The role of directional compatibility in assembling coordination patterns involving the upper and lower limb girdles and the head

The role of directional compatibility was investigated during the production of in-phase and anti-phase coordination patterns involving the four limbs as well as the head. Our first aim was to compare the quality of interlimb coordination between concordant and discordant coordination patterns across girdles at different cycling frequencies. Concordant implied adoption of either the in-phase or anti-phase coordination mode across both girdles whereas discordant implied a combination of both modes. The second aim was to study the effect of periodic head movements upon the assembling of a coordinative synergy among the limbs. Findings revealed that concordant coordination modes were produced with higher accuracy and consistency than discordant coordination modes and this effect was more distinct at higher cycling frequencies. Inclusion of head movements was found to destabilize in-phase coordination but stabilize anti-phase coordination patterns, particularly during discordant conditions at higher cycling frequencies. This observation contrasts with previous findings in which anti-phase modes have invariably been shown to be more vulnerable to experimental perturbations than in-phase modes. The findings are discussed within the context of the coalition of egocentric and allocentric constraints during multilimb coordination and the role of direction as an organizing principle in movement control.     

Parieto-premotor areas mediate directional interference during bimanual movements

In bimanual movements, interference emerges when limbs are moved simultaneously along incompatible directions. The neural substrate and mechanisms underlying this phenomenon are largely unknown. We used functional magnetic resonance imaging to compare brain activation during directional incompatible versus compatible bimanual movements. Our main results were that directional interference emerges primarily within superior parietal, intraparietal and dorsal premotor areas of the right hemisphere. The same areas were also activated when the unimanual subtasks were executed in isolation. In light of previous findings in monkeys and humans, we conclude that directional interference activates a parieto-premotor circuit that is involved in the control of goal-directed movements under somatosensory guidance. Moreover, our data suggest that the parietal cortex might represent an important locus for integrating spatial aspects of the limbs' movements into a common action. It is hypothesized to be the candidate structure from where interference arises when directionally incompatible movements are performed. We discuss the possibility that interference emerges when computational resources in these parietal areas are insufficient to code two incompatible movement directions independently from each other.     

The expanding role of the otolaryngologist in managing infants and children with hearing loss

Universal newborn hearing screening will increase the number of very young children requiring care from an otolaryngologist. Although the otolaryngologist is the perceived expert in managing hearing loss, he or she must collaborate with a team of specialists to provide comprehensive treatment for the newly diagnosed child and its family. Working within a team that includes a pediatrician, audiologist, otolaryngologist, speech pathologist, teachers, and care coordinators allows each professional to contribute significantly to the well-being of the child and parents. Group cooperation and parental support can increase the chances of normal speech and language development in an infant with hearing loss. By identifying related or syndromal associations, the otolaryngologist can prevent complications related to other organ systems such as the heart and eyes. Most importantly, parents and patients look up to the validation of the care plan by the ear physician.     

Directional interference during bimanual coordination: is interlimb coupling mediated by afferent or efferent processes

The role of afferent information in bimanual directional interference was studied by means of a modulation of the response-produced information in one of both limbs. In Experiment 1, visual information was either present, withdrawn, or shown with a directional transformation on a LCD screen. In Experiment 2, the technique of muscle tendon vibration was used to bias the kinesthetic afferent information associated with movement. The findings revealed strong evidence for directional interference between both limbs. Nevertheless, no evidence could be advanced that the observed interference from the right onto the left limb movement was modulated by manipulation of the afferent sources of information. It is concluded that directional interference primarily emerges at the efferent level of movement planning and organization.     

Modified implant surfaces show different biofilm compositions under in vivo conditions

Objective: Plaque accumulation on implant surfaces can result in peri-implantitis with potential implant loss. The aim of the present study was to examine the influence of zirconium nitride (ZrN) as a potential implant surface on the biofilm composition and diversity in vivo .
Material and methods: ZrN- or titanium (Ti)-coated glass specimens and ZrN or roughened Ti discs were used as substrates. Pure glass and polished titanium served as controls. The specimens were mounted on removable intraoral splints in five adults. After 24 h of intraoral exposure, the biofilms were analyzed applying single-strand conformation polymorphism (SSCP analysis) of 16S rRNA genes. Sequence analysis of the dominant bands excised from the SSCP fingerprints allowed to taxonomically describe bacteria derived from biofilm samples.
Results: The highest number of bands was counted on pure glass and Ti 800. ZrN-coated glass and ZrN-coated titanium discs showed the lowest values for species richness. However, no significant differences were observed regarding the diversity of the identified bacterial species among all the surfaces examined. A total of 46 different bacteria were identified. The dominant bands within the fingerprints indicated bacteria belonging to the Streptococcus group as identified by their 16S rDNA sequence.
Conclusion: A coating of glass surfaces with ZrN significantly reduced the species richness in early bacterial colonization but the diversity was not significantly changed. In consideration of the results obtained by this and former studies a ZrN coating appears to rather modify the quantity of early bacterial adherence than the quality of the microbial community structure.     

Dichoptic reduction of the direction illusion is not due to binocular rivalry

Simultaneous direction repulsion (the direction illusion) occurs in bidirectional motion displays, typically transparent motion random dot kinematograms. Several laboratories have reported a greatly reduced illusion with dichoptic presentation of the two coherently translating stimuli as compared to monocular or binocular presentation. Some researchers have argued that those results might be due to a confounding factor, namely binocular rivalry occurring between test and inducing stimuli in the dichoptic condition, and so have attributed decisive weight to the results reported by Kim and Wilson (1997, Vision Research, 37, 991-1005) who used centre-surround grating stimuli and found large monocular as well as large dichoptic effects. Here we use centre-surround dot stimuli - with which no binocular rivalry occurs - to confirm a strong monocular contribution to the direction illusion. In addition, we fail to find evidence of a direction illusion with centre-surround grating stimuli, even when seeking to replicate the methods of Kim and Wilson (1997). In light of other evidence that a global motion-sensitive mechanism can determine the magnitude of the direction illusion, we propose that simultaneous direction repulsion can result from activity at multiple stages of the motion processing hierarchy.     

Neural substrates of the tilt illusion.

PURPOSE: It has been suggested that direct and indirect tilt illusions and after-effects have different mechanisms, namely that the direct effects arise in VI and are sensitive to differences in spatial and temporal parameters between test and inducing stimuli, whereas indirect effects arise in extrastriate cortex and are insensitive to such parameters. When Wolfe (Vision Research 1984; 24: 1959-64) reported that large direct tilt after-effects occurred with short test flashes, he postulated that either there are distinct mechanisms which process brief and longer duration stimuli or that there are distinct mechanisms that are not primarily concerned with duration but are differentially responsive to temporal parameters amongst several others. RESULTS: In three experiments we demonstrate that large direct tilt illusions can be induced when parameters other than duration are manipulated, including contrast and spatial frequency, and that such large effects can occur when stimulus parameters are chosen to favour preferentially either the transient (magnocellular-like) system or the sustained (parvocellular-like) system. CONCLUSIONS: These results are thus consistent with Wolfe's second hypothesis. None of these stimulus manipulations had any effect on indirect tilt illusions, consistent with previous findings and hypotheses about the different mechanisms of the direct and indirect effects.     

Force requirements of observed object lifting are encoded by the observer’s motor system: a TMS study

Several transcranial magnetic stimulation (TMS) studies have reported facilitation of the primary motor cortex (M1) during the mere observation of actions. This facilitation was shown to be highly congruent, in terms of somatotopy, with the observed action, even at the level of single muscles. With the present study, we investigated whether this muscle‐specific facilitation of the observer’s motor system reflects the degree of muscular force that is exerted in an observed action. Two separate TMS experiments are reported in which corticospinal excitability was measured in the hand area of M1 while subjects observed the lifting of objects of different weights. The type of action ‘grasping‐and‐lifting‐the‐object’ was always identical, but the grip force varied according to the object’s weight. In accordance to previous findings, excitability of M1 was shown to modulate in a muscle‐specific way, such that only the cortical representation areas in M1 that control the specific muscles used in the observed lifting action became increasingly facilitated. Moreover, muscle‐specific M1 facilitation was shown to modulate to the force requirements of the observed actions, such that M1 excitability was considerably higher when observing heavy object lifting compared with light object lifting. Overall, these results indicate that different levels of observed grip force are mirrored onto the observer’s motor system in a highly muscle‐specific manner. The measured force‐dependent modulations of corticospinal excitability in M1 are hypothesized to be functionally relevant for scaling the observed grip force in the observer’s own motor system. In turn, this mechanism may contribute, at least partly, to the observer’s ability to infer the weight of the lifted object.     

Interaction of sound and sight during action perception: Evidence for shared modality-dependent action representations

Seeing or hearing manual actions activates the mirror neuron system, i.e., specialized neurons within motor areas which fire not only when an action is performed but also when it is passively perceived. Although it has been shown that mirror neurons respond to either action-specific vision or sound, it remains a topic of debate whether and how vision and sound interact during action perception.Here we used transcranial magnetic stimulation to explore multimodal interactions in the human motor system, namely at the level of the primary motor cortex (M1). Corticomotor excitability in M1 was measured while subjects perceived unimodal visual (V), unimodal auditory (A), or multimodal (V + A) stimuli of a simple hand action. In addition, incongruent multimodal stimuli were included, in which incongruent vision or sound was presented simultaneously with the auditory or visual action stimulus. A selective response increase was observed to the congruent multimodal stimulus as compared to the unimodal and incongruent multimodal stimuli.These findings speak in favour of ‘shared’ action representations in the human motor system that are evoked in a ‘modality-dependent’ way, i.e., they are elicited most robustly by the simultaneous presentation of congruent auditory and visual stimuli. Multimodality in the perception of hand movements bears functional similarities to speech perception, suggesting that multimodal convergence is a generic feature of the mirror system which applies to action perception in general.     

Proprioceptive sensibility in the elderly: degeneration, functional consequences and plastic-adaptive processes

As the percentage of individuals over the age of 60 years continues to rise, determining the extent and functional significance of age-related declines in sensorimotor performance is of increasing importance. This review examines the specific contribution of proprioceptive feedback to sensorimotor performance in older adults. First, a global perspective of proprioceptive acuity is provided assimilating information from studies where only one of several aspects of proprioceptive function (e.g. sense of position, motion or dynamic position) was quantified, and/or a single joint or limb segment tested. Second, the consequences of proprioceptive deficits are established with particular emphasis placed on postural control. Lastly, the potential for plastic changes in the aging proprioceptive system is highlighted, including studies which relate physical activity to enhanced proprioceptive abilities in older adults. Overall, this review provides a foundation for future studies regarding the proprioceptive feedback abilities of elderly individuals. Such studies may lead to greater advances in the treatment and prevention of the sensorimotor deficits typically associated with the aging process.