Biomedical subjects

Marc Schönwiesner

Publications and source records attributed to Marc Schönwiesner.

9 recordsLinked to original sources

PubMed2006

Heschl's gyrus, posterior superior temporal gyrus, and mid-ventrolateral prefrontal cortex have different roles in the detection of acoustic changes.

A part of the auditory system automatically detects changes in the acoustic environment. This preattentional process has been studied extensively, yet its cerebral origins have not been determined with sufficient accuracy to allow comparison to established anatomical and functional parcellations. Here we used event-related functional MRI and EEG in a parametric experimental design to determine the cortical areas in individual brains that participate in the detection of acoustic changes. Our results suggest that automatic change processing consists of at least three stages: initial detection in the primary auditory cortex, detailed analysis in the posterior superior temporal gyrus and planum temporale, and judgment of sufficient novelty for the allocation of attentional resources in the mid-ventrolateral prefrontal cortex.

Acoustic Stimulation↗

PubMed2006

Cortical response to auditory motion suggests an asymmetry in the reliance on inter-hemispheric connections between the left and right auditory cortices.

The aim of the current study was to measure the brain's response to auditory motion using electroencephalography (EEG) to gain insight into the mechanisms by which hemispheric lateralization for auditory spatial processing is established in the human brain. The onset of left- or rightward motion in an otherwise continuous sound was found to elicit a large response, which appeared to arise from higher-level nonprimary auditory areas. This motion onset response was strongly lateralized to the hemisphere contralateral to the direction of motion. The response latencies suggest that the ipsilateral response to the leftward motion was produced by indirect callosal projections from the opposite hemisphere, whereas the ipsilateral response to the rightward motion seemed to receive contributions from direct thalamocortical projections. These results suggest an asymmetry in the reliance on inter-hemispheric projections between the left and right auditory cortices for auditory spatial processing.

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↗

PubMed2006

Vowel processing evokes a large sustained response anterior to primary auditory cortex.

The present study uses electroencephalography (EEG) and a new stimulation paradigm, the 'continuous stimulation paradigm', to investigate the neural correlate of phonological processing in human auditory cortex. Evoked responses were recorded to stimuli consisting of a control sound (1000 ms) immediately followed by a test sound (150 ms). On half of the trials, the control sound was a noise and the test sound a vowel; to control for unavoidable effects of spectral change at the transition, the roles of the stimuli were reversed on the other half of the trials. The acoustical properties of the vowel and noise sounds were carefully matched to isolate the response specific to phonological processing. As the unspecific response to sound energy onset has subsided by the transition to the test sound, we hypothesized that the transition response from a noise to a vowel would reveal vowel-specific processing. Contrary to this expectation, however, the most striking difference between vowel and noise processing was a large, vertex-negative sustained response to the vowel control sound, which had a fast onset (30-50 ms) and remained constant throughout presentation of the vowel. The vowel-specific response was isolated using a subtraction technique analogous to that commonly applied in neuroimaging studies. This similarity in analysis methodology enabled close comparison of the EEG data collected in the present study with relevant functional magnetic resonance (fMRI) literature. Dipole source analysis revealed the vowel-specific component to be located anterior and inferior to primary auditory cortex, consistent with previous data investigating speech processing with fMRI.

Adult↗

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↗

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↗