Biomedical subjects

Jean Delbeke

Publications and source records attributed to Jean Delbeke.

11 recordsLinked to original sources

PubMed2006

Intraorbital implantation of a stimulating electrode for an optic nerve visual prosthesis. Case report.

Research into visual prosthetics is expected to revolutionize the treatment of blind patients with incurable outer retinal degenerative disease. Substantial evidence shows that useful visual sensations can be produced by controlled electrical stimulation of the optic nerve. To make the optic nerve visual prosthesis more acceptable, implantation techniques safer and less invasive than those previously used have been developed. A medial transconjunctival approach is now used to implant a stimulating electrode around the intraorbital section of the optic nerve. This new technique allows sufficient exposure of the nerve after detaching only one rectus muscle and performing a lateral canthotomy. Previously, an electrode was implanted in the intracranial part of the optic nerve, which required more invasive surgery. The new technique was first developed in cadavers and in patients undergoing eye enucleations. Finally, a 68-year-old blind man suffering from retinitis pigmentosa underwent long-term implantation. In this case report the authors describe the technique and outline some of the challenges involved.

Aged↗

PubMed2006

Object localization, discrimination, and grasping with the optic nerve visual prosthesis.

PURPOSE: This study involved a volunteer completely blind from retinis pigmentosa who had previously been implanted with an optic nerve visual prosthesis. The aim of this two-year study was to train the volunteer to localize a given object in nine different positions, to discriminate the object within a choice of six, and then to grasp it. METHODS: In a closed-loop protocol including a head worn video camera, the nerve was stimulated whenever a part of the processed image of the object being scrutinized matched the center of an elicitable phosphene. The accessible visual field included 109 phosphenes in a 14 degrees x 41 degrees area. RESULTS: Results showed that training was required to succeed in the localization and discrimination tasks, but practically no training was required for grasping the object. The volunteer was able to successfully complete all tasks after training. The volunteer systematically performed several left-right and bottom-up scanning movements during the discrimination task. Discrimination strategies included stimulation phases and no-stimulation phases of roughly similar duration. CONCLUSION: This study provides a step towards the practical use of the optic nerve visual prosthesis in current daily life.

Blindness↗

PubMed2005

Three-dimensional topography of the motor endplates of the rat gastrocnemius muscle.

Spatial distribution of motor endplates affects the shape of the electrical activity recorded from muscle. In order to provide information for realistic models of action potential propagation within muscles, we assembled three-dimensional maps of the motor endplates of the rat medial gastrocnemius (MGM) and lateral gastrocnemius (MGL) muscles. The maps were assembled from histological cross sections stained for acetylcholinesterase activity. Within MGL, the motor endplates formed three columns along its longitudinal axis. Within MGM, the motor endplates were arranged in a leaf-like body that shifted obliquely from proximal to distal. As inferred from the proximo-distal distribution of the cross-sectional projection area, the majority of the motor endplates were concentrated in the middle of MGL and in the distal third of MGM. Regions of maximal motor endplate concentration are considered most suitable for injections of neuroactive substances, such as neuronal tracers. The assembled maps of the gastrocnemius muscles can be used as guides for such injections within the motor endplate zones.

Acetylcholine↗

PubMed2005

Anti-TNF-alpha reduces the inflammatory reaction associated with cuff electrode implantation around the sciatic nerve.

Extraneural cuff electrodes have been extensively used to investigate the nervous system. Their implantation is, however, associated with epineurial fibrosis, fiber loss, limited reproducibility of recordings and variability in stimulating conditions. It has recently been shown that TNF-alpha is involved in nerve alterations after electrode implantation. This study investigated whether a peri-operative anti-TNF-alpha treatment could modify the inflammation and fibrosis associated with cuff electrode implantation. Morphometrical and immunohistochemical methods were used to show that a single systemic injection of TNF-alpha neutralizing antibodies is sufficient to reduce the early inflammatory events, but not the long lasting fibrotic reaction.

Animals↗

PubMed2005

Nitric oxide synthases II and III and vascular endothelial growth factor are up-regulated in sciatic nerve after spiral cuff electrode implantation.

Nerve cuff electrodes, commonly used in functional electrical stimulation systems, induce local morphological changes that can affect nerve functionality. Nitric oxide (NO) and vascular endothelial growth factor (VEGF) have both neural and vascular effects. We investigated the time-dependent regulation of nitric oxide synthases (NOS) and of VEGF after implantation of spiral cuff electrode around rat sciatic nerve. NOSIII as well as VEGF were up-regulated in both epineurial and endoneurial compartments in cuff-implanted animals along with microvascular changes. Our results suggest that VEGF and NO are implied in morphological and functional alterations occurring in the early time after cuff implantation.

Animals↗

PubMed2004

Cuff electrode implantation around the sciatic nerve is associated with an upregulation of TNF-alpha and TGF-beta 1.

Epineurial fibrosis, fiber loss, limited reproducibility of recordings and variability of stimulation conditions have been documented after extraneural cuff electrode implantation. These morphological and electrophysiological modifications could be due to the local release of cytokines. We report the expression of two cytokines, tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta1 (TGF-beta1) in the rat sciatic nerve after 'cuff' implantation for 18 h, 7 days and 1 month. Immunohistochemical and Western blot analyses showed a transient upregulation of TNF-alpha, during the first week, and a prolonged increase of TGF-beta1, over the 1-month period duration of this study. Considering the known pro-inflammatory roles of TNF-alpha and the pro-fibrotic action of TGF-beta, our results strongly suggest that these cytokines may contribute to nerve alterations occurring within the acute and sub-acute phases after cuff electrode implantation.

Animals↗

PubMed2004

Prediction of visual perceptions with artificial neural networks in a visual prosthesis for the blind.

Within the framework of the OPTIVIP project, an optic nerve based visual prosthesis is developed in order to restore partial vision to the blind. One of the main challenges is to understand, decode and model the physiological process linking the stimulating parameters to the visual sensations produced in the visual field of a blind volunteer. We propose to use adaptive neural techniques. Two prediction models are investigated. The first one is a grey-box model exploiting the neurophysiological knowledge available up to now. It combines a neurophysiological model with artificial neural networks, such as multi-layer perceptrons and radial basis function networks, in order to predict the features of the visual perceptions. The second model is entirely of the black-box type. We show that both models provide satisfactory prediction tools and achieve similar prediction accuracies. Moreover, we demonstrate that significant improvement (25%) was gained with respect to linear statistical methods, suggesting that the biological process is strongly non-linear.

Blindness↗

PubMed2004

Vision rehabilitation in the case of blindness.

This article examines the various vision rehabilitation procedures that are available for early and late blindness. Depending on the pathology involved, several vision rehabilitation procedures exist, or are in development. Visual aids are available for low vision individuals, as are sensory aids for blind persons. Most noninvasive sensory substitution prostheses as well as implanted visual prostheses in development are reviewed. Issues dealing with vision rehabilitation are also discussed, such as problems of biocompatibility, electrical safety, psychosocial aspects, and ethics. Basic studies devoted to vision rehabilitation such as simulation in mathematical models and simulation of artificial vision are also presented. Finally, the importance of accurate rehabilitation assessment is addressed, and tentative market figures are given.

Blindness↗

PubMed2003

Position, size and luminosity of phosphenes generated by direct optic nerve stimulation.

Pulses of low intensity current, delivered through a cuff electrode chronically implanted around the optic nerve of a blind retinitis pigmentosa patient generate visual sensations. These phosphenes are obtained at lower thresholds for a train of stimuli than for single pulses, which suggests the existence of a spatial and temporal integrating mechanism. The perceptions are much smaller than those predicted from model simulations. A set of equations are derived which show the effect of pulse current, duration, number and frequency on the position, size and, to some extent, luminosity of the resulting phosphenes.

Adult↗

PubMed2003

Pattern recognition with the optic nerve visual prosthesis.

A volunteer with retinitis pigmentosa and no residual vision was chronically implanted with an optic nerve electrode connected to an implanted neurostimulator and antenna. An external controller with telemetry was used for electrical activation of the nerve which resulted in phosphene perception. Open-loop stimulation allowed the collection of phosphene attributes and the ability to elicit perception of simple geometrical patterns. Low perception thresholds allowed for large current intensity range within safety limits. In a closed-loop paradigm, the volunteer was using a head-worn video camera to explore a projection screen. The volunteer underwent performance evaluation during the course of a training program with 45 simple patterns. After learning, the volunteer reached a recognition score of 63% with a processing time of 60 s. Mean performance in orientation discrimination reached 100% with a processing time of 8 s.

Electric Stimulation↗

PubMed2002

The microsystems based visual prosthesis for optic nerve stimulation.

The microsystems based visual prosthesis (MiViP) visual prosthesis generates visual perceptions well below safety and stimulator saturation limits. These perceptions, called phosphenes, are of reasonably small size and are broadly distributed in the visual field. They can thus be used to convey useful visual information. Psychophysical evaluations are being performed in order to assess the implantee's benefits in the use of the MiViP optic nerve visual prosthesis. In a pattern-recognition task, the performance improved regularly with practice with an increasing score and a decreasing delay to recognition. These observations open the way toward an evaluation of general mobility improvement with the portable system. In conclusion, the results obtained so far still support the potential usefulness of the optic nerve visual prosthesis. A low-resolution artificial vision can be expected from the prosthesis after extensive training.

Electric Stimulation↗