Correlation-based decomposition of surface electromyograms at low contraction forces

The paper studies a surface electromyogram (SEMG) decomposition technique suitable for identification of complete motor unit (MU) firing patterns and their motor unit action potentials (MUAPs) during low-level isometric voluntary muscle contractions. The algorithm was based on a correlation matrix of measurements, assumed unsynchronised (uncorrelated) MU firings, exhibited a very low computational complexity and resolved the superimposition of MUAPs. A separation index was defined that identified the time instants of an MU's activation and was eventually used for reconstruction of a complete MU innervation pulse train. In contrast with other decomposition techniques, the proposed approach worked well also when the number of active MUs was slightly underestimated, if the MU firing patterns partly overlapped and if the measurements were noisy. The results on synthetic SEMG show 100% accuracy in the detection of innervation pulses down to a signal-to-noise ratio (SNR) of 10 dB, and 93±4.6% (mean± standard deviation) accuracy with 0 dB additive noise. In the case of real SEMG, recorded with an array of 61 electrodes from biceps brachii of five subjects at 10% maximum voluntary contraction, seven active MUs with a mean firing rate of 14.1 Hz were identified on average.     

Adaptive motor unit action potential clustering using shape and temporal information

An adaptive algorithm is described that groups motor unit action potentials (MUAPs), detected in a composite EMG signal during signal decomposition, and creates partial motor unit action potential trains (MUAPTs). Data-driven MUAP shape and motor unit firing-pattern based criteria are used to form the clusters. An algorithm for estimating MUAPT temporal parameter, which provides accurate estimates even for partially defined trains, is used to obtain firing-pattern information. No a priori knowledge is required regarding the number of clusters or the distribution of their template shapes. The clustering algorithm when applied to real concentric-needle detected MUAP data provides accurate and useful clustering results. Compared to a classical leader-based algorithm, it provides more robust performance, is better able to estimate the true number of motor units represented in a set of detected MUAPs, and obtains more complete and accurate MUAPTs.     

肌萎缩侧索硬化患者重复神经电刺激的观察

目的：观察肌萎缩侧索硬化（ALS）患者重复神经电刺激（RNS）时复合肌肉动作电位（CMAP）波幅衰减和递增的特点及意义。方法：对确诊的42例ALS患者与42例重症肌无力（MG）患者的尺神经3Hz（低频）与15Hz（高频）RNs的结果进行比较。结果：42例ALS患者中,低频RNS有明确衰减者30例,无明确衰减或递增者12例;高频RNS有明确衰减者4例,明确递增者22例,无明确衰减或递增者16例。以上结果均与以作对照的MG组比较,差异均有统计学意义（P〈0．05）。结论：ALS患者存在神经肌肉传递障碍,RNS衰减或递增可能与突触前机制有关,或许与突触前、后均受损害有关,RNS结果异常是病情活跃的标志,确切意义有待进一步探讨。     

Asymmetric responses to repetitive transcranial magnetic stimulation (rTMS) over the left and right primary motor cortex in a patient with lateralized progressive limb-kinetic apraxia

Repetitive transcranial magnetic stimulation (5 Hz-rTMS, 10 stimuli, 120% resting motor threshold intensity, RMT) produces in healthy subjects a progressive facilitation of motor-evoked potential (MEP) amplitude probably through a short-term enhancement of cortical excitatory interneurones. We had the opportunity to investigate the effect of 5 Hz-rTMS delivered over the right and left primary motor cortex (M1) in a patient with limb-kinetic apraxia of the left hand and fingers and reduced cerebral perfusion in the fronto-parietal cortex of the right hemisphere documented by single-photon emission computed tomography scans. Changes in the MEP size during the trains and the RMT were measured and compared between the hemispheres. 5 Hz-rTMS was also delivered in a group of healthy subjects over both hemispheres in order to compare changes in the MEP size from the right and left M1. In the patient, 5 Hz-rTMS delivered over the left hemisphere elicited normal MEPs that progressively increased in size during the trains whereas 5 Hz-rTMS delivered over the right affected hemisphere failed to facilitate the MEP size. RMT was similar in both hemispheres. In healthy subjects, 5 Hz-rTMS delivered over either hemisphere elicited a similar, significant MEP size facilitation. Despite the limitations of a single case, our findings suggest an altered response to 5 Hz-rTMS over the M1 of the affected hemisphere. This asymmetric response correlated with the altered perfusion in the right hemisphere and the patient's lateralized clinical manifestations of apraxia.     

Identification of a unique library of complex, but ordered, arrays of repetitive elements in the human genome and implication of their potential involvement in pathobiology

Approximately 2% of the human genome is reported to be occupied by genes. Various forms of repetitive elements (REs), both characterized and uncharacterized, are presumed to make up the vast majority of the rest of the genomes of human and other species. In conjunction with a comprehensive annotation of genes, information regarding components of genome biology, such as gene polymorphisms, non-coding RNAs, and certain REs, is found in human genome databases. However, the genome-wide profile of unique RE arrangements formed by different groups of REs has not been fully characterized yet. In this study, the entire human genome was subjected to an unbiased RE survey to establish a whole-genome profile of REs and their arrangements. Due to the limitation in query size within the bl2seq alignment program (National Center for Biotechnology Information [NCBI]) utilized for the RE survey, the entire NCBI reference human genome was fragmented into 6206 units of 0.5 M nucleotides. A number of RE arrangements with varying complexities and patterns were identified throughout the genome. Each chromosome had unique profiles of RE arrangements and density, and high levels of RE density were measured near the centromere regions. Subsequently, 175 complex RE arrangements, which were selected throughout the genome, were subjected to a comparison analysis using five different human genome sequences. Interestingly, three of the five human genome databases shared the exactly same arrangement patterns and sequences for all 175 RE arrangement regions (a total of 12,765,625 nucleotides). The findings from this study demonstrate that a substantial fraction of REs in the human genome are clustered into various forms of ordered structures. Further investigations are needed to examine whether some of these ordered RE arrangements contribute to the human pathobiology as a functional genome unit.     

Effects of repetitive cortical stimulation on the silent period evoked by magnetic stimulation

 The effects of repetitive transcranial stimulation (rTMS) on brain activity remain unknown. In healthy subjects, we studied the effects of rTMS on the duration of the cortical silent period (SP). Repetitive stimuli were delivered with a Cadwell High Speed Magnetic Stimulator and a figure-of-eight coil placed over the hand motor area. rTMS was delivered in trains of 11 or 20 stimuli at frequencies of 3 and 5 Hz and at stimulation intensities of 110 and 120% of motor threshold. The SP was recorded from the forearm muscles during a voluntary contraction (20% of maximum effort). rTMS delivered at a frequency of 3 and 5 Hz and intensities of 110 and 120% motor threshold prolonged the duration of the SP, without modifying either the size or the latency of the muscle-evoked potentials (MEP). A conditioning train of 11 stimuli at 3 Hz had no effect on the duration of the SP evoked by a single magnetic shock delivered 600 ms after the train. These findings show that rTMS increases the duration of the cortical SP, but does so only during the train of stimuli. rTMS probably changes the duration of the SP by facilitating cortical inhibitory interneurons. Received: 4 December 1997 / Accepted: 11 August 1998     

Modulation of reflex responses in hand muscles during rhythmical finger tasks in a subject with writer’s cramp

The objective of this study was to examine phase- and task-dependent modulation of stretch reflexes during repetitive finger movements in writer’s cramp, and compare them with normal controls from our previous study. A subject with writer’s cramp conducted two rhythmic tasks, index finger abduction (RFA) and a pen-squeezing (RPS) task akin to handwriting. Stretch reflexes were evoked by mechanical perturbations at random phases of each task. Surface electromyograms (EMG) were recorded from two hand muscles, first dorsal interosseous (FDI) and flexor digitorum superficialis (FDS). The reflex response and background EMG activity of each muscle were modulated in a phase-dependent manner in both tasks. However, they varied largely in phase during the RFA task, but in approximately inverse phase-relationship during RPS. Reflex sensitivity, as represented by the slope of the linear regression between response and background, was much lower for both muscles in the ‘writing’ task (RPS) than in the RFA task with its positively correlated responses. These phase- and task-related modulation patterns differed dramatically from those observed in our control subjects, where reflex responses were modulated largely in phase with background activity and reflex sensitivity was much higher, particularly in FDI during RFA and FDS during RPS. The altered reflex modulation patterns in writer’s cramp may reflect deficiencies of integration of proprioceptive afferent inputs and reduced inhibition at cortical and spinal levels during writing performance. Results from this case study support clinically identified task-specific feature of focal hand dystonia.     

The relationship between worry,rumination, and comorbidity: Evidence for repetitive negative thinking as a transdiagnostic construct

Background

Repetitive negative thinking (RNT) increases vulnerability to multiple anxiety and depressive disorders and, as a common risk factor, elevated RNT may account for the high levels of comorbidity observed between emotional disorders. The aims of this study were to (a) compare two common forms of RNT (worry and rumination) across individuals with non-comorbid anxiety or depressive disorders, and (b) to examine the relationship between RNT and comorbidity.

Methods

A structured diagnostic interview and measures of rumination, worry, anxiety, and depression were completed by a large clinical sample with an anxiety disorder or depression (N=513) presenting at a community mental health clinic.

Results

Patients without (n=212) and with (n=301) comorbid diagnoses did not generally differ across the principal diagnosis groups (depression, generalised anxiety disorder, social anxiety disorder, panic disorder) on worry or rumination. As predicted, comorbidity was associated with a higher level of RNT.

Limitations

Cross-sectional design precluded causal conclusions and findings may not generalize to excluded anxiety disorders.

Conclusions

Consistent with the transdiagnostic hypothesis, RNT was associated with a range of anxiety disorders and depression and with comorbidity for those with a principal depressive disorder, supporting recent evidence that RNT is a transdiagnostic process. The presence of RNT, specifically worry and rumination, should be assessed and treated regardless of diagnostic profile. Future research may show that both pure and comorbid depressed or anxious patients receive incremental benefit from transdiagnostic protocols developed to treat core pathological processes of RNT traditionally associated with separate disorders.