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We attempted to replicate a potential tinnitus biomarker in humans based on the Sensory Precision Integrative Model of Tinnitus called the Intensity Mismatch Asymmetry. A few advances on the design were also included, including tighter matching of participants for gender, and a control stimulus frequency of 1 kHz to investigate whether any differences between control and tinnitus groups are specific to the tinnitus frequency or domain-general. The expectation was that there would be asymmetry in the MMN responses between tinnitus and control groups at the tinnitus frequency, but not at the control frequency, where the tinnitus group would have larger, more negative responses to upward deviants than downward deviants, and the control group would have the opposite pattern or lack of a deviant direction effect. However, no significant group differences were found. There was a striking difference in response amplitude to control frequency stimuli compared to tinnitus frequency stimuli, which could be an intrinsic quality of responses to these frequencies or could reflect high frequency hearing loss in the sample. Additionally, the upward deviants elicited stronger MMN responses in both groups at tinnitus frequency, but not at the control frequency. Factors contributing to these discrepant results at the tinnitus frequency could include hyperacusis, attention, and wider contextual effects of other frequencies used in the experiment (i.e. the control frequency in other blocks).

IntroductionGenerative mechanisms of perception such as predictive coding are used to explain how the brain perceives the world; such mechanisms are often experimentally probed using “deviant” stimuli that violate established patterns (including mismatch negativity), which also elicit responses related to lower-level processes such as stimulus-specific adaptation. However, little is still known about brain responses that indicate the strength of sensory predictions or reinforcement of sensory representations. Repetition positivity (RP) is a positive polarity evoked potential that gradually increases with each repetition of a stimulus, and is thought to reflect progressive strengthening of auditory sensory memory and/or habituation to repetitive stimuli. The aim of this study was to compare RP that follows a change in stimulus frequency with that following a change in stimulus intensity, the latter having not previously been studied.MethodsWe used roving sequences of isochronous 5 kHz pure tones (300 ms duration, 300ms inter-stimulus interval), which changed in frequency by 1 kHz (Experiment 1) or in intensity by 12 dB (Experiment 2) after every 30 stimuli. All changes were roving, such that an increase would be followed by a decrease, and vice versa.ResultsEvent-related potentials recorded with EEG indicated that frequency changes in either direction were followed by RP, whilst only intensity increases were followed by RP, and only a weak visual trend toward RP was apparent for intensity decreases. Observed RP was best explained by a logarithmic function over successive stimuli.ConclusionsRP robustly follows increases, but not necessarily decreases, in stimulus intensity, which appears smaller in amplitude than that elicited by similarly salient frequency changes, and reaches a plateau sooner. These observations offer insight into how intensity is processed similarly yet differently to other sensory attributes in an adaptive or predictive coding framework, and might have future utility in the study of clinical conditions related to aberrant predictive mechanisms.

What determines how we move in the world? Motor neuroscience often focusses either on intrinsic rhythmical properties of motor circuits or extrinsic sensorimotor feedback loops. Here we show that the interplay of both intrinsic and extrinsic dynamics is required to explain the intermittency observed in continuous tracking movements. Using spatiotemporal perturbations in humans, we demonstrate that apparently discrete submovements made 2–3 times per second reflect constructive interference between motor errors and continuous feedback corrections that are filtered by intrinsic circuitry in the motor system. Local field potentials in monkey motor cortex revealed characteristic signatures of a Kalman filter, giving rise to both low-frequency cortical cycles during movement, and delta oscillations during sleep. We interpret these results within the framework of optimal feedback control, and suggest that the intrinsic rhythmicity of motor cortical networks reflects an internal model of external dynamics, which is used for state estimation during feedback-guided movement. Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter ).

MRI experiments have revealed how throat singers from Tuva produce their characteristic sound.

Introduction The differentiation of Lewy body dementia from other common dementia types clinically is difficult, with a considerable number of cases only being found post-mortem. Consequently, there is a clear need for inexpensive and accurate diagnostic approaches for clinical use. Electroencephalography (EEG) is one potential candidate due to its relatively low cost and non-invasive nature. Previous studies examining the use of EEG as a dementia diagnostic have focussed on the eyes closed (EC) resting state; however, eyes open (EO) EEG may also be a useful adjunct to quantitative analysis due to clinical availability. Methods We extracted spectral properties from EEG signals recorded under research study protocols (1024 Hz sampling rate, 10:5 EEG layout). The data stems from a total of 40 dementia patients with an average age of 74.42, 75.81 and 73.88 years for Alzheimer’s disease (AD), dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD), respectively, and 15 healthy controls (HC) with an average age of 76.93 years. We utilised k-nearest neighbour, support vector machine and logistic regression machine learning to differentiate between groups utilising spectral data from the delta, theta, high theta, alpha and beta EEG bands. Results We found that the combination of EC and EO resting state EEG data significantly increased inter-group classification accuracy compared to methods not using EO data. Secondly, we observed a distinct increase in the dominant frequency variance for HC between the EO and EC state, which was not observed within any dementia subgroup. For inter-group classification, we achieved a specificity of 0.87 and sensitivity of 0.92 for HC vs dementia classification and 0.75 specificity and 0.91 sensitivity for AD vs DLB classification, with a k-nearest neighbour machine learning model which outperformed other machine learning methods. Conclusions The findings of our study indicate that the combination of both EC and EO quantitative EEG features improves overall classification accuracy when classifying dementia types in older age adults. In addition, we demonstrate that healthy controls display a definite change in dominant frequency variance between the EC and EO state. In future, a validation cohort should be utilised to further solidify these findings.

During auditory perception, we are required to abstract information from complex temporal sequences such as those in music and speech. Here, we investigated how higher-order statistics modulate the neural responses to sound sequences, hypothesizing that these modulations are associated with higher levels of the peri-Sylvian auditory hierarchy. We devised second-order Markov sequences of pure tones with uniform first-order transition probabilities. Participants learned to discriminate these sequences from random ones. Magnetoencephalography was used to identify evoked fields in which second-order transition probabilities were encoded. We show that improbable tones evoked heightened neural responses after 200ms post-tone onset during exposure at the learning stage or around 150ms during the subsequent test stage, originating near the right temporoparietal junction. These signal changes reflected higher-order statistical learning, which can contribute to the perception of natural sounds with hierarchical structures. We propose that our results reflect hierarchical predictive representations, which can contribute to the experiences of speech and music. ►Humans can perceptually learn higher-order statistical structure in sound sequences. ►Sounds that violate learned higher-order statistics heighten right temporoparietal junction-evoked responses. ►Intraparietal sulci responses decrease with more learning. ►Higher levels of the right hemisphere auditory hierarchy contribute to learning hierarchical statistical structures similar to those in speech and music.

Laughter is an ancient signal of social communication among humans and non-human primates. Laughter types with complex social functions (e.g., taunt and joy) presumably evolved from the unequivocal and reflex-like social bonding signal of tickling laughter already present in non-human primates. Here, we investigated the modulations of cerebral connectivity associated with different laughter types as well as the effects of attention shifts between implicit and explicit processing of social information conveyed by laughter using functional magnetic resonance imaging (fMRI). Complex social laughter types and tickling laughter were found to modulate connectivity in two distinguishable but partially overlapping parts of the laughter perception network irrespective of task instructions. Connectivity changes, presumably related to the higher acoustic complexity of tickling laughter, occurred between areas in the prefrontal cortex and the auditory association cortex, potentially reflecting higher demands on acoustic analysis associated with increased information load on auditory attention, working memory, evaluation and response selection processes. In contrast, the higher degree of socio-relational information in complex social laughter types was linked to increases of connectivity between auditory association cortices, the right dorsolateral prefrontal cortex and brain areas associated with mentalizing as well as areas in the visual associative cortex. These modulations might reflect automatic analysis of acoustic features, attention direction to informative aspects of the laughter signal and the retention of those in working memory during evaluation processes. These processes may be associated with visual imagery supporting the formation of inferences on the intentions of our social counterparts. Here, the right dorsolateral precentral cortex appears as a network node potentially linking the functions of auditory and visual associative sensory cortices with those of the mentalizing-associated anterior mediofrontal cortex during the decoding of social information in laughter.

Spoken language, in contrast to written text, provides prosodic information such as rhythm, pauses, accents, amplitude and pitch variations. However, little is known about when and how these features are used by the listener to interpret the speech signal. Here we use event–related brain potentials (ERP) to demonstrate that intonational phrasing guides the initial analysis of sentence structure. Our finding of a positive shift in the ERP at intonational phrase boundaries suggests a specific on–line brain response to prosodic processing. Additional ERP components indicate that a false prosodic boundary is sufficient to mislead the listener's sentence processor. Thus, the application of ERP measures is a promising approach for revealing the time course and neural basis of prosodic information processing.

Due to the heterogeneous causes, symptoms and associated comorbidities with tinnitus, there remains an unmet need for a clear biomarker of tinnitus presence. Previous research has suggested a “final pathway” of tinnitus presence, which occurs regardless of the specific mechanisms that resulted in alterations of auditory predictions and, eventually, tinnitus perception. Predictive inference mechanisms have been proposed as the possible basis for this final unifying pathway. A commonly used measure of prediction violation is mismatch negativity (MMN), an electrical potential generated in response to most stimuli that violate an established regularity. This narrative review discusses 16 studies comparing MMN between tinnitus and non-tinnitus groups. Methods varied considerably, including type of deviant, type of paradigm and carrier frequency. A minority of studies matched groups for age, sex and hearing, with few measuring hyperacusis. Frequency deviants were the most widely studied; at frequencies remote from tinnitus, MMN was consistently smaller in tinnitus groups, though hyperacusis or altered distress or attention could not be ruled out as explanatory factors. Few studies have used tinnitus-related frequencies; these showed larger MMN to upward frequency deviants above the tinnitus frequency, and larger MMN to upward intensity deviants at or close to the tinnitus frequency. However, the latter appears a correlate of hyperacusis rather than tinnitus, and tinnitus groups without hyperacusis instead show larger MMN to downward intensity deviants than controls. Other factors that affect MMN amplitudes included age, attention, and the specific characteristics of the range of stimuli across a particular experiment paradigm. As such, MMN cannot presently be considered a specific biomarker of tinnitus, but showed potential to objectively characterise a number of auditory processing traits relevant to tinnitus and hyperacusis.

Laughter is highly relevant for social interaction in human beings and non-human primates. In humans as well as in non-human primates laughter can be induced by tickling. Human laughter, however, has further diversified and encompasses emotional laughter types with various communicative functions, e.g. joyful and taunting laughter. Here, it was evaluated if this evolutionary diversification of ecological functions is associated with distinct cerebral responses underlying laughter perception. Functional MRI revealed a double-dissociation of cerebral responses during perception of tickling laughter and emotional laughter (joy and taunt) with higher activations in the anterior rostral medial frontal cortex (arMFC) when emotional laughter was perceived, and stronger responses in the right superior temporal gyrus (STG) during appreciation of tickling laughter. Enhanced activation of the arMFC for emotional laughter presumably reflects increasing demands on social cognition processes arising from the greater social salience of these laughter types. Activation increase in the STG for tickling laughter may be linked to the higher acoustic complexity of this laughter type. The observed dissociation of cerebral responses for emotional laughter and tickling laughter was independent of task-directed focusing of attention. These findings support the postulated diversification of human laughter in the course of evolution from an unequivocal play signal to laughter with distinct emotional contents subserving complex social functions. ►bullet point 1: distinct neural activity during perception of tickling and emotional laughter. ►bullet point 2: emotional laughter (joy, taunt) shows stronger responses in the arMFC. ►bullet point 3: tickling laughter shows stronger responses in the right STG. ►bullet point 4: human laughter diversified to accommodate increasingly complex social interactions.