Perception of effort reflects central motor command during movement execution

It is thought that perception of effort during physical tasks is the conscious awareness of the central motor command sent to the active muscles. The aim of this study was to directly test this hypothesis by experimentally varying perception of effort and measuring movement-related cortical potential (MRCP). Sixteen healthy, recreationally active men made unilateral dynamic elbow flexions to lift a light (20% one repetition maximum, 1RM) and a heavier (35% 1RM) weight with a fatigued arm and a nonfatigued arm while rating of perceived effort (RPE), biceps brachii electromyogram (EMG), and MRCP were recorded. RPE, EMG amplitude, and MRCP amplitude at Cz during weight raising increased with weight and with muscle fatigue. There was a significant correlation between RPE and MRCP amplitude at the vertex during the weight raising epoch. This study provides direct neurophysiological evidence that perception of effort correlates with central motor command during movement execution.     

The preparation and control of reversal movements as a single unit of action

Previous research has demonstrated that movement time and kinematic properties of limb trajectories to the first target of a two-target reversal movement differ to that of single-target responses. In the present study we investigated whether two-target reversal movements are organized as a single unit of action or two separate components by perturbing the number of targets prior to and during movement execution. In one experiment, participants performed single-target movements and on one-third of the trials a second target was presented either at target presentation, movement onset or peak velocity. On those trials in which a second target was presented, participants were required to complete their movement to the first target and then move to the second target. In a second experiment, the reverse was the case with participants performing two-target movements that changed to single-target movement on one-third of the trials. A two-target movement time advantage was observed only when the required response was specified prior to movement initiation. Also, participants failed to prevent movement towards the second target when the requirements of the task changed from a two-target to single-target response at movement onset or later. These results indicate that two-target reversal movements were organized as a single unit of action prior to response initiation.     

Difficulty in terminating the preceding movement/posture explains the impaired initiation of new movements in Parkinson's disease

To determine whether the difficulty of initiating volitional movements in Parkinson's disease is primarily due to impaired termination of preceding movement/posture or to impaired initiation of new movement, patients with Parkinson's disease and age-matched controls were first asked to visually fixate a stationary spot and simultaneously align wrist position accurately with it. They were then requested to make rapid movements of eyes and wrist to a test stimulus presented in the peripheral visual field. We analyzed latencies of ocular and manual movements to the test stimulus in two conditions; in the overlap task the stationary spot remained on during illumination of the test stimulus requiring subjects to terminate fixation and wrist positioning themselves to initiate new movements. In the gap task, the stationary spot was turned off 200 ms before illuminating the test stimulus. Latencies of ocular and manual movements were prolonged in the overlap task than those in the gap task. Effects of fixation/wrist positioning on the latency of new movement were evaluated by the difference in latencies between the overlap and gap tasks normalized by the latency difference of the controls. These ratios increased exponentially as Parkinson's stage increased, suggesting the latency prolongation in patients with stage III and IV Parkinson's disease under the overlap condition primarily reflected the contribution of difficulty to terminate existing fixation/wrist positioning.     

Analysis and processing of laser Doppler perfusion monitoring signals recorded from the beating heart

Laser Doppler perfusion monitoring (LDPM) can be used for monitoring myocardial perfusion in the non-beating heart. However, the movement of the beating heart generates large artifacts. Therefore the aim of the study was to develop an LDPM system capable of correlating the laser Doppler signals to the cardiac cycle and to process the signals to reduce the movement artifacts. Measurements were performed on three calves, both on the normal beating heart and during occlusion of the left anterior descending coronary artery (LAD). The recorded LDPM signals were digitally processed and correlated to the sampled ECG. Large variations in the output (perfusion) and DC signals during the cardiac cycle were found, with average coefficients of variation of 0.36 and 0.14 (n-14), respectively. However, sections with a relatively low, stable output signal were found in late diastole, where the movement of the heart is at a minimum. Occlusion of the LAD showed the importance of recording the laser Doppler signals at an appropriate point in the cardiac cycle, in this case late systole, to minimise movement artifacts. It is possible to further reduce movement artifacts by increasing the lower cutoff frequency when calculating the output signal.     

Acquisition of anticipatory postural adjustments in a bimanual load-lifting task: normal and pathological aspects

Anticipatory adjustments of forearm posture are associated with a voluntary load-lifting movement in bimanual load-lifting tasks. Three aspects of these adjustments are analyzed: their goal, their central organization, and their acquisition. The goal of the anticipatory adjustment in this task is to minimize the perturbation of forearm posture that occurs during unloading. The central organization is based on two parallel controls responsible, respectively, for the lifting movement of the moving forearm and the anticipatory postural adjustment of the postural forearm, their coordination depending on a central timing signal. The acquisition of the anticipatory postural adjustment was tested using a paradigm where the voluntary movement performed by one hand triggered, via an electronic switch, the load release of the postural forearm. It was achieved after 40–60 trials and was not graded as a function of the voluntary movement parameters, but of the disturbance of the postural arm about to occur. The learned anticipation was not transferred when, after a first acquisition session with one forearm as the postural forearm, a second learning session was performed with the other forearm as the postural forearm. The acquisition was tested in Parkinsonian and in hemiparetic patients with capsular lesion. The highest acquisition deficit was observed in hemiparetic patients, when the contralateral forearm was the postural forearm; the deficit was less important when the ipsilateral arm was postural. Surprisingly, the anticipatory postural adjustments in hemiparetic patients were rather well preserved when the natural load-lifting task was tested. These results suggest that the basal-ganglia SMA circuit and M1 premotor areas are important in the acquisition process. Received: 20 October 1998 / Accepted: 24 March 1999     

经颅电刺激在急性脑梗死患者运动功能康复中的作用

目的:研究经颅电刺激(TES)对急性脑梗死偏瘫患者运动功能的康复作用。方法:选取经CT或MRI确诊的急性脑梗死患者60例,随机分为TES组和对照组各30例,两组在基本治疗相同的情况下,TES组自患病后第八天始加作TES治疗共14天,每天给予TES治疗1次,每次磁刺激患侧运动皮层10回。两组分别于患病后第七天(第一次)和患病后第二十一天(第二次)进行TES运动诱发电位(MEP)检查,记录MEP波幅和中枢运动传导时间(CMCT);用简式Fugl-Meyer运动功能量表(FMS)评分和徒手肌力检查法进行运动功能评分。结果:在患病后第七天,MEP波幅和CMCT、FMS和肌力评分等方面,两组结果比较差异无显著意义;在患病后第二十一天(TES组治疗14天)后,两组上述结果均有改善,与治疗前相比差异均有显著意义,特别是TES组运动功能改善更为明显,两组比较差异有显著意义。同时发现当第一次给患者行TES治疗后即刻,部分患者肌力即可提高Ⅰ-Ⅱ级,数小时后又减退至原肌力,经数次治疗后患者肌力得到巩固而且逐步提高。治疗前有15例患者未引出MEP,其中TES组8例,对照组7例;治疗后,未引出MEP的15例患者TES组8例中有3例引出MEP,但潜伏期及CMCT明显延长,而对照组无1例引出MEP。结论:脑梗死急性期进行TES治疗可明显促进患者运动功能的恢复。     

Effects of brefeldin A on the localization of Tobamovirus movement protein and cell-to-cell movement of the virus

It has been demonstrated that the subcellular location of Tobamovirus movement protein (MP) which was fused with green fluorescent protein (MP:GFP) changed during the infection process. However, the intracellular route through which MP is transported and its biological meaning are still obscure. Treatment with brefeldin A (BFA), which disrupts ER-to-Golgi transport, inhibited the formation of irregularly shaped and filamentous structures of MP. In this condition, MP was still targeted to plasmodesmata in leaf cells. Furthermore, the viral cell-to-cell movement was not inhibited by BFA treatment. These data indicated that the targeting of viral replication complexes (VRCs) to plasmodesmata is mediated by a BFA-insensitive pathway and that the ER-to-Golgi transport pathway is not involved in viral intercellular movement.     

Abutilon mosaic virus DNA B component supports mechanical virus transmission, but does not counteract begomoviral phloem limitation in transgenic plants

Different Nicotiana benthamiana lines stably transformed with Abutilon mosaic virus (AbMV) dimeric DNA B were capable of systemically spreading complete bipartite AbMV genomes, following agroinoculation of DNA A alone. Constitutively expressed viral movement protein (BC1) did not induce any persistent disease phenotype, but plants developed transient morphological abnormalities such as radially symmetric leaves after kanamycin withdrawal. Systemic AbMV infection produced symptoms and virus titers indistinguishable from those in non-transgenic plants. In systemically invaded leaves, the begomovirus remained phloem-limited, whereas the plants' susceptibility to mechanical transmission of AbMV was enhanced by a factor of three to five, as compared to non-transgenic controls. Hence, DNA B-encoded movement functions can complement local movement to the phloem after mechanical transmission, but fail to support viral invasion of non-phloem cells in systemically infected organs, indicating that the phloem restriction of AbMV does not result predominantly from a lack of transport competence in mesophyll tissues.     

Covert unimanual response preparation triggers attention shifts to effectors rather than goal locations

The premotor theory of attention postulates that during response preparation, attention shifts are elicited towards the goal of a prepared movement. Support for this claim comes from research demonstrating enhanced performance at the location of upcoming saccades. To investigate whether attention shifts occur towards effectors or goal locations during the covert preparation of unimanual movements, we recorded event related brain potentials (ERPs) to task-irrelevant tactile probes that were presented while participants prepared to move one hand towards the index finger of the other hand, as directed by visual response cues presented at the start of each trial. These cues specified either the effector or the goal location of an upcoming movement. The somatosensory N140 component was enhanced when probes were presented to the effector hand relative to the goal hand, regardless of cue instructions. Analogous modulations of the N80 component were only present with effector cues. These results demonstrate a close link between covert response preparation and attention shifts, and strongly suggest that attention shifts are directed to the effector, and not to the goal location of manual movements.