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Leo A. Bullara

Bio: Leo A. Bullara is an academic researcher from Huntington Medical Research Institutes. The author has contributed to research in topics: Stimulation & Microstimulation. The author has an hindex of 31, co-authored 48 publications receiving 3682 citations.

Papers
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Journal ArticleDOI
TL;DR: Results show that charge density (as measured at the surface of the stimulating electrode) and charge per phase interact in a synergistic manner to determine the threshold of stimulation-induced neural injury.
Abstract: Stimulating electrodes of various sizes were used to investigate the interactions of two stimulus parameters, charge density and charge per phase, in determining the threshold of neural injury induced by electrical stimulation. Platinum electrodes ranging in size from 0.002 to 0.5 cm/sup 2/ were implanted over the parietal cortex of adult cats. Ten days after implantation, the electrodes were pulsed continuously for 7 h using charge-balanced, current-regulated, symmetric pulse pairs 400 mu s per phase in duration and at a repetition rate of 50 Hz. The results show that charge density (as measured at the surface of the stimulating electrode) and charge per phase interact in a synergistic manner to determine the threshold of stimulation-induced neural injury. This interaction occurs over a wide range of both parameters: for charge density from at least 10 to 800 mu C/cm/sup 2/, and for charge per phase from at least 0.05 to 5.0 mu C per phase. The significance of these findings in elucidating the mechanisms underlying stimulation-induced injury is discussed. >

752 citations

Patent
16 Sep 1974
TL;DR: In this article, a surgically implantable pressure transducer for measuring pressure of fluid or tissue in a body chamber such as brain ventricle of a patient suffering hydrocephalus or a severe head injury is described.
Abstract: A wireless, surgically implantable pressure transducer for measuring pressure of fluid or tissue in a body chamber such as brain ventricle of a patient suffering hydrocephalus or a severe head injury. The transducer includes a coaxial variable capacitor electrically connected across an inductor to form a parallel resonant L-C circuit. Alternatively, a coaxially variable inductor may be connected across a capacitor to form the L-C circuit. A bellows is mechanically connected to the variable component to vary the value of capacitance or inductance and hence the resonant frequency of the L-C circuit in response to pressure changes of the fluid in which the bellows is immersed. The transducer is electromagnetically coupled to an external source of variable-frequency oscillatory energy such as a grid-dip oscillator which enables external detection of the transducer resonant frequency which is in turn indicative of the level of fluid pressure being sensed.

284 citations

Journal ArticleDOI
01 Sep 1999
TL;DR: The results indicate that, after implantation, the electrode-tissue interface may change from day-to-day over the first 1-2 weeks, week- to-week for 1- 2 months, and become quite stable thereafter, and a stability index is proposed to quantify the stability of the electrodes-tissues interface.
Abstract: The stability of the interface between neural tissue and chronically implanted microelectrodes is very important for obtaining reliable control signals for neuroprosthetic devices. Stability is also crucial for chronic microstimulation of the cerebral cortex. However, changes of the electrode-tissue interface can be caused by a variety of mechanisms. In the present study, intracortical microelectrode arrays were implanted into the pericruciate gyrus of cats and neural activities were recorded on a regular basis for several months. An algorithm based on cluster analysis and interspike interval analysis was developed to sort the extracellular action potentials into single units. We tracked these units based on their waveform and their response to somatic stimulation or stereotypical movements by the cats. Our results indicate that, after implantation, the electrode-tissue interface may change from day-to-day over the first 1-2 weeks, week-to-week for 1-2 months, and become quite stable thereafter. A stability index is proposed to quantify the stability of the electrode-tissue interface. The reasons for the pattern of changes are discussed.

277 citations

Journal ArticleDOI
TL;DR: It is demonstrated that axons in peripheral nerves can be irreversely damaged by 8–16 hours of continuous stimulation at 50 Hz, and the extent to which these axons may subsequently regenerate is uncertain.
Abstract: Helical electrodes were implanted around the left and right common peroneal nerves of cats. Three weeks after implantation one nerve was stimulated for 4–16 hours using charge-balanced, biphasic, constant current pulses. Compound action potentials (CAP) evoked by the stimulus were recorded from over the cauda equina before, during and after the stimulation. Light and electron microscopy evaluations were conducted at various times following the stimulation. The mere presence of the electrode invariably resulted in thickened epineurium and in some cases increased peripheral endoneurial connective tissue beneath the electrodes. Physiologic changes during stimulation included elevation of the electrical threshold of the large axons in the nerve. This was reversed within one week after stimulation at a frequency of 20 Hz, but often was not reversed following stimulation at 50–100 Hz. Continuous stimulation at 50 Hz for 8–16 hours at 400 μA or more resulted in neural damage characterized by endoneurial edema beginning within 48 hours after stimulation, and early axonal degeneration (EAD) of the large myelinated fibers, beginning by 1 week after stimulation. Neural damage due to electrical stimulation was decreased or abolished by reduction of the duration of stimulation, by stimulating at 20 Hz (vs. 50 Hz) or by use of an intermittent duty cycle. These results demonstrate that axons in peripheral nerves can be irreversely damaged by 8–16 hours of continuous stimulation at 50 Hz. However, the extent to which these axons may subsequently regenerate is uncertain. Therefore, protocols for functional electrical stimulation in human patients probably should be evaluated individually in animal studies.

180 citations

Journal ArticleDOI
TL;DR: Recommendations have been made for the selection of electrical stimulus parameters to be used in central nervous system prostheses based on the relationship of charge density per phase and total charge to neural damage investigated after surface stimulation of the parietal cortex in normal cats.
Abstract: The relationship of charge density per phase, or QD/ph (expressed in units of microcoulombs per cm2 per phase of the charge-balanced wave form), and total charge (QDt) to neural damage has been investigated by light and electron microscopy after surface stimulation of the parietal cortex in normal cats. QD/ph values ranging from 40 to 400 were achieved by varying several stimulus parameters. The least amount of neural damage in this study was observed at QD/ph 40). The extent of neural injury at stimulated sites increased with the charge density and was evident as disruption of cell membranes, intracytoplasmic vacoulation, an increasing glycogen content, the deposition of intracellular calcium hydroxyapatite, and neuronal and astrocytic degeneration. Although individual factors contributing to neural damage are isolated with difficulty, charge density and total charge seem to be predominant among the contributing parameters. In view of these findings, recommendations have been made for the selection of electrical stimulus parameters to be used in central nervous system prostheses.

174 citations


Cited by
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Journal ArticleDOI
TL;DR: With adequate recognition and effective engagement of all issues, BCI systems could eventually provide an important new communication and control option for those with motor disabilities and might also give those without disabilities a supplementary control channel or a control channel useful in special circumstances.

6,803 citations

Journal ArticleDOI
TL;DR: The brain's electrical signals enable people without muscle control to physically interact with the world through the use of their brains' electrical signals.
Abstract: The brain's electrical signals enable people without muscle control to physically interact with the world.

2,361 citations

Journal ArticleDOI
TL;DR: The guidelines for the use of rTMS cover the ethical issues, recommended limits on stimulation parameters, monitoring of subjects (both physiologically and neuropsychologically), expertise and function of the rT MS team, medical and psychosocial management of induced seizures, and contra-indications to r TMS.

2,313 citations

Journal ArticleDOI
01 Jun 2000
TL;DR: The first international meeting devoted to brain-computer interface research and development is summarized, which focuses on the development of appropriate applications, identification of appropriate user groups, and careful attention to the needs and desires of individual users.
Abstract: 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.

2,121 citations

Journal ArticleDOI
TL;DR: The physical basis for electrical stimulation of excitable tissue, as used by electrophysiological researchers and clinicians in functional electrical stimulation, is presented with emphasis on the fundamental mechanisms of charge injection at the electrode/tissue interface.

1,875 citations