Biomedical subjects

H F Voigt

Publications and source records attributed to H F Voigt.

10 recordsLinked to original sources

PubMed1992

Neural organization and responses to complex stimuli in the dorsal cochlear nucleus.

The dorsal division of the cochlear nucleus (DCN) is the most complex of its subdivisions in terms of both anatomical organization and physiological response types. Hypotheses about the functional role of the DCN in hearing are as yet primitive, in part because the organizational complexity of the DCN has made development of a comprehensive and predictive model of its input-output processing difficult. The responses of DCN cells to complex stimuli, especially filtered noise, are interesting because they demonstrate properties that cannot be predicted, without further assumptions, from responses to narrow band stimuli, such as tones. In this paper, we discuss the functional organization of the DCN, i.e. the morphological organization of synaptic connections within the nucleus and the nature of synaptic interactions between its cells. We then discuss the responses of DCN principal cells to filtered noise stimuli that model the spectral sound localization cues produced by the pinna. These data imply that the DCN plays a role in interpreting sound localization cues; supporting evidence for such a role is discussed.

Acoustic Stimulation↗

PubMed1992

Sound-power collection by the auditory periphery of the Mongolian gerbil Meriones unguiculatus. I: Middle-ear input impedance.

This is the first paper of a series dealing with sound-power collection by the auditory periphery of the gerbil. The purpose of the series is to quantify the physiological action of the gerbil's relatively large tympanic membrane and middle-ear air cavities. To this end the middle-ear input impedance ZT was measured at frequencies between 10 Hz and 18 kHz before and after manipulations of the middle-ear cavity. The frequency dependence of ZT is consistent with that of the middle-ear transfer function computed from extant data. Comparison of the impedance and transfer function suggests a middle-ear transformer ratio of 50 at frequencies below 1 kHz, substantially smaller than the anatomical value of 90 [Lay, J. Morph. 138, 41-120 (1972)]. Below 1 kHz the data suggest a low-frequency acoustic stiffness KT for the middle ear of 970 Pa/mm3 and a stiffness of the middle-ear cavity of 720 Pa/mm3 (middle-ear volume V MEC of 195 mm3); thus the middle-ear air spaces contribute about 70% of the acoustic stiffness of the auditory periphery. Manipulations of a middle-ear model suggest that decreases in V MEC lead to proportionate increases in KT but that further increases in middle-ear cavity volume produce only limited decreases in middle-ear stiffness. The data and the model point out that the real part of the middle-ear impedance at frequencies below 100 Hz is determined primarily by losses within the middle-ear cavity. The measured impedance is comparable in magnitude and frequency dependence to the impedance in several larger mammalian species commonly used in auditory research. A comparison of low-frequency stiffness and anatomical dimensions among several species suggests that the large middle-ear cavities in gerbil act to reduce the middle-ear stiffness at low frequencies. A description of sound-power collection by the gerbil ear requires a description of the function of the external ear.

Acoustic Impedance Tests↗

PubMed1990

Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). III: Additivity of click level and rate with noise level.

Two experiments were performed that evaluated the effects of ipsilateral-direct broadband noise maskers on the gerbil brain-stem auditory-evoked response (BAER) to click stimuli. In experiment 1, clicks were presented at 27 Hz at levels including 70, 80, 90, and 100 dB pSPL. Noise conditions included a no-noise control, and included noise levels varying in 10-dB increments from 20 dB SPL to a maximum noise level of 50, 60, 70, and 80 dB SPL for click levels of 70, 80, 90, and 100 dB pSPL, respectively. Gerbil BAER peaks were labeled with small roman numerals to distinguish them from human BAER peaks. The dependent variables included waves i and v latencies and amplitudes. Peak latencies increased and peak amplitudes decreased with decreasing click level and increasing noise level. To a first approximation, peak latencies and amplitudes showed changes with increasing noise level that were similar across click level. With increasing click level, there was little or no effect on the i-v interval. There was an increase in the i-v interval with increasing noise level. In experiment 2, click level was held constant at 90 dB pSPL, and click rates included 15, 40, 65, and 90 Hz. For each click rate, noise conditions included a no-noise control, and noise levels included 20, 30, 40, 50, 60, and 70 dB SPL. With increasing click rate and noise level, there was an increase in peak latencies, an increase in the i-v interval, and a decrease in peak amplitudes. The magnitude of peak latency and amplitude shifts with increasing click rate was dependent on noise level. Specifically, the magnitude of rate-dependent changes decreased with increasing level of broadband noise. These data are compared to human BAER experiments, and are found to be in fundamental agreement.

Animals↗

PubMed1990

Cross-correlation analysis of inhibitory interactions in dorsal cochlear nucleus.

1. Cross-correlation analysis was used to study the organization of inhibitory connections between type II or type III units and type IV principal cells in cat dorsal cochlear nucleus (DCN). Pairs of units were isolated using two microelectrodes so that information about the distance over which connections are made could be analyzed. Data were obtained from 51 pairs consisting of a type II and a type IV unit and from 22 pairs consisting of a type III and a type IV unit. The analyses in this paper concentrate on type II-type IV pairs. 2. Inhibitory troughs (ITs) are observed in the cross-correlograms of type II-type IV pairs (21/51 cases). An IT is a transient decrease in discharge probability in the postsynaptic (type IV) unit immediately after spikes in the presynaptic unit (type II). The average latency to the start of ITs is 0.73 ms, and the troughs are asymmetric with a faster leading phase. Small excitatory peaks accompany the ITs in type II units, but these are probably secondary effects associated with the IT. ITs are consistent with a monosynaptic, inhibitory connection between type II and type IV units. A variety of evidence suggests that type II responses are recorded from vertical cells, an interneuron in the deep layer of the DCN that may be glycinergic. 3. The cross-correlograms of type III-type IV pairs are more complex and variable than those of type II-type IV pairs--ITs are seen in 4/22 cases, and peaks of correlation that are symmetrically located around the origin (central mound or CM) are seen in 4/22 cases; two cases have both an IT and a CM. CMs result from shared sources of input. Whereas type II-type IV correlogram features change primarily in amplitude as stimulus conditions change, correlogram features in some type III-type IV pairs change qualitatively with stimulus conditions; correlograms are flat for some stimuli and show ITs or CMs or mixtures of the two for others. This variability suggests that the circuitry associated with type III-type IV pairs is more complex than a monosynaptic connection, and further analysis of type III-type IV pairs was not done. 4. The strength of inhibition for an IT is measured as the area under the IT (effectiveness) and as effectiveness divided by the postsynaptic discharge rate (association index).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Brainstem auditory-evoked response in the rat. Normative studies, with observations concerning the effects of ossicular disruption.

Six young adult Sprague-Dawley rats were unilaterally cochleotomized, Brain-stem auditory-evoked responses (BAERs) to clicks and to 1-, 2-, 4-, 8- and 16-kHz tone bursts were obtained. In addition, response thresholds were estimated before and after ossicular disruption in the noncochleotomized ear of 4 animals. With increasing tone burst frequency, there was a decrease in BAER peak latencies as well as a decrease in threshold. With increasing click and tone burst intensity, there was a decrease in peak latencies and an increase in peak amplitudes. BAER peak latency/intensity functions to click stimuli ranged from -.013 to -.018 ms/dB. With increasing tone burst frequency there was a decrease in the slope of the latency/intensity function. Following ossicular disruption, BAER thresholds to clicks were elevated by an average of 49 dB. Threshold shifts to tone burst stimuli were smallest for 1- and 2-kHz tone bursts (35-36 dB) and increased with increasing frequency up to a maximum of 65 dB for 16-kHz tone bursts.

Animals↗

PubMed1989

Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). I: Effects of click level, rate, and polarity.

Three experiments evaluating the effects of various stimulus manipulations on the click-evoked gerbil brain-stem auditory-evoked response (BAER) are reported. In experiment 1, click polarity and level were covaried. With increasing click level, there is a parallel decrease in the latency of the first five BAER peaks (i-v) and an increase in BAER peak amplitudes. Mean wave i amplitude was greater for rarefaction than condensation clicks at high click levels; mean wave v amplitude was greater for condensation clicks at higher click levels. Experiment 2 covaried click rate and polarity. The latency of the BAER peaks increased with increasing click repetition rate. This rate-dependent latency increase was greater for the later BAER peaks, resulting in an increase in the i-v interval with increasing click rate. As rate increased, the amplitudes of waves i and v decreased monotonically, whereas the amplitudes of waves ii-iv were largely uninfluenced by click rate. As in experiment 1, mean wave i amplitude was greater for rarefaction clicks, whereas mean wave v amplitude was greater for condensation clicks. The magnitude of these polarity dependencies on waves i and v amplitude decreased with increasing click rate. Experiment 3 evaluated the effects of click polarity on BAERs to high-intensity (100 dB pSPL) clicks presented at a rate of 10 Hz. In eight of ten gerbils evaluated, wave i amplitude was greater to rarefaction clicks, and, in all ten animals, wave v amplitude was greater to condensation clicks. The effects of click level and rate on BAER peak amplitudes, latencies, and interwave intervals are reminiscent of stimulus dependencies reported for the human BAER. The effects of click polarity on the amplitudes of waves i and v of the gerbil BAER have also been reported for the human BAER.

Acoustic Stimulation↗

PubMed1989

Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). II: Effects of broadband noise level and high-pass masker cutoff frequency across click polarity.

Two experiments concerning the effects of masking noise on the gerbil brain-stem auditory-evoked response (BAER) are reported. Experiment 1 evaluated the effects of broadband masking noise on the BAER obtained to condensation and rarefaction clicks. With increasing noise level, there was an increase in BAER peak latencies, an increase in the i-v interval, and a decrease in peak amplitudes. Experiment 2 evaluated the effects of high-pass masking noise on the BAER obtained to condensation and rarefaction clicks. Both high-pass responses and derived-band responses were evaluated. For high-pass responses, with decreasing masker cutoff frequency, there was an increase in BAER peak latencies, a decrease in the i-v interval, and a decrease in peak amplitudes. For derived-band responses, with decreasing derived-band frequency, there was an increase in peak latencies and a decrease in the i-v interval. A comparison of wave i and wave v amplitudes across derived-band frequency demonstrates a greater contribution of high-frequency cochlear regions to wave i than wave v. Small, insignificant, effects of click polarity on BAER peak amplitudes were observed. These trends were in the direction seen in a companion paper [R. Burkard and H. F. Voigt, J. Acoust. Soc. Am. 85, 2514-2525 (1989)] and were, in general, reduced by the presence of broadband or high-pass maskers.

Acoustic Stimulation↗

PubMed1988

Neural correlations in the dorsal cochlear nucleus: pairs of units with similar response properties.

1. Cross-correlation analysis of simultaneously recorded spike trains can be used to gain insight into functional interactions among neurons. In this paper, we report on cross-correlation analysis of neuron pairs in the dorsal cochlear nucleus (DCN) of the cat. Neuron pairs were isolated with two independent electrodes, which allow systematic study of the effects on correlation of distances between units and differences in their best frequencies (BFs). The data in this paper were obtained from 51 pairs consisting of two neurons of the same type. 2. Cross-correlograms were obtained for 35 pairs composed of type IV units, which are recorded from the principal cells of the DCN. Pairs of type IV units with correlated activities give cross-correlograms with increased correlation near zero delay. This feature is called a central mound (CM) and most likely results from shared excitatory or shared inhibitory inputs. 3. Records of spontaneous activity were obtained from 31 pairs of type IV units. Six of these pairs have correlated spontaneous activities. All six pairs have BFs that differ by less than 0.2 octaves. The shared input inducing these correlations must be a spontaneously active and tonotopically organized projection, like the auditory nerve. Type II units, thought to be DCN inhibitory interneurons that project to type IV units, are not spontaneously active, and thus cannot be the cause of correlated spontaneous activity. Similarly, cochlear granule cells, whose axons project orthogonally to the tonotopic sheets of DCN, cannot be the cause of correlated spontaneous activity because their projection is not confined tonotopically. 4. Stimulus-driven activities were studied for 12 type IV pairs that have uncorrelated spontaneous activities. Five of these pairs have correlated driven activities, with CMs whose sizes depend on the frequency and sound level of the acoustic stimulus. A frequency vs. sound level correlation response map shows the V-shaped tuning properties of the correlation-inducing mechanism. The properties of stimulus-driven correlation in these type IV pairs are consistent with the hypothesis that the correlation is induced by shared input from DCN type II units, although this is not the only possibility. 5. All six type IV pairs with correlated spontaneous activities have correlated driven activities. In five of these pairs, the degree of correlation decreases from its value with spontaneous activity when a low-level acoustic stimulus is applied. Three of these five pairs were tested at higher stimulus levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1987

A simple device for the computer quantification of depth measurements in thick light microscope sections.

The use of computerized techniques to characterize quantitatively the anatomy of individual neurons has been increasing. One difficulty has been the quantification of the z-axis or depth measurements within thick light microscopic sections. In the present report we describe a simple device which employs an incremental optical encoder to transduce the movements of the focusing knob of the microscope so that depth information can be recorded directly by a computer. A resolution of 0.13 micron over a range of approximately 8.5 cm is achieved. The mechanical interface to the microscope is simple and applicable to a wide variety of microscopes. Interfacing circuits which allow the optical encoder to be used with an IBM-PC compatible computer are presented and described. The accuracy of the depth measurements is limited only by the mechanical tolerances of the focusing mechanism and by the optics of the microscope.

Electric Wiring↗

PubMed1985

Stimulus dependent neural correlation: an example from the cochlear nucleus.

Results of several recent cross-correlation studies have been interpreted in terms of "neuronal plasticity" and "stimulus dependent wiring diagrams" produced by presumed dynamic neural reorganization mechanisms. Presented here are examples of stimulus-dependent cross-correlograms observed in a pair of type IV units recorded in the dorsal cochlear nucleus (DCN). The interpretation of these correlation data is based on current hypotheses of DCN circuitry. It is suggested that plasticity mechanisms are not responsible for these stimulus-dependent correlations. A more likely mechanism is one that allows various portions of a hard wired neural circuit to be selectively activated by the stimuli.

Acoustic Stimulation↗