voluntary contraction till SPE. Amplitude and mean power frequency (MPF) of EMG signals of the biceps brachii, brachioradialis, and triceps brachii muscles were evaluated when the individuals experienced minimal, moderate, and severe fatigue.

RESULTS

CRF patients perceived physical "exhaustion" significantly sooner than the controls. The myoelectrical manifestation of muscular fatigue assessed by EMG amplitude and MPF was less significant in CRF than controls. The lower MPF even at minimal fatigue stage in CRF may indicate pathophysiologic condition of the muscle.

CONCLUSIONS

CRF patients experience less myoelectrical manifestation of muscle fatigue than healthy individuals near the time of SPE. The data suggest that central nervous system fatigue plays a more important role in limiting endurance-type of motor performance in patients with CRF.

Kinesthetic imagery training of forceful muscle contractions increases brain signal and muscle strength

The purpose of this study was to compare the effect of training using internal imagery (IMI; also known as kinesthetic imagery or first person imagery) with that of external imagery (EMI; also known as third-person visual imagery) of strong muscle contractions on voluntary muscle strengthening. Eighteen young, healthy subjects were randomly assigned to one of three groups (6 in each group): internal motor imagery (IMI), external motor imagery (EMI), or a no-practice control (CTRL) group. Training lasted for 6 weeks (~15 min/day, 5 days/week). The participants' right arm elbow-flexion strength, muscle electrical activity, and movement-related cortical potential (MRCP) were evaluated before and after training. Only the IMI group showed significant strength gained (10.8%) while the EMI (4.8%) and CTRL (-3.3%) groups did not. Only the IMI group showed a significant elevation in MRCP on scalp locations over both the primary motor (M1) and supplementary motor cortices (EMI group over M1 only) and this increase was significantly greater than that of EMI and CTRL groups. These results suggest that training by IMI of forceful muscle contractions was effective in improving voluntary muscle strength without physical exercise. We suggest that the IMI training likely strengthened brain-to-muscle (BTM) command that may have improved motor unit recruitment and activation, and led to greater muscle output. Training by IMI of forceful muscle contractions may change the activity level of cortical motor control network, which may translate into greater descending command to the target muscle and increase its strength.

Neurophysiological correlates of aging-related muscle weakness

Muscle weakness associated with aging implicates central neural degeneration. However, role of the primary motor cortex (M1) is poorly understood, despite evidence that gains in strength in younger adults are associated with its adaptations. We investigated whether weakness of biceps brachii in aging analogously relates to processes in M1. We enrolled 20 young (22.6 ± 0.87 yr) and 28 old (74.79 ± 1.37 yr) right-handed participants. Using transcranial magnetic stimulation, representation of biceps in M1 was identified. We examined the effect of age and sex on strength of left elbow flexion, voluntary activation of biceps, corticospinal excitability and output, and short-interval intracortical and interhemispheric inhibition. Interhemispheric inhibition was significantly exaggerated in the old (P = 0.047), while strength tended to be lower (P = 0.075). Overall, women were weaker (P < 0.001). Processes of M1 related to strength or voluntary activation of biceps, but only in older adults. Corticospinal excitability was lower in weaker individuals (r = 0.38), and corticospinal output, intracortical inhibition and interhemispheric inhibition were reduced too in individuals who poorly activated biceps (r = 0.43, 0.54 and 0.38). Lower intracortical inhibition may reflect compensation for reduced corticospinal excitability, allowing weaker older adults to spread activity in M1 to recruit synergists and attempt to sustain motor output. Exaggerated interhemispheric inhibition, however, conflicts with previous evidence, potentially related to greater callosal damage in our older sample, our choice of proximal vs. distal muscle and differing influence of measurement of inhibition in rest vs. active states of muscle. Overall, age-specific relation of M1 to strength and muscle activation emphasizes that its adaptations only emerge when necessitated, as in a weakening neuromuscular system in aging.

Brain white matter shape changes in amyotrophic lateral sclerosis (ALS): a fractal dimension study

Amyotrophic lateral sclerosis (ALS) is a fatal progressive neurodegenerative disorder. Current diagnosis time is about 12-months due to lack of objective methods. Previous brain white matter voxel based morphometry (VBM) studies in ALS reported inconsistent results. Fractal dimension (FD) has successfully been used to quantify brain WM shape complexity in various neurological disorders and aging, but not yet studied in ALS. Therefore, we investigated WM morphometric changes using FD analyses in ALS patients with different clinical phenotypes. We hypothesized that FD would better capture clinical features of the WM morphometry in different ALS phenotypes than VBM analysis. High resolution MRI T1-weighted images were acquired in controls (n = 11), and ALS patients (n = 89). ALS patients were assigned into four subgroups based on their clinical phenotypes.VBM analysis was carried out using SPM8. FD values were estimated for brain WM skeleton, surface and general structure in both controls and ALS patients using our previously published algorithm. No significant VBM WM changes were observed between controls and ALS patients and among the ALS subgroups. In contrast, significant (p<0.05) FD reductions in skeleton and general structure were observed between ALS with dementia and other ALS subgroups. No significant differences in any of the FD measures were observed between control and ALS patients. FD correlated significantly with revised ALS functional rating scale (ALSFRS-R) score a clinical measure of function. Results suggest that brain WM shape complexity is more sensitive to ALS disease process when compared to volumetric VBM analysis and FD changes are dependent on the ALS phenotype. Correlation between FD and clinical measures suggests that FD could potentially serve as a biomarker of ALS pathophysiology, especially after confirmation by longitudinal studies.

Functional somatotopy revealed across multiple cortical regions using a model of complex motor task

The primary motor cortex (M1) possesses a functional somatotopic structure-representations of adjacent within-limb joints overlap to facilitate coordination while maintaining discrete centers for individuated movement. We examined whether similar organization exists across other sensorimotor cortices. Twenty-four right-handed healthy subjects underwent functional magnetic resonance imaging (fMRI) while tracking complex targets with flexion/extension at right finger, elbow and ankle separately. Activation related to each joint at false discovery rate of 0.005 served as its representation across multiple regions. Within each region, we identified the center of mass (COM) for each representation, and the overlap between the representations of within-limb (finger and elbow) and between-limb joints (finger and ankle). Somatosensory (S1) and premotor cortices (PMC) demonstrated greater distinction of COM and minimal overlap for within- and between-limb representations. In contrast, M1 and supplementary motor area (SMA) showed more integrative somatotopy with higher sharing for within-limb representations. Superior and inferior parietal lobule (SPL and IPL) possessed both types of structure. Some clusters exhibited extensive overlap of within- and between-limb representations, while others showed discrete COMs for within-limb representations. Our results help to infer hierarchy in motor control. Areas such as S1 may be associated with individuated movements, while M1 may be more integrative for coordinated motion; parietal associative regions may allow switch between both modes of control. Such hierarchy creates redundant opportunities to exploit in stroke rehabilitation. The use of complex rather than traditionally used simple movements was integral to illustrating comprehensive somatotopic structure; complex tasks can potentially help to understand cortical representation of skill and learning-related plasticity.

Influence of nerve supply on hand electromyography coherence during a three-digit task

Intermuscular coupling has been investigated to understand neural inputs to coordinate muscles in a motor performance. However, little is known on the role of nerve innervation on intermuscular coupling. The purpose of this study was to investigate how the anatomy of nerve distribution affected intermuscular coupling in the hand during static grip. Electromyographic (EMG) signals were recorded from intrinsic and extrinsic muscles while subjects performed a static grip. Coherence was computed for muscle pairs innervated by either the same or different nerves. The results did not support the hypothesis that muscles sharing the same nerve exhibit greater coupling than muscles innervated by different nerves. In general, extrinsic muscle pairs displayed higher coherence than intrinsic pairs. The results suggest that intermuscular coupling in a voluntary motor task is likely modulated in a functional manner and that different nerves might transport common neural inputs to functionally coupled muscles.

T2 relaxometry measurements in low spatial frequency brain regions differ between fast spin-echo and multiple-echo spin-echo sequences

OBJECT

Dual-echo fast spin-echo (FSE) sequences are used in T2 relaxometry studies of neurological disorders because of shorter clinical scanning times and protocol simplicity. However, FSE sequences have possible spatial frequency-dependent effects, and derived T2 values may include errors that depend on the spatial frequency characteristics of the brain region of interest.

MATERIALS AND METHODS

Dual-echo FSE and multi-echo spin-echo (MESE) sequences were acquired in nine subjects. The T2 decay curves for FSE and MESE sequences were estimated and percent error maps were generated. T2 error values were obtained along each patient's corticospinal tract (CST). Whole-brain white matter (WM) and gray matter (GM) T2 error values were also obtained. The paired t test was performed to evaluate differences in T2 values in the CST between FSE and MESE sequences.

RESULTS

Histograms of error values in CST and in whole-brain WM and GM structures revealed systematic errors in FSE sequences. Significant differences (P < 0.001) in CST T2 values were also observed between FSE and MESE sequences.

CONCLUSION

Our findings indicate that T2 values derived from FSE sequences are prone to large errors, even in low spatial frequency regions such as the CST, when compared to MESE sequences. Future studies should be aware of this limitation of FSE sequences.

Lack of muscle contractile property changes at the time of perceived physical exhaustion suggests central mechanisms contributing to early motor task failure in patients with cancer-related fatigue

CONTEXT

Fatigue is one of the most common symptoms reported by cancer survivors, and fatigue worsens when patients are engaged in muscle exertion, which results in early motor task failure. Central fatigue plays a significant role, more than muscle (peripheral) fatigue, in contributing to early task failure in cancer-related fatigue (CRF).

OBJECTIVES

The purpose of this study was to determine if muscle contractile property alterations (reflecting muscle fatigue) occurred at the end of a low-intensity muscle contraction to exhaustion and if these properties differed between those with CRF and healthy controls.

METHODS

Ten patients (aged 59.9±10.6 years, seven women) with advanced solid cancer and CRF and 12 age- and gender-matched healthy controls (aged 46.6±12.8 years, nine women) performed a sustained contraction of the right arm elbow flexion at 30% maximal level until exhaustion. Peak twitch force, time to peak twitch force, rate of peak twitch force development, and half relaxation time derived from electrical stimulation-evoked twitches were analyzed pre- and post-sustained contraction.

RESULTS

CRF patients reported significantly greater fatigue as measured by the Brief Fatigue Inventory and failed the motor task earlier, 340±140 vs. 503±155 seconds in controls. All contractile property parameters did not change significantly in CRF but did change significantly in controls.

CONCLUSION

CRF patients perceive physical exhaustion sooner during a motor fatigue task with minimal muscular fatigue. The observation supports that central fatigue is a more significant factor than peripheral fatigue in causing fatigue feelings and limits motor function in cancer survivors with fatigue symptoms.

EEG for evaluation of “chemobrain.”

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Background: Cognitive impairment is a poorly understood and worrisome potential complication of adjuvant chemotherapy (CT). We sought to evaluate electroencephalography (EEG) as a means to measure neurophysiologic function in women receiving CT for early breast cancer. Methods: Women planning to undergo CT for operable breast cancer and age-similar controls were evaluated at baseline, during CT and at 1 year with neurophysiologic assessments. Testing included a brief fatigue inventory (BFI), brief mental fatigue assessment (BMF), Processing Speed Index (PSI) derived from Digit Symbol Coding and Symbol Search subtests of the Wechsler Adult Intelligence Scale, and a sustained elbow flexion physical task (PT). EEG recordings were obtained at rest and after the cognitive and physical tasks. Data were analyzed using repeated measures of analysis of variance. Results: Eight patient/control pairs completed baseline and on-treatment evaluations; 7 pairs also completed the 1 year assessment (1 pair withdrawn due to a second malignancy). Subjective mental fatigue measured by BMF is similar for patients and controls at baseline but BMF scores increase significantly during CT for patients relative to controls (p=0.033), recovering to no difference at one year. Differences in PSI are not observed between patients and controls or at the different time points. BFI scores are greater in patients at all 3 time points but endurance on the PT is no different from controls. During chemotherapy EEG total spectrum amplitudes in patients are greater than in controls at rest (p=0.05) and following both the cognitive (p<0.001) and physical (p<0.001) tasks. EEG activity prior to chemotherapy and at one year is not different between patients and controls. For patients but not controls EEG readings after the cognitive task demonstrate greater amplitude than pre-task readings during the time of CT treatment only (p=0.012) with a similar trend seen for the physical task (p=0.06). Conclusions: Patient-perceived mental and physical fatigue during chemotherapy correspond to significant changes in EEG brain activity patterns but not to cognitive testing or physical endurance testing. EEG may offer a sensitive means to measure alterations in brain function associated with CT.

Time-dependent cortical activation in voluntary muscle contraction

This study was to characterize dynamic source strength changes estimated from high-density scalp electroencephalogram (EEG) at different phases of a submaximal voluntary muscle contraction. Eight healthy volunteers performed isometric handgrip contractions of the right arm at 20% maximal intensity. Signals of the handgrip force, electromyography (EMG) from the finger flexor and extensor muscles and 64-channel EEG were acquired simultaneously. Sources of the EEG were analyzed at 19 time points across preparation, execution and sustaining phases of the handgrip. A 3-layer boundary element model (BEM) based on the MNI (Montréal Neurological Institute) brain MRI was used to overlay the sources. A distributed current density model, LORETA L1 norm method was applied to the data that had been processed by independent component analysis (ICA). Statistical analysis based on a mixed-effects polynomial regression model showed a significant and consistent time-dependent non-linear source strength change pattern in different phases of the handgrip. The source strength increased at the preparation phase, peaked at the force onset time and decreased in the sustaining phase. There was no significant difference in the changing pattern of the source strength among Brodmann’s areas 1, 2, 3, 4, and 6. These results show, for the first time, a high time resolution increasing-and-decreasing pattern of activation among the sensorimotor regions with the highest activity occurs at the muscle activity onset. The similarity in the source strength time courses among the cortical centers examined suggests a synchronized parallel function in controlling the motor activity.