Raymundo Machado de Azevedo Neto

On the functional integration between postural and supra-postural tasks on the basis of contextual cues and task constraint

In order to evaluate the effects of uncertainty about direction of mechanical perturbation and supra-postural task constraint on postural control, young adults had their upright stance perturbed while holding a tray in a horizontal position. Stance was perturbed by moving forward or backward a supporting platform, contrasting situations of certainty versus uncertainty of direction of displacement. Increased constraint on postural stability was imposed by a supra-postural task of equilibrating a cylinder on the tray. Performance was assessed through EMG of anterior leg muscles, angular displacement of the main joints involved in the postural reactions and displacement of the tray. Results showed that both certainty on the direction of perturbation and increased supra-postural task constraint led to decreased angular displacement of the knee and the hip. Furthermore, combination of certainty and high supra-postural task constraint produced shorter latency of muscular activation. Such postural responses were paralleled by decreased displacement of the tray. These results suggest a functional integration between the tasks, with central set priming reactive postural responses from contextual cues and increased stability demand.

Is early manual preference in infants defined by intermanual performance asymmetry in reaching

In the present study we evaluated the relationship between manual preference and intermanual performance asymmetry in reaching of 5-month-old infants. Manual preference was assessed through frequency of reaches toward toys presented at midline, left or right in egocentric coordinates. Intermanual performance asymmetry was evaluated through kinematic analysis. Results showed that performance was predominantly symmetric between hands. Lateral toy positions induced predominance of ipsilateral reaching, while the midline position led to equivalent distribution between right and left handed reaches. No significant correlation between manual preference and intermanual performance asymmetry was observed. These results converge against the notion that manual preference derives from a genetically determined advantage of movement control favoring the right hand.

Intercepting moving targets: does memory from practice in a specific condition of target displacement affect movement timing?

This investigation aimed at assessing the extent to which memory from practice in a specific condition of target displacement modulates temporal errors and movement timing of interceptive movements. We compared two groups practicing with certainty of future target velocity either in unchanged target velocity or in target velocity decrease. Following practice, both experimental groups were probed in the situations of unchanged target velocity and target velocity decrease either under the context of certainty or uncertainty about target velocity. Results from practice showed similar improvement of temporal accuracy between groups, revealing that target velocity decrease did not disturb temporal movement organization when fully predictable. Analysis of temporal errors in the probing trials indicated that both groups had higher timing accuracy in velocity decrease in comparison with unchanged velocity. Effect of practice was detected by increased temporal accuracy of the velocity decrease group in situations of decreased velocity; a trend consistent with the expected effect of practice was observed for temporal errors in the unchanged velocity group and in movement initiation at a descriptive level. An additional point of theoretical interest was the fast adaptation in both groups to a target velocity pattern different from that practiced. These points are discussed under the perspective of integration of vision and motor control by means of an internal forward model of external motion.

Immunohistochemical expression of podocyte markers in the variants of focal segmental glomerulosclerosis

BACKGROUND Focal segmental glomerulosclerosis (FSGS) is the most prevalent primary glomerulopathy in Brazil and its incidence is increasing worldwide. Pathogenesis is related to podocyte injury, which may be due to several factors including viruses, drugs, immunology. In 2004, the Columbia classification of FSGS identified five histologic variants of the disease: collapsing (COL), usual (not otherwise specified, NOS), tip lesion (TIP), perihilar (PHI) and cellular variant (CEL). Several studies have demonstrated molecular changes in podocytes of FSGS patients. This study sought to classify a large series of FSGS biopsies according to the Columbia classification and analyze the occurrence of immunohistochemical differences among the five variants. METHODS Approximately 131 cases of renal biopsies with a diagnosis of primary FSGS during the period from 1996-2006 were classified according to the criteria of Columbia and were then submitted to immunohistochemical staining to the following antibodies: CD10, WT-1, Vimentin, Synaptopodin, α-actinin-4, GLEPP-1, cytokeratin (CK) 8-18, CK19 and Ki-67. RESULTS The FSGS classification resulted in 38.2% of NOS variant, in 36.6% COL, in 14.5% TIP, in 6.9% PHI and in 3.8% CEL. COL variant distinguished themselves among the others for having loss of expression of CD10, WT1 and α-actinin-4 (P < 0.05). Furthermore, COL gained expression of the CK8-18 and CK19 diverging from the other variants (P < 0.05). CONCLUSIONS COL variant of FSGS presented immunohistochemical characteristics that distinguished it from others pointing to additional studies in this area. The distinct immunohistochemical properties of COL might be of help in the comprehension of this aggressive form of FSGS.

An fMRI-compatible force measurement system for the evaluation of the neural correlates of step initiation

Knowledge of brain correlates of postural control is limited by the technical difficulties in performing controlled experiments with currently available neuroimaging methods. Here we present a system that allows the measurement of anticipatory postural adjustment of human legs to be synchronized with the acquisition of functional magnetic resonance imaging data. The device is composed of Magnetic Resonance Imaging (MRI) compatible force sensors able to measure the level of force applied by both feet. We tested the device in a group of healthy young subjects and a group of elderly subjects with Parkinson’s disease using an event-related functional MRI (fMRI) experiment design. In both groups the postural behavior inside the magnetic resonance was correlated to the behavior during gait initiation outside the scanner. The system did not produce noticeable imaging artifacts in the data. Healthy young people showed brain activation patterns coherent with movement planning. Parkinson’s disease patients demonstrated an altered pattern of activation within the motor circuitry. We concluded that this force measurement system is able to index both normal and abnormal preparation for gait initiation within an fMRI experiment.

Predictive saccades in children and adults: A combined fMRI and eye tracking study

Saccades were assessed in 21 adults (age 24 years, SD = 4) and 15 children (age 11 years, SD = 1), using combined functional magnetic resonance imaging (fMRI) and eye-tracking. Subjects visually tracked a point on a horizontal line in four conditions: time and position predictable task (PRED), position predictable (pPRED), time predictable (tPRED) and visually guided saccades (SAC). Both groups in the PRED but not in pPRED, tPRED and SAC produced predictive saccades with latency below 80 ms. In task versus group comparisons, children’s showed less efficient learning compared to adults for predictive saccades (adults = 48%, children = 34%, p = 0.05). In adults brain activation was found in the frontal and occipital regions in the PRED, in the intraparietal sulcus in pPRED and in the frontal eye field, posterior intraparietal sulcus and medial regions in the tPRED task. Group–task interaction was found in the supplementary eye field and visual cortex in the PRED task, and the frontal cortex including the right frontal eye field and left frontal pole, in the pPRED condition. These results indicate that, the basic visuomotor circuitry is present in both adults and children, but fine-tuning of the activation according to the task temporal and spatial demand mature late in child development.

Bilateral dorsal fronto-parietal areas are associated with integration of visual motion information and timed motor action

Abstract Interaction with the environment often involves situations requiring visuomotor integration. For instance, in fast interceptive actions, the brain must integrate visual information of motion with the appropriate motor action. In such dynamic situation, the brain may control movement based on predictions of where the object will be in the future and when it will arrive there. Although previous studies have analyzed brain regions associated with processing visual information of motion, motor control and visuomotor integration with static objects, less is known about visuomotor integration with moving objects. In the present study we used an event‐related fMRI experiment to investigate brain areas integrating visual information of motion with motor action in response to moving objects. Twenty healthy volunteers performed an interceptive task where they had to press a button in synchrony with the arrival of a horizontally moving target at a predefined location. They also performed two control tasks—simple reaction and attention to visual motion—in order to identify and exclude brain areas that would be involved in motor or visual motion processing components that are inherent to interceptive tasks. Through a conjunction analysis, we show greater BOLD signal in a bilateral dorsal fronto‐parietal network, as well as the intraparietal sulcus, angular gyrus, and human visual motion area hV5+. We discuss these results with respect to their previously identified functions, and suggest they play a role in visuomotor integration with moving objects.Interaction with the environment often involves situations requiring visuomotor integration. For instance, in fast interceptive actions, the brain must integrate visual information of motion with the appropriate motor action. In such dynamic situation, the brain may control movement based on predictions of where the object will be in the future and when it will arrive there. Although previous studies have analyzed brain regions associated with processing visual information of motion, motor control and visuomotor integration with static objects, less is known about visuomotor integration with moving objects. In the present study we used an event-related fMRI experiment to investigate brain areas integrating visual information of motion with motor action in response to moving objects. Twenty healthy volunteers performed an interceptive task where they had to press a button in synchrony with the arrival of a horizontally moving target at a predefined location. They also performed two control tasks-simple reaction and attention to visual motion-in order to identify and exclude brain areas that would be involved in motor or visual motion processing components that are inherent to interceptive tasks. Through a conjunction analysis, we show greater BOLD signal in a bilateral dorsal fronto-parietal network, as well as the intraparietal sulcus, angular gyrus, and human visual motion area hV5+. We discuss these results with respect to their previously identified functions, and suggest they play a role in visuomotor integration with moving objects.