Biomedical subjects

Rudolf Rübsamen

Publications and source records attributed to Rudolf Rübsamen.

13 recordsLinked to original sources

PubMed2006

Mismatch negativity on the cone of confusion.

Localization of sounds by the auditory system is based on the analysis of three sources of information: interaural level differences (ILD, caused by an attenuation of the sound as it travels to the more distant ear), interaural time differences (ITD, caused by the additional amount of time it takes for the sound to arrive at the more distant ear), and spectral cues (caused by direction-specific spectral filter properties of the pinnae). Although in a number of psychophysiological studies cortical processes of ITD and ILD analysis were investigated, there is hitherto no evidence on the cortical processing of spectral cues for sound localization. The objective of the present experiment was to test whether it is possible to observe electrophysiological correlates of sound localization based on spectral cues. In an auditory oddball experiment, 80 ms of broadband noise from varying free field locations were presented to inattentive participants. Mismatch negativities (MMNs) were observed for pairs of standards and location deviants located symmetrically with respect to the interaural axis. As interaural time and level differences are identical for such pairs of sounds, the observed MMNs most likely reflect cognitive processes of sound localization utilizing the spectral filter properties of the pinnae. MMN latencies suggest that sound localization based on spectral cues is slower than ITD- or ILD-based localization.

Acoustic Stimulation↗

PubMed2006

Hemispheric asymmetry for auditory processing in the human auditory brain stem, thalamus, and cortex.

We report evidence for a context- and not stimulus-dependent functional asymmetry in the left and right human auditory midbrain, thalamus, and cortex in response to monaural sounds. Neural activity elicited by left- and right-ear stimulation was measured simultaneously in the cochlear nuclei, inferior colliculi (ICs), medial geniculate bodies (MGBs), and auditory cortices (ACs) in 2 functional magnetic resonance imaging experiments. In experiment 1, pulsed noise was presented monaurally to either ear, or binaurally, simulating a moving sound source. In experiment 2, only monaural sounds were presented. The results show a modulation of the neural responses to monaural sounds by the presence of binaural sounds at a time scale of tens of seconds: In the absence of binaural stimulation, the left and right ICs, MGBs, and ACs responded stronger to stimulation of the contralateral ear. When blocks of binaural stimuli were interspersed in the sound sequence, the contralateral preference vanished in those structures in the right hemisphere. The resulting hemispheric asymmetry was similar to the asymmetry demonstrated for spatial sound processing. Taken together, the data demonstrate that functional asymmetries in auditory processing are modulated by context. The observed long time constant suggests that this effect results from a "top-down" mechanism.

Acoustic Stimulation↗

PubMed2005

Hierarchical processing of sound location and motion in the human brainstem and planum temporale.

Horizontal sound localization relies on the extraction of binaural acoustic cues by integration of the signals from the two ears at the level of the brainstem. The present experiment was aimed at detecting the sites of binaural integration in the human brainstem using functional magnetic resonance imaging and a binaural difference paradigm, in which the responses to binaural sounds were compared with the sum of the responses to the corresponding monaural sounds. The experiment also included a moving sound condition, which was contrasted against a spectrally and energetically matched stationary sound condition to assess which of the structures that are involved in general binaural processing are specifically specialized in motion processing. The binaural difference contrast revealed a substantial binaural response suppression in the inferior colliculus in the midbrain, the medial geniculate body in the thalamus and the primary auditory cortex. The effect appears to reflect an actual reduction of the underlying activity, probably brought about by binaural inhibition or refractoriness at the level of the superior olivary complex. Whereas all structures up to and including the primary auditory cortex were activated as strongly by the stationary as by the moving sounds, non-primary auditory fields in the planum temporale responded selectively to the moving sounds. These results suggest a hierarchical organization of auditory spatial processing in which the general analysis of binaural information begins as early as the brainstem, while the representation of dynamic binaural cues relies on non-primary auditory fields in the planum temporale.

Acoustic Stimulation↗

PubMed2005

Hemispheric asymmetry for spectral and temporal processing in the human antero-lateral auditory belt cortex.

The present study investigates the acoustic basis of the hemispheric asymmetry for the processing of speech and music. Experiments on this question ideally involve stimuli that are perceptually unrelated to speech and music, but contain acoustic characteristics of both. Stimuli in previous studies were derived from speech samples or tonal sequences. Here we introduce a new class of noise-like sound stimuli with no resemblance of speech or music that permit independent parametric variation of spectral and temporal acoustic complexity. Using these stimuli in a functional MRI experiment, we test the hypothesis of a hemispheric asymmetry for the processing of spectral and temporal sound structure by seeking cortical areas in which the blood oxygen level dependent (BOLD) signal covaries with the number of simultaneous spectral components (spectral complexity) or the temporal modulation rate (temporal complexity) of the stimuli. BOLD-responses from the left and right Heschl's gyrus (HG) and part of the right superior temporal gyrus covaried with the spectral parameter, whereas covariation analysis for the temporal parameter highlighted an area on the left superior temporal gyrus. The portion of superior temporal gyrus in which asymmetrical responses are apparent corresponds to the antero-lateral auditory belt cortex, which has been implicated with spectral integration in animal studies. Our results support a similar function of the anterior auditory belt in humans. The findings indicate that asymmetrical processing of complex sounds in the cerebral hemispheres does not depend on semantic, but rather on acoustic stimulus characteristics.

Acoustic Stimulation↗

PubMed2005

Spectral and temporal processing in the human auditory cortex--revisited.

We use novel noise-like sound stimuli to identify cortical areas in which the functional magnetic resonance signal covaries with spectral and temporal acoustic complexity. The results support a model of hemispheric functional asymmetry for fine-grained spectral and fast temporal processing.

Acoustic Stimulation↗

PubMed2004

Representation of interaural temporal information from left and right auditory space in the human planum temporale and inferior parietal lobe.

The localization of low-frequency sounds mainly relies on the processing of microsecond temporal disparities between the ears, since low frequencies produce little or no interaural energy differences. The overall auditory cortical response to low-frequency sounds is largely symmetrical between the two hemispheres, even when the sounds are lateralized. However, the effects of unilateral lesions in the superior temporal cortex suggest that the spatial information mediated by lateralized sounds is distributed asymmetrically across the hemispheres. This paper describes a functional magnetic resonance imaging experiment, which shows that the interaural temporal processing of lateralized sounds produces an enhanced response in the contralateral planum temporale (PT). The response is stronger and extends further into adjacent regions of the inferior parietal lobe (IPL) when the sound is moving than when it is stationary. This suggests that the interaural temporal information mediated by lateralized sounds is projected along a posterior pathway comprising the PT and IPL of the respective contralateral hemisphere. The differential responses to moving sounds further revealed that the left hemisphere responded predominantly to sound movement within the right hemifield, whereas the right hemisphere responded to sound movement in both hemifields. This rightward asymmetry parallels the asymmetry associated with the allocation of visuo-spatial attention and may underlie unilateral auditory neglect phenomena.

Adult↗

PubMed2003

Decreased temporal precision of auditory signaling in Kcna1-null mice: an electrophysiological study in vivo.

The voltage-gated potassium (Kv) channel subunit Kv1.1, encoded by the Kcna1 gene, is expressed strongly in the ventral cochlear nucleus (VCN) and the medial nucleus of the trapezoid body (MNTB) of the auditory pathway. To examine the contribution of the Kv1.1 subunit to the processing of auditory information, in vivo single-unit recordings were made from VCN neurons (bushy cells), axonal endings of bushy cells at MNTB cells (calyces of Held), and MNTB neurons of Kcna1-null (-/-) mice and littermate control (+/+) mice. Thresholds and spontaneous firing rates of VCN and MNTB neurons were not different between genotypes. At higher sound intensities, however, evoked firing rates of VCN and MNTB neurons were significantly lower in -/- mice than +/+ mice. The SD of the first-spike latency (jitter) was increased in VCN neurons, calyces, and MNTB neurons of -/- mice compared with +/+ controls. Comparison along the ascending pathway suggests that the increased jitter found in -/- MNTB responses arises mostly in the axons of VCN bushy cells and/or their calyceal terminals rather than in the MNTB neurons themselves. At high rates of sinusoidal amplitude modulations, -/- MNTB neurons maintained high vector strength values but discharged on significantly fewer cycles of the amplitude-modulated stimulus than +/+ MNTB neurons. These results indicate that in Kcna1-null mice the absence of the Kv1.1 subunit results in a loss of temporal fidelity (increased jitter) and the failure to follow high-frequency amplitude-modulated sound stimulation in vivo.

Acoustic Stimulation↗

PubMed2003

Inharmonicity detection. Effects of age and contralateral distractor sounds.

Detection of mistuned partials in otherwise harmonic complex tones was investigated in naïve subjects of three different age groups. Signals were presented at constant sensation level to compensate for differences in hearing sensitivity and to specifically examine age-related changes in inharmonicity perception. Performance was measured under two conditions, monaural signal presentation and dichotic signal-noise presentation, with the latter aiming at the influence of contralateral distractor sounds. Stimuli were complex tones with ten harmonics and 125-Hz fundamental frequency. Mistuning detection was measured for the first, second, fourth, and eighth harmonic. In a three-interval, three-alternative forced-choice procedure, subjects were required to distinguish a complex tone containing one mistuned partial from two reference tones, with all partials at their harmonic frequencies. Thresholds were measured as the amount of frequency shift necessary for the mistuning to be detected. Performance deteriorated moderately with age for the two higher partials tested, but not for the lower ones. Thresholds for dichotic signal/noise presentation did not differ significantly from monaural ones in any of the age groups. Results are discussed in relation to hypotheses of harmonicity perception in auditory scene analysis and with respect to the investigation of patients suffering form respective deficits due to acquired brain lesions.

Adult↗

PubMed2003

Characterization of the human superior olivary complex by calcium binding proteins and neurofilament H (SMI-32).

This study provides a morphologic characterization of the human superior olivary complex as revealed by immunohistochemistry by using antibodies against the calcium binding proteins parvalbumin, calbindin, calretinin, and the nonphosphorylated neurofilament H SMI-32. By combining these markers, it was possible to establish the neuronal architecture and details of the morphologic organization (including axonal terminals) of the different nuclei. The medial superior olivary nucleus is formed by a sheet of parallel-oriented cells. A clear segregation of axon terminals was noticed on the medially and laterally oriented dendrites of the mostly bipolar neurons. The lateral superior olivary nucleus lacked a distinct nuclear shape but was formed by several patches of rather irregularly arranged neurons. Calretinin or parvalbumin immunoreactive afferent terminals were observed which contacted somata or dendrites of these neurons. The immunolabeling also revealed the boundaries of the dorsal periolivary nucleus and morphologic detail of its neurons. A coherent nuclear structure that could be addressed as the medial nucleus of the trapezoid body was not identified by any single one or by combinations of the markers used. The data were also used to establish a three-dimensional-reconstruction of the three major subnuclei of the superior olivary complex. The results are discussed with respect to the possible role of the superior olivary complex in the processing of spatial acoustic information in the azimuthal plane.

Calbindin 2↗

PubMed2002

Interaction of excitation and inhibition in anteroventral cochlear nucleus neurons that receive large endbulb synaptic endings.

Spherical bushy cells (SBCs) of the anteroventral cochlear nucleus (AVCN) receive their main excitatory input from auditory nerve fibers (ANFs) through large synapses, endbulbs of Held. These cells are also the target of inhibitory inputs whose function is not well understood. The present study examines the role of inhibition in the encoding of low-frequency sounds in the gerbil's AVCN. The presynaptic action potentials of endbulb terminals and postsynaptic action potentials of SBCs were monitored simultaneously in extracellular single-unit recordings in vivo. An input-output analysis of presynaptic and postsynaptic activity was performed for both spontaneous and acoustically driven activity. Two-tone stimulation and neuropharmacological experiments allowed the effects of neuronal inhibition and cochlear suppression on SBC activity to be distinguished. Ninety-one percent of SBCs showed significant neuronal inhibition. Inhibitory sidebands enclosed the high- or low-frequency, or both, sides of the excitatory areas of these units; this was reflected as a presynaptic to postsynaptic increase in frequency selectivity of up to one octave. Inhibition also affected the level-dependent responses at the characteristic frequency. Although in all units the presynaptic recordings showed monotonic rate-level functions, this was the case in only half of the postsynaptic recordings. In the other half of SBCs, postsynaptic inhibitory areas overlapped the excitatory areas, resulting in nonmonotonic rate-level functions. The results demonstrate that the sound-evoked spike activity of SBCs reflects the integration of acoustically driven excitatory and inhibitory input. The inhibition specifically affects the processing of the spectral, temporal, and intensity cues of acoustic signals.

Acoustic Stimulation↗

PubMed2002

The medial nucleus of the trapezoid body in the gerbil is more than a relay: comparison of pre- and postsynaptic activity.

The medial nucleus of the trapezoid body (MNTB) plays an important role in the processing of interaural intensity differences, a feature that is critical for the localization of sound sources. It is generally believed that the MNTB functions primarily as a passive relay in converting excitatory input originating from the contralateral cochlear nucleus (CN) into an inhibitory input to the ipsilateral lateral superior olive. However, studies showing that the MNTB itself is also the target of inhibitory input suggest that the MNTB may serve more than a sign-converting function. To examine the fidelity of signal transmission at the CN-MNTB synapse, presynaptic calyceal potentials ("prepotentials"), reflecting the excitatory input to the MNTB neuron, and postsynaptic action potentials were simultaneously monitored with the same electrode during in vivo extracellular recordings from the gerbil's MNTB. Presynaptic activity differed from postsynaptic activity in several respects: (1) Spontaneous and sound-evoked discharge rates were greater presynaptically than postsynaptically. (2) Frequency tuning was sharper postsynaptically than presynaptically. (3) Calyceal terminals and MNTB neurons both showed phasic-tonic response patterns to tonal stimulation, but the duration of the onset response and the level of the tonic component were reduced postsynaptically. (4) Phase-locking to sound frequencies up to 1 kHz was greater postsynaptically than presynaptically. (5) The rate-intensity characteristics of pre- and postsynaptic activities differed significantly from each other in half of the MNTB neurons. To test the hypothesis that acoustically evoked inhibition of MNTB neurons contributed to the relatively lower levels of postsynaptic discharge, two-tone stimulation was applied, wherein the response to one tone-burst, set at the neuron's characteristic frequency, can be reduced by addition of a second "inhibitory" tone. The inhibitory tone caused a much larger reduction in post- than in presynaptic activity, indicating an acoustically evoked inhibitory influence directly on MNTB units. These findings show that transmission at the CN-MNTB synapse does not occur in a fixed one-to-one manner and that the response of MNTB neurons reflects the integration of their excitatory and inhibitory inputs.

Action Potentials↗

PubMed2002

Is it tonotopy after all?

In this functional MRI study the frequency-dependent localization of acoustically evoked BOLD responses within the human auditory cortex was investigated. A blocked design was employed, consisting of periods of tonal stimulation (random frequency modulations with center frequencies 0.25, 0.5, 4.0, and 8.0 kHz) and resting periods during which only the ambient scanner noise was audible. Multiple frequency-dependent activation sites were reliably demonstrated on the surface of the auditory cortex. The individual gyral pattern of the superior temporal plane (STP), especially the anatomy of Heschl's gyrus (HG), was found to be the major source of interindividual variability. Considering this variability by tracking the frequency responsiveness to the four stimulus frequencies along individual Heschl's gyri yielded medio-lateral gradients of responsiveness to high frequencies medially and low frequencies laterally. It is, however, argued that with regard to the results of electrophysiological and cytoarchitectonical studies in humans and in nonhuman primates, the multiple frequency-dependent activation sites found in the present study as well as in other recent fMRI investigations are no direct indication of tonotopic organization of cytoarchitectonical areas. An alternative interpretation is that the activation sites correspond to different cortical fields, the topological organization of which cannot be resolved with the current spatial resolution of fMRI. In this notion, the detected frequency selectivity of different cortical areas arises from an excess of neurons engaged in the processing of different acoustic features, which are associated with different frequency bands. Differences in the response properties of medial compared to lateral and frontal compared to occipital portions of HG strongly support this notion.

Adult↗

PubMed2002

Electrophysiological characterization of the superior paraolivary nucleus in the Mongolian gerbil.

The superior paraolivary nucleus (SPN) of the superior olivary complex (SOC) though morphologically well described, has not been characterized physiologically. Here we report the basic response properties of SPN units acquired with extracellular recording techniques under monaural acoustic stimulation in the Mongolian gerbil. Poststimulus-time histograms corresponded to those described earlier for the cat's cochlear nucleus (onset, chopper, primary-like), and partly to those previously acquired in other SOC nuclei (tonic, off/rebound). Two-thirds of the units responded solely to contralateral stimulation (40% excitatory [E], 19% inhibitory [I], 6% mixed [EI]). Most of the remainder responded equally to stimulation from either ear (18% I.I, 9% E.E). Overall, the monaural contralateral input was more effective than the ipsilateral and bilateral input. Characteristic frequencies and response areas covered the entire hearing range of the gerbil and the units mostly showed broad frequency-tuning. In combination, these properties suggest that the SPN might be a constituent of an afferent pathway encoding stimulus features across broad frequency ranges.

Acoustic Stimulation↗