Biomedical subjects

L Langhofer

Publications and source records attributed to L Langhofer.

6 recordsLinked to original sources

PubMed1989

The firing properties of second-order vestibular neurons in correlation with the far-field recorded vestibular-evoked response.

Action potentials of the second-order vestibular neurons of ten cats were recorded, both in rest and responding to sinusoidal and intense impulse acceleration stimuli. The data were compared with the far-field recorded vestibular-evoked response induced by the same impulse stimuli. It was found that the irregular (kinetic) neurons, which had a phase lead relative to head velocity, were capable of responding to these impulses with a latency as short as 3.5 msec after the start of head acceleration. It is assumed, therefore, that these neurons are the generators of the second wave of the vestibular-evoked response, having a similar latency. A high correlation was found between the latency of the first peak in the poststimulus time histogram in response to acceleration impulses and the phase of the response to sinusoidal rotations. The regular (tonic) vestibular neurons did not respond to acceleration impulses and probably did not contribute to the vestibular-evoked response.

Animals↗

PubMed1987

The neural generators of the vestibular evoked response.

A new method for the induction and recording of a short-latency vestibular evoked response (VsER) to intense acceleration impulses with skin electrodes was studied in cats. The first two waves, P1 and P2, had latencies of 2.5 and 3.5 ms, respectively, and coincided with the recorded gross neural activity in the vestibular nerve and nuclei, respectively. Single second-order vestibular neurons with low and irregular activity responded to the same acceleration impulses with a latency as short as 3.5 ms.

Animals↗

PubMed1987

Recording of short-latency vestibular evoked potentials induced by acceleration impulses in experimental animals: current status of the method and its applications.

The short-latency vestibular evoked potential (VsEP) induced by angular acceleration impulses (maximal amplitude 30,000 deg/sec2, rise time 2-3 msec) was recorded by skin electrodes in intact cats after various surgical and pharmacological procedures. The normal VsEP consists of 5-8 waves, several microvolts in amplitude, during the first 10 msec. The latency of the first wave (P1) is about 2 msec with respect to the start of head acceleration. The first and the second waves (P1 and P2) were shown to originate from the vestibular nerve and nucleus, respectively. The VsEP disappears permanently after bilateral labyrinthectomy, excision of the 8th nerves, or administration of large doses of gentamicin. Temporary disappearance is caused by anoxia induced for a brief period of time or injection of lidocaine (4%) into the vestibular nerve or into the inner ear after contralateral labyrinthectomy. The VsEPs in the intact cat are similar whether clockwise or counterclockwise stimuli are used and are not affected by changing the position of the head. Unilaterally labyrinthectomized animals, however, show asymmetric response whereby excitatory stimulation of any of the intact semicircular canals evokes prominent P1 and P2 waves which are absent with inhibitory stimulation. The rate and input-output intensity functions of the VsEP are described. The threshold of the VsEP was found to be 1000-1500 deg/sec2. In addition to the neurogenic waves, 2 other potentials appear occasionally in the response: large-amplitude and longer-duration waves with latencies of 8-20 msec, which are of myogenic origin, and smaller waves with shorter latency which probably represent vestibular microphonics and generator potentials. Extracellular recordings of the responses of single second-order neurons in the vestibular nuclei to the same acceleration impulses confirmed that the kinetic vestibular neurons can respond to these stimuli with a latency as short as 3.5 msec. This method for inducing and recording VsEPs has proved to be a powerful tool for the evaluation of vestibular function in experimental animal models.

Acceleration↗

PubMed1984

Quantitative vestibular testing.

Our standard rotational test battery includes tests of optokinetic nystagmus (OKN), the vestibulo-ocular reflex (VOR), and visual-vestibular interaction. Lesions of the peripheral vestibular system characteristically impair only the VOR, whereas lesions of the central system impair OKN and visual-vestibular interaction. The pattern of abnormal responses can help localize lesions within the central vestibular pathways.

Electronystagmography↗

PubMed1980

Quantitative eye tracking tests in lead workers.

A microcomputer system for on-lone analysis of saccadic and smooth-pursuit tracking eye movements is described. Results from a longitudinal study of lead workers and matched controls reveal a consistent decrease in saccade accuracy in the lead workers compared to the controls. Saccade peak velocity and latency and smooth pursuit were not significantly different in the two groups. The abnormal saccade accuracy measurements may indicate a subclinical effect of increased lead absorption, but because of the large scatter in normal values, saccade accuracy measurements are not a reliable indicator of early lead toxicity in a single lead worker.

Environmental Exposure↗

PubMed1980

On-line analysis of eye movements using a digital computer.

We describe a microcomputer system for on-line analysis of eye movement recordings. Quantitative data from the patient and statistical comparison with normative data is available within seconds of test completion. Three types of eye movements are analyzed--voluntary saccades, smooth pursuit, and nystagmus. The first two are induced by a computer-controlled laser dot projected onto a screen and the third by a computer-controlled optokinetic drum, caloric infusion, and rotatory chair. The computer algorithm differentiates the eye position signal to yield an instantaneous eye velocity record. Saccades are identified based on their characteristic velocity profile. For pursuit and nystagmus. The first two are induced by a computer-controlled laser dot projected onto a screen and the third by a computer-controlled optokinetic drum, caloric infusion, and rotatory chair. The computer algorithm differentiates the eye position signal to yield an instaneous eye velocity record. Saccades are identified based on their characteristic velocity profile. For pursuit and nystagmus, the velocity record is modified by linearly interpolating across segments in which saccades occurred. The gain (output eye velocity/input eye velocity) is calculated after Fourier analysis of the data.

Computers↗