Robert H. Pudenz

Evaluation of electrode array material for neural prostheses.

Matrix support materials for brain surface electrodes used in neuroprosthetic applications were evaluated after chronic subdural implantation over the parietal cortex of the cat. Four types of array fabricated with Silastic, Dacron mesh, or platinum wire annuli were implanted for periods ranging from 5 weeks to 1 year. We evaluated the arrays by access resistance measurements and gross and histological observations of the tissue beneath both nonstimulated and stimulated electrodes. A porous type matrix constructed of Dacron mesh proved to be the superior design because of its minimal compression of the cortical surface, facility of handling during implantation and autopsy, and satisfactory electrical characteristics provided by a good electrode-brain interface. (Neurosurgery, 5: 681--686, 1979).

Effects of Electrical Stimulation of Brain

The use of implantable neural prostheses activated by radiofrequency transmission requires that the materials in the device and the stimulation techniques are not injurious to neural tissue, particularly the neurons. In this report, we discuss our experiences in the search for safe stimulation techniques. Acute and chronic experiments have been performed to evaluate electrode design and materials and to observe the effects of various stimulus protocols on the blood-brain barrier and brain. Neural tissue underlying the stimulated and control electrodes has been examined with both light and electron microscopy. Observations up to the present time indicate that the charge per phase is the most relevant stimulus parameter although the importance of charge density and current density cannot be underestimated.

Neuropathological Effects of Intracerebral Platinum Salt Injections

Multiple intracerebral injections of a mixture of platinum salts were made in 9 adult cats and the brains studied by light and electron microscopy at 5–12 days post injection. At the center of the lesions normal cortical architecture was completely replaced by edematous areas containing lipid-laden macrophages and cellular debris. The lesion periphery was characterized by perivascular edema and degenerative changes including cytoplasmic lipid inclusions and vacuolations with selective vulnerability of neurons. Membranous cytoplasmic bodies (MCB), zebra bodies and multiple nucleoli were observed in several cell types. This ultrastructural pattern, mimicked to some extent, that observed following electrical stimulation of brain following chronically implanted platinum and rhodium electrodes. The induction of zebra bodies and MCB, both of which are morphologic features of human neurolipidoses associated with congenital enzyme deficiencies, suggests an inhibitory effect of platinum on brain enzymes. Functional electrical stimulation of brain and other organs is currently being employed in a wide variety of clinical applications (14, 15). A mandatory consideration is that of the long-term effects of the stimuli as well as the electrodes themselves on the tissues involved. The histological effects and mechanisms of tissue damage following chronic application of electrical stimuli to brain have been the subject of several investigations in this laboratory (1, 14–18). Factors contributing to neural damage induced by electrical stimulation include noxious products resulting from electrode dissolution. In vitro studies employing electrochemical (3, 9) and scanning electron microscopy (6) techniques have established that erosion of noble metal electrodes occurs, even when passing relatively small stimulation currents. Such electrode dissolution is of particular importance in long term applications of neural prostheses. The present study was initiated to assess the contribution of platinum electrode erosion products to neural damage following electrical stimulation of brain, specifically to distinguish morphological changes resulting directly from electrode solubilization as opposed to electrical factors. Accordingly.

Neural stimulation : clinical and laboratory experiences

This is a report of some of the experiences of the author and his associates with electrical stimulation of the animal and human nervous systems. It was presented as a personal history rather than a review of recent investigations and publications concerned with safe and effective stimulation of neural tissue with the ultimate goals of developing neural prostheses. Much of the information presented herein has been published.

Electrical stimulation of the human visual cortex; preliminary report.

A feasibility study for the development of a human visual prosthesis has led several workers to observe the effects of electrical stimulation of the human visual cortex. Experience with such stimulations of three normal-sighted patients is reported. The results confirm some of the findings of other workers, but do not show that multiple phosphenes were experienced by our patients, using strictly limited parameters of stimulation.

Development and clinical capabilities of a new implantable biostimulator

Abstract During the past nine years we have used experimentally and clinically various types of implantable electronic units to stimulate or block nerve impulses. Tissue tolerance and reliability have been excellent, but electronic design and production factors limited their versatility. Our recent studies, a part of the visual prosthesis program, revealed the importance of a need for a device with the capability of receiving a wide variety of signals. The type of current, wave form, pulse width, and frequency have proved to be of critical importance and the available devices cannot meet these demands. Our experiments have shown that for chronic electrical stimulation or inhibition of nervous tissue the most critical factor is “current density” at the point of contact. Heat production and impedance are other important considerations. The unit discussed has been designed and built to allow precise control of these parameters. Until recently the only neurosurgical methods to alter function of the nervous system were destruction of a given area or interruption of nervous pathways. In selected situations this has been effective but, generally, an associated loss of either motor or sensory function results. Electronic methods hold promise for selective or partial alteration of function that can be programmed according to a temporal schedule. An area can now be stimulated or blocked without local destruction. By controlled stimulation, information can be fed into the system which may alter the subjective response and the nature of the reflex arc, or even amplify cerebral inhibition. Using multiple circuits one structure can be stimulated while function in an adjacent area can be inhibited. The clinical application of the system is discussed with particular reference to the electronic control of pain secondary to malignant disease. A brief discussion is given regarding the probable origin of pain and how involved pathways can be altered electrically. Future clinical applications are mentioned.

Adverse effects of electrical energy applied to the nervous system.

Neural prostheses activated by radiofrequency transmission are currently being implanted to treat a variety of clinical problems. It is essential that neither the materials used in these prostheses, particularly the electrodes, nor the stimulus parameters that are employed will cause neural damage. The experiences of investigators engaged in both the experimental laboratory and clinical studies of the effects of electrical stimulation are reported herein.

New method of closure of the scalp.

A n y m e t h o d of closure of the scalp has two essent ia l f a c t o r s a p p r o x i m a t i o n of the marg ins of the wound and a d e q u a t e hemostas is . The twol aye r m e t h o d e m p l o y i n g silk su tures was the accep ted s t a n d a r d for m a n y years . In 1943, while in the N a v y , we began to use an inve r t ed m a t t r e s s su ture of t a n t a l u m wire for closure of the scalp. Th is m e t h o d was more rap id , allowed b e t t e r hemostas i s , and , when removed , lef t no foreign m a t e r i a l in the wound. Stainless steel wire has since rep laced t a n t a l u m b u t the m e t h o d of use and a d v a n tages are s imilar .