Perceptual Structures and Distributed Motor Control

The role of the anterior temporal cortex in action: evidence from fMRI multivariate searchlight analysis during real object grasping

Intelligent manipulation of handheld tools marks a major discontinuity between humans and our closest ancestors. Here we identified neural representations about how tools are typically manipulated within left anterior temporal cortex, by shifting a searchlight classifier through whole-brain real action fMRI data when participants grasped 3D-printed tools in ways considered typical for use (i.e., by their handle). These neural representations were automatically evocated as task performance did not require semantic processing. In fact, findings from a behavioural motion-capture experiment confirmed that actions with tools (relative to non-tool) incurred additional processing costs, as would be suspected if semantic areas are being automatically engaged. These results substantiate theories of semantic cognition that claim the anterior temporal cortex combines sensorimotor and semantic content for advanced behaviours like tool manipulation.

Imitation of a bimanual task in preschool- and school-age children: a hierarchical construction

The present study examined the development of bimanual interaction during the imitation of a live demonstration. To this end, children of five different age groups observed an adult model performing in an object manipulation task consisting to open a box with one hand, taking out an object with the other hand, and closing the box again, before they were asked to imitate this motor task under different imitation conditions. The children's responses were videotaped, coded in dichotomous data, and then transformed in percentage scores. The main results showed that all children were able to imitate/attain the goal of the task. However, differences were observed for the different imitation conditions, which were also reflected in some age effects, while hand dominance was a strong constraint on imitation. Also, practice did not seem to increase the likelihood of model imitation. These findings confirm that imitation is a reconstruction mechanism hierarchically organized.

A model for altered neural network dynamics related to prehension movements in Parkinson disease

In this paper, we present a neural network model of the interactions between cortex and the basal ganglia during prehensile movements. Computational neuroscience methods are used to explore the hypothesis that the altered kinematic patterns observed in Parkinson's disease patients performing prehensile movements is mainly due to an altered neuronal activity located in the networks of cholinergic (ACh) interneurons of the striatum. These striatal cells, under a strong influence of the dopaminergic system, significantly contribute to the neural processing within the striatum and in the cortico-basal ganglia loops. In order to test this hypothesis, a large-scale model of neural interactions in the basal ganglia has been integrated with previous models accounting for the cortical organization of goal directed reaching and grasping movements in normal and perturbed conditions. We carry out a discussion of the model hypothesis validation by providing a control engineering analysis and by comparing results of real experiments with our simulation results in conditions resembling these original experiments.

Automatic determination of synergies by radial basis function artificial neural networks for the control of a neural prosthesis

This paper describes an automatic method for synthesizing the control for a neural prosthesis (NP) that could augment elbow flexion/extension and forearm pronation/supination in persons with hemiplegia. The basis for the control was a synergistic model of reaching and grasping that uses temporal and spatial synergies between the arm and body segments. The synergies were determined from the movement data measured in nondisabled persons during the performance of functional tasks. The work space was divided into six zones: distance (two attributes) and laterality (three attributes). Radial basis function artificial neural networks (RBF ANN) were used to determine synergies. Sets of RBF ANN characterized with good generalization were selected as control laws for elbow flexion/extension and forearm pronation/supination. The validation was performed for three categories: inter-subject, distance, and laterality generalization. For all of the defined spatial synergies, the correlation was high for inter-subject and distance, yet low for the laterality scenario. This suggests the necessity for implementing different maps for different directions, but the same maps for different distances. The natural movements of the upper arm then drive the lower arm (elbow flexion/extension and forearm pronation/supination) in a way that is very well suited for the administration of functional electrical therapy (FET) in persons with hemiplegia soon after the onset of impairment.

Functional Segregation within Pars Opercularis of the Inferior Frontal Gyrus: Evidence from fMRI Studies of Imitation and Action Observation

Recent neuroimaging studies have suggested that the inferior frontal gyrus (IFG) is important for action observation and imitation. In order to further explore the role of IFG in action observation and imitation, we pooled data from seven functional magnetic resonance imaging studies involving observation and imitation of simple finger movements performed in our laboratory. For imitation we found two peaks of activation in the pars opercularis, one in its dorsal sector and the other in its ventral sector. The dorsal sector of the pars opercularis was also activated during action observation, whereas the ventral sector was not. In addition, the pars triangularis was activated during action observation but not during imitation. This large dataset suggests a functional parcellation of the IFG that we discuss in terms of human mirror areas and the computational motor control architecture of internal models.

Sensor scheduling in mobile robots using incomplete information via Min-Conflict with Happiness

This paper develops and applies a variant of the Min-Conflict algorithm to the problem of sensor allocation with incomplete information for mobile robots. A categorization of the types of contention over sensing resources is provided, as well as a taxonomy of available information for the sensor scheduling task. The Min-Conflict with Happiness (MCH) heuristic algorithm, which performs sensor scheduling for situations in which no information is known about future assignments, is then described. The primary contribution of this modification to Min-Conflict is that it permits the optimization of sensor certainty over the set of all active behaviors, thereby producing the best sensing state for the robot at any given time. Data are taken from simulation experiments and runs from a pair of Nomad200 robots using the SFX hybrid deliberative/reactive architecture. Results from these experiments demonstrate that MCH is able to satisfy more sensor assignments (up to 142%) and maintain a higher overall utility of sensing than greedy or random assignments (a 7-24% increase), even in the presence of sensor failures. In addition, MCH supports behavioral sensor fusion allocations. The practical advantages of MCH include fast, dynamic repair of broken schedules allowing it to be used on computationally constrained systems, compatibility with the dominant hybrid robot architectural style, and least-disturbance of prior assignments minimizing interruptions to reactive behaviors.

An information-processing analysis of the functional architecture of the primate neocortex

Working at the systems level of analysis, we will use the term functional architecture to concern what processing components exist, how they are interconnected, and what information-processing functions each is involved in. In this paper, experimental evidence for the primate neocortex is analysed for conclusions concerning the existence of neural areas, for corticocortical connectivity among neural areas, and for the involvement of each cortical neural area in the functioning of the brain. We characterize the information-processing function for each neural area in terms of the types of information it is associated with, and conceive of its activity as processing, storage and transmission of data of the corresponding types for that area. We also adapt concepts of goal, plan, sequence, event and context for the description of information processing in the neocortex. This analysis shows that the primate neocortex consists in the main of a perception hierarchy, an action hierarchy and connections between them. In other words, from an information-processing point of view, the primate neocortex has a hierarchical perception-action architecture.

Deficits in the evolution of hand preshaping in Parkinson's disease

Parkinson's disease (PD) results in various types of motor impairments including bradykinesia, tremor and rigidity. Recent research has implicated more fundamental processes at the source of the observed motor deficits. Among these, problems in the sequencing and/or timing of complex movements and in the execution of internally-guided tasks. Furthermore, PD patients exhibit procedural learning deficits which may complicate the interpretation of experimental results of studies involving novel sensorimotor tasks. The reach-to-grasp movement is a complex, overlearned sensorimotor task consisting of two semi-independent components, a relatively simple reach or transport phase and a more complex manipulation or prehension phase. In the present study, we used a novel technique in order to study the evolution of hand preshaping during the reach-to-grasp movement of PD patients and age-matched controls to objects of different shapes in three different spatial locations. Our results indicate that while PD patients are able to specify movement direction as well as controls, their hand preshaping exhibits substantial impairments. Other prehension measures, such as the time to peak aperture (TPA), indicate that PD patients delayed execution of the grasp until visual feedback of their hand was available. Overall, our results suggest that PD patients' internal guidance processes are severely disrupted, having to rely on visual feedback in order to modulate their hand shape to fit the contours of the target objects during a reach-to-grasp movement.

Rana computatrix to human language: towards a computational neuroethology of language evolution

Walter's Machina speculatrix inspired the name Rana computatrix for a family of models of visuomotor coordination in the frog, which contributed to the development of computational neuroethology. We offer here an 'evolutionary' perspective on models in the same tradition for rat, monkey and human. For rat, we show how the frog-like taxon affordance model provides a basis for the spatial navigation mechanisms that involve the hippocampus and other brain regions. For monkey, we recall two models of neural mechanisms for visuomotor coordination. The first, for saccades, shows how interactions between the parietal and frontal cortex augment superior colliculus seen as the homologue of frog tectum. The second, for grasping, continues the theme of parieto-frontal interactions, linking parietal affordances to motor schemas in premotor cortex. It further emphasizes the mirror system for grasping, in which neurons are active both when the monkey executes a specific grasp and when it observes a similar grasp executed by others. The model of human-brain mechanisms is based on the mirror-system hypothesis of the evolution of the language-ready brain, which sees the human Broca's area as an evolved extension of the mirror system for grasping.

The prefrontal cortex and its relation to behavior

The prefrontal cortex is critical for temporal organization of behavior. It mediates cross-temporal sensory-motor contingencies, integrating motor action (including speech) with recent sensory information. It performs this role through cooperation of two cognitive functions represented in its dorsolateral areas: short-term memory (STM) and preparatory set. Supporting data have been obtained from monkeys performing delay tasks, which epitomize the principle of cross-temporal contingency. In a given trial, the animal performs an act contingent on a sensory cue given a few seconds or minutes earlier. During the delay between cue and response, cells in dorsolateral prefrontal cortex show sustained activation. Two cell categories can be identified in tasks in which cue and response are spatially separate. Cells of the first participate in STM: Their activation tends to diminish as the delay progresses; in some, the activation level depends on the particular cue received. Similar cells are found elsewhere in cortex. Cells of the second category seem to take part in preparation of motor response: Their activation tends to increase in anticipation of it and may be attuned to the particular movement the cue calls for. This cell type is rare outside of frontal cortex. The temporally integrative function of the prefrontal cortex is probably based on local interactions between "memory" and "motor-set" cells, as well as on neural associations between prefrontal cortex and posterior cortical areas.