The time course for kinetic versus kinematic planning of goal-directed human motor behavior

The neural basis of hand choice: An fMRI investigation of the Posterior Parietal Interhemispheric Competition model

The current study investigates a new neurobiological model of human hand choice: The Posterior Parietal Interhemispheric Competition (PPIC) model. The model specifies that neural populations in bilateral posterior intraparietal and superior parietal cortex (pIP-SPC) encode actions in hand-specific terms, and compete for selection across and within hemispheres. Actions with both hands are encoded bilaterally, but the contralateral hand is overrepresented. We use a novel fMRI paradigm to test the PPIC model. Participants reach to visible targets while in the scanner, and conditions involving free choice of which hand to use (Choice) are compared with when hand-use is instructed. Consistent with the PPIC model, bilateral pIP-SPC is preferentially responsive for the Choice condition, and for actions made with the contralateral hand. In the right pIP-SPC, these effects include anterior intraparietal and superior parieto-occipital cortex. Left dorsal premotor cortex, and an area in the right lateral occipitotemporal cortex show the same response pattern, while the left inferior parietal lobule is preferentially responsive for the Choice condition and when using the ipsilateral hand. Behaviourally, hand choice is biased by target location - for targets near the left/right edges of the display, the hand in ipsilateral hemispace is favoured. Moreover, consistent with a competitive process, response times are prolonged for choices to more ambiguous targets, where hand choice is relatively unbiased, and fMRI responses in bilateral pIP-SPC parallel this pattern. Our data provide support for the PPIC model, and reveal a selective network of brain areas involved in free hand choice, including bilateral posterior parietal cortex, left-lateralized inferior parietal and dorsal premotor cortices, and the right lateral occipitotemporal cortex.

Sensory-motor deficits in children with fetal alcohol spectrum disorder assessed using a robotic virtual reality platform

BACKGROUND

Fetal alcohol spectrum disorder (FASD) is associated with a large number of cognitive and sensory-motor deficits. In particular, the accurate assessment of sensory-motor deficits in children with FASD is not always simple and relies on clinical assessment tools that may be coarse and subjective. Here we present a new approach: using robotic technology to accurately and objectively assess motor deficits of children with FASD in a center-out reaching task.

METHODS

A total of 152 typically developing children and 31 children with FASD, all aged between 5 and 18 were assessed using a robotic exoskeleton device coupled with a virtual reality projection system. Children made reaching movements to 8 peripheral targets in a random order. Reach trajectories were subsequently analyzed to extract 12 parameters that had been previously determined to be good descriptors of a reaching movement, and these parameters were compared for each child with FASD to a normative model derived from the performance of the typically developing population.

RESULTS

Compared with typically developing children, the children with FASD were found to be significantly impaired on most of the parameters measured, with the greatest deficits found in initial movement direction error. Also, children with FASD tended to fail more parameters than typically developing children: 95% of typically developing children failed fewer than 3 parameters compared with 69% of children with FASD. These results were particularly pronounced for younger children.

CONCLUSIONS

The current study has shown that robotic technology is a sensitive and powerful tool that provides increased specificity regarding the type of motor problems exhibited by children with FASD. The high frequency of motor deficits in children with FASD suggests that interventions aimed at stimulating and/or improving motor development should routinely be considered for this population.

Whole-body isometric force/torque measurements for functional assessment in neuro-rehabilitation: user interface and data pre-processing techniques

A diagnostic platform for the early functional assessment of post-stroke patients was designed in order to perform isometric measurements during activities of daily living (ADL) tasks. The outcome of these measurements can contribute to verify the integrity of a post-stroke existing or altered "internal model" for a particular functional task. A complete and reliable software application for the diagnostic platform was designed, developed and tested in three European hospitals. The software application was divided into two main modules: a graphical user interface (GUI) and the data pre-processing techniques for the interpretation of recorded biomedical and clinical data. This paper presents the software application associated to the platform, aimed at analysing and interpreting the huge amount of data recorded and collected during the experimental trials. Its main objective is related to validating the onset detection and data reduction. The software application presented in this paper has been working and validated with success in three different clinical centres in Europe and it can be effectively used both as assessment tool in rehabilitation and as research tool in neuroscience.

Spatial anisotropy in the encoding of three-dimensional passive limb position by the spinocerebellum

In an earlier study, we found that the encoding of limb position in the sagittal plane across the population of spinocerebellar Purkinje cells was anisotropic with a preferential gradient along horizontal direction. The aim of this study was to extend to a three-dimensional (3D) workspace the analysis of the relationships between Purkinje cells activity and rat's forelimb spatial position. In anesthetized animals, the extracellular activity of 121 neurons was recorded while a robot passively placed the limb in 18 positions within a cubic workspace (3x3x3 cm). In order to characterize the relationship between spatial locations and Purkinje cell activity we performed a backward stepwise regression starting from a model with three independent variables representing the antero-posterior, the medial-lateral and the vertical axes of workspace. Regression analysis showed that the firing of most cells was modulated exclusively along the antero-posterior (25%) or the medial-lateral (38%) axis, while a small portion was related only to the vertical axis (8%), indicating a generalized nonuniform sensitivity of Purkinje cells to limb displacement in 3D space.

Efficient control of arm movements in advanced age

The present study addresses the influence of aging on the ability to regulate mechanical effects arising during arm movements due to the multi-joint structure of the arm. Two mechanical factors were considered, interaction torque (IT) and inertial resistance (IR). Regulation of these two factors can be demanding in terms of the timing and magnitude of the required muscle torque (MT), specifically during fast movements. We hypothesized that aging exacerbates the challenge regarding the regulation of these effects with muscular control due to declines in the motor system. This hypothesis was tested by comparing performance of a cyclic line-drawing task in two age groups, young and older adults. Only two joints, the shoulder and elbow, participated in motion. Four orientations of the lines were used to provide variations in the requirements for regulation of IT and IR. Cyclic frequency was manipulated to emphasize the dependence of the mechanical factors on movement speed. Various characteristics of fingertip motion showed that there were no age-related deteriorations in accuracy of line drawing. However, older adults were systematically slower, particularly in the directions of high IR. A detailed analysis of the magnitude of MT and the contribution of this torque to production of net torque at each joint demonstrated that older adults modified joint control and decreased the demands for MT by skillful exploitation of IT in a way specific for each particular line orientation. The results point to a tendency in older adults to decrease the production of muscle force. Nevertheless, older adults also demonstrated an ability to partially compensate for declines in the force production by developing sophisticated strategies of joint control that exploit the multi-joint mechanical structure of the arm. This ability suggests that the internal representation of inter-segmental dynamics and the capability to use it for movement control does not decay with age. The study emphasizes the importance of analysis of joint motion and control characteristics for the investigation of arm movements and for comparison of these movements between different subject populations.

Use of an EMG-Driven Biomechanical Model to Study Virtual Injuries

INTRODUCTION

How the CNS activates muscles to produce coordinated movement is a matter of debate and great interest. We are attempting to answer this question, in part, by investigating how individual muscles and groups of muscles are activated under different physiologic and environmental conditions. We have developed an EMG-driven virtual arm to assist in this endeavor.

PURPOSE

To demonstrate how the virtual arm can be used to simulate a neuromuscular injury and to examine whether a virtual injury can evoke a change in muscle activation patterns.

METHODS

The virtual arm is a three-dimensional graphical representation and biomechanical model of a human arm including the major flexor and extensor muscles crossing the elbow. The muscles are actuated based on experimentally recorded electromyograms. A Hill-type muscle model was used to predict muscle forces, which in turn were used to move the graphical display of the arm on the screen. Two subjects, one considered highly trained and the other a novice, participated in this study. Virtual movements, before and after simulating an injury were evaluated, and model performance was assessed by comparing the virtual arm-predicted moment and the actual moment generated by the subjects.

RESULTS

The highly trained subject was proficient at controlling the virtual arm. For this subject, simulating a neuromuscular injury evoked a different pattern of activation compared to the preinjured state.

CONCLUSIONS

The virtual arm may be a useful tool for the study of motor coordination and how muscle activation patterns change in response to injury. Future work involving more subjects and experimental conditions is planned to better assess the efficacy of the virtual arm as a research tool for investigating motor control strategies.