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Biomedical subjects

J T Rubinstein

Publications and source records attributed to J T Rubinstein.

At least 19 recordsLinked to original sources
PubMed2000

Channel noise in neurons.

The probabilistic gating of voltage-dependent ion channels is a source of electrical 'channel noise' in neurons. This noise has long been implicated in limiting the reliability (repeatability) of neuronal responses to repeated presentations of identical stimuli. More recently, it has been shown to increase the range of spiking behaviors exhibited in some neural populations. Channel numbers are tied to metabolic efficiency and the stability of resting potential, and channel noise might be exploited by future cochlear implants in order to improve the temporal representation of sound.

Action Potentials↗
PubMed2000

The neuronal response to electrical constant-amplitude pulse train stimulation: evoked compound action potential recordings.

The purpose of this study was to gain a greater understanding of the electrically evoked compound action potential (EAP) responses to pulse train stimulation. Analysis of EAP amplitude responses suggested that an alternating pattern varied depending upon stimulus level, interpulse interval (IPI), stimulus waveform, and stimulus polarity. Stimulus level-dependent recovery was seen in the cat and the guinea pig: higher stimulus level tended to provide faster recovery. Both polarity-dependent recovery and polarity-dependent adaptation were observed in the cat and these stimulus polarity effects were less consistent in the guinea pig. The polarity-dependent recovery effect supports the hypothesis that anodal and cathodal stimuli excite different sites along auditory nerve fibers. Amplitude differences between the response to the second pulse and the steady-state response at the same IPI are significantly greater for anodal stimuli than for cathodal stimuli in all cats. These data suggest that there is a cumulative refractory effect in the auditory nerve of cats, especially in response to anodal stimuli.

Action Potentials↗
PubMed2000

The neuronal response to electrical constant-amplitude pulse train stimulation: additive Gaussian noise.

Experimental results from humans and animals show that electrically evoked compound action potential (EAP) responses to constant-amplitude pulse train stimulation can demonstrate an alternating pattern, due to the combined effects of highly synchronized responses to electrical stimulation and refractory effects (Wilson et al., 1994). One way to improve signal representation is to reduce the level of across-fiber synchrony and hence, the level of the amplitude alternation. To accomplish this goal, we have examined EAP responses in the presence of Gaussian noise added to the pulse train stimulus. Addition of Gaussian noise at a level approximately -30 dB relative to EAP threshold to the pulse trains decreased the amount of alternation, indicating that stochastic resonance may be induced in the auditory nerve. The use of some type of conditioning stimulus such as Gaussian noise may provide a more 'normal' neural response pattern.

Action Potentials↗
PubMed2000

Digital X-ray stereophotogrammetry for cochlear implantation.

Multielectrode, intracochlear implant systems are effective treatment for profound sensorineural hearing loss. In some cases, these systems do not perform well, which may be partially due to variations in implant location within the cochlea. Determination of each electrode's position in a patient's inner ear provides an in vivo basis for both the cochlear modeling of electrical fields and the future design of electrode arrays that deliver electrical stimulation to surviving auditory neurons, and may improve speech processor programming for better speech recognition. We developed an X-ray stereophotogrammetric approach to localize implanted electrodes in three dimensions. Stereophotogrammetry of implanted electrodes is formulated in weak perspective geometry, with knowledge of a three-dimensional (3-D) reference structure and electrode positions in each of two digital stereo-images. The localization error is theoretically, numerically, and experimentally quantified. Both numerical and experimental results demonstrate the feasibility of the technique.

Biomedical Engineering↗
PubMed2000

Three-dimensional geometric modeling of the cochlea using helico-spiral approximation.

In this paper, the three-dimensional geometry of the human cochlea is modeled by the helico-spiral seashell model. The 3-D helico-spiral model, the generalized representation of the Archimedian spiral model, provides a framework for measuring cochlear features based on consistent estimation of model parameters. Nonlinear least square minimization based algorithms are developed for the identification of rotation, center and intrinsic parameters of the helico-spiral representation. Two algorithms are designed for the rotation axis aligned to the modiolar axis: one is more susceptible in the presence of noise, while the other allows applicability to two-dimensional data sets. The estimated center and intrinsic parameters allow the calculation of length, height and angular positions needed for frequency mapping of multichannel cochlear implant electrodes. Model performance is evaluated with numerically synthesized curves with different levels of added random noise, histologic data and real human cochlear spiral computed tomography data.

Algorithms↗
PubMed2000

Three-dimensional modeling and visualization of the cochlea on the Internet.

Three-dimensional (3-D) modeling and visualization of the cochlea using the World Wide Web (WWW) is an effective way of sharing anatomic information for cochlear implantation over the Internet, particularly for morphometry-based research and resident training in otolaryngology and neuroradiology. In this paper, 3-D modeling, visualization, and animation techniques are integrated in an interactive and platform-independent manner and implemented over the WWW. Cohen's template shape with mean cross-sectional areas of the human cochlea is extended into a 3-D geometrical model. Also, spiral computer tomography data of a patient's cochlea is digitally segmented and geometrically represented. The cochlear electrode array is synthesized according to its specification. Then, cochlear implantation is animated with both idealized and real cochlear models. Insertion length, angular position, and characteristic frequency of individual electrodes are estimated online during the virtual insertion. The optimization of the processing parameters is done to demonstrate the feasibility of this technology for clinical applications.

Cochlea↗
PubMed2000

Localization of cochlear implant electrodes in radiographs.

Multielectrode cochlear implantation is the most effective treatment for profound sensorineural hearing loss. In vivo three-dimensional 3-D localization of cochlear implant electrodes is important for modeling of the electrical field in the cochlea, design of electrode arrays, and may improve speech processor programming for better speech recognition. The prerequisite for 3-D localization of the electrodes is their 2-D localization in x-ray radiographs. In this paper, we develop a practical method to localize the electrodes with high efficiency, accuracy, and reproducibility. In this method, a priori knowledge of the electrodes and their approximate positions are utilized, an intelligent thresholding and segmentation mechanism is embedded, and the electrode center is computed as the weighted geometric center of segmented electrode pixels. Experiments with physical phantoms and human data demonstrate the feasibility and utility of this method. The PC-based program developed for this project is disseminated on the Web.

Cochlear Implants↗
PubMed2000

Rheumatoid arthritis of the temporomandibular joint with herniation into the external auditory canal.

Previous authors have shown that soft tissue can present in the external auditory canal via a patent foramen of Huschke. One case represented a patient with psoriatic arthritis and a polyp in the external auditory canal. Typically, neoplastic, inflammatory, or degenerative lesions of the temporomandibular joint do not present in the external auditory canal. We present a patient with rheumatoid arthritis of the temporomandibular joint and soft tissue herniation into the external auditory canal. The case, and a discussion of possible causes, are presented.

Arthritis, Rheumatoid↗
PubMed1999

Pseudospontaneous activity: stochastic independence of auditory nerve fibers with electrical stimulation.

We describe a novel signal processing strategy for cochlear implants designed to emphasize stochastic independence across the excited neural population. The strategy is based on the observation that high rate pulse trains may produce random spike patterns in auditory nerve fibers that are statistically similar to those produced by spontaneous activity in the normal cochlea. We call this activity 'pseudospontaneous'. A supercomputer-based computational model of a population of auditory nerve fibers suggests that different average rates of pseudospontaneous activity can be created by varying the stimulus current of a fixed-amplitude, high-rate pulse train, e.g. 5000 pps. Electrically-evoked compound action potentials recorded in a human cochlear implant subject are consistent with the hypothesis that such a stimulus can desynchronize the fiber population. This desynchronization may enhance neural representation of temporal detail and dynamic range with a cochlear implant and eliminate a major difference between acoustic and electric hearing.

Cochlear Implants↗
PubMed1999

Electrically evoked single-fiber action potentials from cat: responses to monopolar, monophasic stimulation.

We recorded action potentials from single auditory-nerve fibers of cats using monophasic current pulses delivered by a monopolar intracochlear electrode. These simple stimuli provided a means of investigating basic properties and hypotheses of electrical excitation. Standard micropipette recording techniques were used. Responses to anodic (positive) and cathodic (negative) stimulus pulses were recorded separately to evaluate stimulus polarity effects. Mean spike (action potential) latency was polarity dependent, with greater latencies for cathodic stimulation. Threshold stimulus level was also polarity dependent, with relatively lower cathodic thresholds. Both effects are consistent with trends reported in the compound action potential. Variability in single-fiber latency (i.e., jitter) was dependent upon stimulus polarity. In contrast, the slope of single-fiber input-output functions failed to show a clear polarity dependence, although such trends have been seen in the compound action potential data. We also observed a relatively greater degree of adaptation over time with anodic stimulation. Bimodal post-stimulus-time histograms were recorded in a small number (2%) of fibers, supporting the hypothesis that both the peripheral (dendritic) and central axonal processes are excitable with the same stimulus polarity, in a limited number of cases. This observation, together with analyses of interactions among measures of latency, threshold, and jitter, is consistent with the hypothesis that, with monopolar intracochlear stimulation, most fibers are stimulated at axonal (modiolar) sites and a minority of fibers nearest the electrode are stimulable at their peripheral processes.

Action Potentials↗
PubMed1999

An empirically based model of the electrically evoked compound action potential.

The relationship between electrically evoked single-fiber action potentials and the electrically evoked compound action potential of the auditory nerve is of interest to those attempting to model such responses with computational techniques. It also relates to efforts to exploit the gross potentials that can now be recorded by some implantable cochlear prostheses. In this paper, we develop a computational model of the auditory nerve response to single, pulsatile, electrical stimuli based upon the response characteristics obtained from 230 single fibers of 13 cats. These fibers were stimulated by brief (39s) monophasic cathodic stimuli delivered by a monopolar intracochlear electrode. The data were pooled to obtain an estimate of the distribution of fiber thresholds. Post-stimulus time histograms were modeled using Poisson functions and adjusted to account for empirically determined latency and jitter characteristics. The probabilistic nature of single-fiber input-output functions (i.e. Verveen's (1961) 'relative spread') was also modelled. PST histograms from 5000 modelled fibers were then summed and convolved with an estimated 'unit potential' following the method of Goldstein and Kiang (1958). This convolution produced modelled compound action potentials, which were then compared with experimentally obtained data. Manipulations of model parameters affecting threshold, jitter, and relative spread suggest that the most important determinant of the shape of the EAP amplitude-level function is the threshold distribution. A model based solely on threshold distribution produces an EAP input-output function similar to one that accounts for probabilistic single-fiber input-output functions. Discrepancies between these two models do occur if the threshold distribution function is compressed significantly, as might be the case in pathological cochleae with altered distributions or numbers of nerve fibers.

Algorithms↗
PubMed1999

How do cochlear prostheses work?

The past two decades have witnessed a revolution in the treatment of sensorineural hearing loss. Cochlear prostheses have evolved from laboratory experiment to a commercial technology that has benefited over 20,000 people. Paralleling this phenomenal development has been a substantial increase in our understanding of the biophysical, physiological and psychophysical mechanisms underlying the function of these devices.

Animals↗
PubMed1999

Surgical management of Bell's palsy.

OBJECTIVES: Incomplete return of facial motor function and synkinesis continue to be long-term sequelae in some patients with Bell's palsy. The aim of this report is to describe a prospective study in which a well-defined surgical decompression of the facial nerve was performed in a population of patients with Bell's palsy who exhibit the electrophysiologic features associated with poor outcomes. In addition, management issues related to Bell's palsy including herpes simplex virus typel etiology, the natural history, electrodiagnostic testing, and efficacy of surgical strategies are reviewed. STUDY DESIGN AND METHODS: A multicenter prospective clinical trial was designed utilizing electroneurography (ENOG) and voluntary electromyography (EMG) to identify patients with Bell's palsy who would most likely develop poor return of facial function, as suggested by Fisch and Esslen. Patients who displayed electrodiagnostic features of poor outcome, >90% degeneration on ENOG testing and no voluntary motor unit EMG potentials within 14 days of onset of total paralysis, were offered a surgical decompression of the facial nerve through a middle cranial fossa surgical exposure, including the tympanic segment, geniculate ganglion, labyrinthine segment, and meatal foramen. Control subjects were those who displayed similar electrodiagnostic features and time course. RESULTS: Subjects who did not reach 90% degeneration on ENOG within 14 days of paralysis all returned to House-Brackmann grade I (n = 48) or II (n = 6) at 7 months after onset of the paralysis. Control subjects self-selecting not to undergo surgical decompression when >90% degeneration on ENOG and no motor unit potentials on EMG were identified had a 58% chance of developing a poor outcome at 7 months after onset of paralysis (House-Brackmann grade III or IV [n = 19]). A group with similar ENOG and EMG findings undergoing middle fossa facial nerve decompression exhibited House-Brackmann grade I (n = 14) or II (n = 17) in 91% of the cases. An exact permutation test confirmed that the surgical group had a significantly higher proportion of patients with a good outcome (House-Brackmann grade I or II) (P = .0002). CONCLUSION: Electroneurography in combination with voluntary EMG successfully identified patients who will most likely return to normal from those who had a greater chance of long-term sequelae from Bell's palsy. Surgical decompression medial to the geniculate ganglion significantly improves the chances of normal or near-normal return of facial function in the group that has a high probability of a poor result. Surgical decompression must be performed within 2 weeks of onset of total paralysis for it to be effective.

Adult↗
PubMed1999

Residual speech recognition and cochlear implant performance: effects of implantation criteria.

OBJECTIVE: This study aimed to determine the effects of preoperative speech reception on postoperative speech recognition with a cochlear implant and to develop a statistical index allowing prediction of postoperative speech recognition before implantation. STUDY DESIGN: The study design was a retrospective case review with statistical modeling. SETTING: The study was conducted at a tertiary referral center with an associated Veteran's Administration hospital. PATIENTS: Postlingually deafened adults with and without residual speech reception participated. INTERVENTION: Cochlear implantation with Cochlear Corporation CI-22 and CI-24 devices was performed. MAIN OUTCOME MEASURES: Monosyllabic word recognition was measured. RESULTS: Duration of deafness and preoperative sentence recognition are both significant predictors of word recognition with a cochlear implant and can account for 80% of the variance in word recognition. CONCLUSIONS: Cochlear implant outcomes are variable but predictable within specific ranges.

Adult↗
PubMed1999

Facial nerve grafts: from cerebellopontine angle and beyond.

OBJECTIVES: To review the outcomes from facial nerve cable grafting in a variety of pathologic conditions and to determine the possible causes of poor facial function after facial nerve grafting. STUDY DESIGN: A retrospective review of patients undergoing facial nerve grafts through a neurotologic procedure. SETTING: This study was performed at a university-based tertiary referral center. PATIENTS: All 27 patients undergoing a neurotologic procedure that required a facial nerve graft from 1982 to 1997 were reviewed. Fourteen patients had grafts from the facial nerve stump at the brainstem. INTERVENTIONS: All patients had facial nerve function determined by the senior neurotologist and through use of historical data and photographs. MAIN OUTCOME MEASURE: A facial nerve repair recovery score was developed for facial nerve transection and repair. The House-Brackmann scale was found to be inappropriate for transected and repaired nerves. RESULTS: Facial function was found in 23/25 (92%) patients with at least 8 months follow-up. Statistical analysis revealed no significant correlation between graft length and recovery score. Patients who had the nerve grafted to a site distal to the meatal foramen had a mean outcome that was nearly one grade level better than those with an anastomosis proximal to the meatal foramen (i.e., at the brainstem), but this did not reach statistical significance. CONCLUSIONS: Facial nerve grafting is an effective way of restoring facial motor function. A new facial recovery grading scale is proposed for repaired or grafted facial nerves.

Adolescent↗
PubMed1999

Management of cochlear implant infections.

OBJECTIVE: The aim of this study was to illustrate and discuss management of cochlear implant infections. STUDY DESIGN: The study design was a retrospective case review. SETTING: This study was performed at a tertiary referral center with an associated Veterans Administration Hospital. PATIENTS: Postlingually deafened adults who had revision surgery for delayed cochlear implant infections were included in this study. INTERVENTION: Medical and surgical management of device infection without explantation. MAIN OUTCOME MEASURES: Eradication of infection without loss of speech reception. RESULTS: All four patients were successfully managed without explantation. CONCLUSIONS: Explantation of an infected but functioning multichannel implant is not mandatory in the absence of systemic sepsis.

Adult↗
PubMed1998

Electrically evoked compound action potentials of guinea pig and cat: responses to monopolar, monophasic stimulation.

We recorded electrically evoked compound action potentials (EAPs) from guinea pigs and cats using monophasic current pulses delivered by a monopolar intracochlear electrode. By using simple stimuli, we sought results that could shed light on basic excitation properties of the auditory nerve. In these acute experiments, the recording electrode was placed directly on the auditory nerve. Responses to anodic and cathodic stimulus pulses were recorded separately to evaluate stimulus polarity effects. Several polarity-dependent properties were observed. Both EAP morphology and latency were polarity-dependent, with greater latencies for cathodic stimulation. Threshold stimulus level was also polarity-dependent, but in different directions in the two species: cats had lower cathodic thresholds while guinea pigs had lower anodic thresholds. We also observed that the slopes of the EAP amplitude-level functions depended upon stimulus polarity. In most cases where EAP saturation amplitude could be measured, that amplitude was similar for anodic and cathodic stimuli, suggesting that either stimulus polarity can recruit all fibers, or at least a comparable numbers of fibers. The common findings (e.g., EAP morphology and polarity-dependent latency) observed in these two species suggest results that can be extrapolated to responses obtained in humans, while the species-specific findings (e.g., dependence of threshold on polarity) may point to underlying anatomical differences that caution against overgeneralization across species. Some of our observations also bear upon hypotheses of how electrical stimuli may excite different sites on auditory nerve fibers.

Action Potentials↗