Change of facilitation during voluntary bilateral hand activation after stroke

BACKGROUND AND PURPOSE: The relearning of daily activities after stroke also involves performance of bimanual tasks. This raises the possibility that concurrent activation of the healthy hemisphere interferes with reorganization processes in the affected hemisphere due to inhibitory pathways between homologous motor cortex representations. This study investigated the effect of voluntary, simultaneous activation of both hands upon the non-dominant (healthy subjects) or affected (stroke patients) hemisphere. METHODS: Eleven healthy subjects and 16 stroke patients were investigated using transcranial stimulation (TMS). TMS was applied over the non-dominant/affected hemisphere during performance of an isometric pinch grip at different force levels (10% or 50% of maximal voluntary contraction) with the contralateral hand. The ipsilateral hand had to perform the pinch grip at various force levels (10%, 50%, or 100% of maximal voluntary contraction) simultaneously. Peak-to-peak amplitudes of motor evoked potentials (MEPs) were compared to assess differences in motor cortex excitability. RESULTS: Unilateral activity of either hand alone exerted a facilitatory effect upon the non-dominant or affected hemisphere. In healthy subjects, the activation of the ipsilateral hand simultaneously with the contralateral hand did not produce any significant change of the MEP amplitudes compared to unilateral activation of the contralateral hand. In patients, however, the additional activation of the ipsilateral hand caused an additional increase of the peak-to-peak amplitudes. CONCLUSION: In healthy subjects voluntary activation of the ipsilateral hand does not change the excitability of the motor cortex of the non-dominant hemisphere, when the contralateral hand is simultaneously activated. The facilitation of the contralateral hand seems to gate further facilitation by the ipsilateral hand. However, in stroke patients simultaneous activation of both hands causes an additional facilitation compared to activation of the affected hand alone.     

Cognitive, perceptual and action-oriented representations of falling objects

We interact daily with moving objects. How accurate are our predictions about objects' motions? What sources of information do we use? These questions have received wide attention from a variety of different viewpoints. On one end of the spectrum are the ecological approaches assuming that all the information about the visual environment is present in the optic array, with no need to postulate conscious or unconscious representations. On the other end of the spectrum are the constructivist approaches assuming that a more or less accurate representation of the external world is built in the brain using explicit or implicit knowledge or memory besides sensory inputs. Representations can be related to naive physics or to context cue-heuristics or to the construction of internal copies of environmental invariants. We address the issue of prediction of objects' fall at different levels. Cognitive understanding and perceptual judgment of simple Newtonian dynamics can be surprisingly inaccurate. By contrast, motor interactions with falling objects are often very accurate. We argue that the pragmatic action-oriented behaviour and the perception-oriented behaviour may use different modes of operation and different levels of representation.     

The influence of future gaze orientation upon eye-head coupling during saccades

Mammals with foveas (or analogous retinal specializations) frequently shift gaze without moving the head, and their behavior contrasts sharply with afoveate mammals, in which eye and head movements are strongly coupled. The ability to move the eyes without moving the head could reflect a gating mechanism that blocks a default eye-head synergy when an attempted head movement would be energetically wasteful. Based upon such considerations of efficiency, we predicted that for saccades to targets lying within the ocular motor range, the tendency to generate a head movement would depend upon a subjects expectations regarding future directions of gaze. We tested this hypothesis in two experiments with normal human subjects instructed to fixate sequences of lighted targets on a semicircular array. In the target direction experiment, we determined whether subjects were more likely to move the head during a small gaze shift if they expected that they would be momentarily required to make a second, larger shift in the same direction. Adding the onward-directed target increased significantly the distribution of final head positions (customary head orientation range, CHOR) observed during fixation of the primary target from 16.6±4.9° to 25.2±7.8°. The difference reflected an increase in the probability, and possibly the amplitude, of head movements. In the target duration experiment, we determined whether head movements were potentiated when subjects expected that gaze would be held in the vicinity of the target for a longer period of time. Prolonging fixation increased CHOR significantly from 53.7±18.8° to 63.2±15.9°. Larger head movements were evoked for any given target eccentricity, due to a narrowing in the gap between the x-intercepts of the head amplitude:target eccentricity relationship. The results are consistent with the idea that foveate mammals use knowledge of future gaze direction to influence the coupling of saccadic commands to premotor circuitry of the head. While the circuits ultimately mediating the coupling may lie within the brainstem, our results suggest that the cerebrum plays a supervisory role, since it is a likely seat of expectation regarding target behavior. Eye-head coupling may reflect separate gating and scaling mechanisms, and changes in head movement tendencies may reflect parametric modulation of either mechanism.     

Correlation of orofacial speeds with voice acoustic measures in the fluent speech of persons who stutter

Stuttering is often viewed as a problem in coordinating the movements of different muscle systems involved in speech production. From this perspective, it is logical that efforts be made to quantify and compare the strength of neural coupling between muscle systems in persons who stutter (PS) and those who do not stutter (NS). This problem was addressed by correlating the speeds of different orofacial structures with vowel fundamental frequency (F0) and intensity as subjects produced fluent repetitions of a simple nonsense phrase at habitual, high, and low intensity levels. It is assumed that resulting correlations indirectly reflect the strength of neural coupling between particular orofacial structures and the respiratory-laryngeal system. An electromagnetic system was employed to record movements of the upper lip, lower lip, tongue, and jaw in 43 NS and 39 PS. The acoustic speech signal was recorded and used to obtain measures of vowel F0 and intensity. For each subject, correlation measures were obtained relating peak orofacial speeds to F0 and intensity. Correlations were significantly reduced in PS compared to NS for the lower lip and tongue, although the magnitude of these group differences covaried with the correlation levels relating F0 and intensity. It is suggested that the group difference in correlation pattern reflects a reduced strength of neural coupling of the lower lip and tongue systems to the respiratory-laryngeal system in PS. Consideration is given to how this may contribute to temporal discoordination and stuttering.     

Physiologically mediated self/non-self discrimination in roots

Recent evidence suggests that self/non-self discrimination exists among roots; its mechanisms, however, are still unclear. We compared the growth of Buchloe dactyloides cuttings that were grown in the presence of neighbors that belonged to the same physiological individual, were separated from each other for variable periods, or originated from adjacent or remote tillers on the same clone. The results demonstrate that B. dactyloides plants are able to differentiate between self and non-self neighbors and develop fewer and shorter roots in the presence of other roots of the same individual. Furthermore, once cuttings that originate from the very same node are separated, they become progressively alienated from each other and eventually relate to each other as genetically alien plants. The results suggest that the observed self/non-self discrimination is mediated by physiological coordination among roots that developed on the same plant rather than allogenetic recognition. The observed physiological coordination is based on an as yet unknown mechanism and has important ecological implications, because it allows the avoidance of competition with self and the allocation of greater resources to alternative functions.     

Human medial intraparietal cortex subserves visuomotor coordinate transformation

In the macaque, the posterior parietal cortex (PPC) integrates multimodal sensory information for planning and coordinating complex movements. In particular, the areas around the intraparietal sulcus (IPS) serve as an interface between the sensory and motor systems to allow for coordinated movements in space. Because recent imaging studies suggest a comparable functional and anatomical organization of human and monkey IPS, we hypothesized that in humans, as in macaques, the medial intraparietal cortex (area MIP) subserves visuomotor transformations. To test this hypothesis, changes of neural activity were measured using functional magnetic resonance imaging (fMRI) while healthy subjects performed a joystick paradigm similar to the ones previously employed in macaques for studying area MIP. As hypothesized, visuomotor coordinate transformation subserving goal-directed hand movements activated superior parietal cortex with the local maximum of increased neural activity lying in the medial wall of IPS. Compared to the respective visuomotor control conditions, goal-directed hand movements under predominantly proprioceptive control activated a more anterior part of medial IPS, whereas posterior medial IPS was more responsive to visually guided hand movements. Contrasting the two coordinate transformation conditions, changing the modality of movement guidance (visual/proprioceptive) did not significantly alter the BOLD signal within IPS but demonstrated differential recruitment of modality specific areas such as V5/MT and sensorimotor cortex/area 5, respectively. The data suggest that the human medial intraparietal cortex subserves visuomotor transformation processes to control goal-directed hand movements independently from the modality-specific processing of visual or proprioceptive information.     

Interjoint coordination in lower limbs in patients with a rupture of the anterior cruciate ligament of the knee joint

Previous studies of movement kinematics in patients with a ruptured anterior cruciate ligament (ACL) have focused on changes in angular displacement in a single joint, usually flexion/extension of the knee. In the present study, we investigated the effect of an ACL injury on the overall limb interjoint coordination. We asked healthy and chronic ACL-deficient male subjects to perform eight types of movements: forward squats, backward squats, sideways squats, squats on one leg, going up a step, going down a step, walking three steps, and stepping in place. Depending on the movement concerned, we applied principal component (PC) analysis to 3 or 4 degrees of freedom (DFs): thigh flexion/extension, knee flexion/extension, ankle flexion/extension, thigh abduction/adduction. The first three DFs were investigated in all movements. PC analysis identifies linear combinations of DFs. Movements with a fixed ratio between DFs are thus described by only one PC or synergy. PCs were computed for the entire movement as well as for the period of time when the foot was in contact with the ground. For both the control and the injured groups, two synergies (PC vectors) usually accounted for more than 95% of the DFs angular excursions. It was possible to describe 95–99% of some movements using only one synergy. Compared to control subjects, injured subjects employed different synergies for going up a step, walking three steps, squatting sideways, and squatting forward, both in the injured and uninjured legs. Those movements may thus be more indicative of injury than other movements. Although ACL-deficiency did not increase asymmetry (angle between the PCs of the same movement performed on the right and the left sides), this result is not conclusive because of the comparatively low number of subjects who participated in the study. However, the finding that synergies in both legs of patients were different from those in control subjects for going up a step and walking three steps suggests that interjoint coordination was affected for both legs, so that the asymmetry index might have been preserved despite the injury. There was also a relationship between the asymmetry index for squatting on one leg, squatting forward, walking three steps and some of the outcomes of the knee injury and osteoarthritis outcome score (pain, symptoms, activities of daily living, sport and recreation function, and knee-related quality of life). This suggests that significant differences in the asymmetry index could be obtained if more severely-injured patients participated in this study. It is possible that subjects compensated for their mechanical deficiencies by modifying muscle activation patterns. Synergies were not only modified in injured subjects, but also rearranged: the percentage of movement explained by the first PC was different for the injured and/or uninjured legs of patients, as compared to the legs of the control group, for going up a step, going down a step, walking three steps, and squatting forward. We concluded that the analysis of interjoint coordination may be efficient in characterizing motor deficits in people with knee injuries.     

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.     

Preparing patients and caregivers to participate in care delivered across settings: the Care Transitions Intervention

OBJECTIVES: To test whether an intervention designed to encourage older patients and their caregivers to assert a more active role during care transitions can reduce rehospitalization rates. DESIGN: Quasi-experimental design whereby subjects receiving the intervention (n=158) were compared with control subjects derived from administrative data (n=1,235). SETTING: A large integrated delivery system in Colorado. PARTICIPANTS: Community-dwelling adults aged 65 and older admitted to the study hospital with one of nine selected conditions. INTERVENTION: Intervention subjects received tools to promote cross-site communication, encouragement to take a more active role in their care and assert their preferences, and continuity across settings and guidance from a transition coach. MEASUREMENTS: Rates of postdischarge hospital use at 30, 60, and 90 days. Intervention subjects' care experience was assessed using the care transitions measure. RESULTS: The adjusted odds ratio comparing rehospitalization of intervention subjects with that of controls was 0.52 (95% confidence interval (CI)=0.28-0.96) at 30 days, 0.43 (95% CI=0.25-0.72) at 90 days, and 0.57 (95% CI=0.36-0.92) at 180 days. Intervention patients reported high levels of confidence in obtaining essential information for managing their condition, communicating with members of the healthcare team, and understanding their medication regimen. CONCLUSION: Supporting patients and caregivers to take a more active role during care transitions appears promising for reducing rates of subsequent hospitalization. Further testing may include more diverse populations and patients at risk for transitions who are not acutely ill.     

Coordination of suck-swallow and swallow respiration in preterm infants

Safe oral feeding of infants necessitates the coordination of suck-swallow-breathe. Healthy full-term infants demonstrate such skills at birth. But, preterm infants are known to have difficulty in the transition from tube to oral feeding. AIM: To examine the relationship between suck and swallow and between swallow and breathe. It is hypothesized that greater milk transfer results from an increase in bolus size and/or swallowing frequency, and an improved swallow-breathe interaction. METHODS: Twelve healthy preterm (<30 wk of gestation) and 8 full-term infants were recruited. Sucking (suction and expression), swallowing, and respiration were recorded simultaneously when the preterm infants began oral feeding (i.e. taking 1-2 oral feedings/d) and at 6-8 oral feedings/d. The full-term infants were similarly monitored during their first and 2nd to 4th weeks. Rate of milk transfer (ml/min) was used as an index of oral feeding performance. Sucking and swallowing frequencies (#/min), average bolus size (ml), and suction amplitude (mmHg) were measured. RESULTS: The rate of milk transfer in the preterm infants increased over time and was correlated with average bolus size and swallowing frequency. Average bolus size was not correlated with swallowing frequency. Bolus size was correlated with suction amplitude, whereas the frequency of swallowing was correlated with sucking frequency. Preterm infants swallowed preferentially at different phases of respiration than those of their full-term counterparts. CONCLUSION: As feeding performance improved, sucking and swallowing frequency, bolus size, and suction amplitude increased. It is speculated that feeding difficulties in preterm infants are more likely to result from inappropriate swallow-respiration interfacing than suck-swallow interaction.