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Biomedical subjects

R J Peterka

Publications and source records attributed to R J Peterka.

33 records · Page 2Linked to original sources
PubMed1987

Quantitative diagnostic test for perilymph fistulas.

Clinically, the definitive diagnosis of perilymph fistulas can only be made by tympanotomy. Results of various fistula tests based upon the vestibulo-ocular reflex have not correlated well with findings during tympanotomy. A new fistula test has been developed based upon vestibulo-spinal responses. By systematic removal of both visual and support-surface orientation references from the subject--leaving only vestibular control of postural reflexes--patients with perilymph fistulas demonstrated an increased (sometimes phase-locked) postural sway in response to sinusoidal changes in external auditory canal pressures. Results from 100 consecutively operated ears (64 patients)--77 of whom underwent preoperative and postoperative moving-platform fistula tests--indicate that the test sensitivity is 97 percent for this highly selective patient population. Absolute specificity could not be determined because, on patients without clinical indications for surgery, tympanotomy is contraindicated.

Adolescent↗
PubMed1987

Vestibular reflex changes following aminoglycoside induced ototoxicity.

The effects of aminoglycoside-induced changes on the vestibular system were evaluated in three subjects who suffered significant damage over the course of treatment. Measurements of vestibulo-ocular reflex (VOR) function were made using sinusoidal and pseudorandom rotational stimuli between 0 to 5 days after initiation of drug therapy, during drug therapy, and up to 579 days following drug administration. All subjects tested at baseline evaluations had normal VOR function. During aminoglycoside therapy there was a precipitous drop in both the VOR time and gain constants. The decline in VOR function was larger at lower stimulus frequencies compared to high frequencies, resulting in a relative preservation of function in the high frequencies. Over a period of about a year, VOR high frequency gains recovered to within normal limits. However, the VOR time constants showed only a modest recovery and remained well below the normal range.

Aminoglycosides↗
PubMed1987

Optokinetic and vestibulo-ocular reflex responses to an unpredictable stimulus.

Horizontal plane optokinetic (OKR) and vestibulo-ocular reflex (VOR) eye movements were obtained from normal subjects in response to pseudorandom rotational stimulation. Results showed large intersubject variability in OKR responses. Typical OKR responses had approximately constant gain (Mean 0.65) over 0.02-1.5 Hz. Response phase was near zero below 0.1 Hz with increasing phase lags as frequency increased consistent with time delays of 180 ms (Mean value). Variations in OKR responses included declining gains with increasing frequency and phase lags consistent with time delays of 90 to 268 ms. Significant interactions of visual and vestibular motion information were detected at the highest stimulus frequency at which both were tested (1.5 Hz). Results suggested that visual motion information could be significant in the control of eye movements up to 6.1 Hz. Pseudorandom optokinetic stimulation induced motion sickness symptoms in approximately 20% of 213 subjects tested. Pseudorandom vestibular stimulation of twice the amplitude and duration did not initiate motion sickness symptoms in any subject.

Humans↗
PubMed1985

Neural modeling and model identification.

The complexity of the nervous system poses challenging experimental and theoretical problems to the investigator. While experimental studies have provided a broad understanding of the physiological and anatomical role of neural elements, a comprehensive description of how the nervous system acquires and processes information is still lacking. Neural modeling addresses itself to the quantitative interpretation of neurophysiological experiments, to the assimilation of diverse experimental results into unified theories, and to the investigation of mechanisms of information-processing units, codes, and networks and their relation to capabilities of living systems. This review will emphasize neural models which can be tested by physiological or psychophysical experiments and will include the identification of model parameters based on experimental measurements. An overview of neural firing models, neural interaction models, neural variability and coding, design of input-output experiments for model identification, and description of small network interactions through multiunit and gross potential recording will be included.

Action Potentials↗
PubMed1984

Differences between cats in response properties of horizontal semicircular canal primary afferents.

The response properties of cat horizontal canal afferents (N = 81) were characterized by three parameters: their long time constants (tau), low frequency gain constants (G1), and middle frequency gain constants (Gm). An average value of each of these parameters was calculated for each of eight animals and comparisons were made across animals. There were significant differences between individual animals in their average values of tau and Gm. There was also a significant negative correlation between tau's and Gm's. An animal with a larger average tau tended to have a smaller average Gm. We also used anatomic data on membranous canal duct diameter from the literature to independently estimate the potential effect of interanimal anatomic variability on the predicted range of tau and Gm values in a population. We then compared the data from our 81 afferents with the predictions from the anatomic data.

Animals↗
PubMed1981

Responses to head tilt in cat eighth nerve afferents.

Responses to head tilt were recorded from eighth nerve axons in barbiturate anesthetized cats. The maximally excitatory head tilt (polarization vector), a zero-force discharge rate, and tilt sensitivity were measured for each cell. In one population of afferents, the maximum discharge frequency was obtained by aligning the saccular plane with gravity. The response properties of these saccular afferents were compared with a second population arising from the utriculus. Both the resting discharge rate and the response sensitivity were lower for saccular than utricular afferents in the cat. The average resting discharge was about 20% lower and the sensitivity about 15% higher in the cat than in the squirrel monkey.

Afferent Pathways↗
PubMedDate not supplied

Vestibulo-ocular and vestibulospinal function before and after cochlear implant surgery.

Vestibular function in cochlear implant candidates varies from normal to total absence of function. In patients with intact vestibular function preoperatively, invasion of the otic capsule places residual vestibular function at risk. Speech-processing strategies that result in large amplitude electrical transients or strategies that employ high amplitude broad frequency carrier signals have the potential for disrupting vestibular function. Five patients were tested with and without electrical stimulation via cochlear electrodes. Two patients experienced subjective vestibular effects that were quickly resolved. No long-term vestibular effects were noted for the two types of second generation cochlear implants evaluated. Histopathological findings from another patient, who had electrically generated vestibular reflex responses to intramodiolar electrodes, indicated that responses elicited were a function of several variables including electrode location, stimulus intensity, stimulus amplitude, and stimulus frequency. Differential auditory, vestibulocolic, and vestibulospinal reflexes were demonstrated from the same electrode as a function of stimulus amplitude, frequency, and duration.

Aged↗
PubMedDate not supplied

Age-related changes in human vestibulo-ocular reflexes: sinusoidal rotation and caloric tests.

The dynamic response properties of horizontal vestibulo-ocular reflex (VOR) were characterized in 216 human subjects ranging in age from 7 to 81 y. The effects of aging on VOR dynamics and parameter distributions that describe VOR responses to caloric and to sinusoidal rotational stimuli were determined in a putatively normal population. Caloric test parameters showed no consistent trend with age. Rotation test parameters showed declining response amplitude and slightly less compensatory response phase with increasing age. The magnitudes of these changes were not large relative to the variability within the population. The age-related trends in VOR were not consistent with the anatomic changes in the periphery reported by others that showed an increasing rate of peripheral hair cell and nerve fiber loss in subjects over 55 y. The poor correlation between physiological and anatomical data suggest that adaptive mechanisms in the central nervous system are important in maintaining the VOR.

Adolescent↗
PubMedDate not supplied

Age-related changes in human vestibulo-ocular and optokinetic reflexes: pseudorandom rotation tests.

The dynamic response properties of horizontal vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) were characterized in 216 human subjects ranging in age from 7 to 81 y. The object of this cross-sectional study was to determine the effects of aging on VOR and OKR reflex dynamics, and to identify the distributions of parameters that describe VOR and OKR responses to pseudorandom stimuli in a putatively normal population. In general, VOR and OKR response parameters changed in a manner consistent with declining function with increasing age. For the VOR this was reflected in declining response amplitudes, although the magnitude of the decline was small relative to the variability of the data. For the OKR the lag time of the response, probably associated with the time required for visual information processing, increased linearly with age at a rate of about 1 ms per year.

Adolescent↗
PubMedDate not supplied

Age-related changes in human posture control: sensory organization tests.

Postural control was measured in 214 human subjects ranging in age from 7 to 81 y. Sensory organization tests measured the magnitude of anterior-posterior body sway during six 21 s trials in which visual and somatosensory orientation cues were normal, altered (by rotating the visual surround and support surface in proportion to the subject's sway), or vision eliminated (eyes closed). No age-related increase in postural sway was found for subjects standing on a fixed support surface with eyes open or closed. However, age- related increases in sway were found for conditions involving altered visual or somatosensory cues. Subjects older than about 55 y showed the largest sway increases. Subjects younger than about 15 y were also sensitive to alteration of sensory cues. On average, the older subjects were more affected by altered visual cues, whereas younger subjects had more difficulty with altered somatosensory cues.

Adolescent↗
PubMedDate not supplied

Age-related changes in human posture control: motor coordination tests.

Postural responses to support surface displacements were measured in 214 normal human subjects ranging in age from 7 to 81 y. Motor tests measured leg muscle electromyographic (EMG) latencies, body sway, and the amplitude and timing of changes in center of pressure displacements in response to sudden forward and backward horizontal translations of the support surface upon which the subjects stood. There were small increases in both EMG latencies and the time to reach the peak amplitude of center of pressure responses with increasing age. The amplitude of center of pressure responses showed no change with age if the amplitude measures were normalized by a factor related to subject height. In general, postural responses to sudden translations showed minimal changes with age, and all age-related trends that were identified were small relative to the variability within the population.

Adolescent↗