Brain responses to auditory and visual stimulus offset: shared representations of temporal edges.
ABSTRACT Edges are crucial for the formation of coherent objects from sequential sensory inputs within a single modality. Moreover, temporally coincident boundaries of perceptual objects across different sensory modalities facilitate crossmodal integration. Here, we used functional magnetic resonance imaging in order to examine the neural basis of temporal edge detection across modalities. Onsets of sensory inputs are not only related to the detection of an edge but also to the processing of novel sensory inputs. Thus, we used transitions from input to rest (offsets) as convenient stimuli for studying the neural underpinnings of visual and acoustic edge detection per se. We found, besides modality-specific patterns, shared visual and auditory offset-related activity in the superior temporal sulcus and insula of the right hemisphere. Our data suggest that right hemispheric regions known to be involved in multisensory processing are crucial for detection of edges in the temporal domain across both visual and auditory modalities. This operation is likely to facilitate cross-modal object feature binding based on temporal coincidence.
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ABSTRACT: Training can change the functional and structural organization of the brain, and animal models demonstrate that the hippocampus formation is particularly susceptible to training-related neuroplasticity. In humans, however, direct evidence for functional plasticity of the adult hippocampus induced by training is still missing. Here, we used musicians' brains as a model to test for plastic capabilities of the adult human hippocampus. By using functional magnetic resonance imaging optimized for the investigation of auditory processing, we examined brain responses induced by temporal novelty in otherwise isochronous sound patterns in musicians and musical laypersons, since the hippocampus has been suggested previously to be crucially involved in various forms of novelty detection. In the first cross-sectional experiment, we identified enhanced neural responses to temporal novelty in the anterior left hippocampus of professional musicians, pointing to expertise-related differences in hippocampal processing. In the second experiment, we evaluated neural responses to acoustic temporal novelty in a longitudinal approach to disentangle training-related changes from predispositional factors. For this purpose, we examined an independent sample of music academy students before and after two semesters of intensive aural skills training. After this training period, hippocampal responses to temporal novelty in sounds were enhanced in musical students, and statistical interaction analysis of brain activity changes over time suggests training rather than predisposition effects. Thus, our results provide direct evidence for functional changes of the adult hippocampus in humans related to musical training.Journal of Neuroscience 01/2010; 30(4):1377-84. · 6.91 Impact Factor
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ABSTRACT: Assessing the size of objects rapidly and accurately clearly has survival value. A central multisensory module for subjective magnitude assessment is therefore highly likely, suggested by psychophysical studies, and proposed on theoretical grounds. Given that pain perception is fundamentally an assessment of stimulus intensity, it must necessarily engage such a central module. Accordingly, we compared functional magnetic resonance imaging (fMRI) activity of pain magnitude ratings to matched visual magnitude ratings in 14 subjects. We show that brain activations segregate into two groups, one preferentially activated for pain and another equally activated for both visual and pain magnitude ratings. The properties of regions in the first group were consistent with encoding nociception, whereas those in the second group with attention and task control. Insular cortex responses similarly segregated to a pain-specific area and an area (extending to the lateral prefrontal cortex) conjointly representing perceived magnitudes for pain and vision. These two insular areas were differentiated by their relationship to task variance, ability to encode perceived magnitudes for each stimulus epoch, temporal delay differences, and brain intrinsic functional connectivity. In a second group of subjects (n=11) we contrasted diffusion tensor imaging-based white matter connectivity for these two insular areas and observed anatomical connectivity closely corresponding to the functional connectivity identified with fMRI. These results demonstrate that pain perception is due to the transformation of nociceptive representation into subjective magnitude assessment within the insula. Moreover, we argue that we have identified a multisensory cortical area for "how much" complementary and analogous to the "where" and "what" as described for central visual processing.Journal of Neurophysiology 01/2009; 101(2):875-87. · 3.30 Impact Factor
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ABSTRACT: Multisensory events in our natural environment unfold at multiple temporal scales over extended periods of time. This functional magnetic resonance imaging study investigated whether the brain uses transient (onset, offset) or sustained temporal codes to effectively integrate incoming visual and auditory signals within the cortical hierarchy. Subjects were presented with 1) velocity-modulated radial motion, 2) amplitude-modulated sound, or 3) an in phase combination of both in blocks of variable durations to dissociate transient and sustained blood oxygen level-dependent responses. Audiovisual interactions emerged primarily for transient onset and offset responses highlighting the importance of rapid stimulus transitions for multisensory integration. Strikingly, audiovisual interactions for onset and offset transients were dissociable at the functional and anatomical level. Low-level sensory areas integrated audiovisual inputs at stimulus onset in a superadditive fashion to enhance stimulus salience. In contrast, higher order association areas showed subadditive integration profiles at stimulus offset possibly reflecting the formation of higher order representations. In conclusion, multisensory integration emerges at multiple levels of the cortical hierarchy using different temporal codes and integration profiles. From a methodological perspective, these results highlight the limitations of conventional event related or block designs that cannot characterize these rich dynamics of audiovisual integration.Cerebral Cortex 04/2011; 21(4):920-31. · 8.31 Impact Factor