Biomedical subjects

S S Saunders

Publications and source records attributed to S S Saunders.

At least 19 recordsLinked to original sources

PubMed1998

Acquisition of noise-induced hearing loss by railway workers.

OBJECTIVE: The rate of growth of hearing loss was examined in a population of workers exposed to noise. Of special interest was the course of loss in the first 10 yr of work, for which international standards provide little information. Based on the International Standards Organization (ISO) 1999 compilation, it was hypothesized that the proportional growth of hearing loss would be constant in log years. DESIGN: Of 5000 workers compensated for hearing loss by a railroad, 500 were selected at random for analysis. For these workers, 2660 audiograms were available. The audiograms were distributed unsystematically over work careers, and for most workers were sparsely distributed. Thresholds were age corrected using ISO 1999 Annex B and averaged as a function of years on the job for two partitions, 0.5, 1, 2, and 3 kHz and 2 and 4 kHz. The average curves were compared with projections based on the ISO 1999 data as suggested by Dobie (1993a). A subset of workers with substantial hearing loss when hired was examined to evaluate the effect of pre-existing hearing loss. RESULTS: Hearing was worse at hire for this sample of workers than suggested by ISO 1999 Annex B for an unscreened sample of the general population at comparable ages. As a result, the early hearing loss was underpredicted by the ISO 1999 projection. Except at the earliest years of employment, the rate of growth toward the final hearing loss for the mean of the sample of workers was approximated by the projection from ISO 1999. The ISO 1999 projection is based on growth of the percentage of loss at the final audiogram obtained each year. In subgroups of workers, i.e., for the lower quartile and for the upper quartile of the sample, the projection based on ISO 1999 was similarly effective. Workers hired with prior loss showed growth of hearing loss that was flatter than that of either the mean of all workers or the ISO 1999 projection, but the growth curve for these workers approximated the average curve shifted to later years to bring the initial loss into correspondence with the predicted loss. CONCLUSIONS: For a group of workers exposed to a noisy environment, growth of hearing loss can be projected fairly well based on ISO 1999, without knowledge of the details of spectrum or level of noise exposure. This suggests that it would be possible to allocate the percentage of a known total hearing loss acquired in a group of workers on a year-by-year basis, given knowledge of work history for a claimant population in the absence of detailed knowledge of the exposure or detailed sequential audiometric data.

Adult↗

PubMed1995

Alpha 1-adrenergic receptor antagonist blocks acute cocaine action on the compound action potential of the auditory nerve in the chinchilla.

Acute systemic cocaine injection is known to significantly decrease the compound action potential (CAP) amplitude of the auditory nerve. In an attempt to elucidate the mechanism underlying this phenomenon, the present study investigated the influence of prazosin, an adrenergic alpha 1-receptor antagonist, on the effect of cocaine on the CAP. Amplitude-intensity functions at 1 and 8 kHz were obtained before and after treatment with cocaine (experimental group) or saline (control group) in prazosin pretreated subjects. The characteristic reduction in CAP amplitude after an acute cocaine injection was blocked by 0.05 mg/kg prazosin. When subjects were re-injected with cocaine or saline one h after prazosin, the reduction in CAP amplitude following cocaine injection had recovered.

Adrenergic alpha-Antagonists↗

PubMed1995

Recovery of thresholds and temporal integration in adult chickens after high-level 525-Hz pure-tone exposure.

Three adult, female chickens, previously trained to detect pure tones using a positive reinforcement paradigm, were exposed to pure tones at 525 Hz at 120-dB sound-pressure level for 48 h. Immediately after exposure, pure-tone thresholds were elevated between 10 and 56 dB compared to pre-exposure values. The configuration of the initial hearing loss was essentially flat between 500 and 2000 Hz, with slightly less loss at lower and higher frequencies. Over the course of 100 to 600 h, depending on subject and test frequency, thresholds returned to preexposure levels. The slopes of the threshold-duration functions measured shortly after exposure were shallower than normal, but returned to the normal slope of approximately 3 dB per doubling of duration as hearing loss resolved to less than 15 to 20 dB. The cochleas from additional chickens examined by scanning electron microscopy (SEM) and fluorescence microscopy between 0 and 1512 h post-exposure showed extensive damage to the tectorial membrane over the middle two-thirds of the cochlea, with mild to moderate hair cell loss in the region of the cochlea associated with the exposure frequency.

Animals↗

PubMed1995

Pure tone masking patterns in adult chickens before and after recovery from acoustic trauma.

Three female adult chickens were trained to detect pure tones using a positive reinforcement technique and an adaptive threshold tracking procedure. Masked thresholds for tone bursts were measured in the presence of pure-tone maskers at 500, 1000, and 2000 Hz. Masker levels of 40-, 60-, and 70-dB sound-pressure level (SPL) were employed. Masking was maximal at the frequency of the masker. Tone-on-tone masking patterns were symmetrical at low masker levels, but at higher masker levels, more masking was evident at frequencies above the masker than below the masker. Distinct low threshold notches were frequently observed above and below the peak in the masking pattern. After the normal masking patterns had been measured, the chickens were exposed to a 525-Hz traumatizing tone at 120 dB SPL for 48 h and then allowed to recover. After thresholds had returned to their pre-exposure levels, tone-on-tone masking patterns were remeasured. The post-exposure masking patterns were virtually identical to the pre-exposure masking patterns.

Animals↗

PubMed1994

Effects of repeated cocaine injections on cochlear function.

The effects of repeated cocaine administration on cochlear function were evaluated by measuring amplitude-intensity and latency-intensity functions of the whole-nerve action potential of the auditory nerve. Whole-nerve action potential input/output functions obtained using tone-pips of 0.5, 1, 2, 4 and 8 kHz in a group of cocaine-treated subjects were compared with those obtained in saline-treated animals. All measurements were made 24 h after the last treatment. Amplitudes of whole-nerve action potentials were enhanced in the cocaine-treated animals compared to the control group. No statistically significant differences in latency-intensity functions were seen after cocaine treatment. The effect of chronic cocaine exposure also was examined on catecholamine innervation in the cochlea using immunohistochemical techniques. The density of adrenergic innervation was reduced in the cocaine-treated animals.

Acoustic Stimulation↗

PubMed1994

Discharge patterns of chicken cochlear ganglion neurons following kanamycin-induced hair cell loss and regeneration.

Hair cells in the basal, high frequency region (> 1100 Hz) of the chicken cochlea were destroyed with kanamycin (400 mg/kg/d x 10 d) and allowed to regenerate. Afterwards, single unit recordings were made from cochlear ganglion neurons at various times post-treatment. During the first few weeks post-treatment, only neurons with low characteristic frequencies (< 1100 Hz) responded to sound. Despite the fact that the low frequency region of the cochlea was not destroyed, neurons with low characteristic frequencies had elevated thresholds, abnormally broad U-shaped or W-shaped tuning curves and low spontaneous discharge rates. At 2 days post-treatment, the spontaneous discharge rates of some acoustically unresponsive units fluctuated in a rhythmical manner. As recovery time increased, thresholds decreased, tuning curves narrowed and developed a symmetrical V-shape, spontaneous rate increased and neurons with higher characteristic frequencies began to respond to sound. In addition, the proportion of interspike interval histograms with regularly spaced peaks increased. These improvements progressed along a low-to-high characteristic frequency gradient. By 10-20 weeks post-treatment, the thresholds and tuning curves of neurons with characteristic frequencies below 2000 Hz were within normal limits; however, the spontaneous discharge rates of the neurons were still significantly lower than those from normal animals.

Animals↗

PubMed1993

Neural correlates of temporal integration in the cochlear nucleus of the chinchilla.

Single unit thresholds were measured as a function of stimulus duration for Primary-like and Chopper units in the anteroventral cochlear nucleus (AVCN) of the chinchilla to examine the neural correlates of temporal integration. Thresholds were measured with a two-alternative, forced-choice (2AFC) adaptive tracking procedure. The time constants and the slopes of the threshold-duration functions were estimated by fitting the threshold data with an exponential function and a power law function. The results showed that Primary-like units exhibited greater threshold improvement and a longer time constant than Chopper units. Units with low characteristic frequencies (CF) showed a larger decrease in threshold with increasing duration and a longer time constant than mid-CF or high-CF units. Units with low spontaneous rates (SR) showed a smaller threshold decrease with increasing duration and a shorter time constant than mid-SR or high-SR units. The single unit time constants and the rate of threshold improvement are similar to those measured psychophysically in the chinchilla.

Acoustic Stimulation↗

PubMed1993

Acute effects of cocaine on cochlear function.

The effects of a single administration of cocaine on the cochlea was evaluated by measuring amplitude-intensity functions of the N1 response of the auditory nerve. Amplitude-intensity functions of the N1 response to tone-pips of 500 Hz, 1, 2, 4 and 8 kHz were obtained before and after intraperitoneal injection of either saline, 3 mg/kg or 25 mg/kg of cocaine. N1 amplitudes were decreased after the administration of cocaine and this reduction was found to be dose dependent. The influence of cocaine on cochlear blood flow (CBF) was examined in order to test the possibility that cocaine induced reductions in CBF underlie these electro-physiological changes. Corresponding decreases in cochlear blood flow after cocaine exposure were observed.

Acoustic Stimulation↗

PubMed1993

Psychoacoustics of normal adult chickens: thresholds and temporal integration.

Three adult female chickens were trained to detect pure tones using a positive reinforcement paradigm. A modified perometer estimation-through sequential testing (PEST) threshold determination procedure was used to measure the audiogram between 250 and 5500 Hz, at 0.1-octave steps over most of the range. For the mean audiogram, threshold increased rapidly below 400 Hz and above 4000 Hz. Between these extremes was a broad low threshold area where thresholds varied between 11 and 23 dB, with the lowest thresholds between 1000 and 2000 Hz. Audiograms were similar for all three subjects over the middle of the frequency range, but there was more variability across subjects at the extreme high and low frequencies. After determination of the audiogram, thresholds for 12 frequencies were measured as a function of stimulus duration (ranging from 16 to 750 ms) to determine a threshold-duration function. Average time constants varied from 148 to 348 ms, increasing with increasing stimulus frequency. Average slopes varied from 2.18 dB per doubling of duration to 2.61 dB per doubling of duration, increasing with increasing stimulus frequency. The increases in slope and time constant with stimulus frequency, while consistent, were small compared to the variability of these parameters across subjects.

Animals↗

PubMed1992

Effects of noise and salicylate on hair cell loss in the chinchilla cochlea.

Chinchillas were exposed to octave band noise, sodium salicylate (300 mg/kg per day intraperitoneally), or the combination of both agents for 15 days. The octave band noise exposure was centered at 500 Hz at an intensity of either 80 or 105 dB sound pressure level. The effects of the experimental treatments were evaluated by determining the number of missing hair cells after recovery as a function of location within the cochlea using a surface preparation technique. Average cochleograms were calculated for each of five experimental groups. Animals given salicylate alone showed little or no hair cell loss. Noise exposure at 80 dB resulted in a mild (less than 30%) outer hair cell loss in the apical turn of the cochlea, whereas exposure at 105 dB resulted in moderate (50%) outer hair cell loss (outer hair cell first row particularly) in the apical half of the cochlea, mild outer hair cell loss in the basal region of the cochlea, and a mild loss of inner hair cells. The amount of hair cell loss in the groups exposed to the combination of salicylates and noise was not significantly different from the corresponding groups exposed to noise alone. Statistical analysis of the data suggest that the combination of salicylate plus noise does not produce any greater hair cell loss than noise alone.

Acoustic Stimulation↗

PubMed1992

Discharge patterns of cochlear ganglion neurons in the chicken.

Physiological recordings were made of the compound action potential from the round window and single neurons in the cochlear ganglion of normal adult chickens (Gallus domesticus). The compound action potential threshold to tone bursts decreased from approximately 42 dB at 0.25 kHz to 30 dB between 1 and 2 kHz and then increased to 51 dB at 4 kHz. Most of the cochlear ganglion cells had characteristic frequencies below 2 kHz and the thresholds of most neurons were roughly 30-35 dB lower than the compound action potential thresholds. At any given characteristic frequency, thresholds varied by as much as 60 dB and units with the highest thresholds tended to have the lowest spontaneous rates. Spontaneous discharge rates ranged from 0 to 200 spikes/s with a mean rage of 86 spikes/s. Interspike interval histograms of spontaneous activity often contained regular peaks with the time interval between peaks approximately equal to 1/(characteristic frequency). Tuning curves were sharply tuned and V-shaped with approximately equal slopes to the curves above and below characteristic frequency. Q10dB and Q30dB values for the tuning curves increased with characteristic frequency. Post stimulus time histograms showed sustained firing during the stimulus and were characterized by a slight-to-moderate peak at stimulus onset. Most units showed vigorous phase-locking to tones at characteristic frequency although the degree of phase-locking declined sharply with increasing characteristic frequency. Discharge rate-level functions at characteristic frequency had a mean dynamic range of 42 dB and a mean saturation firing rate of 327 spikes/s. In general, the firing patterns of cochlear ganglion neurons are similar in most respects to those reported in other avians, but differ in several important respects from those seen in mammals.

Acoustic Stimulation↗

PubMed1992

Detection of intensity decrements by the chinchilla.

Three monaural chinchillas were trained to detect intensity decrements in broadband noise (20 kHz) using a shock-avoidance conditioning procedure. The intensity decrements were presented at one of nine different durations between 2 and 35 ms at noise levels of 25, 45, and 65 dB SPL. At each intensity-duration combination, the level of the decrement was varied to obtain a decrement threshold. The minimal detectable decrement decreased from approximately 20 dB at the shortest duration to an asymptote of roughly 4 dB at approximately 30 ms. The data were modeled by a low-pass filter with an 11-ms time constant. The decrement detection function of the chinchilla is similar to that of humans. However, long-duration decrement thresholds are larger in the chinchilla, as would be predicted from the large intensity difference limen of the chinchilla. In general, there was little change in the decrement function across background intensities except that 2-ms decrements were not detected at the 25-dB SPL background intensity.

Animals↗

PubMed1991

Impact noise: the importance of level, duration, and repetition rate.

The applicability of the equal energy hypothesis (EEH) to impact noise exposures was studied using chinchillas. Hearing thresholds were estimated by recording the evoked potentials from a chronic electrode implanted in the inferior colliculus. The animals were exposed to broadband impacts of 200-ms duration. The study was carried out in two parts. In experiment I, six exposure levels (107, 113, 119, 125, 131, and 137 dB SPL) and three repetition rates (4/s, 1/s and 1/4s) were employed. In the second experiment, the total duration of the exposure as well as the total energy were kept constant by trading level and rate. Results indicate that hearing loss resulting from exposure to impact noise does not conform to the predictions of the EEH. The permanent threshold shift as well as the hair cell loss are more or less equal across the lower peak exposure levels. However, both the hearing loss and the hair cell damage increase for exposures with higher peak levels. Furthermore, hearing loss and cochlear damage are dependent upon the rate of exposure. Thus the amount of hearing loss and hair cell damage appears to depend on the interaction of several factors including peak level, rate, and the susceptibility of the animal.

Animals↗

PubMed1991

Discrimination performance of single neurons: rate and temporal-pattern information.

1. A new method of measuring the performance of neurons in sensory discrimination tasks was developed and then applied to single-neuron responses recorded in the auditory nerve of chinchilla and in the striate visual cortex of cat. 2. Most previous methods of measuring discrimination performance have employed decision rules that involve comparing the total counts of action potentials (spikes) produced by two different stimuli. Such measures ignore response pattern and hence may not reflect all the information transmitted by a neuron. The proposed method attempts to measure all (or most) of the transmitted information by constructing descriptive models of the neuron's response to each stimulus in the discrimination experiment; these descriptive models consist of measured probability distributions of the spike counts in small time bins. The measured probability distributions are then used to define an optimal decision rule (an ideal observer) for discriminating the two stimuli. Finally, discrimination performance is measured by applying this decision rule to novel presentations of the same two stimuli. 3. Intensity and temporal-phase discrimination were measured for three neurons in the auditory nerve of chinchilla. The discrimination stimuli were low-frequency pure tones of 70-ms duration. Intensity thresholds were found to be 5-20 dB lower at low intensities using the new pattern method compared with the traditional counting method. The pattern method led to better performance because it utilized both rate and temporal pattern information. Phase discrimination performance using the counting method was at chance because the average spike rate did not change with phase. On the other hand, using the pattern method, phase discrimination thresholds were found to decrease with intensity, often reaching values equivalent to 30-40 microseconds of temporal offset. These thresholds are as good as or better than behavioral thresholds in chinchilla. 4. Contrast and temporal-phase discrimination were measured for three neurons in the striate visual cortex of cat. The discrimination stimuli were drifting sine-wave gratings of 100- to 160-ms duration. Contrast discrimination functions measured by the pattern method and the counting method were found to be essentially identical. Phase discrimination using the counting method was at chance. However, using the pattern method, phase thresholds were found to decrease with contrast, reaching values equivalent to 7 ms of temporal offset for the two simple cells. 5. Our results suggest that temporal response pattern carries substantial information for intensity and phase discrimination in the auditory nerve and for phase discrimination in the striate visual cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Neural correlates of gap detection in auditory nerve fibers of the chinchilla.

The neural correlates of gap detection were examined in a population of single auditory nerve fibers in the chinchilla. Acoustic stimuli consisted of 120 ms noise bursts (30-80 dB SPL) which contained silent intervals (gaps: 1, 2, 3, 4,5, 6 and 10 ms) at the midpoint. The neural response to the gap was quantified by the modulation index, (MAX-MIN)/AVE, which accounts for the steady state discharge rate before the gap (AVE), the minimum firing rate during the gap (MIN), and the maximum firing rate after the gap (MAX). In general, the modulation index increased as a function of gap width and stimulus level. Furthermore, there was a positive correlation between the modulation index and the characteristic frequency of the fiber. To estimate how detection could be based on the neuronal response, a criterion-free measure, analogous to d'. was calculated using z-scores obtained from the distributions of modulation index values collected before and during the gap and used to predict percent correct values for chinchilla psychophysical studies. The values increased with gap duration in a sigmoidal manner much like the psychometric functions in the chinchilla. In general, the neural gap thresholds obtained approximated those obtained psychophysically, although they were less affected by stimulus level.

Acoustic Stimulation↗

PubMed1990

Interaction of cisplatin and noise on the peripheral auditory system.

The potentiation of cisplatin ototoxicity by noise was explored in the chinchilla. The effects of exposure to cisplatin alone, noise alone or concurrent exposure to both agents were compared in terms of the threshold shift of the auditory evoked potential and the amount of hair cell loss. The combination of cisplatin plus noise produced significantly more hair cell loss and hearing loss at the high frequencies than did either the noise or cisplatin alone when the noise level was 85 dB SPL or higher; no interaction was seen when the noise level was 70 dB SPL. The amount of the interaction, when present, was constant regardless of the noise level. These results indicate that moderate to high levels of noise can exacerbate cisplatin ototoxicity.

Animals↗

PubMed1990

Enhanced evoked response amplitudes in the inferior colliculus of the chinchilla following acoustic trauma.

Evoked response amplitude-level functions were measured from electrodes in the inferior colliculus of the chinchilla before and after exposure to a 2 kHz pure tone of 105 dB SPL. The exposure produced approximately 20-30 dB of permanent threshold shift from 2 to 8 kHz, but little or no hearing loss at higher or lower frequencies. Generally less than 60% of the outer hair cells were missing in the region of hearing loss. The amplitude-level functions measured at 4 and 8 kHz generally showed a loss in sensitivity at low sound levels, a reduction in the maximum amplitude and sometimes steeper than normal slopes. The amplitude-level functions measured at 2 kHz also showed a loss in sensitivity; however, the maximum amplitude was often greater than normal. Even though there was no loss in sensitivity at 0.5 kHz, the amplitude-level function was steeper than normal and the maximum amplitude of the evoked response was almost always substantially larger than normal. The enhancement of the evoked response amplitude from the inferior colliculus does not appear to originate in the cochlea, but may reflect a reorganization of neural activity in the central auditory pathway.

Acoustic Stimulation↗

PubMed1990

Recovery from short-term adaptation in single neurons in the cochlear nucleus.

Recovery from short-term adaptation was measured in single neurons in the cochlear nucleus using a forward masking stimulus paradigm. The response to a short-duration, low-level probe tone at a unit's characteristic frequency (CF) was measured before and after presentation of a masker tone at the unit's CF. The degree of adaptation was defined as the ratio of firing to the probe in the adapted and unadapted conditions. The level of the masker and time difference between the masker offset and probe onset ('DT') were varied. As DT increased, the response to the probe increased in most Primarylike, Primarylike-notch, and Chopper units. Recovery was approximately linear in log time for most of these units. However, approximately half the Pauser/Buildup and On units showed very different recovery patterns, ranging from no adaptation to very non-linear recovery patterns. The results suggest that little alteration in the recovery process occurs between the auditory nerve and Primarylike, Primarylike-notch, and Chopper units, but that significant changes in the recovery process occur in Pauser-Buildup and On units.

Acoustic Stimulation↗