Selective auditory attention within naturalistic scenes modulates reactivity to speech sounds.

Rapid recognition and categorization of sounds are essential for humans and animals alike, both for understanding and reacting to our surroundings and for daily communication and social interaction. For humans, perception of speech sounds is of crucial importance. In real life, this task is complicated by the presence of a multitude of meaningful non-speech sounds. The present behavioural, magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) study was set out to address how attention to speech versus attention to natural non-speech sounds within complex auditory scenes influences cortical processing. The stimuli were superimpositions of spoken words and environmental sounds, with parametric variation of the speech-to-environmental sound intensity ratio. The participants' task was to detect a repetition in either the speech or the environmental sound. We found that specifically when participants attended to speech within the superimposed stimuli, higher speech-to-environmental sound ratios resulted in shorter sustained MEG responses and stronger BOLD fMRI signals especially in the left supratemporal auditory cortex and in improved behavioural performance. No such effects of speech-to-environmental sound ratio were observed when participants attended to the environmental sound part within the exact same stimuli. These findings suggest stronger saliency of speech compared with other meaningful sounds during processing of natural auditory scenes, likely linked to speech-specific top-down and bottom-up mechanisms activated during speech perception that are needed for tracking speech in real-life-like auditory environments.

Increased fronto-temporal connectivity by modified melody in real music.

In real music, the original melody may appear intact, with little elaboration only, or significantly modified. Since a melody is most easily perceived in music, hearing significantly modified melody may change a brain connectivity. Mozart KV 265 is comprised of a theme with an original melody of "Twinkle Twinkle Little Star" and its significant variations. We studied whether effective connectivity changes with significantly modified melody, between bilateral inferior frontal gyri (IFGs) and Heschl's gyri (HGs) using magnetoencephalography (MEG). Among the 12 connectivities, the connectivity from the left IFG to the right HG was consistently increased with significantly modified melody compared to the original melody in 2 separate sets of the same rhythmic pattern with different melody (p = 0.005 and 0.034, Bonferroni corrected). Our findings show that the modification of an original melody in a real music changes the brain connectivity.

Musical Expectations Enhance Auditory Cortical Processing in Musicians: A Magnetoencephalography Study.

The present study investigated the influence of musical expectations on auditory representations in musicians and non-musicians using magnetoencephalography (MEG). Neuroscientific studies have demonstrated that musical syntax is processed in the inferior frontal gyri, eliciting an early right anterior negativity (ERAN), and anatomical evidence has shown that interconnections occur between the frontal cortex and the belt and parabelt regions in the auditory cortex (AC). Therefore, we anticipated that musical expectations would mediate neural activities in the AC via an efferent pathway. To test this hypothesis, we measured the auditory-evoked fields (AEFs) of seven musicians and seven non-musicians while they were listening to a five-chord progression in which the expectancy of the third chord was manipulated (highly expected, less expected, and unexpected). The results revealed that highly expected chords elicited shorter N1m (negative AEF at approximately 100 ms) and P2m (positive AEF at approximately 200 ms) latencies and larger P2m amplitudes in the AC than less-expected and unexpected chords. The relations between P2m amplitudes/latencies and harmonic expectations were similar between the groups; however, musicians' results were more remarkable than those of non-musicians. These findings suggest that auditory cortical processing is enhanced by musical knowledge and long-term training in a top-down manner, which is reflected in shortened N1m and P2m latencies and enhanced P2m amplitudes in the AC.

Altered resting-state functional connectivity in patients with obsessive-compulsive disorder: A magnetoencephalography study.

Aberrant cortical-striatal-thalamic-cortical circuits have been implicated in the pathophysiology of obsessive-compulsive disorder (OCD). However, the neurobiological basis of OCD remains unclear. We compared patterns of functional connectivity in patients with OCD and in healthy controls using resting-state magnetoencephalography (MEG). Participants comprised 24 patients with OCD (21 men, 3 women) and 22 age- and sex-matched healthy controls (19 men, 3 women). Resting-state measurements were obtained over a 6-min period using a 152-channel whole-head MEG system. We examined group differences in oscillatory activity and distribution of functional cortical hubs based on the nodal centrality of phase-locking value (PLV) maps. Differences in resting-state functional connectivity were examined through PLV analysis in selected regions of interest based on these two findings. Patients with OCD demonstrated significantly lower delta band activity in the cortical regions of the limbic lobe, insula, orbitofrontal, and temporal regions, and theta band activity in the parietal lobe regions than healthy controls. Patients with OCD exhibited fewer functional hubs in the insula and orbitofrontal cortex and additional hubs in the cingulate and temporo-parietal regions. The OCD group exhibited significantly lower phase synchronization among the insula, orbitofrontal cortex, and cortical regions of the limbic lobe in all band frequencies, except in the delta band. Altered functional networks in the resting state may be associated with the pathophysiology of OCD. These MEG findings indicate that OCD is associated with decreased functional connectivity in terms of phase synchrony, particularly in the insula, orbitofrontal cortex, and cortical regions of the limbic lobe.

Melody effects on ERANm elicited by harmonic irregularity in musical syntax.

Recent studies have reported that early right anterior negativity (ERAN) and its magnetic counterpart (ERANm) are evoked by harmonic irregularity in Western tonal music; however, those studies did not control for differences of melody. Because melody and harmony have an interdependent relationship and because melody (in this study melody is represented by the highest voice part) in a chord sequence may dominate, there is controversy over whether ERAN (or ERANm) changes arise from melody or harmony differences. To separate the effects of melody differences and harmonic irregularity on ERANm responses, we designed two magnetoencephalography experiments and behavioral test. Participants were presented with three types of chord progression sequences (Expected, Intermediate, and Unexpected) with different harmonic regularities in which melody differences were or were not controlled. In the uncontrolled melody difference experiment, the unexpected chord elicited a significantly largest ERANm, but in the controlled melody difference experiment, the amplitude of the ERANm peak did not differ among the three conditions. However, ERANm peak latency was delayed more than that in the uncontrolled melody difference experiment. The behavioral results show the difference between the two experiments even if harmonic irregularity was discriminated in the uncontrolled melody difference experiment. In conclusion, our analysis reveals that there is a relationship between the effects of harmony and melody on ERANm. Hence, we suggest that a melody difference in a chord progression is largely responsible for the observed changes in ERANm, reaffirming that melody plays an important role in the processing of musical syntax.

Functional cortical hubs in the eyes-closed resting human brain from an electrophysiological perspective using magnetoencephalography.

It is not clear whether specific brain areas act as hubs in the eyes-closed (EC) resting state, which is an unconstrained state free from any passive or active tasks. Here, we used electrophysiological magnetoencephalography (MEG) signals to study functional cortical hubs in 88 participants. We identified several multispectral cortical hubs. Although cortical hubs vary slightly with different applied measures and frequency bands, the most consistent hubs were observed in the medial and posterior cingulate cortex, the left dorsolateral superior frontal cortex, and the left pole of the middle temporal cortex. Hubs were characterized as connector nodes integrating EC resting state functional networks. Hubs in the gamma band were more likely to include midline structures. Our results confirm the existence of multispectral cortical cores in EC resting state functional networks based on MEG and imply the existence of optimized functional networks in the resting brain.

Discrimination of timbre in early auditory responses of the human brain.

BACKGROUND: The issue of how differences in timbre are represented in the neural response still has not been well addressed, particularly with regard to the relevant brain mechanisms. Here we employ phasing and clipping of tones to produce auditory stimuli differing to describe the multidimensional nature of timbre. We investigated the auditory response and sensory gating as well, using by magnetoencephalography (MEG). METHODOLOGY/PRINCIPAL FINDINGS: Thirty-five healthy subjects without hearing deficit participated in the experiments. Two different or same tones in timbre were presented through conditioning (S1)-testing (S2) paradigm as a pair with an interval of 500 ms. As a result, the magnitudes of auditory M50 and M100 responses were different with timbre in both hemispheres. This result might support that timbre, at least by phasing and clipping, is discriminated in the auditory early processing. The second response in a pair affected by S1 in the consecutive stimuli occurred in M100 of the left hemisphere, whereas both M50 and M100 responses to S2 only in the right hemisphere reflected whether two stimuli in a pair were the same or not. Both M50 and M100 magnitudes were different with the presenting order (S1 vs. S2) for both same and different conditions in the both hemispheres. CONCLUSIONS/SIGNIFICANCES: Our results demonstrate that the auditory response depends on timbre characteristics. Moreover, it was revealed that the auditory sensory gating is determined not by the stimulus that directly evokes the response, but rather by whether or not the two stimuli are identical in timbre.

How reliable are the functional connectivity networks of MEG in resting states?

We investigated the reliability of nodal network metrics of functional connectivity (FC) networks of magnetoencephalography (MEG) covering the whole brain at the sensor level in the eyes-closed (EC) and eyes-open (EO) resting states. Mutual information (MI) was employed as a measure of FC between sensors in theta, alpha, beta, and gamma frequency bands of MEG signals. MI matrices were assessed with three nodal network metrics, i.e., nodal degree (Dnodal), nodal efficiency (Enodal), and betweenness centrality (normBC). Intraclass correlation (ICC) values were calculated as a measure of reliability. We observed that the test-retest reliabilities of the resting states ranged from a poor to good level depending on the bands and metrics used for defining the nodal centrality. The dominant alpha-band FC network changes were the salient features of the state-related FC changes. The FC networks in the EO resting state showed greater reliability when assessed by Dnodal (maximum mean ICC = 0.655) and Enodal (maximum mean ICC = 0.604) metrics. The gamma-band FC network was less reliable than the theta, alpha, and beta networks across the nodal network metrics. However, the sensor-wise ICC values for the nodal centrality metrics were not uniformly distributed, that is, some sensors had high reliability. This study provides a sense of how the nodal centralities of the human resting state MEG are distributed at the sensor level and how reliable they are. It also provides a fundamental scientific background for continued examination of the resting state of human MEG.