Audiovisual structural connectivity in musicians and non-musicians: a cortical thickness and diffusion tensor imaging study.

Our sensory systems provide complementary information about the multimodal objects and events that are the target of perception in everyday life. Professional musicians' specialization in the auditory domain is reflected in the morphology of their brains, which has distinctive characteristics, particularly in areas related to auditory and audio-motor activity. Here, we combined diffusion tensor imaging (DTI) with a behavioral measure of visually induced gain in pitch discrimination, and we used measures of cortical thickness (CT) correlations to assess how auditory specialization and musical expertise are reflected in the structural architecture of white and grey matter relevant to audiovisual processing. Across all participants (n = 45), we found a correlation (p < 0.001) between reliance on visual cues in pitch discrimination and the fractional anisotropy (FA) in the left inferior fronto-occipital fasciculus (IFOF), a structure connecting visual and auditory brain areas. Group analyses also revealed greater cortical thickness correlation between visual and auditory areas in non-musicians (n = 28) compared to musicians (n = 17), possibly reflecting musicians' auditory specialization (FDR < 10%). Our results corroborate and expand current knowledge of functional specialization with a specific focus on audition, and highlight the fact that perception is essentially multimodal while uni-sensory processing is a specialized task.

Correction to: Visually induced gains in pitch discrimination: Linking audio-visual processing with auditory abilities.

During copy-editing, the y-axes of Fig. 2 (top) and Fig. 3 (top) were erroneously labelled mean BCG (d') in the version of the paper published as Online First. The correct label is meanCE (d').

Visually induced gains in pitch discrimination: Linking audio-visual processing with auditory abilities.

Perception is fundamentally a multisensory experience. The principle of inverse effectiveness (PoIE) states how the multisensory gain is maximal when responses to the unisensory constituents of the stimuli are weak. It is one of the basic principles underlying multisensory processing of spatiotemporally corresponding crossmodal stimuli that are well established at behavioral as well as neural levels. It is not yet clear, however, how modality-specific stimulus features influence discrimination of subtle changes in a crossmodally corresponding feature belonging to another modality. Here, we tested the hypothesis that reliance on visual cues to pitch discrimination follow the PoIE at the interindividual level (i.e., varies with varying levels of auditory-only pitch discrimination abilities). Using an oddball pitch discrimination task, we measured the effect of varying visually perceived vertical position in participants exhibiting a wide range of pitch discrimination abilities (i.e., musicians and nonmusicians). Visual cues significantly enhanced pitch discrimination as measured by the sensitivity index d', and more so in the crossmodally congruent than incongruent condition. The magnitude of gain caused by compatible visual cues was associated with individual pitch discrimination thresholds, as predicted by the PoIE. This was not the case for the magnitude of the congruence effect, which was unrelated to individual pitch discrimination thresholds, indicating that the pitch-height association is robust to variations in auditory skills. Our findings shed light on individual differences in multisensory processing by suggesting that relevant multisensory information that crucially aids some perceivers' performance may be of less importance to others, depending on their unisensory abilities.

Listen, learn, like! Dorsolateral prefrontal cortex involved in the mere exposure effect in music.

We used functional magnetic resonance imaging to investigate the neural basis of the mere exposure effect in music listening, which links previous exposure to liking. Prior to scanning, participants underwent a learning phase, where exposure to melodies was systematically varied. During scanning, participants rated liking for each melody and, later, their recognition of them. Participants showed learning effects, better recognising melodies heard more often. Melodies heard most often were most liked, consistent with the mere exposure effect. We found neural activations as a function of previous exposure in bilateral dorsolateral prefrontal and inferior parietal cortex, probably reflecting retrieval and working memory-related processes. This was despite the fact that the task during scanning was to judge liking, not recognition, thus suggesting that appreciation of music relies strongly on memory processes. Subjective liking per se caused differential activation in the left hemisphere, of the anterior insula, the caudate nucleus, and the putamen.

An investigation of brain processes supporting meditation.

Meditation is an ancient spiritual practice, which aims to still the fluctuations of the mind. We investigated meditation with fMRI in order to identify and characterise both the "neural switch" mechanism used in the voluntary shift from normal consciousness to meditation and the "threshold regulation mechanism" sustaining the meditative state. Thirty-one individuals with 1.5-25 years experience in meditation were scanned using a blocked on-off design with 45 s alternating epochs during the onset of respectively meditation and normal relaxation. Additionally, 21 subjects were scanned during 14.5 min of sustained meditation. The data were analysed with SPM and ICA. During the onset of meditation, activations were found bilaterally in the putamen and the supplementary motor cortex, while deactivations were found predominately in the right hemisphere, the precuneus, the posterior cingulum and the parieto-temporal area. During sustained meditation, SPM analysis revealed activation in the head of nucleus caudatus. Extensive deactivations were observed in white matter in the right hemisphere, i.e. mainly in the posterior occipito-parieto-temporal area and in the frontal lobes. ICA identified 38 components including known baseline-resting state components, one of which not only overlaps with the activated area revealed in the SPM analysis but extends further into frontal, temporal, parietal and limbic areas, and might presumably constitute a combination of frontoparietal and cinguloopercular task control systems. The identified component processes display varying degrees of correlation. We hypothesise that a proper characterisation of brain processes during meditation will require an operational definition of brain dynamics matching a stable state of mind.

Music in minor activates limbic structures: a relationship with dissonance?

Using functional magnetic resonance imaging, we contrasted major and minor mode melodies controlled for liking to study the neural basis of musical mode perception. To examine the influence of the larger dissonance in minor melodies on neural activation differences, we further introduced a strongly dissonant stimulus, in the form of a chromatic scale. Minor mode melodies were evaluated as sadder than major melodies, and in comparison they caused increased activity in limbic structures, namely left parahippocampal gyrus, bilateral ventral anterior cingulate, and in left medial prefrontal cortex. Dissonance explained some, but not all, of the heightened activity in the limbic structures when listening to minor mode music.