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Sensory Information from Afferent Neurons


Principal Investigator Affiliation Contract Number
Andy Hoffer, Ph.D. Simon Fraser University N01-NS6-2339

ARTICLE C.1 Introduction.

In patients with spinal cord injuries, sensation below the level of injury is lost despite the fact that the tactile and proprioceptive receptors and their associated afferent neurons are usually intact. If appropriate connections to these afferent neurons could be achieved, they could be used as transducers for touch, force and position in functional neuromuscular stimulation (FNS) systems. This sensory information is needed for closed loop control of FNS and for restoring sensation. In on-going studies in Denmark, step lift-off information, obtained from a chronically implanted electrode on the sural nerve, has been used to control lifting of the foot during the swing phase in an individual with stroke related foot-drop. In another study, the feasibility of obtaining contact/release information from the lateral surface of the index finger has been demonstrated in a quadriplegic volunteer using a cuff electrode placed on a digital nerve in the hand.

A contract was initiated two years ago to investigate, in an animal model, the feasibility of extracting signals for control and for sensory feedback from electrical recordings in peripheral nerves using cuff electrodes. This research has demonstrated stable physiological function, as measured by conduction latency, of cuffed peripheral nerves in cats for periods of 6 months. The signals recorded from these cuff electrodes reflect the mixture of cutaneous and proprioceptive receptors in skin and muscle and typically show a rapidly-adapting response to contact and a lesser rapidly-adapting response to release.

Nerve cuff recordings can provide event related information such as time of contact and release of objects. They might also provide joint position and contact force information but more selective chronic recording techniques may be more suitable. This investigation will study the feasibility of obtaining sensory information including force and position related signals from peripheral nerves in animals on a chronic basis. Although human studies are not solicited, it is anticipated that this research will lead to future studies in humans.

This RFP represents a competitive renewal of a contract that will expire in January, 1996. A bibliography listing publications from current and prior NPP supported studies is available from the Neural Prosthesis Program, NINDS, NIH, Room 916, Federal Bldg., Bethesda, MD. 20892-9170.

Article C.2 Statement of Work

Independently and not as an agent of the Government, the contractor shall exert its best efforts to develop and perfect in an animal model, chronic recording methods for extracting sensory information about human fingertip contact, grasped object slip, finger position, and grasp force from chronic recordings of the afferent activity of sensory receptors.

Specifically the contractor shall:

1. Give consideration to selecting recording methods that:

a. Have the potential of providing safe, reliable recordings in humans for periods of years.

b. When used in human applications, could provide relatively isolated information from the sensory endings in the thumb pad and in the finger pads of the second and third fingers.

c. Could, in human applications, provide information from the proprioceptive receptors in the muscles of the hand and wrist.

2. Select a suitable animal model for chronic recording of afferent nerve activity. Consideration shall be given to modeling electrode placement sites for a potential human neural prosthesis application.

3. Obtain or fabricate chronic electrodes and associated cables and percutaneous connectors for chronic recording of sensory afferent activity.

a. Electrodes and cables shall be designed using biocompatible materials that would be suitable for potential future human implants.

b. Electrodes and cables shall be designed with the goal of producing a chronic implant that causes minimal nerve damage.

4. Investigate the possibility of extracting information about contact, grasped object slip, limb position and contact force from chronically recorded neural activity using the animal model and electrodes from parts 2 and 3.

a. Devise recording, processing, and detection methods to extract this information from recorded neural activity in a restrained animal.

b. Modify these methods as needed to function in an unrestrained animal and in the presence of stimulation artifacts associated with functional electrical stimulation.

c. Record activity for periods of at least 6 months and devise functional measures to track any change in neural response over this time.

d. Evaluate any histological changes in the nerves that occurred over the period of chronic recording and, if possible, correlate these changes to changes in functional response

5. Cooperate with other investigators in the Neural Prosthesis Program by collaboration and sharing of experimental findings.

Last updated November 24, 2008