Biomedical subjects

H Versnel

Publications and source records attributed to H Versnel.

12 recordsLinked to original sources

PubMed2000

Responses to linear and logarithmic frequency-modulated sweeps in ferret primary auditory cortex.

Multi-unit responses to frequency-modulated (FM) sweeps were studied in the primary auditory cortex of ferrets using six different stimulation paradigms. In particular, the differences between the responses to linear FM sweeps (where frequency changes linearly with time) and logarithmic FM sweeps (where frequency changes exponentially with time) were emphasized. Some general features of the responses to FM sweeps are independent of the exact details of the frequency trajectory. Both for linear and for logarithmic FM sweeps, a short burst of spikes occurred when the sweep reached a triggering frequency close to the best frequency of the cluster. The neuronal preference for FM velocity was also independent of frequency trajectory. Thus, clusters that responded best to slow logarithmic FM also preferred slow linear FM and vice versa. Consequently, topographic distributions of velocity preference were roughly independent of the stimulation paradigm. Other characteristics of the responses, however, depended on the exact details of the frequency trajectory. A significant number of clusters showed large differences in directional sensitivity between linear and logarithmic FM sweeps; these differences depended on the velocity preference of the clusters in some paradigms but not in others. Consequently, topographic distributions of directional sensitivity differed between linear and logarithmic paradigms. In conclusion, some characteristics of cluster responses to FM sweeps depend on the exact details of the stimulation paradigm and are not 'invariants' of the cluster.

Acoustic Stimulation↗

PubMed1998

Spectral-ripple representation of steady-state vowels in primary auditory cortex.

Responses to various steady-state vowels were recorded in single units in the primary auditory cortex (AI) of the barbiturate-anaesthetized ferret. Six vowels were presented (/a/, /epsilon/, 2 different /i/'s, and 2 different /u/'s) in a natural voiced and a synthetic unvoiced mode. In addition, the responses to broadband stimuli with a sinusoidally shaped spectral envelope (called ripple stimuli) were recorded in each cell, and the response field (RF), which consists of both excitatory and inhibitory regions, was derived from the ripple transfer function. We examined whether the vowel responses could be predicted using a linear ripple analysis method [Shamma et al., Auditory Neurosci. 1, 233-254 (1995)], i.e., by cross correlating the RF of the single unit, and the smoothed spectral envelope of the vowel. We found that for most AI cells (71%) the relative responses to natural vowels could be predicted on the basis of this method. Responses and prediction results for unvoiced and voiced vowels were very similar, suggesting that the spectral fine structure may not play a significant role in the neuron's response to the vowels. Predictions on the basis of the entire RF were significantly better than based solely on best frequency (BF) (or "place"). These findings confirm the ripple analysis method as a valid method to characterize AI responses to broadband sounds as we proposed in a previous paper using synthesized spectra [Shamma and Versnel, Auditory Neurosci. 1, 255-270 (1995)].

Animals↗

PubMed1997

Auditory-nerve fiber responses to clicks in guinea pigs with a damaged cochlea.

This paper describes auditory-nerve single-fiber responses to clicks in noise-damaged cochleas. Poststimulus time histograms (PSTHs) were recorded for various click intensities and for the two click polarities. The PSTHs found in fibers with elevated thresholds are discussed in relation to the frequency threshold curves (FTCs) measured in these fibers. Five types of abnormal FTCs are distinguished. Type I is elevated as a whole, type II has an elevated (and often broadened) tip and a tail at normal level, type III has low thresholds in the tail (often hypersensitive), type IV represents a flat tuning, and type V has no tip but shows a clear appearance of the tail (often hypersensitive). The click PSTHs of abnormal fibers were compared to normal PSTHs at equal sound-pressure levels, and various abnormal trends were found corresponding to the type of FTC. PSTHs for type I have longer dominant-peak latencies and smaller amplitudes; PSTHs for type II were normal well above the fiber's threshold; PSTHs for type III revealed remarkable patterns with multiple peaks, part of them with a latency strongly varying with polarity; PSTHs for type IV showed narrow peaks and steep amplitude/intensity curves; PSTHs for type V showed a multiple peaked pattern and large amplitudes and steep amplitude/intensity curves to rarefaction polarity. The various features in the click responses were in most cases consistent with the type of FTC. The results can be used to explain deviations in whole-nerve recordings in abnormal cochleas.

Acoustic Stimulation↗

PubMed1995

Multi-electrode array for measuring evoked potentials from surface of ferret primary auditory cortex.

Using silicon-integrated circuit technology, we have fabricated a flexible multi-electrode array and used it for measuring evoked potentials at the surface of the ferret primary auditory cortex (AI). Traditionally, maps of cortical activity are recorded from numerous sequential penetrations with a single electrode. A common problem with this approach is that the state of the cortex (defined in part by level of anesthesia and number of active cells) changes during the time required to generate these maps. The multi-electrode array reduces this problem by allowing the recording of 24 locations simultaneously. The specific array described in this report is designed to record cortical activity over a 1 mm2 area. It is comprised of 24 gold electrodes (40 x 40 microns2) each spaced 210 microns apart. These electrodes are connected to contact pads via gold leads (5 cm in length). The electrodes, leads, and contact pads are sandwiched between two layers of polyimide. The polyimide passivates the device and makes the device flexible enough to conform to the shape of the cortex. The fabrication procedures described here allow various other layouts and areas to be readily implemented. Measurements of the electrical properties of the electrodes, together with details of the multichannel amplification, acquisition, and display of the data are also discussed. Finally, results of AI mapping experiments with these arrays are illustrated.

Acoustic Stimulation↗

PubMed1995

Comparison of responses in the anterior and primary auditory fields of the ferret cortex.

1. Characteristics of an anterior auditory field (AAF) in the ferret auditory cortex are described in terms of its electrophysiological responses to tonal stimuli and compared with those of primary auditory cortex (AI). Ferrets were barbiturate-anesthetized and tungsten microelectrodes were used to record single-unit responses from both AI and AAF fields. Units in both areas were presented with the same stimulus paradigms and their responses analyzed in the same manner so that a direct comparison of responses was possible. 2. The AAF is located dorsal and rostral to AI on the ectosylvian gyrus and extends into the suprasylvian sulcus rostral to AI. The tonotopicity is organized with high frequencies at the top of the sulcus bordering the high-frequency area of AI, then reversing with lower BFs extending down into the sulcus. AAF contained single units that responded to a frequency range of 0.3-30 kHz. 3. Stimuli consisted of single-tone bursts, two-tone bursts and frequency-modulated (FM) stimuli swept in both directions at various rates. Best frequency (BF) range, rate-level functions at BF, FM directional sensitivity, and variation in asymmetries of response areas were all comparable characteristics between AAF and AI. Responses in both areas were primarily phasic. 4. The characteristics that were different between the two cortical areas were: latency to tone onset, excitatory bandwidth 20 dB above threshold (BW20), and preferred FM rate as parameterized with the centroid (a weighted average of spike counts). The mean latency of AAF units was shorter than in AI (AAF: 16.8 ms, AI: 19.4 ms). BW20 measurements in AAF were typically twice as large as those found in AI (AAF: 2.5 octaves, AI 1.3 octaves). The AI centroid population had a significantly larger standard deviation than the AAF centroid population. 5. We examined the relationship between centroid and BW20 to see whether wider bandwidths were a factor in a unit's ability to detect fast sweeps. There was significant (P < 0.05) linear correlation in AAF but not in AI. In both fields the variance of the centroid population decreased with increasing BW20. BW20 decreased as BF increased for units in both auditory fields.

Acoustic Stimulation↗

PubMed1994

A dual filter model describing single-fiber responses to clicks in the normal and noise-damaged cochlea.

This paper presents a composite model of the normal and noise-damaged guinea pig cochlea. The model incorporates a phenomenologically defined cochlear filter, and physiological descriptions of inner hair cell transduction, synaptic adaptation, and spike generation. The latter three model sections were taken from recent literature. The paper first deals with validation and evaluation of the model and adaptation of the relevant parameters to the guinea pig. Then the model is applied to explore to what extent changes in the cochlear filter can be held responsible for abnormal responses to clicks that were recorded in single auditory nerve fibers in noise-damaged animals. Focus is on those fibers in which the tip-to-tail sensitivity ratio of the frequency threshold curve (FTC) has decreased and/or in which the FTC tail has become hypersensitive. Inspired by this type of W-shaped FTC the mechanical response of the basilar membrane is phenomenologically modeled by two parallel filters, one responsible for the tip of the FTC, the other for its tail. Model simulations show that most abnormal temporal response properties can be explained by pathological alterations in the mechanical response. Residual discrepancies between model and experiment are identified which presumably point to pathological changes in other stages of cochlear processing.

Acoustic Stimulation↗

PubMed1993

Recovery characteristics of auditory nerve fibres in the normal and noise-damaged guinea pig cochlea.

Spontaneous activity was analysed in auditory-nerve fibres innervating normal and noise-damaged cochleas. Spike occurrences were conceived as point processes. Joint interval distributions and serial correlation coefficients reveal a weak history effect for succeeding intervals. The point process is regarded as a renewal and the recovery function, being proportional to the hazard function, is determined from the interval probability density function. In 29 out of 60 fibres the latter shows peculiarities which result in a deviation from a monotonically increasing recovery function. For three fibers of low characteristic frequency the interval probability function shows an oscillatory pattern and for 26 fibres this function exhibits an early, sharp peak around 1.1 ms irrespective of characteristic frequency, spontaneous rate, or cochlear damage. The recovery function is not different between fibres with normal and those with abnormally high thresholds and exhibits an exponential recovery with one time constant of average value 1.6 ms. Bursting activity is found in only one fibre from the abnormally high threshold group.

Animals↗

PubMed1993

Organization of response areas in ferret primary auditory cortex.

1. We studied the topographic organization of the response areas obtained from single- and multiunit recordings along the isofrequency planes of the primary auditory cortex in the barbiturate-anesthetized ferret. 2. Using a two-tone stimulus, we determined the excitatory and inhibitory portions of the response areas and then parameterized them in terms of an asymmetry index. The index measures the balance of excitatory and inhibitory influences around the best frequency (BF). 3. The sensitivity of responses to the direction of a frequency-modulated (FM) tone was tested and found to correlate strongly with the asymmetry index of the response areas. Specifically, cells with strong inhibition from frequencies above the BF preferred upward sweeps, and those from frequencies below the BF preferred downward sweeps. 4. Responses to spectrally shaped noise were also consistent with the asymmetry of the response areas. For instance, cells that were strongly inhibited by frequencies higher than the BF responded best to stimuli that contained least spectral energy above the BF, i.e., stimuli with the opposite asymmetry. 5. Columnar organization of the response area types was demonstrated in 66 single units from 16 penetrations. Consistent with this finding, it was also shown that response area asymmetry measured from recordings of a cluster of cells corresponded closely with those measured from its single-unit constituents. Thus, in a local region, most cells exhibited similar response area types and other response features, e.g., FM directional sensitivity. 6. The distribution of the asymmetry index values along the isofrequency planes revealed systematic changes in the symmetry of the response areas. At the center, response areas with narrow and symmetric inhibitory sidebands predominated. These gave way to asymmetric inhibition, with high-frequency inhibition (relative to the BF) becoming more effective caudally and low-frequency inhibition more effective rostrally. These response types tended to cluster along repeated bands that paralleled the tonotopic axis. 7. Response features that correlated with the response area types were also mapped along the isofrequency planes. Thus, in four animals, a map of FM directional sensitivity was shown to be superimposed on the response area map. Similarly, it was demonstrated in six animals that the spectral gradient of the most effective noise stimulus varied systematically along the isofrequency planes. 8. One functional implication of the response area organization is that cortical responses encode the locally averaged gradient of the acoustic spectrum by their differential distribution along the isofrequency planes. This enhances the representation of such features as the symmetry of spectral peaks and edges and the spectral envelope.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1992

Single-fibre and whole-nerve responses to clicks as a function of sound intensity in the guinea pig.

This paper describes a study of the intensity dependence of click-evoked responses of auditory-nerve fibres in relation to the simultaneously recorded compound action potential (CAP). Condensation and rarefaction clicks were presented to normal hearing guinea pigs over an intensity range of 60 dB. The recorded poststimulus time histograms (PSTHs) were characterized by the latency (tp), amplitude (Ap) and synchronization (Sp) of their dominant peak, parameters that are particularly important for the understanding of the CAP. For all fibres tp decreased monotonically with increasing intensity, in a continuous way for fibres with high characteristic frequency (CF greater than 3 kHz), and in discrete steps of one CF-cycle for low-CF (CF less than or equal to 3 kHz) fibres. An additional analysis of PSTH envelopes revealed that average latency shifts with intensity are similar for all CFs above 2 kHz. For all fibres Ap increased monotonically with intensity; the increase was stronger and maximum values were larger for low-CF than for high-CF fibres. A schematic model PSTH was then formulated on the basis of the experimental data. A sum of these model PSTHs from a hypothesized fibre population was convolved with an elemental unit response (Versnel et al., 1992) in order to simulate the compound action potential. Synthesized CAPs agreed with experimental CAPs in their main aspects.

Acoustic Stimulation↗

PubMed1992

Round-window recorded potential of single-fibre discharge (unit response) in normal and noise-damaged cochleas.

Unit responses (URs) of eighth-nerve fibres have been determined at the round window by spike-triggered averaging in both normal and pathological guinea pig cochleas. The pathology was mainly noise-induced damage. The URs have been analysed with respect to their dependence on the fibre's threshold, characteristic frequency (CF) and spontaneous rate (SR). The results from normal cochleas confirmed earlier data (Prijs, 1986): the UR has a diphasic waveform and the amplitude of its negative first peak is about 0.1 microV. From the six parameters (amplitude, latency, and width of the two peaks) by which the UR was described only the amplitude of the positive peak showed a significant variation with CF: a small decrease with increasing CF (CF-range 0.1 to 20 kHz). This finding may possibly be caused by oscillations in the spike-triggered average for low CFs. URs for most low- and medium-SR fibres were found to be large (greater than 0.3 microV). However, this result is interpreted as an artefact caused by synchrony of fibre spontaneous activity. In damaged cochleas only slight changes of the UR were found: the waveform duration became significantly shorter and on some occasions the positive peak increased in amplitude, but latency and amplitude of the negative component of the UR remained unchanged.

Acoustic Stimulation↗

PubMed1990

Latencies of eighth nerve fibre responses with respect to their relative contribution to the compound action potential in the guinea pig.

We present a study of the latencies of click-evoked post-stimulus time histograms (PSTHs) in the guinea pig in the context of the auditory nerve fibre's contribution to the compound action potential (CAP) recorded at the round window. The latencies of the dominant PSTH peak were studied as a function of relevant physiological fibre properties, in particular the characteristic frequency (CF) and the spontaneous discharge rate (SR). We found that high-SR fibres have shorter latencies than low-SR fibres. These findings are discussed in the context of correlation between synaptic morphology and SR as described in the literature. The PSTH latency as a function of CF is described separately for low- and high-CF fibres for each of the two SR subgroups. Finally, we discuss to what extent the various subgroups of fibres contribute to the N1 peak of the CAP, the most commonly studied component.

Action Potentials↗

PubMed1990

Single-fibre responses to clicks in relationship to the compound action potential in the guinea pig.

Poststimulus time histograms (PSTHs) to clicks of standard level were measured in eighth-nerve fibres of normal-hearing guinea pigs. In the context of studying the fibres' contribution to the compound action potential (CAP), the PSTHs are described with the parameters latency (tp), amplitude (Ap) and synchronization (Sp) of the dominant PSTH peak. These parameters are considered in relation to characteristic frequency (CF) and spontaneous rate (SR). An adequate description for tp is one in which tp is constant for non-phase-locking fibres (CF above 3 kHz) and it is an exponential function of CF for phase-following fibres. The low-SR fibres (SR below 5 spikes/s) had smaller amplitudes and longer latencies than the other ones. The variations of Ap with CF can be explained by the varying synchronization of the response.

Acoustic Stimulation↗