A study of variable origins of arteries in arm

A series of anomalous arterial supply of the arm and shoulder is presented. In these cases, the deep brachial artery arose from a common trunk with posterior circumflex humeral artery. In one case, the superior ulnar collateral artery and deep brachial artery originated from the posterior circumflex humeral artery. The common trunk or posterior circumflex humeral artery arose from the brachial artery at the level of the lower border of the teres major (at the origin of the brachial artery). A possible ontogenetic explanation is provided for this situation. Awareness of the variations of arteries of the arm or shoulder is important for angiographers and the surgeon who operates in this region. Preliminary part of this study was presented at the 1st Joint Meeting of EACA (European Association of Clinical Anatomy), AACA (American Association of Clinical Anatomists), Graz, Austria, 7–11 July, 2003.     

Partially overlapping neural networks for real and imagined hand movements

Neuroimagery findings have shown similar cerebral networks associated with imagination and execution of a movement. On the other hand, neuropsychological studies of parietal-lesioned patients suggest that these networks may be at least partly distinct. In the present study, normal subjects were asked to either imagine or execute auditory-cued hand movements. Compared with rest, imagination and execution showed overlapping networks, including bilateral premotor and parietal areas, basal ganglia and cerebellum. However, direct comparison between the two experimental conditions showed that specific cortico-subcortical areas were more engaged in mental simulation, including bilateral premotor, prefrontal, supplementary motor and left posterior parietal areas, and the caudate nuclei. These results suggest that a specific neuronal substrate is involved in the processing of hand motor representations.     

Cortical mechanisms of feature-based attentional control

A network of fronto-parietal cortical areas is known to be involved in the control of visual attention, but the representational scope and specific function of these areas remains unclear. Recent neuroimaging evidence has revealed the existence of both transient (attention-shift) and sustained (attention-maintenance) mechanisms of space-based and object-based attentional control. Here we investigate the neural mechanisms of feature-based attentional control in human cortex using rapid event-related functional magnetic resonance imaging (fMRI). Subjects viewed an aperture containing moving dots in which dot color and direction of motion changed once per second. At any given moment, observers attended to either motion or color. Two of six motion directions and two of six colors embedded in the stimulus stream cued subjects either to shift attention from the currently attended to the unattended feature or to maintain attention on the currently attended feature. Attentional modulation of the blood oxygenation level dependent (BOLD) fMRI signal was observed in early visual areas that are selective for motion and color. More importantly, both transient and sustained BOLD activity patterns were observed in different fronto-parietal cortical areas during shifts of attention. We suggest these differing temporal profiles reflect complementary roles in the control of attention to perceptual features.     

A discrete-time optimal adaptive control law for a robot arm

The equations of motion describing a robot's dynamics are coupled and non-linear, making the design of an optimum controller difficult using classical techniques. In this work an explicit adaptive control law is proposed based on a discrete linear model for each link and on the minimization of a quadratic performance criterion for position error and total control effort. The system parameters are recursively estimated at each control step by use of least squares, with a typical sample time of 0.02 s. A computer simulation of the resulting scheme is performed to evaluate the controller. The simulation model, based on the first three links of an existing robot, includes detailed motor dynamics and treats the wrist assembly as a load mass. Simulated test paths requiring movement of the outer two links indicate that the controller adapts and that its behaviour is stable and convergent.     

Cortical network for gaze control in humans revealed using multimodal MRI

Functional magnetic resonance imaging (fMRI) techniques allow definition of cortical nodes that are presumed to be components of large-scale distributed brain networks involved in cognitive processes. However, very few investigations examine whether such functionally defined areas are in fact structurally connected. Here, we used combined fMRI and diffusion MRI-based tractography to define the cortical network involved in saccadic eye movement control in humans. The results of this multimodal imaging approach demonstrate white matter pathways connecting the frontal eye fields and supplementary eye fields, consistent with the known connectivity of these regions in macaque monkeys. Importantly, however, these connections appeared to be more prominent in the right hemisphere of humans. In addition, there was evidence of a dorsal frontoparietal pathway connecting the frontal eye field and the inferior parietal lobe, also right hemisphere dominant, consistent with specialization of the right hemisphere for directed attention in humans. These findings demonstrate the utility and potential of using multimodal imaging techniques to define large-scale distributed brain networks, including those that demonstrate known hemispheric asymmetries in humans.     

Spinal functions in sensorimotor control of movements

The transformation of sensory information to movement patterns in spinal interneuronal systems is far from just being a stereotyped reflex pattern. Information from the different sensory modalities (skin-, muscle, and joint receptors) is integrated at the interneuronal level and transformed into patterns of coordinated movements which are adapted to the current position and the phase of movement of a limb. In addition, spinal interneuronal systems are capable of generating rhythmic motor activities like locomotion or scratching without a sensory feed-back from the periphery and without a corresponding drive from supraspinal structures.The same interneuronal systems which are engaged in the reflexogenic control and generation of movements at the spinal level also convey information for the performance of supraspinally-induced, goal-directed (voluntary) movements. The inherent convergence between descending and peripheral afferent information onto common interneuronal systems implies an improved coordination and adaptation of movements in dependence on the peripheral conditions. Disturbance of the supraspinal control of these interneuronal systems leads to an impairment of the transformation of sensory inputs into motor acts. Spasticity is probably partly caused by such a disturbed control of the transmission in the interneuronal systems.     

Recruitment of spinal motor pools during voluntary movements versus stepping after human spinal cord injury

We investigated the activation of lower limb motor pools by supraspinal and spinal networks after human spinal cord injury (SCI). We compared electromyographic (EMG) activity from six muscles during voluntarily attempted non-weight-bearing single-joint movements, multijoint movements approximating stepping in a supine position, and weight-bearing stepping on a treadmill with body weight support (BWST) in seven clinically incomplete and three clinically complete SCI subjects. Seven SCI subjects had previously completed Laufband therapy (a specific step training using variable levels of body weight support and manual assistance). Significant coactivation of agonists and antagonists and multijoint flexion or extension movements of the entire limb occurred during attempts at isolated knee or ankle single-joint movements in clinically incomplete SCI subjects. Further, some muscles that were not recruited during voluntary attempts at single-joint movements were activated during voluntary step-like multijoint movements (5/16 comparisons). This suggests that the residual voluntary motor control in incomplete SCI subjects evokes more generalized motor patterns (limb flexion or extension) rather than selective activation of individual muscles. Clinically incomplete and clinically complete SCI subjects could achieve greater activation of motor pools and more reciprocal patterns of activity between agonists and antagonists during weight bearing stepping than during non-weight-bearing voluntary movements. The EMG mean amplitudes were higher during stepping than during voluntary movements in 50/60 muscles studied (p < 0.05). These results suggest that stepping with knee and hip extension and flexion and alternating lower limb loading and unloading provides proprioceptive inputs to the spinal cord that increases motor recruitment and improves reciprocity between agonists and antagonists compared to voluntary efforts.     

Contribution of arm movement to the force components of a maximum vertical jump

Vertical jump is used commonly as a measure of leg power for evaluation prior to participation in sports activities (RK Gray, KB Start, DJ Glencross, Res Q 33:230-235, 1962; DO Klotz, Doctoral dissertation, University of Iowa, 1948). Unless vertical jump meets the definition of mechanical leg power, it should not be used as a measure of leg power. Measurement of leg power in a vertical jump should not be started with a countermovement of the arms prior to jumping. The purpose of this research was to investigate the kinetic and kinematic contributions of arm movement to the vertical jump. Eighteen subjects performed three vertical jumps on a force platform with arm movement and three jumps without arm movement. The contribution of arm movement to maximum force, work done, power, and the release velocity was found as 6, 14, 15, and 6%, respectively, for this population. The contribution of the arm action to reduce the impact force was 12%. The contribution of arm movement to vertical jump maximum force in this study was less than reported in previous studies. J Orthop Sports Phys Ther 1989;11(5):198-201.