Biomedical subjects

Pim van Dijk

Publications and source records attributed to Pim van Dijk.

At least 19 recordsLinked to original sources

PubMed2006

Representation of lateralization and tonotopy in primary versus secondary human auditory cortex.

Functional MRI was performed to investigate differences in the basic functional organization of the primary and secondary auditory cortex regarding preferred stimulus lateralization and frequency. A modified sparse acquisition scheme was used to spatially map the characteristics of the auditory cortex at the level of individual voxels. In the regions of Heschl's gyrus and sulcus that correspond with the primary auditory cortex, activation was systematically strongest in response to contralateral stimulation. Contrarily, in the surrounding secondary active regions including the planum polare and the planum temporale, large-scale preferences with respect to stimulus lateralization were absent. Regarding optimal stimulus frequency, low- to high-frequency spatial gradients were discernable along the Heschl's gyrus and sulcus in anterolateral to posteromedial direction, especially in the right hemisphere, consistent with the presence of a tonotopic organization in these primary areas. However, in the surrounding activated secondary areas frequency preferences were erratic. Lateralization preferences did not depend on stimulus frequency, and frequency preferences did not depend on stimulus lateralization. While the primary auditory cortex is topographically organized with respect to physical stimulus properties (i.e., lateralization and frequency), such organizational principles are no longer obvious in secondary and higher areas. This suggests a neural re-encoding of sound signals in the transition from primary to secondary areas, possibly in relation to auditory scene analysis and the processing of auditory objects.

Adult↗

PubMed2006

Temperature dependence of anuran distortion product otoacoustic emissions.

To study the possible involvement of energy-dependent mechanisms in the transduction of sound within the anuran ear, distortion product otoacoustic emissions (DPOAEs) were recorded in the northern leopard frog over a range of body temperatures. The effect of body temperature depended on the stimulus levels used and on the hearing organ under investigation. Low-level DPOAEs from the amphibian papilla (AP) were reversibly depressed for decreased body temperatures. Apparently, DPOAE generation in the AP depends on metabolic rate, indicating the involvement of active processes in the transduction of sound. In contrast, in the other hearing organ, the basilar papilla (BP), the effects of body temperature on DPOAEs were less pronounced, irrespective of the stimulus levels used. Apparently, metabolic rate is less influencing DPOAE generation. We interpret these results as evidence that no amplifier is involved in sound transduction in the BP. The passive functioning of the anuran BP would place this hearing organ in a unique position within tetrapod hearing, but may actually be beneficial to ectothermic species because it will provide the animal with a consistent spectral window, regardless of ambient or body temperature.

Animals↗

PubMed2006

Analysis of responses to noise in the ventral cochlear nucleus using Wiener kernels.

Responses to noise were recorded in ventral cochlear nucleus (VCN) neurons of anesthetized chinchillas and cats, then analyzed using Wiener-kernel theory. First-order kernels, which are proportional to reverse-correlation functions, of primary-like (PL) and primary-like with notch (PLN) neurons having low characteristic frequency (CF) are similar to those obtained in auditory nerve fibers (ANFs). Such kernels consist of lightly damped transient oscillations with frequency equal to the neuron's CF. The first-order kernel of high-CF PL and PLN neurons displays no evidence of tuning to CF. Second-order kernels of the aforementioned VCN neuron types also resemble those in the nerve, irrespective of CF. In general, first- and second-order Wiener kernels of chopper neurons are similar to those obtained in high-CF ANFs. This is likely the consequence of the poor phase-locking capabilities to near-CF tones exhibited by chopper neurons. By analyzing second-order kernels using singular-value decomposition, it was possible to estimate group delays for the entire neuronal population, regardless of the neuron's type or CF. This was done by analyzing the highest-ranking singular vector (FSV). Amplitude values of FSVs in chopper neurons in the cat are substantially larger than in high-spontaneous ANFs.

Acoustic Stimulation↗

PubMed2006

Neural responses to silent lipreading in normal hearing male and female subjects.

In the past, researchers investigated silent lipreading in normal hearing subjects with functional neuroimaging tools and showed how the brain processes visual stimuli that are normally accompanied by an auditory counterpart. Previously, we showed activation differences between males and females in primary auditory cortex during silent lipreading, i.e. only the female group significantly activated the primary auditory region during lipreading. Here we report and discuss the overall activation pattern in males and females. We used positron emission tomography to study silent lipreading in 19 normal hearing subjects (nine females). Prior to scanning, subjects were tested on their lipreading ability and only good lipreaders were included in the study. Silent lipreading was compared with a static image. In the whole group, activations were found mainly in the left hemisphere with major clusters in superior temporal, inferior parietal, inferior frontal and precentral regions. The female group showed more clusters and these clusters were larger than in the male group. Sex differences were found mainly in right inferior frontal and left inferior parietal regions and to a lesser extent in bilateral angular and precentral gyri. The sex differences in the parietal multimodal region support our previous hypothesis that the male and female brain process visual speech stimuli differently without differences in overt lipreading ability. Specifically, females associate the visual speech image with the corresponding auditory speech sound whereas males focus more on the visual image itself.

Adult↗

PubMed2005

Lateralization, connectivity and plasticity in the human central auditory system.

Although it is known that responses in the auditory cortex are evoked predominantly contralateral to the side of stimulation, the lateralization of responses at lower levels in the human central auditory system has hardly been studied. Furthermore, little is known on the functional interactions between the involved processing centers. In this study, functional MRI was performed using sound stimuli of varying left and right intensities. In normal hearing subjects, contralateral activation was consistently detected in the temporal lobe, thalamus and midbrain. Connectivity analyses showed that auditory information crosses to the contralateral side in the lower brainstem followed by ipsilateral signal conduction towards the auditory cortex, similar to the flow of auditory signals in other mammals. In unilaterally deaf subjects, activation was more symmetrical for the cortices but remained contralateral in the midbrain and thalamus. Input connection strengths were different only at cortical levels, and there was no evidence for plastic reorganization at subcortical levels.

Acoustic Stimulation↗

PubMed2005

Detailed f1, f2 area study of distortion product otoacoustic emissions in the frog.

Distortion product otoacoustic emissions (DPOAEs) are weak sounds emitted from the ear when it is stimulated with two tones. They are a manifestation of the nonlinear mechanics of the inner ear. As such, they provide a noninvasive tool for the study of the inner ear mechanics involved in the transduction of sound into nerve fiber activity. Based on the DPOAE phase behavior as a function of frequency, it is currently believed that mammalian DPOAEs are the combination of two components, each generated by a different mechanism located at a different location in the cochlea. In frogs, instead of a cochlea, two separate hearing papillae are present. Of these, the basilar papilla (BP) is a relatively simple structure that essentially functions as a single auditory filter. A two-mechanism model of DPOAE generation is not expected to apply to the BP. In contrast, the other hearing organ, the amphibian papilla (AP), exhibits a tonotopic organization. In the past it has been suggested that this papilla supports a traveling wave in its tectorial membrane. Therefore, a two-mechanism model of DPOAE generation may be applicable for DPOAEs from the AP. In the present study we report on the amplitude and phase of DPOAEs in the frog ear in a detailed f1, f2 area study. The result is markedly different from that in the mammalian cochlea. It indicates that DPOAEs generated by neither papilla agree with the two-mechanism traveling wave model. This confirms our expectation for the BP and does not support the hypothesized presence of a mechanical traveling wave in the AP.

Acoustic Stimulation↗

PubMed2005

Wiener-kernel analysis of responses to noise of chinchilla auditory-nerve fibers.

Responses to broadband Gaussian white noise were recorded in auditory-nerve fibers of deeply anesthetized chinchillas and analyzed by computation of zeroth-, first-, and second-order Wiener kernels. The first-order kernels (similar to reverse correlations or "revcors") of fibers with characteristic frequency (CF) <2 kHz consisted of lightly damped transient oscillations with frequency equal to CF. Because of the decay of phase locking strength as a function of frequency, the signal-to-noise ratio of first-order kernels of fibers with CFs >2 kHz decreased with increasing CF at a rate of about -18 dB per octave. However, residual first-order kernels could be detected in fibers with CF as high as 12 kHz. Second-order kernels, 2-dimensional matrices, reveal prominent periodicity at the CF frequency, regardless of CF. Thus onset delays, frequency glides, and near-CF group delays could be estimated for auditory-nerve fibers innervating the entire length of the chinchilla cochlea.

Acoustic Stimulation↗

PubMed2005

Wiener kernels of chinchilla auditory-nerve fibers: verification using responses to tones, clicks, and noise and comparison with basilar-membrane vibrations.

Responses to tones, clicks, and noise were recorded from chinchilla auditory-nerve fibers (ANFs). The responses to noise were analyzed by computing the zeroth-, first-, and second-order Wiener kernels (h0, h1, and h2). The h1s correctly predicted the frequency tuning and phases of responses to tones of ANFs with low characteristic frequency (CF). The h2s correctly predicted the frequency tuning and phases of responses to tones of all ANFs, regardless of CF. Also regardless of CF, the kernels jointly predicted about 77% of the features of ANF responses to "frozen" samples of noise. Near-CF group delays of kernels and signal-front delays of responses to intense rarefaction clicks exceeded by 1 ms the corresponding basilar-membrane delays at both apical and basal sites of the chinchilla cochlea. This result, confirming that synaptic and neural processes amount to 1 ms regardless of CF, permitted drawing a map of basilar-membrane delay as a function of position for the entire length of the chinchilla cochlea, a first for amniotic species.

Acoustic Stimulation↗

PubMed2005

Effect of peri-modiolar cochlear implant positioning on auditory nerve responses: a neural response telemetry study.

CONCLUSIONS: There was no evidence that a reduction in current was needed for nerve stimulation as a result of modiolar placement of a cochlear implant. However, modiolus hugging did reduce the spread of excitation for the basal and apical electrodes. This improved stimulation selectivity may result in improved speech discrimination by implant users. OBJECTIVE: To test the effect of modiolar placement of a cochlear implant on stimulation thresholds, and to confirm whether peri-modiolar electrode placement resulted in the hypothesized reduced spread of excitation. MATERIAL AND METHODS: Auditory nerve responses were measured by means of neural response telemetry (NRT) in 14 subjects. All subjects received a Nucleus CI24R(CS) Contour implant. For each subject, the stimulation threshold and response growth rate were determined on all the odd-numbered electrodes, using a masker-and-probe paradigm. In addition, the spatial spread of excitation was measured on electrodes 1, 6, 11, 16 and 20, using a variable-masker paradigm. All NRT measurements were performed intra-operatively, both before and after peri-modular placement of the electrode by removal of surgical stylet. RESULTS: Removal of the stylet had no significant effect on the threshold and growth rate of NRT responses. It caused a reduction in the spread of excitation for electrodes 1, 6 and 20, but not for electrodes 11 and 16.

Adolescent↗

PubMed2005

Comparison between distortion product otoacoustic emissions and nerve fiber responses from the basilar papilla of the frog.

The basilar papilla (BP) is one of the three end organs in the frog inner ear that is sensitive to airborne sound. Its anatomy and physiology are unique among all classes of vertebrates. Essentially, the BP functions as a single auditory filter presumably arising from a mechanically-tuned mechanism. As such, both neural and distortion product otoacoustic emission (DPOAE) tuning may reflect a single mechanical filtering mechanism. Using the Duffing oscillator as a simple model for both neural and DPOAE tuning from the BP, two predictions can be made: [1] the characteristic frequency (CF) of neural tuning and the best frequency (BF) of DPOAE tuning will coincide and [2] the neural tuning curve and DPOAE-audiogram have a similar shape when the neural tuning curve is scaled by a factor of 4 along the y-axis. We recorded both neural tuning curves and DPOAE-audiograms from the BP of the leopard frog. These recordings show good agreement with the model predictions when the stimulus tones are related by relatively small stimulus frequency ratios. For larger stimulus frequency ratios, DPOAE recordings clearly deviate from model predictions. These differences are most likely caused by the oversimplified representation of the frog BP by the model.

Acoustic Stimulation↗

PubMed2005

Characteristics of distortion product otoacoustic emissions in the frog from L1,L2 maps.

For a given set of stimulus frequencies (f1 ,f2), the level of distortion product otoacoustic emissions (DPOAEs) varies with the levels of the stimulus tones. By variation of the stimulus levels, L1,L2-maps for DPOAEs can be constructed. Here, we report on L1 ,L2-maps for DPOAEs from the frog ear. In general, these maps were similar to those obtained from the mammalian cochlea. We found a conspicuous difference between the equal-level contour lines for low-level and high-level DPOAEs, which could be modeled by a saturating and an expansive nonlinearity, respectively. The transition from the high-level to the low-level response was accompanied by a DPOAE phase-change, which increased from 0 to pi rad with increasing frequency. These results suggest that in the frog low-level and high-level DPOAEs are generated by separate nonlinear mechanisms. Also, there was a conspicuous difference in the growth of the low-level emissions from the two anuran auditory papillae. In the basilar papilla, this growth was expansive for the lowest stimulus levels and saturated for intermediate levels. This is consistent with the behavior of a Boltzman nonlinearity. In the amphibian papilla this growth was compressive, suggesting the additional effect of a compressive amplification mechanism on the generation of DPOAEs.

Acoustic Stimulation↗

PubMed2005

Delays of stimulus-frequency otoacoustic emissions and cochlear vibrations contradict the theory of coherent reflection filtering.

When stimulated by tones, the ear appears to emit tones of its own, stimulus-frequency otoacoustic emissions (SFOAEs). SFOAEs were measured in 17 chinchillas and their group delays were compared with a place map of basilar-membrane vibration group delays measured at the characteristic frequency. The map is based on Wiener-kernel analysis of responses to noise of auditory-nerve fibers corroborated by measurements of vibrations at several basilar-membrane sites. SFOAE group delays were similar to, or shorter than, basilar-membrane group delays for frequencies >4 kHz and <4 kHz, respectively. Such short delays contradict the generally accepted "theory of coherent reflection filtering" [Zweig and Shera, J. Acoust. Soc. Am. 98, 2018-2047 (1995)], which predicts that the group delays of SFOAEs evoked by low-level tones approximately equal twice the basilar-membrane group delays. The results for frequencies higher than 4 kHz are compatible with hypotheses of SFOAE propagation to the stapes via acoustic waves or fluid coupling, or via reverse basilar membrane traveling waves with speeds corresponding to the signal-front delays, rather than the group delays, of the forward waves. The results for frequencies lower than 4 kHz cannot be explained by hypotheses based on waves propagating to and from their characteristic places in the cochlea.

Acoustic Stimulation↗

PubMed2004

Level dependence of distortion product otoacoustic emissions in the leopard frog, Rana pipiens pipiens.

The inner ear of frogs holds two papillae specialized in detecting airborne sound, the amphibian papilla (AP) and the basilar papilla (BP). We measured input-output (I/O) curves of distortion product otoacoustic emissions (DPOAEs) from both papillae, and compared their properties. As in other vertebrates, DPOAE I/O curves showed two distinct segments, separated by a notch or kneepoint. The slope of the low-level segment was conspicuously different between the AP and the BP. For DPOAE I/O curves from the AP, slopes were < or = 1 dB/dB, similar to what is found in mammals, birds and some lizards. For DPOAE I/O curves from the BP these slopes were much steeper (approximately 2 dB/dB). Slopes found at high stimulus levels were similar in the AP and the BP (approximately 2 dB/dB). This quantitative difference between the low-level slopes for DPOAEs from the AP and the BP may signify the involvement of different mechanisms in low-level DPOAE generation for the two papillae, respectively.

Acoustic Stimulation↗

PubMed2004

New variation on the derivation of spectro-temporal receptive fields for primary auditory afferent axons.

The spectro-temporal receptive field [Hear. Res 5 (1981) 147; IEEE Trans BME 15 (1993) 177] provides an explicit image of the spectral and temporal aspects of the responsiveness of a primary auditory afferent axon. It exhibits the net effects of the competition between excitatory and inhibitory (or suppressive) phenomena. In this paper, we introduce a method for derivation of the spectro-temporal receptive field directly from a second-order Wiener kernel (produced by second-order reverse correlation between spike responses and broad-band white-noise stimulus); and we expand the concept of the spectro-temporal receptive field by applying the new method not only to the second-order kernel itself, but also to its excitatory and inhibitory subkernels. This produces separate spectro-temporal images of the excitatory and inhibitory phenomena putatively underlying the competition. Applied, in simulations, to models with known underlying excitatory and suppressive tuning and timing properties, the method successfully extracted a faithful image of those properties for excitation and one for inhibition. Applied to three auditory axons from the frog, it produced images consistent with previously published physiology.

Animals↗

PubMed2003

Brain activity during auditory backward and simultaneous masking tasks.

Normal-hearing adult subjects performed a simultaneous and a backward auditory masking task, while their brain activity was recorded using functional magnetic resonance imaging. No differences between these tasks were observed in the auditory brain regions on the superior temporal lobes. Brain activity was larger for simultaneous than backward masking in the left inferior parietal lobe, the left inferior frontal cortex, the posterior cingulate cortex, and the cerebellum. In contrast, backward masking gave more activation in the left and right anterior temporal poles, and the anterior cingulate cortex. Apparently, backward and simultaneous masking tasks activate different auditory processing streams and require different cognitive brain resources.

Acoustic Stimulation↗

PubMed2003

New variations on the derivation of spectro-temporal receptive fields for primary auditory afferent axons.

Acoustic Stimulation↗

PubMed2003

Spectrotemporal features of the auditory cortex: the activation in response to dynamic ripples.

Functional MRI was used to investigate the characteristics of the human cerebral response to dynamic ripples. Dynamic ripples are sound stimuli containing regular spectrotemporal modulations, which are of major importance in speech processing; however, in contrast to speech, dynamic ripples can be characterized fully by a limited number of parameters. Extensive activation consisting of multiple separate regions was found bilaterally in the auditory cortex, particularly along the Heschl's gyri. This agrees with the presence of a structural cortical subdivision into functional fields. The level and the extent of activation were measured and correlated highly (R(2) = 0.97). Both measures depended strongly on the spectral density, temporal frequency, and amplitude of the modulations and matched the perceptual discernibility of the spectrotemporal modulations. The largest responses occurred for parameter values near the optimal human sensitivity. The drift direction of the modulations did not influence the activation. No quantitative differences were found between the two hemispheres. Average brain activation levels proved to be separable with regard to the spectral density and temporal frequency of the modulations. Topographic mappings of the modulation density and frequency onto the cortical surface were shown, approximately in posterolateral-to-anteromedial and lateral-to-medial directions, respectively. Posterolateral regions were most sensitive to spectrotemporal features at a scale similar to phonemes. Anteromedial regions, however, were also relatively sensitive to smaller scale acoustic features. This spatially dependent sensitivity suggests a functional topographic and hierarchical organization of the auditory cortex.

Acoustic Stimulation↗

PubMed2003

Physiological vulnerability of distortion product otoacoustic emissions from the amphibian ear.

The physiological vulnerability of distortion product otoacoustic emissions (DPOAEs) was investigated in the leopard frog, Rana pipiens pipiens. For each frog, DPOAEs were recorded from the amphibian and the basilar papillae. Measurements were taken before and after either the arrest of oxygen supply due to cardioectomy, or the destruction of the central nervous system (CNS). DPOAEs in response to high-level stimuli (> 75 dB SPL) were rather robust to these insults during the first two hours post surgery. In contrast, DPOAE amplitudes in response to low-level stimuli (< 75 dB SPL) decreased significantly. On average, low-level emissions from the amphibian papilla disappeared within 6 min for cardioectomy, and after 13 min for CNS destruction. In the basilar papilla, low-level DPOAEs disappeared more slowly: on average after 34 min following cardioectomy, and after 58 min for CNS destruction. The difference in physiological vulnerability between low- and high-level emissions is similar to that in mammals and a lizard. The difference between the DPOAE decay rate of the frog's amphibian and basilar papillae suggests important differences between the hearing mechanisms of the papillae.

Acoustic Stimulation↗