Esther P. Gardner - US grants

This project is designed to determine the role of the cerebral cortex in the sensory function of the primate hand. Neurophysiological and psychophysical techniques will be used to examine how the somatosensory system integrates spatial information on the skin. A new computer controlled tactile stimulator which delivers spatially complex stimuli to a dense array of 144 miniature probes, developed during the previous project period, will be used to measure single unit responses in both primary and secondary somatosensory areas of the cerebral cortex of awake monkeys. These animals are trained in psychophysical experiments to respond to specific features of the stimulus, such as spatial frequency or direction of motion, permitting properties of single unit discharges to be correlated with the sensations produced by the stimulus in both monkeys and humans. The experiments described in this proposal address four major topics: (A) the coding of motion and its direction across the skin, (B) the coding of spatial frequency of textured surfaces, (C) the spatial organization of receptive fields of cortical neurons receiving inputs from different classes of cutaneous mechanoreceptors, and (D) functional comparison of activity in SI and SII cortices. These studies will provide the first neurophysiological studies of responses evoked by the OPTACON tactile display normally used as a sensory substitution aid for the blind and deaf. We will obtain important neurophysiological data on the tactile information processing capabilities of the cerebral cortex, the functional organization of three different cytoarchitectural areas, and the integration of information between the two hemispheres. The findings may have important clinical applications such as the development of more quantitative tests of sensory function in patients with neurological disorders or peripheral nerve injuries, and the improvement of sensory substitution aids for visually and/or hearing impaired individuals.

DESCRIPTION (provided by applicant): This project integrates neurophysiological research into the visual and somatosensory mechanisms that govern planning of skilled motor behaviors of the hand with development and distribution of neuroinformatics tools useful for data visualization, analysis and manipulation required for such studies. Aim 1 establishes a Neuroinformatics Resource to distribute integrated tools enabling quantitative analyses of spike trains obtained with digital video (DV), and their correlation to the kinematics of hand actions. Interactive tools will be provided over the Internet for 1) spike recognition and separation, 2) event- linked rasters and PSTHs, 3) continuous firing rate graphs, and 4) metrics of spike synchrony. An international network of neuroscientists studying primate hand function will evaluate the tools, and provide research synergies from diverse studies of hand function. The tools are used in Aims 2 and 3 to assess the contribution of visual and haptic information about object size, shape and location in motor planning of acquisition and manipulation by the hand. Spike trains recorded in posterior parietal cortex (PPC) from single neurons, and from neuronal assemblies studied with multielectrode arrays, are synchronized to simultaneously acquired images of hand kinematics with DV. We postulate that skilled hand behaviors require the registration and coordination of an external map that locates an object's spatial coordinates and encodes its intrinsic geometry, and an internal map of the body's own image that represents the hand posture and dynamics. Protocols comparing shape and location-dependent cues distinguish intention-related activity planning grasping behaviors, from sensory responses to views of objects and hand-object interactions during performance of a trained grasp-and-lift task. Aim 2 analyzes firing patterns obtained when objects can be viewed, and when an opaque barrier, requiring the use of memory, blocks vision and haptic cues for object acquisition and manipulation. Aim 3 measures the integration of vision and touch during tool use when grasped objects are inserted into matching slots to illuminate a target. These experiments test hypotheses that synchronization and/or coherence of firing between PPC regions dominated by vision and touch enable a match-to-sample mode of sensorimotor control and error correction that enables efficient, adaptive behaviors. This research has important clinical implications for understanding dysmetrias, optic ataxias, grasp abnormalities and neglect syndromes resulting from neurological damage to PPC, and provides basic insights into mechanisms of visuomotor control of the hand that may prove useful for rehabilitation after stroke or injury.

DESCRIPTION (provided by applicant): This project analyzes the role of somatosensory neurons in the parietal lobe during performance of skilled manual tasks. We use a prehension task, in which the hand grasps and manipulates objects, as a model system to examine how sensory cues and previous experience are used to plan and implement skilled hand movements. It aims to understand how information about objects is acquired by the hand through the senses of touch, proprioception, and vision. We propose that sensory responses are perceived in the context of task goals. Neural activity in the posterior parietal cortex (PPC) is hypothesized to reflect task planning needed to grasp objects efficiently and to secure them for manipulation. Neural responses in the primary somatosensory (S-I) cortex confirms or rebuts the subject's expectation of object features, and provides feedback needed for error correction. We will record spike trains and local field potentials of neural populations in PPC and S-I during performance of the task using multiple electrode arrays and digital video measurements of hand kinematics. Aim 1 analyzes the role of sensory information provided by the behavioral cue in modulating neural responses to prehension. We examine how the shape and location of an object are represented in PPC when it is grasped with different instructions and expectations. The studies test hypotheses that the behavioral relevance of object features modifies the motor program developed during task planning, and somatosensory information fed back to the cortex from the hand during task performance. Aim 2 addresses the neural control of bilateral hand movements when both hands perform the same movements together. We will quantify the prevalence of bilateral neurons in each hemisphere that respond equivalently to similar actions performed by each hand, or are specialized for bimanual actions, by comparing temporally uncoupled grasping movements performed separately by the left and right hands, with similar bimanual movements that require coordinated and synergistic actions of the two hands. We also examine whether bimanual behaviors are implemented by synchronous bilateral activation of the two hemispheres using simultaneous recordings from the left and right parietal cortex. Aim 3 explores the role of PPC in decision making when cues are ambiguous. We assess the role of handedness preferences, reward probability and short-term memory in choice of the hand used and object grasped in each trial. This research provides basic insights into the dynamic organization of cortical circuits, the role of prediction in normal hand use, and integration of somatosensory information between hemispheres needed for fine motor control of the hand. An understanding of these cortical processes may have clinical importance for rehabilitation following neurological disorders such as stroke or peripheral nerve injury. Principles of sensorimotor integration derived from this research may prove useful for developing better sensory prostheses or robotic manipulators based on biological models of hand function. This project analyzes the role of neurons in the parietal lobe of the cerebral cortex during performance of skilled manual tasks. It aims to understand how information about objects is acquired by the hand through the senses of touch and proprioception, and is used by the brain when objects are grasped and manipulated skillfully. An understanding of these brain mechanisms may have clinical importance for rehabilitation of hand function following neurological disorders such as stroke or peripheral nerve injury, and for development of better sensory prostheses or robotic manipulators based on biological models of hand function.

Manual dexterity enables humans to manipulate small objects with our fingers, perform highly skilled tasks as well as simple activities of daily living. These actions require independent finger movements, and precise control of the direction and magnitude of fingertip forces such as those involved in grasping objects. We grasp objects of various textures, weights, and shapes by adapting our fingertip forces to friction at the grasping surface, the weight of the object, and its shape. The grip force must be optimized to prevent excessive squeezing of the object (wasted force and/or object damage) or slippage of the object from grasp (and possible breakage) due to insufficient, weak forces. The sense of touch is used perceive friction at the object surface; without tactile feedback humans tend to use too much force when grasping, or apply insufficient forces. In this study we use high-resolution 3D printing to create textured surfaces whose physical dimensions are specified and quantified in psychophysical tests. We propose to quantify and analyze manual dexterity using a grasp-and-lift task in which we measure the effects of load and surface texture on performance in healthy human adults of ages 18-80, and in subjects with central and/or peripheral neurological impairments. These experiments will provide quantitative metrics of manual dexterity and force control in young, middle-aged, and elderly subjects that can serve as baseline values for evaluating treatment and rehabilitation therapies following stroke, or peripheral nerve injury, as well as the well-known reduction in hand function as a result of aging.