Brain-computer interfaces for communication and control.

The brain's electrical signals enable people without muscle control to physically interact with the world.

Brain-computer interfaces for communication and control

http://www.tmslab.org/tms%20articles%20safety/017.pdf

Risk and safety of repetitive transcranial magnetic stimulation: report and suggested guidelines from the International Workshop on the Safety of Repetitive Transcranial Magnetic Stimulation, June 5–7, 1996

Over the past decade, many laboratories have begun to explore brain-computer interface (BCI) technology as a radically new communication option for those with neuromuscular impairments that prevent them from using conventional augmentative communication methods. BCI's provide these users with communication channels that do not depend on peripheral nerves and muscles. This article summarizes the first international meeting devoted to BCI research and development. Current BCI's use electroencephalographic (EEG) activity recorded at the scalp or single-unit activity recorded from within cortex to control cursor movement, select letters or icons, or operate a neuroprosthesis. The central element in each BCI is a translation algorithm that converts electrophysiological input from the user into output that controls external devices. BCI operation depends on effective interaction between two adaptive controllers, the user who encodes his or her commands in the electrophysiological input provided to the BCI, and the BCI which recognizes the commands contained in the input and expresses them in device control. Current BCI's have maximum information transfer rates of 5-25 b/min. Achievement of greater speed and accuracy depends on improvements in signal processing, translation algorithms, and user training. These improvements depend on increased interdisciplinary cooperation between neuroscientists, engineers, computer programmers, psychologists, and rehabilitation specialists, and on adoption and widespread application of objective methods for evaluating alternative methods. The practical use of BCI technology depends on the development of appropriate applications, identification of appropriate user groups, and careful attention to the needs and desires of individual users. BCI research and development will also benefit from greater emphasis on peer-reviewed publications, and from adoption of standard venues for presentations and discussion.

/pdf/brain-computer-interface-technology-a-review-of-the-first-4t5zj40dij.pdf

Brain-computer interface technology: a review of the first international meeting

Electrical stimulation of excitable tissue: design of efficacious and safe protocols.

A microelectrode for delivery of defined charge densities.

Histological evaluations of dog sacral nerves were carried out after stimulation for electromicturition with three types of circumneural electrodes. The use of two types of cuff arrays was associated with a marked buildup of connective tissue around the nerve and filling the lumen of the array. Nerves within the first type of cuff array (having diameters approximately that of the nerve they surrounded) were often extruded from the lumen of the cuff. In some cases, this was accompanied by moderate or marked loss of axons. It is not clear whether this phenomenon was the result of the growth of connective tissue within the cuff or tension on the electrical leads. The damage cannot be attributed to the electrical stimulation because nerves enclosed by nonpulsed electrodes showed similar damage. The second type of cuff array used in the study had an oversize lumen. There was often considerable growth of connective tissue within the cuffs, but minimal or no mechanical deformation of the included nerves and minimal loss of axons. Because of sealable lips, extrusion of the nerve from this electrode was impossible. The nerves and arrays both functioned well, and there was minimal, if any, mechanical distortion of the nerves and minimal neural damage. Nerves within a third type of array ("spinal" array) also showed no or minimal damage. The array was implanted easily, and the delicate, springlike nature of the matrix allowed close apposition to nerves of different diameters while avoiding constriction of the nerve.

Histopathological evaluation of dog sacral nerve after chronic electrical stimulation for micturition.

Partial pressure of oxygen in brain and peripheral nerve during damaging electrical stimulation

The effects of electrical stimulation of the cat cerebral cortex have been evaluated by light and electron microscopy following a wide variety of stimulation parameters (QD/ph of 10 - 300 muC/cm2/ph). Platinum or rhodium disc electrode arrays were bilaterally implanted subdurally on the parietal cortex and subjected to 36-hour stimulations (9 hrs./day for 4 days). Prominent among the degenerative changes shown by electron microscopy were dense crystalline inclusions that were identified as calcium hydroxyapatite (CHA) crystals by electron diffraction and energy dispersive X-ray analysis. The appearance of intracellular calcification generally paralleled the onset of other degenerative changes in stimulated tissue, including gliosis, mitochondrial swelling, lipid inclusions, degenerating cells, neuronal loss, and phagocytic activity. A preferential deposition of calcium was noted in mitochondria of several cell types and in postsynaptic dendrites. The mechanism of the apparently electroresponsive calcium deposition is obscure; however, a plausible explanation is that increased cyclic AMP levels, known to occur with electrical stimulation of nervous tissue, result in enhanced calcium plasmalemmal permeability.

Intracellular calcium deposition in brain following electrical stimulation.

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, intracerebral injections of graded volumes of platinum salts were made in an attempt to simulate the presence of platinum electrode dissolution products.

Leo A. Bullara

Papers

A microelectrode for delivery of defined charge densities.

Histopathological evaluation of dog sacral nerve after chronic electrical stimulation for micturition.

Partial pressure of oxygen in brain and peripheral nerve during damaging electrical stimulation

Intracellular calcium deposition in brain following electrical stimulation.

Neuropathological effects of intracerebral platinum salt injections.