Tactile activity in primate primary somatosensory cortex during active arm movements: cytoarchitectonic distribution

1. Cells were recorded in areas 3b and 1 of the primary somatosensory cortex (SI) of three monkeys during active arm movements. Successful reconstructions were made of 46 microelectrode penetrations, and 298 cells with tactile receptive fields (RFs) were located as to cytoarchitectonic area, lamina, or both. 2. Area 3b contained a greater proportion of cells with slowly adapting responses to tactile stimuli and fewer cells with deep modality inputs than did area 1. Area 3b also showed a greater level of movement-related modulation in tactile activity than area 1. Other cell properties were equally distributed in the two areas. 3. The distribution of cells with low-threshold tactile RFs that also responded to lateral stretch of the skin or to passive arm movements was skewed toward deeper laminae than for tactile cells that did not respond to those manipulations. 4. The variation of activity of tactile neurons during arm movements in different directions was weaker in the superficial laminae than in deeper cortical laminae. 5. Cells with only increases in activity during arm movements were preferentially but not exclusively located in middle and superficial layers. Cells with reciprocal responses were found mainly in laminae III and V, whereas cells with only decreases in activity were concentrated in lamina V. 6. Overall, active arm movements evoke directionally tuned tactile and "deep" activity in areas 3b and 1, in particular in the deeper cortical laminae that are the source of the descending output pathways from SI.     

Coupling of grip force and load force during arm movements with grasped objects

Numerous studies have investigated the kinematics of arm movements; others have examined grip forces during static holding of objects. However, the coordination of grip force and arm movement when moving grasped objects has not been documented. We show that grip force is finely modulated in phase with load force during movements with grasped objects in which load force varies with acceleration. A tight coupling between grip and load force is seen in point-to-point and cyclic movements of varying rate and direction. We conclude that in transporting an object, the programming of grip force is part and parcel of the process of planning the arm movement.     

Neuromuscular propagation after fatiguing contractions of the paralyzed soleus muscle in humans

We analyzed the M wave and torque after repetitive activation and recovery of the human soleus muscle in individuals with spinal cord injury. Fifteen individuals with complete paralysis had the tibial nerve activated for 330 ms every second with a 20-Hz train. The M wave and torque were analyzed before fatigue, immediately after fatigue, and during recovery. The torque and three M-wave measurements (amplitude, duration, median frequency) changed significantly after fatigue in the chronic group, but the M-wave area was not changed. The M wave was completely recovered after 5 min of rest, even though the torque remained depressed during recovery. The M-wave changes appeared to contribute minimally to the reduced torque in individuals with chronic paralysis. The disassociation in the M-wave-torque relationship during fatigue and recovery suggests, that electrical stimulation under electromyography control is not an ideal method to optimize torque in paralyzed muscle.     

Motor-unit recruitment in self-reinnervated muscle

1. Recruitment order of motor units in self-reinnervated medial gastrocnemius (MG) muscles was studied in decerebrate cats 16 mo after surgical reunion of the cut MG nerve. Pairs of MG motor units were isolated by dual microelectrode penetration of ventral roots to measure their recruitment sequence during cutaneous reflexes in relation to their physiological properties. 2. Physiological properties of reconstituted motor units appeared normal, as expected. Also normal were the relationships among these properties: twitch and tetanic tension tended to increase with axonal conduction velocity and decrease with twitch contraction time. A small fraction of motor units (10/116) in reinnervated muscles produced either no measurable tension or unusually large amounts of tension compared with controls. This was the only distinct feature of the sample of reconstituted units. 3. In muscles reinnervated after nerve section, stretch was notably ineffective in eliciting reflex contraction of MG muscles or their constituent motor units (only 5/116 units). Incomplete recovery from nerve section was probably the cause of this impairment, because stretch reflexes were readily evoked in adjacent untreated muscles and in one reinnervated MG muscle that was studied 16 mo after nerve crush. In contrast with the ineffectiveness of muscle stretch, sural nerve stimulation succeeded in recruiting 49/116 units, a proportion fairly typical of normal MG muscles. 4. The contractions of the first unit recruited in cutaneous reflexes tended to be slower and less forceful than those of the other unit in a pair. By these measures, recruitment obeyed the size principle. This recruitment order with respect to unit contractile properties was not significantly different (P > 0.05) between untreated and reinnervated muscles but was significantly (P < 0.005) different from random order in both groups. The same recruitment pattern was observed for pairs of motor units sampled from the muscle reinnervated after nerve crush, whether units were recruited by muscle stretch or sural nerve stimulation. 5. The usual tendency for motor units with slower conduction velocity (CV) to be recruited in sural nerve reflexes before those with faster CV was not strong in reinnervated muscles. After nerve section the proportion of units exhibiting the usual recruitment pattern was not significantly different (P > 0.05) from a random pattern for CV. 6. The central finding is that the normal recruitment patterns recover from nerve injury in a muscle that is reinnervated by its original nerve. By contrast, stretch reflexes do not recover well from nerve section, and this deficiency may contribute to motor disability.     

Patterns of arm muscle activation involved in octopus reaching movements

The extreme flexibility of the octopus arm allows it to perform many different movements, yet octopuses reach toward a target in a stereotyped manner using a basic invariant motor structure: a bend traveling from the base of the arm toward the tip (Gutfreund et al., 1996a). To study the neuronal control of these movements, arm muscle activation [electromyogram (EMG)] was measured together with the kinematics of reaching movements. The traveling bend is associated with a propagating wave of muscle activation, with maximal muscle activation slightly preceding the traveling bend. Tonic activation was occasionally maintained afterward. Correlation of the EMG signals with the kinematic variables (velocities and accelerations) reveals that a significant part of the kinematic variability can be explained by the level of muscle activation. Furthermore, the EMG level measured during the initial stages of movement predicts the peak velocity attained toward the end of the reaching movement. These results suggest that feed-forward motor commands play an important role in the control of movement velocity and that simple adjustment of the excitation levels at the initial stages of the movement can set the velocity profile of the whole movement. A simple model of octopus arm extension is proposed in which the driving force is set initially and is then decreased in proportion to arm diameter at the bend. The model qualitatively reproduces the typical velocity profiles of octopus reaching movements, suggesting a simple control mechanism for bend propagation in the octopus arm.     

Possible explanations for trajectory curvature in multijoint arm movements.

Although the straightness of hand paths is a widely accepted feature of human multijoint reaching movement, detailed examinations have revealed slight curvatures in some regions of the workspace. This observation raises the question of whether planned trajectories are straight or curved. If they are straight, 3 possible factors can explain the observed curvatures: (a) imperfect control, (b) visual distortion, or (c) interaction between straight virtual trajectories and the dynamics of the arm. Participants instructed to generate straight movement paths produced movements much straighter than those generated spontaneously. Participants generated spontaneously curved trajectories in the frontoparallel plane, where visual distortion is not expected. Electromyograms suggested that participants generated straighter paths without an increase in arm stiffness. These findings argue against the 3 factors. It follows that planned trajectories are likely to be curved. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of prior arm exercise on pulmonary gas exchange kinetics during high-intensity leg exercise in humans

The activation of MAPKs is controlled by the balance between MAPK kinase and MAPK phosphatase activities. The latter is mediated by a subset of phosphatases with dual specificity (VH-1 family). Here, we describe a new member of this family encoded by the puckered gene of Drosophila. Mutations in this gene lead to cytoskeletal defects that result in a failure in dorsal closure related to those associated with mutations in basket, the Drosophila JNK homolog. We show that puckered mutations result in the hyperactivation of DJNK, and that overexpression of puc mimics basket mutant phenotypes. We also show that puckered expression is itself a consequence of the activity of the JNK pathway and that during dorsal closure, JNK signaling has a dual role: to activate an effector, encoded by decapentaplegic, and an element of negative feedback regulation encoded by puckered.     

Neural dynamics of planned arm movements: Emergent invariants and speed-accuracy properties during trajectory formation.

A real-time neural network model, called the vector-integration-to-endpoint (VITE) model is developed and used to simulate quantitatively behavioral and neural data about planned and passive arm movements. Invariants of arm movements emerge through network interactions rather than through an explicitly precomputed trajectory. Quantitative simulations are provided of Woodworth's law, of the speed–accuracy trade-off known as Fitts's law, of isotonic arm-movement properties before and after deafferentation, of synchronous and compensatory "central-error-correction" properties of isometric contractions, of velocity amplification during target switching, of velocity profile invariance and asymmetry, of the changes in velocity profile asymmetry at higher movement speeds, of the automatic compensation for staggered onset times of synergetic muscles, of vector cell properties in precentral motor cortex, of the inverse relation between movement duration and peak velocity, and of peak acceleration as a function of movement amplitude and duration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation of the mandibular stretch reflex sensitivity during various phases of rhythmic open-close movements in humans

Enzymatically formed peptides show positional variations as well as highly conserved amino acids. In the cases of gramicidin S, tyrocidine, linear gramicidins, enniatins, echinocandins and viridogrisein in vivo and in vitro studies indicate substrate selection at the level of amino acid activation as a major control step. Evidence for proof-reading steps beyond activation has been obtained in penicillin and cyclosporin biosynthesis. Activated substrate analogues may promote the formation of side products such as dipeptides and cyclodipeptides. Modifications of intermediates, such as N-methylation, influence the rates of peptide synthesis. These control steps pose limitations for the application of such enzyme systems in the production of peptide libraries. They may originate from a target oriented evolution of these synthetases.     

Cerebellar complex spikes encode both destinations and errors in arm movements

Purkinje cells of the cerebellum discharge complex spikes, named after the complexity of their waveforms, with a frequency of approximately 1 Hz during arm movements. Despite the low frequency of firing, complex spikes have been proposed to contribute to the initiation of arm movements or to the gradual improvement of motor skills. Here we recorded the activity of Purkinje cells from the hemisphere of cerebellar lobules IV-VI while trained monkeys made short-lasting reaching movements (of approximately 200 milliseconds in duration) to touch a visual target that appeared at a random location on a tangent screen. We examined the relationship between complex-spike discharges and the absolute touch position, and between complex-spike discharges and relative errors in touching the screen. We used information theory to show that the complex spikes occurring at the beginning of the reach movement encode the absolute destination of the reach, and the complex spikes occurring at the end of the short-lasting movements encode the relative errors. Thus, complex spikes convey multiple types of information, consistent with the idea that they contribute both to the generation of movements and to the gradual, long-term improvement of these movements.     

Effect of fatiguing exercise on longitudinal bone strain as related to stress fracture in humans

BACKGROUND: It has already been shown that the production of fucosylceramide, an aberrant glycolipid, is associated with neoplastic changes in human tissues. The authors of this study designed a sandwich radioimmunoassay (RIA) using a mouse monoclonal anti-fucosylceramide antibody, PC47H, designated as PC/PC RIA, and measured the level of u-FCC, an antigen of PC47H, in the urine of cancer patients. METHODS: The cohort comprised 41 patients with gastric carcinoma, 35 with colorectal carcinoma, 34 with other malignancies, 14 with cholelithiasis, 18 with gastric ulcer, and 110 healthy individuals. The u-FCC was quantified by PC/PC RIA. The cutoff value of u-FCC was obtained from the 110 healthy individuals, and the rates of positivity for gastric and colorectal carcinoma patients were evaluated. RESULTS: The rates of u-FCC positivity were 63% for patients with gastric carcinoma and 69% for colorectal carcinoma patients. The rate was only 1% (1/110) for the healthy individuals. The u-FCC value did not correlate with the values of either CA 19-9 or carcinoembryonic antigen (CEA). In a combination assay of u-FCC with CA 19-9 and CEA, the positivity rates were 84% for gastric carcinoma patients and 85% for colorectal carcinoma patients. CONCLUSIONS: Gastric and colorectal carcinoma patients have significantly high levels of u-FCC in their urine compared with normal individuals.     

Locomotor-like movements evoked by leg muscle vibration in humans

We attempted to elicit automatic stepping in healthy humans using appropriate afferent stimulation. It was found that continuous leg muscle vibration produced rhythmic locomotor-like stepping movements of the suspended leg, persisting up to the end of stimulation and sometimes outlasting it by a few cycles. Air-stepping elicited by vibration did not differ from the intentional stepping under the same conditions, and involved movements in hip and knee joints with reciprocal electromyogram (EMG) bursts in corresponding flexor and extensor muscles. The phase shift between evoked hip and knee movements could be positive or negative, corresponding to 'backward' or 'forward' locomotion. Such an essential feature of natural human locomotion as alternating movements of two legs, was also present in vibratory-evoked leg movements under appropriate conditions. It is suggested that vibration evokes locomotor-like movements because vibratory-induced afferent input sets into active state the central structures responsible for stepping generation.     

Cortical activation during fast repetitive finger movements in humans: dipole sources of steady-state movement-related cortical potentials

Fast repetitive finger movements are associated with characteristic EEG patterns described in humans as steady-state movement-related cortical potentials (ssMRCPs). The objective of the present study was to determine the electrical generators of ssMRCPs (movement rate, 2 Hz) by dipole modelling. The generators for the initial ssMRCP phase (peak approximately 60 msec before EMG onset) were located in the central region bilaterally, with largely radial orientation, consistent with activation of the crown of the precentral gyrus. The generator of the next phase (peak approximately 10 msec after EMG onset) was located in the contralateral central region with tangential posterior orientation, consistent with activation of the anterior wall of the central sulcus. The postmovement phase (peak approximately 95 msec after EMG onset) was explained by another source in the contralateral central region with tangential anterior orientation, consistent with activation of the posterior wall of the central sulcus. This pattern probably corresponds to a sequence of activation of the bilateral dorsal premotor cortex, contralateral primary motor, and primary somatosensory cortex that takes place within approximately 200 msec around EMG onset. Steady-state movement-related cortical potentials in combination with dipole modelling provide a novel, noninvasive approach to assessing changes of human cortical premotor, motor, and somatosensory activation in the millisecond range.     

Effects of aging on planning and implementing arm movements.

In Exps 1 and 2, aiming movements were performed with and without visual feedback in young and elderly adults. The initial (acceleration and deceleration phases) and secondary movement components were analyzed. Although deceleration phase accuracy decreased without visual feedback in both age groups, accuracy diminished as movement amplitude increased only in the elderly. This suggested that the elderly were more dependent on visual feedback to modify motor programs for longer duration movements. Velocity also increased less with increasing amplitude and target size in the elderly, which was related to impaired preprogramming (acceleration phase) and implementation (deceleration phase) of higher forces. This conclusion was confirmed directly in Exp 2 because only the deceleration phase was affected by the removal of a visual feedback of arm position when availability of visual information could not be predicted before movement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Position of the egocentric reference and directional arm movements in right-brain-damaged patients

An increasing number of economic evaluations are being conducted alongside clinical trials. While this practice offers the prospect of collecting comprehensive and accurate cost data, it requires considerable time and effort. In the case of clinical data, key analytic decisions such as which data to collect and sample size are often made with reference to smaller (pilot) trials. However, this approach is not normally followed in the case of economic evaluation. This study was based on a recently completed health technology assessment comparing conventional radiotherapy with continuous hyperfractionated accelerated radiotherapy (CHART) for patients with head and neck cancer or carcinoma of the bronchus. In the full health technology assessment, cost data were available for 526 head and neck patients (314 CHART and 212 conventional therapy) and 286 bronchus patients (175 CHART and 109 conventional therapy). In order to simulate a pilot study, data were extracted for the patients recruited to both trials in the first 3 months. These were then compared with the full data set in order to assess whether such a pilot study would have given useful guidance on: a) the usefulness of undertaking a full study; b) the sample size required; and c) the important resource items for which comprehensive data collection would be required. Pilot studies can be helpful in determining the likely advantages of undertaking full economic evaluations and in identifying important resource items. Therefore, it is important that clinical researchers and research funding bodies create the necessary time window to enable such studies to take place. However, formal sample size calculations are more difficult to perform on limited data, since they also require knowledge of the unit cost (or prices) to be attached to the resource items and the correlation between costs and clinical effects.     

Mechanical output and electromyographic parameters in males and females during fatiguing knee-extensions

Although extensive research has been carried out on the respiratory and renal effects of intra-abdominal pressure increase, there is limited research with regard to its effects on bacterial translocation. The objective of this study was to discuss whether the high intra-abdominal pressure due to carbon dioxide (CO2) insufflation during laparoscopy leads to bacterial translocation. Eighteen male dogs, 7 of which constituted the control group, were used in the study. Two study groups, in which the intra-abdominal pressure was raised to 15 mm Hg and kept at that level for 30 and 120 minutes, respectively, were set. Blood gases and blood pressure values were observed throughout the experiments. Samples of peritoneal smear, portal vein blood, mesenteric lymph node, liver, spleen, and cecum were examined to detect bacterial translocation. Histopathological examinations of all samples were also carried out. No translocation was detected in the samples of peritoneal smear, portal blood, mesenteric lymph node, liver, or spleen, but in the samples of cecum, bacterial colonization for the second group (p<0.05) and for the third group (p<0.05) was significantly higher compared with the control group. There was a considerable difference between the second and third groups (p<0.05). The changes in the mesenteric lymph nodes were interpreted to be a result of bacterial drainage. Histopathological examination disclosed active changes in the mesenteric lymph nodes in all groups, but there was considerable sinus histiocytosis only in the third group. We conclude that the intraabdominal pressure of 15 mm Hg created by carbon dioxide insufflation does not lead to bacterial translocation but causes intraluminal bacterial colonization in the cecum after 30 minutes and after 2 hours.     

Cortical activation during fast repetitive finger movements in humans: steady-state movement-related magnetic fields and their cortical generators

OBJECTIVE: To study the cortical physiology of fast repetitive finger movements. METHODS: We recorded steady-state movement-related magnetic fields (ssMRMFs) associated with self-paced, repetitive, 2-Hz finger movements in a 122-channel whole-head magnetometer. The ssMRMF generators were determined by equivalent current dipole (ECD) modeling and co-registered with anatomical magnetic resonance images (MRIs). RESULTS: Two major ssMRMF components occurred in proximity to EMG onset: a motor field (MF) peaking at 37+/-11 ms after EMG onset, and a postmovement field (post-MF), with inverse polarity, peaking at 102+/-13 ms after EMG onset. The ECD for the MF was located in the primary motor cortex (M1), and the ECD for the post-MF in the primary somatosensory cortex (S1). The MF was probably closely related to the generation of corticospinal volleys, whereas the post-MF most likely represented reafferent feedback processing. CONCLUSIONS: The present data offer further evidence that the main phasic changes of cortical activity occur in direct proximity to repetitive EMG bursts in the contralateral M1 and S1. They complement previous electroencephalography (EEG) findings on steady-state movement-related cortical potentials (ssMRCPs) by providing more precise anatomical information, and thereby enhance the potential value of ssMRCPs and ssMRMFs for studying human sensorimotor cortex activation non-invasively and with high temporal resolution.     

Central modifications of reflex parameters may underlie the fastest arm movements

Descending and reflex pathways usually converge on common interneurons and motoneurons. This implies that active movements may result from changes in reflex parameters produced by control signals conveyed by descending systems. Specifically, according to the lambda-model, a fast change in limb position is produced by a rapid change in the threshold of the stretch reflex. Consequently, external perturbations may be ineffective in eliciting additional reflex modifications of electromyographic (EMG) patterns unless the perturbations are relatively strong. In this way, the model accounts for the relatively weak effects of perturbations on the initial agonist EMG burst (Ag1) usually observed in fast movements. On the other hand, the same model permits robust reflex modifications of the timing and shape of the Ag1 in response to strong perturbations even in the fastest movements. To test the model, we verified the suggestion that the onset time of the Ag1, even in the fastest movements, depends on proprioceptive feedback in a manner consistent with a stretch reflex. In control trials, subjects (n = 6) made fast unopposed elbow flexion movements of approximately 60 degrees (peak velocity 500-700 degrees/s) in response to an auditory signal. In random test trials, a brief (50 ms) torque of 8-15 Nm either assisting or opposing the movement was applied 50 ms after this signal. Subjects had no visual feedback and were instructed not to correct arm deflections in case of perturbations. In all subjects, the onset time of the Ag1 depended on the direction of perturbation: it was 25-60 ms less in opposing compared with assisting load conditions. Assisting torques caused, at a short latency of 37 ms, an additional antagonist EMG burst preceding the Ag1. The direction-dependent effects of the perturbation persisted when cutaneous feedback was suppressed. It was concluded that the direction-dependent changes in the onset time and duration of the Ag1 as well as the antagonist activation preceding the Ag1 resulted from stretch reflex activity elicited by the perturbations rather than from a change in the control strategy or cutaneous reflexes. The results support the hypothesis on the hierarchical scheme of sensorimotor integration in which EMG patterns and movement emerge from the modification of the thresholds and other parameters of proprioceptive reflexes by control systems.     

The effect of head-to-trunk position on the direction of arm movements before, during, and after space flight

This contribution deals with the examination of the consequences of different head-to-trunk positions on arm movements under normal gravity and during prolonged space flight. One of the objectives of this study was to investigate the influence of weightlessness on the condition of the spatial analysis system. Aimed arm movements in the horizontal plane (pointings towards two visual targets) were recorded, first with eyes open, head straight (learning part), then with eyes closed, head straight and during yaw or roll position of the head (performance part). Measurements related to these different head-to-trunk-positions were taken in one short-term and nine long-term cosmonauts preflight, inflight, and postflight. Terrestrial control experiments were carried out with an extended experimental design in 14 healthy volunteers. The analysis of these experiments revealed that, with eyes closed and the head in yaw position, cosmonauts before flight and control subjects exhibit significant slants of the movement plane of the arm. Contrary to terrestrial measurements, in space experiments roll tilt of the head to the right is correlated with considerable counterclockwise slant of the movement plane. This slant of the movement plane of the arm was interpreted as tilt of the internal representation of the horizontal coordinate. The effect is larger with greater distortion induced by the changed head position and with larger muscular involvement to keep this position. This effect is also increased by the reduction of information (for example, in microgravity). The amount and the direction of the horizontal offset of the arm movements are shown to be dependent on the head-to-trunk position, too. Additionally, we have found changes in the amplitude and in the duration of the arm movement, in the vertical offset, and in the curvature of the movement paths, depending on the experimental conditions.