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Biomedical subjects

C Wall

Publications and source records attributed to C Wall.

At least 109 records · Page 6Linked to original sources
PubMed1979

Transient persistence of neural activity after periodic stimulation in the cat LGN.

Oscillatory neural activity recorded from gross concentric electrodes implanted in the lateral geniculate nucleus (LGN) of cat was investigated after trains of periodic electrical shock stimulation were applied to the contralateral optic nerve. Spectral analysis using repeated trials and spectral averaging revealed statistically significant spectral peaks (p less than 0.05) at the stimulus frequency when there was a 0.5 to 1.5 s delay between the last pulse of the stimulus train and the beginning of the data analysis window. This suggests that a loosely coupled neuronal net may allow for the continuation of activity far longer than the time accounted for by neuronal time constants and delays.

Animals↗
PubMed1979

Entrainment of oscillatory neural activity in the cat's lateral geniculate nucleus.

Oscillatory neural activity in the frequency range 7-12 Hz is observed in the lateral geniculate nucleus (LGN) of the lightly anesthetized cat. This paper describes a series of experiments in which the interactions between ongoing oscillatory potentials and periodic photic and electrical stimuli are analyzed using frequency domain techniques. The principal results of these experiments are consistent with a model of the neural system as an entrainable oscillator in which ongoing oscillations are suppressed by stimulation at nearby frequencies, but coexist with stimulus frequencies farther away. The physiological interpretation of these results may be closely tied to the role of the LGN as a "gating" mechanism between retina and cortex.

Alpha Rhythm↗
PubMed1979

Dynamic evaluation of human vestibulo-ocular function using white noise rotation stimulus and linear system parameter estimation techniques.

White noise acceleration inputs were used to determine the human VOR transfer function both for normal subjects and for patients falling into two pilot categories: unilateral labyrinthectomy and reduced bilateral responses. The systematic patterns shown in the transfer function of the pilot abnormal categories as compared to the normal data suggests one method of classifying test results (table I). Frequency domain linear systems parameter fits were also made using the same data. The changes in these fit parameters, when pilot abnormal data is compared to normal data, suggests the use of the parameter fits themselves as a second classification scheme (fig. 1). The second scheme is not appropriate in cases where the response is unrelated to the stimulus.

Eye Movements↗
PubMed1979

Analysis of nonlinear afferent response properties from the guitarfish semicircular canal.

Nonlinear afferent response properties from the isolated guitarfish semicircular canal were investigated using a nonlinear system identification technique of combined high and low frequency rotational acceleration stimuli. Linear system unit impulse responses obtained from the dual inputs were systematically different relative to those obtained from low frequency stimuli only, implying nonlinear interactions. These results were attributed to neurophysiological mechanisms of phase locking and increased afferent excitability. A hypothesis was proposed in which similar nonlinear interactions could result from efferent activity in intact animals, suggesting that the efferents could act as a regulator of afferent response dynamics.

Acceleration↗
PubMed1978

Galvanic disruption of vestibulospinal postural control by cochlear implant devices.

All subjects with implanted cochlear stimulators demonstrated evidence of abnormal postural stability without their stimulators activated. Instability increased when they were tested with cochlear stimulation units turned on, and additional instability was demonstrated in four of these subjects when tested in noise. These findings suggest that the electrical stimulation delivered by the cochlear prosthesis is not limited to the auditory system. The precise characteristics of electrical stimulation devices designed for stimulations limited to the cochlea and their spurious effects upon motor performance should be investigated. The design of future intralabyrinthine auditory electrical prostheses must include hardware designs and stimulus paradigms that avoid undesirable vestibular system stimulation.

Adult↗
PubMed1976

Groote Eylandt studies. 2. Fluoridation of a small domestic water supply, C.M.S. Angurugu mission, Groote Eylandt, N.T., Australia. 1973-1974.

A system is described for fluoridation of a small community water supply. The design of the equipment is presented in relation to the requirements of a particular isolated region and in a basis for application to other similar areas. The problems found during the establishment of this system and their solution can be valuable as a guide for other communities.

Australia↗
PubMedDate not supplied

The quantitative analysis of glass by emission spectrography: a six element survey.

The use of emission spectrography for the analysis of small glass fragments (approximately 1 mg) is described. Levels of Al, Ba, Ca, Fe, Mg and Mn have been determined in approximately 200 samples, and with the exception of Ca their variation appears to be of value in the classification and/or discrimination of glass. The precision of the method has been studied and its accuracy determined by the analysis of standard glasses prepared in the laboratory.

Aluminum↗
PubMedDate not supplied

Normal subject postural sway during the Romberg test.

Analysis of fixed force platform recordings of Romberg tests performed by 132 normal subjects demonstrated no statistically significant sex or age effect for adults aged 20 through 49 years. There was a strong stabilizing influence of vision upon postural control in most, but not all, normal subjects. Comparison trials showed no statistically significant differences between trials for the standard Romberg eyes-open maneuver. However, a significant improvement was demonstrated for the second trial for all other Romberg maneuvers. Tests repeated over a period of five consecutive days yielded results with large variances within normal limits and no systematic individual or group trends. Normal percentiles and confidence intervals for the 95th percentile were calculated for use as a normal data base. These percentile distributions derived from a relatively large population of normal subjects provide a normal statistical base for comparison with postural sway from abnormal subjects.

Adult↗
PubMedDate not supplied

Clinical use of pseudorandom binary sequence white noise in assessment of the human vestibulo-ocular system.

White noise rotational stimulation has been used to evaluate the human vestibulo-ocular response for 30 normal subjects over the frequency range from 0.02 to 1.6 Hz and is being extended to characterize response of patients having documented abnormalities. For clinical use, the white noise stimulus has the advantages of shortening the test time by presenting all stimulus frequencies simultaneously, and being well-tolerated by both normal subjects and patients alike. Cross spectral calculations which compare the computer reconstructed slow phase eye velocity response to the pseudorandom acceleration stimulus yield a set of linear and nonlinear estimates of the vestibulo-ocular response. Pilot data indicate that a classification of the disease state can be made using this set of estimates. This classification will be presented and discussed.

Diagnosis, Computer-Assisted↗
PubMedDate not supplied

Computerized screening of the human vestibulospinal system.

The vestibular nerve projects rostrally via the ascending medial longitudinal fasiculus (MLF) to eventually supply the ocular muscles and also projects caudally via the descending MLF to eventually supply the spinal and limb musculature. Electronystagmographic techniques are designed to evaluate only portions of the vestibulo-ocular and oculomotor systems. Vestibular lesions affecting only the caudal vestibular nerve distributions or lesions affecting both neural distributions, therefore, cannot be objectively assessed except for the vestibulo-ocular component. A promising recording technique for the evaluation of the vestibulospinal system has been developed and tested in the Raymond E. Jordan Human Vestibular Systems Laboratory. A comparison of two data analysis techniques in normal subjects, unilateral vestibular lesion patients and patients with unilateral lesions of the cerebellar hemispheres have provided pilot data which indicate that the vestibulospinal stability test technique holds considerable promise for both research and clinical evaluation of the human vestibulospinal system.

Adult↗
PubMedDate not supplied

Computerized data bank system for temporal bone histopathology.

A computerized data bank system to store and analyze temporal bone histopathologic data is described. This system uses the University of Pittsburgh's Digital Equipment Corporation System 10 computer and the System 1022 data base management software. Data on histology cases are divided into five files: general information, otologic information, summary, histopathologic information about the external ear and middle ear, and histopathologic information about the inner ear. Eleven general terms are used to describe pathologic findings, surgery, postmortem degeneration, and artifacts. In addition, provision is made for the inclusion of more precise qualitative information to be entered as text.

Computer Systems↗
PubMedDate not supplied

Alternate and simultaneous binaural bithermal caloric testing: a comparison.

This study compares the results from simultaneous binaural bithermal and alternate binaural bithermal caloric testing of 652 patients with dizziness. Also compared are the abilities of these tests to distinguish between a population of healthy asymptomatic subjects and our patient population. Caloric testing used a closed-loop irrigation system. Eye movements were monitored with electro-oculography. The agreement between the results from the two tests was low. Also, while the simultaneous test was more sensitive, the alternate test was more specific. Using receiver-operator characteristic methodology, it was found that the ability of the alternate test to distinguish between a healthy population and a patient population was superior to that of the simultaneous test. There was no improvement in the ability to distinguish between a healthy population and a patient population when the results from the two tests were combined as compared to using the alternate caloric test alone.

Algorithms↗
PubMedDate not supplied

Vestibular system abnormalities in otosclerotic subjects.

A technique to quantify the tandem Romberg test (posturography) was used to study ten patients with otosclerosis before (series 1), 48 hours after (series 2), and between two to four months after (series 3) a stapedectomy. The results were analyzed by power spectrum analysis and then compared to findings from electronystagmographic testing performed with series 1 and 3. There was no significant change in the electronystagmography (ENG) test findings between series 1 and 3. Posturography, however, demonstrated an uncompensated vestibular pattern in the immediate postoperative period which, after two months, converted to a compensated vestibular pattern. Posturography serves as a useful quantitative test for the study of patients with balance disorders because the procedure supplements rather than complements the ENG. In addition, posturography detects vestibular reflex abnormalities in stapedectomized patients two months afterwards. Other testing modalities have not consistently demonstrated this postoperative vestibular system instability.

Adult↗
PubMedDate not supplied

Comparison of vestibulo-ocular and vestibulospinal screening tests.

A comparison of a newly developed vestibulospinal screening test and two vestibulo-ocular screening tests (caloric and rotation) was performed on two groups of patients, one with Meniere's disease (MD) the other with benign paroxysmal positional nystagmus (BPPN) and vertigo. Vestibulospinal screening tests were slightly more sensitive (not statistically significant) than caloric tests for detection of a peripheral vestibular disorder. Caloric, rotation, and vestibulospinal screening tests were specific neither for MD nor BPPN groups. The caloric test false-positive rate for the involved ear was unacceptably high for the BPPN group. The rotation test false-positive rate was the highest of the three tests for both groups. The vestibulospinal test combined with either the caloric or the rotational tests increased the sensitivity for detection of a peripheral vestibular disturbance, particularly for the MD patients.

False Positive Reactions↗