Theoretical aspects of sensory substitution and of neurotransmission-related reorganization in spinal cord injury

Abstract

Spinal cord rehabilitation has progressed enormously since World War II, and persons with spinal cord injuries now have long life expectancies. Research has recently concentrated on improvement of the quality of life, and on neural mechanisms of recovery. This article will explore some aspects of both of these areas. In the ®rst section, the potential applications of sensory substitution systems for such functions as sex sensation and sensation from feet and from robotic hands will be examined. In the second section, the potential role of nonsynaptic di usion neurotransmission (NDN) in neural reorganization after spinal cord injury will be considered. This article includes portions of previous publications and reports.Keywords: incomplete SCI; neurotransmission; plasticity; robotic hand; sex sensation; rehabilitation Sensory substitutionBackground For the brain to correctly interpret information from devices, it is not necessary that it be presented in the same form as in natural sensory information systems. We do not SEE with the eyes; 1 the visual image does not go beyond the retina, where it is turned into patterns of pulses along nerves. Those individual pulses are not di erent from the pulses from the big toe. It is the brain which recreates the image from the patterns of pulses. We have previously demonstrated that the brain is able to recreate`visual' images that originate in an arti®cial receptor (a TV camera), which are transduced into a tactile display (the TVSS system), and carried to the brain via tactile nerve pathways. 1 Thus, it is only necessary to present the information from a device in a form of energy that can be mediated by the receptors at the man-machine interface, and for the brain, through a motor system (eg a head-mounted camera under the motor control of the neck muscles, for blind persons), to know the origin of the information. We have previously developed tactile vision substitution systems (TVSS) to deliver visual information to the brain via arrays of stimulators in contact with the skin of one of several parts of the body (abdomen, back, thigh, ®nger-tip). Optical images picked up by a TV camera are transduced into a form of energy (vibratory or direct electrical stimulation) that can be mediated by the skin receptors. The visual information reaches the perceptual levels for analysis and interpretation via somatosensory pathways and structures.After su cient training with the TVSS, our blind subjects reported experiencing the images in space, instead of on the skin. They learned to make perceptual judgments using visual means of analysis, such as perspective, parallax, looming and zooming, and depth judgments. Our studies with the TVSS have been extensively described. 1 ± 10 After training, our blind subjects using the TVSS system did not feel anything on the skin on which the interface was placed; rather they perceived it out in three dimensional space if they controlled the camera movement. Although the TVSS systems have only had between 100 and 1032 point arrays, the low res...

Neuropathology: the foundation for new treatments in spinal cord injury

“…Another even more spectacular example of how with artificial input the CNS may adapt and recover function is provided by the great success of the bionic ear developed by Graeme Clark et al 75 Similar but less outstanding results have been achieved for the substitution of vision using tactile stimulation. 76 Another reason for optimism is the well-known ability of the CNS to respond to external and internal stimuli by changing its synaptic connections by means of plasticity. The relearning of skills and language after stroke or head injury is due to this phenomenon, best seen in the young in whom language centers may even be relocated to another topographic site in the brain.…”

Robotic Prosthetics : Moving Beyond Technical Performance

“…For neuroscientists, the relationship between sensory-motor loops and physical integration appear obvious. Several studies have demonstrated this: research on the subject of the physical integration of vibrotactile devices used to substitute visual loss [33]; work on the development of the sense of orientation through long-term wearing of a "compass-belt" which provides constant vibrotactile information on the direction of North [34], or the "rubber hand" experiments in which the combination of sensory signals (visual and tactile) generate the sensation that a rubber hand is a part of the subject's own body [35].…”

Contrast vision-based grasp force feedback in telemanipulation

“…A video camera signal was converted into a tactile image and projected onto the blind subject's back. In [7] Bach-y-Rita reviews the theoretical aspects and many applications from the beginning to 1999. In the past decade further results were published: Bach-y-Rita, Kaczmarek and Tyler introduced the tongue based man machine interface [8].…”