In this application we investigate how to provide realistic sensory feedback to subjects with upper limb prosthetics. Thousands of soldiers are returning from the war in need of prosthetic limbs that not only can move but also allows them to seamlessly interact with objects. The optimal approach for providing feedback is to tap directly into the neural circuits that underlie tactile perception. Recent studies have shown that areas 3b, 1 and 2 of SI cortex play different roles in processing cutaneous information, with neurons in area 3b responsible for coding orientation, area 1 for motion and area 2 for curvature. In this application we will investigate how to provide sensory feedback by directly stimulation neurons in these cortical areas in animals trained to perform tactile match-to-sample discrimination tasks. There are two specific aims. The first is to investigate how to provide sensory feedback of intensity, orientation, motion and curvature on a single finger pad. After training non-human primates (macaca mulatta) to perform the feature discrimination task, a chronic recording array will be implanted into somatosensory cortex. The goal of the recordings is to simultaneously record from many neurons that are tuned to the feature being studied. The animal will then perform the task under three conditions. 1) Matching a mechanical stimulus with a mechanical stimulus (this is the condition that the animal was trained to perform) 2) Matching a mechanical stimulus with a mechanical and electrical stimulus and 3) Matching a mechanical stimulus with an electrical stimulus. The electrical stimuli will be given to populations of feature tuned cells with the aim of changing the population response of the neurons. This stimulus will be modified in several ways 1) change in current intensity, 2) change in frequency of pulses 3) change in statistical properties of the firing (i.e., biomimetic, uniform, Poisson) and change the degree of correlated firing between cells being modulated. We will develop method to systematically alter the animal's behavior and to determine whether we can produce a population response that mimics the response of the tactile stimulation.
The second aim i s to train animals to perform a tactile one-back task. This task will determine how to stimulate cortex so that the stimuli can be delivered with minimal spatial and temporal smearing of the electrical signals across fingers. The results from the two aims will provide and understanding of how to provide sensory feedback of complex features to the hand.

Public Health Relevance

Thousands of returning soldiers from the wars in Iraq and Afghanistan are in need of an effective upper limb prosthetic arm and hand. Although we have made remarkable progress in understanding how to control the movements of a prosthetic limb, we are far from understanding how to provide effective sensory feedback. The approach that we use in this application is to stimulate the cortex using the inherent processing functions of the somatosensory system. In this application we will determine how to optimally provide the prosthetic users the specific features of intensity, orientation, motion and curvature.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Special Emphasis Panel (BNVT)
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Gnadt, James W
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Johns Hopkins University
Schools of Medicine
United States
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