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Biomedical subjects

J J Eggermont

Publications and source records attributed to J J Eggermont.

At least 19 recordsLinked to original sources
PubMed1992

Stimulus induced and spontaneous rhythmic firing of single units in cat primary auditory cortex.

Recordings were made under ketamine anesthesia from 385 neurons in primary auditory cortex in adult cat and from 265 neurons in 10-55 day old kittens. The temporal Modulation Transfer Function for the response to repetitive click stimuli peaked at 8 Hz. After a click a suppression period of 130- 155 ms in duration, depending on click-rate, was observed. This suppression period limited the response to high click rates and thereby determined the 'resonance' in the click response. The suppression duration in kittens decreased in exponential fashion toward the adult value with a time constant of about 1 month. After the one second duration click-trains an oscillatory rebound with a mean period of 113 ms was observed in about 60% of the recordings in the adult cat. Spontaneous activity showed in about 30% of the neurons an oscillatory autocorrelogram with an average period of 126 ms in the adult cats and 170 ms in kittens.

Acoustic Stimulation↗
PubMed1992

Development of auditory evoked potentials.

The development and maturation of the human auditory system appears to occur in parallel at all levels from middle ear to cortex. The maturation of evoked potentials from auditory brainstem to auditory cortex can be described by equal percentage changes in equal time periods. This is essentially the exponential growth model with equal maturation rate for each station. The auditory nerve maturation occurs at a rate considerably faster than that for more central parts of the nervous system. Premature birth does not seem to affect the maturation rate and time to maturity of the auditory brainstem potentials, so that experience does not seem to affect physiological maturation. However, there is a clear difference in maturation rates for different frequency regions, suggesting that the time course of structural maturation has an effect. Behavioral changes in hearing threshold show maturation rates similar to the physiological ones for the central nervous system.

Adolescent↗
PubMed1992

Frequency-specific maturation of the eighth nerve and brain-stem auditory pathway: evidence from derived auditory brain-stem responses (ABRs).

Previous studies of human auditory development using frequency-specific auditory brain-stem responses (ABRs) have reported that maturation for both peak and interpeak latencies occurs earlier for responses generated by low-frequency stimuli. In two of these studies, low-frequency ABRs presumed to originate from apical locations in the cochlea were likely dominated by activity from higher frequency regions closer to the base. In the present study, the high-pass noise-masking technique was used to generate derived ABRs that represent activity from isolated place specific regions along the basilar membrane. Analysis of auditory brain-stem maturation based on I-V interpeak latency differences with adult means revealed a frequency-specific pattern of development. Developmental changes occurred faster and mature function was attained earlier for ABRs from the mid-center-frequency (CF) derived conditions than from either the highest or lowest CF derived conditions. The differential maturation of mid-CF derived ABRs may reflect the delayed effects of the pattern of development that occurs in the cochlea.

Auditory Pathways↗
PubMed1992

Neural interaction in cat primary auditory cortex. Dependence on recording depth, electrode separation, and age.

1. Neural activity was recorded with two independent electrodes separated by 0.5-2 mm, aligned in parallel, and advanced perpendicular to the surface of the cat auditory cortex. For smaller separations a solid-state multielectrode array with interelectrode distances of 125 microns was used. The difference in recording depths for the two independently movable electrodes was never more than 100 microns; the electrode contacts of the multielectrode array were at the same depth. Thus the correlation studies dominantly explored horizontal interactions. 2. Out of 995 neuron pairs recorded, 478 represented pairs of single units, whereas the other pairs were contaminated with 5-10% misclassified spikes. Only the single-unit pairs were further analyzed. Of those pairs, 338 showed a clear correlation peak, and in 329 of these the peak heights were exceeding the Z > 4 significance level (P < 0.0001). Two hundred fifty-two of the significant correlograms (53% of total) could be attributed to common input; the remaining (16% of total) were indicative of unilateral excitation. For the 181 single-electrode pairs the percentage of unilateral excitation pairs (42%) was about the same as the percentage of common input pairs (38%). For the 297 dual-electrode pairs all but one of the 184 significant correlations were indicative of common input. No correlograms indicative of inhibition were found. 3. The correlograms with clear peaks were classified into three types: narrow (n = 40), mixed (n = 77), and broad (n = 221). Narrow and mixed types were with two exceptions found only for single-electrode pairs; broad types were found for single- and dual-electrode pairs. Narrow-type correlograms were in majority of the unilateral excitation type. Correlograms were calculated both for 1-ms binwidths (50-ms lead/lag time) and for 10-ms binwidth (500-ms lead/lag time). The correlograms were characterized by four parameters; the half width of the central peak, the peak correlation coefficient, the association index, and for unilateral excitation cases also by the effectiveness. 4. Across all three correlogram types the half width of the correlation peaks was significantly smaller for single-electrode pairs (mean, 27 ms) than for dual-electrode pairs (mean, 42 ms). For broad-type correlograms only, the mean half widths were not significantly different between single- and dual-electrode pairs. 5. The correlation coefficients (1-ms bin correlograms) were significantly larger for single-electrode pairs (mean, 0.038) than for dual-electrode pairs (mean, 0.011). The same was found for the 10-ms binwidth correlograms.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1992

Place-specific derived cochlear microphonics from human ears.

The high-pass noise masking technique was used to obtain derived frequency-specific cochlear microphonics (CM) from subtracted waveforms to rarefaction and condensation stimuli recorded with a tympanic membrane electrode. Two characteristics suggest that the response is place-specific CM: the derived response retains the same frequency as the stimulating toneburst and the response follows the stimulus polarity. For click stimulation, derived neural responses make the place-specific CM difficult to observe except in the 2-1 kHz derived band. In contrast, place-specific CM evoked by 0.5 and 1 kHz tonebursts can usually be detected in at least three derived bands. The amplitude of the response is largest in the derived band with center-frequency (CF) just above that of the toneburst. This discovery of a place-specific CM offers the possibility of assessing (outer) hair cell function in the apical part of the human cochlea.

Acoustic Stimulation↗
PubMed1991

Assessment of cisplatin-induced ototoxicity using derived-band ABRs.

Ototoxicity is an adverse side effect of numerous therapeutic agents (amino-glycoside antibiotics, blood chelating agents, diuretics and oncologic drugs) used in treatment of both adult and pediatric patients. Recently, there has been increasing interest in using the auditory brainstem response (ABR) to detect both short-term effects of ototoxicity in adults and long-term effects of drug administration on neonates and children. Since click ABRs have relatively poor frequency selectivity they best approximate the pure-tone hearing threshold in the 2000-4000 Hz frequency range. Hearing loss above or below that frequency range can be present without producing significant abnormalities in the ABR waveform parameters. Frequency-specific ABRs can be obtained using the derived response technique. The purpose of this study was to investigate early cisplatin ototoxicity using both the broadband click and derived ABR and to monitor progressive hearing loss with repeated drug trials in 18 patients studied over a 2-year period. ABRs were obtained serially prior to and following intravenous administration of cisplatin. Derived ABRs were found to be more sensitive than broadband click ABR in detecting early high-frequency hearing loss. For click ABRs, the cumulative dosage of cisplatin at age of ABR examination was correlated with hearing loss in only those patients under 3 years of age. No significant correlation was found between cumulative cisplatin dosage when tested and degree of hearing loss in those patients over 3 years of age.

Adolescent↗
PubMed1991

Maturational aspects of periodicity coding in cat primary auditory cortex.

The click-following responses for single units in the primary auditory cortex of the cat were explored as a function of age. Recordings were obtained in kittens from 9-53 days of age and assembled in four age groups; 10-15 days, 16-21 days, 22-27 days and 30-60 days. Age group means were compared to results obtained in adult cats. The stimulus consisted of one second long click trains presented every three seconds with click rates ranging from 1-32 clicks per second. The response was characterized by entrainment, rate Modulation Transfer Function (rMTF), vector strength (VS) and temporal Modulation Transfer Function (tMTF). Maturational effects on periodicity coding comprised changes in overall responsiveness as well as click-rate dependent changes. The number of spikes elicited by single stimuli increased on average 3-fold between the second post-natal week and adulthood, probably as a result of more efficient synapses in the central auditory pathway and some improvement in thresholds. Adaptation became less pronounced with age; neurons started to respond to the later clicks in the 8/s and 16/s click trains from the third post natal week on. By the end of the first post-natal month the click following responses resembled the adult ones qualitatively, however, increased firing rates and spontaneous rates together with rebound responses continued to produce quantitative differences between the 30-60 days olds and the adults. Limiting rates for the tMTF (50% of the response at 1/s) increased from 6 Hz in the 10-15 day old to 12 Hz in adults. The decrease in the duration of the post-activation suppression coupled with the increased response with age to trains with higher click rates suggested that the maturation of inhibitory processes in the cortex play a major role in this rate dependence.

Acoustic Stimulation↗
PubMed1991

Rate and synchronization measures of periodicity coding in cat primary auditory cortex.

Periodicity coding was studied in primary auditory cortex of the ketamine anesthetized cat by simultaneously recording with two electrodes from up to 6 neural units in response to one second long click trains presented once per 3 s. Trains with click rates of 1, 2, 4, 8, 16 and 32/s were used and the responses of the single units were quantified by both rate measures (entrainment and rate modulation transfer function, rMTF) and synchronization measures (vector strength VS and temporal modulation transfer functions, tMTF). The rate measures resulted in low-pass functions of click rate and the synchrony measures resulted in band-pass functions of click rate. Limiting rates (-6 dB point of maximum response) were in the range of 3-24 Hz depending on the measure used. Best modulating frequencies were in the range of 5-8 Hz again depending on the synchrony measure used. It appeared that especially the VS was highly sensitive to spontaneous firing rate, duration of the post click suppression and the size of the rebound response after the suppression. These factors were dominantly responsible for the band-pass character of the VS-rate function and the peak VS frequency was nearly identical to the inverse of the suppression period. It is concluded that the use of the VS and to a lesser extent also the tMTF as the sole measure for the characterization of periodicity coding is not recommended in cases where there is a strong suppression of spontaneous activity. The combination of entrainment and tMTF appeared to characterize the periodicity coding in an unambiguous way.

Acoustic Stimulation↗
PubMed1991

Maturation of the traveling-wave delay in the human cochlea.

The maturation of the traveling-wave delay in the human cochlea was investigated in 227 subjects ranging in age from 29 weeks conceptional age to 49 years by using frequency specific auditory brain-stem responses (ABRs). The derived response technique was applied to ABRs obtained with click stimuli (presented at a fixed level equal to 60-dB sensation level in normal hearing adults) in the presence of high-pass noise masking (slope 96 dB/oct) to obtain frequency specific responses from octave-wide bands. The estimate of traveling-wave delay was obtained by taking the difference between wave I latencies from adjacent derived bands. It was found that the traveling-wave delay between the octave band with center frequency (CF) of 11.3 kHz and that with CF of 5.7 kHz decreased (about 0.4 ms on average) in exponential fashion with age to reach adult values at 3-6 months of age. This decrease was in agreement with reported data in kitten auditory-nerve fibers. The traveling-wave delays between adjacent octave bands with successive lower CF did not change with age.

Adolescent↗
PubMed1991

Neuronal pair and triplet interactions in the auditory midbrain of the leopard frog.

1. With the use of two independent microelectrodes and multiunit spike separation, 26 neural pairs, 17 triplets, and 8 quadruplets were recorded in the auditory midbrain of the leopard frog, resulting in a total of 125 neural pairs. 2. Functional interrelationships between neurons were studied by analyzing 638 cross-coincidence histograms as functions of stimulus type, stimulus level, and estimated neuron distance. Significance criteria for correlograms were established on the basis of the distribution of extreme values in a large number of correlograms for nonsimultaneously recorded pairs. 3. Simultaneous recordings from three neurons, that all showed significant neural pair correlations were analyzed with the use of the joint occurrence diagram, which displays the joint coincidences for the firings of two units (a and b) with the firings of the trigger unit (c). 4. It was found that 97.5% of the pairs showed a significant stimulus-induced correlation; neighboring neurons exhibited a stronger stimulus correlation (synchrony) than more distant neurons. 5. Positive neural interaction strength (75% to shared excitatory input) was independent of neuron distance (taking into account that the estimated electrode distance in the present investigation was never greater than 300 microns) and occurred in 25% of the pairs investigated. About 25% of the positive neural correlations could be attributed to unidirectional excitation, the majority of which was found for single-electrode pairs. Negative neural correlation occurred in 8% of the pairs and, with one exception, was found only for neurons recorded on the same electrode. 6. Evidence for the presence of feed-forward and/or feedback inhibition was found. 7. There was a strong stimulus-type influence on stimulus correlation and on positive neural correlation, whereas stimulus intensity affected the stimulus correlation but not the neural correlation. 8. From the incidence of triplet correlations, it was concluded that the divergence of afferents onto midbrain neurons was limited; it was unlikely that more than three neurons were contacted by one afferent. In contrast, convergence of afferents on torus semicircularis cells was widespread; 40-50% of the midbrain neurons were bimodally tuned and received input originating from the two auditory papillae. Convergence of fibers from the same papilla was also extensive. 9. Fast modulation of functional neural connectivity through the activity of other neurons was found, although this was probably not the result of actual changes in synaptic strength but of synchronized changes in firing rate.

Acoustic Stimulation↗
PubMed1991

Frequency dependent maturation of the cochlea and brainstem evoked potentials.

The anatomical development of the human cochlea starts in the middle basal turn and progresses both toward the base and the apex. Behavioral responses, in contrast, appear to emerge for lower frequencies first. Cochlear tuning may continue to change during early development and so effect electrophysiological and behavioral measures of maturation. The maturation of the cochlear traveling wave delay as well as the ABR I-V interval was investigated using the derived response technique which permits a frequency dependent analysis of this maturation. It was found that the traveling wave delay decreased significantly with age for the most basal part of the cochlea; however, it was not affected by age for more apical locations. The I-V delay difference with the adult values was found significantly shorter in the derived octave band with CF = 2.8 kHz than in all other bands for the preterm, term and infant groups. This suggests that the frequency dependent electrophysiological maturation of the brainstem parallels the anatomical development of the cochlea.

Acoustics↗
PubMed1979

Summating potentials in Menière's disease.

The summating potentials in response to tonebursts of 2, 4, and 8 kHz were studied in a group of 112 patients diagnosed as having Menière's disease, and the results were compared with recordings from 27 normal human ears. Subdivision of the Menière ears into a low-threshold (threshold less than 50 dB HL) and a high-threshold group (greater than 50 dB HL) proved to be functional in relation to the behaviour of the SP. The data of the low-threshold Menière group did not differ significantly from the normal data, whereas the high-threshold Menière group showed significantly smaller summating potentials. Up to hearing thresholds of 50 dB, the detection threshold for the SP was independent of the hearing threshold; at higher hearing losses, the increase in SP threshold equalled the increase in hearing loss. Analysis showed that the correlation found between the changes in SP and hearing threshold in individual patients did not differ significantly from zero for threshold values below 50 dB. The overall conclusion is that in Menière ears hearing losses up to about 50 dB are not related to changes in the hair cells, since the SP does not change, whereas the increase in the amount of hearing loss above 50 dB HL is paralleled by a loss in sensitivity of the summating potential and is therefore related to a functional loss of hair cells.

Action Potentials↗
PubMed1979

Narrow-band AP latencies in normal and recruiting human ears.

Derived narrow-band action potential latencies increase monotonically with decreasing central frequency, and can be interpreted as reflecting the traveling wave delay in the cochlea. It was found that, for recruiting human ears with average flat hearing losses around 40 dB, this accumulating latency increase was smaller than for normal ears. A comparison of 15 normal ears and 37 recruiting ears showed, however, that in only half of the recruiting ears this difference was significant. These recruiting ears were therefore divided in two groups based on the waveform of the narrow-band action potential AP, which correlated well with the subdivision according to latency. The findings have been explained on the basis that latency of the narrow-band APs is not determined solely by the mechanical traveling-wave delay, but also by the response time of the (second?) cochlear filter. When this filter broadens, one expects a decrease in its impulse response time. Since this impulse response time. Since this impulse response depends on the sum of the high- and low-frequency slope values of the cochlear filter, one expects only a latency decrease when the steep high-frequency slope also becomes more shallow. A support for the influence of the response times of the cochlear filter is found in the narrow-band AP latencies for restricted cochlear losses (e.g., in a 4-kHz noise dip). It appears that the latency in that area actually is shorter than for the higher central frequencies, a fact which cannot be explained solely on the basis of a traveling wave phenomenon.

Acoustic Stimulation↗
PubMed1978

Analysis of the click-evoked brainstem potentials in man unsing high-pass noise masking.

Brainstem electrical responses (BSER) to 60-dB-SL click in noise high passed at various cutoff frequencies separated b 1/2-octave steps were recorded in normal-hearing adult subjects. By applying a derived response technique, narrow-band contributions to the BSER from specific portions of the basilar membrane were revealed. Latencies and amplitudes of the various waves in the derived BSER were recorded. Results indicate that nearly the whole cochlear partition can contribute to the brainstem response. The shifts in latency of waves I, III, and V and amplitude changes of waves I and III as a function of CF appear to be fully comparable to those of the AP. In contrast, the amplitude behavior of wave V as a function of CF is different from waves I and III depending upon frequency range. The discrepency in the behavior of wave V with respect to the earlier waves suggests some sort of neural reorganization at the level where was V is generated. The fact that there are contributions to the brainstem response from apical portions of the cochlea opens the possibility for extending the brainstem technique in assessing the higher cochlear turn function.

Acoustic Stimulation↗