From sensation to percept: The neural signature of auditory event-related potentials

Tinnitus mechanisms and the need for an objective electrophysiological tinnitus test

Tinnitus, the perception of sound with no external auditory stimulus, is a complex, multifaceted, and potentially devastating disorder. Despite recent advances in our understanding of tinnitus, there are limited options for effective treatment. Tinnitus treatments are made more complicated by the lack of a test for tinnitus based on objectively measured physiological characteristics. Such an objective test would enable a greater understanding of tinnitus mechanisms and may lead to faster treatment development in both animal and human research. This review makes the argument that an objective tinnitus test, such as a non-invasive electrophysiological measure, is desperately needed. We review the current tinnitus assessment methods, the underlying neural correlates of tinnitus, the multiple tinnitus generation theories, and the previously investigated electrophysiological measurements of tinnitus. Finally, we propose an alternate objective test for tinnitus that may be valid in both animal and human subjects.

Understanding music and aging through the lens of Bayesian inference

Bayesian inference has recently gained momentum in explaining music perception and aging. A fundamental mechanism underlying Bayesian inference is the notion of prediction. This framework could explain how predictions pertaining to musical (melodic, rhythmic, harmonic) structures engender action, emotion, and learning, expanding related concepts of music research, such as musical expectancies, groove, pleasure, and tension. Moreover, a Bayesian perspective of music perception may shed new insights on the beneficial effects of music in aging. Aging could be framed as an optimization process of Bayesian inference. As predictive inferences refine over time, the reliance on consolidated priors increases, while the updating of prior models through Bayesian inference attenuates. This may affect the ability of older adults to estimate uncertainties in their environment, limiting their cognitive and behavioral repertoire. With Bayesian inference as an overarching framework, this review synthesizes the literature on predictive inferences in music and aging, and details how music could be a promising tool in preventive and rehabilitative interventions for older adults through the lens of Bayesian inference.

Aligning Event-Related Potentials with Transcranial Alternating Current Stimulation for Modulation-a Review

This review aims to demonstrate the connections between event-related potentials (ERPs), event-related oscillations (EROs), and non-invasive brain stimulation (NIBS), with a specific focus on transcranial alternating current stimulation (tACS). We begin with a short examination and discussion of the relation between ERPs and EROs. Then, we investigate the diverse fields of NIBS, highlighting tACS as a potent tool for modulating neural oscillations and influencing cognitive performance. Emphasizing the impact of tACS on individual ERP components, this article offers insights into the potential of conventional tACS for targeted stimulation of single ERP components. Furthermore, we review recent articles that explore a novel approach of tACS: ERP-aligned tACS. This innovative technique exploits the temporal precision of ERP components, aligning tACS with specific neural events to optimize stimulation effects and target the desired neural response. In conclusion, this review combines current knowledge to explore how ERPs, EROs, and NIBS interact, particularly highlighting the modulatory possibilities offered by tACS. The incorporation of ERP-aligned tACS introduces new opportunities for future research, advancing our understanding of the complex connection between neural oscillations and cognitive processes.

Brain vital sign monitoring of sleep deprivation detects situational cognitive impairment

Objective, rapid evaluation of cognitive function is critical for identifying situational impairment due to sleep deprivation. The present study used brain vital sign monitoring to evaluate acute changes in cognitive function for healthy adults. Thirty (30) participants were scanned using portable electroencephalography before and after either a night of regular sleep or a night of total sleep deprivation. Brain vital signs were extracted from three established event-related potential components: (1) the N100 (Auditory sensation); (2) the P300 (Basic attention); and (3) the N400 (Cognitive processing) for all time points. As predicted, the P300 amplitude was significantly reduced in the sleep deprivation group. The findings indicate that it is possible to detect situational cognitive impairment due to sleep deprivation using objective, rapid brain vital sign monitoring.

Mechanisms of sustained perceptual entrainment after stimulus offset

Temporal alignment of neural activity to rhythmic stimulation has been suggested to result from a resonating internal neural oscillator mechanism, but can also be explained by interval-based temporal prediction. Here, we investigate behavioural and brain responses in the post-stimulation period to compare an oscillatory versus an interval-based account. Hickok et al.'s (2015) behavioural paradigm yielded results that relate to a neural oscillatory entrainment mechanism. We adapted the paradigm to an event-related potential (ERP) suitable design: a periodic sequence was followed, in half of the trials, by near-threshold targets embedded in noise. The targets were played in various phases in relation to the preceding sequences' period. Participants had to detect whether targets were played or not, and their EEG was recorded. Both behavioural results and the P300 component of the ERP were not only partially consistent with an oscillatory mechanism but also partially consistent with an interval-based attentional gain mechanism. Instead, data obtained in the post-entrainment period can best be explained with a combination of both mechanisms.

Amplitude Modulation Perception and Cortical Evoked Potentials in Children With Listening Difficulties and Their Typically Developing Peers

PURPOSE

Amplitude modulations (AMs) are important for speech intelligibility, and deficits in speech intelligibility are a leading source of impairment in childhood listening difficulties (LiD). The present study aimed to explore the relationships between AM perception and speech-in-noise (SiN) comprehension in children and to determine whether deficits in AM processing contribute to childhood LiD. Evoked responses were used to parse the neural origins of AM processing.

METHOD

Forty-one children with LiD and 44 typically developing children, ages 8-16 years, participated in the study. Behavioral AM depth thresholds were measured at 4 and 40 Hz. SiN tasks included the Listening in Spatialized Noise-Sentences Test (LiSN-S) and a coordinate response measure (CRM)-based task. Evoked responses were obtained during an AM change detection task using alternations between 4 and 40 Hz, including the N1 of the acoustic change complex, auditory steady-state response (ASSR), P300, and a late positive response (late potential [LP]). Maturational effects were explored via age correlations.

RESULTS

Age correlated with 4-Hz AM thresholds, CRM separated talker scores, and N1 amplitude. Age-normed LiSN-S scores obtained without spatial or talker cues correlated with age-corrected 4-Hz AM thresholds and area under the LP curve. CRM separated talker scores correlated with AM thresholds and area under the LP curve. Most behavioral measures of AM perception correlated with the signal-to-noise ratio and phase coherence of the 40-Hz ASSR. AM change response time also correlated with area under the LP curve. Children with LiD exhibited deficits with respect to 4-Hz thresholds, AM change accuracy, and area under the LP curve.

CONCLUSIONS

The observed relationships between AM perception and SiN performance extend the evidence that modulation perception is important for understanding SiN in childhood. In line with this finding, children with LiD demonstrated poorer performance on some measures of AM perception, but their evoked responses implicated a primarily cognitive deficit.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.25009103.

Event Related Potentials to Native Speech Contrasts Predicts Word Reading Abilities in Early School-Aged Children

Speech perception skills have been implicated in the development of phoneme-grapheme correspondence, yet the exact nature of speech perception and word reading ability remains unknown. We investigate phonological sensitivity to native (English) and nonnative (Spanish) speech syllables within an auditory oddball paradigm using event related potentials (ERPs) collected from lateral temporal electrode sites in 33 monolingual English-speaking children aged 6-8 years (N=33). We further explore the relationship between ERPs to English word reading abilities for this group. Results revealed that language stimuli (English, Spanish), ERP condition (standard, deviant), and hemisphere (left, right) all influenced the lateral N1 component. ERPs recorded from deviant English stimuli were significantly more negative within the left hemisphere compared to all other recorded ERPs. Mean amplitude differences within the N1 in left lateral electrode sites recorded in response to English phoneme contrasts significantly predicted English word reading abilities within this sample. Results indicate that speech perception of native contrasts recorded in left temporal electrode sites for the N1 component are linked to English word reading abilities in early school-aged children.

Amplitude modulation perception and cortical evoked potentials in children with listening difficulties and their typically-developing peers

Purpose

Amplitude modulations (AM) are important for speech intelligibility, and deficits in speech intelligibility are a leading source of impairment in childhood listening difficulties (LiD). The present study aimed to explore the relationships between AM perception and speech-in-noise (SiN) comprehension in children and to determine whether deficits in AM processing contribute to childhood LiD. Evoked responses were used to parse the neural origin of AM processing.

Method

Forty-one children with LiD and forty-four typically-developing children, ages 8-16 y.o., participated in the study. Behavioral AM depth thresholds were measured at 4 and 40 Hz. SiN tasks included the LiSN-S and a Coordinate Response Measure (CRM)-based task. Evoked responses were obtained during an AM Change detection task using alternations between 4 and 40 Hz, including the N1 of the acoustic change complex, auditory steady-state response (ASSR), P300, and a late positive response (LP). Maturational effects were explored via age correlations.

Results

Age correlated with 4 Hz AM thresholds, CRM Separated Talker scores, and N1 amplitude. Age-normed LiSN-S scores obtained without spatial or talker cues correlated with age-corrected 4 Hz AM thresholds and area under the LP curve. CRM Separated Talker scores correlated with AM thresholds and area under the LP curve. Most behavioral measures of AM perception correlated with the SNR and phase coherence of the 40 Hz ASSR. AM Change RT also correlated with area under the LP curve. Children with LiD exhibited deficits with respect to 4 Hz thresholds, AM Change accuracy, and area under the LP curve.

Conclusions

The observed relationships between AM perception and SiN performance extend the evidence that modulation perception is important for understanding SiN in childhood. In line with this finding, children with LiD demonstrated poorer performance on some measures of AM perception, but their evoked responses implicated a primarily cognitive deficit.

Estimating statistical power for ERP studies using the auditory N1, Tb, and P2 components

The N1, Tb, and P2 components of the event-related potential (ERP) are thought to reflect the sequential processing of auditory stimuli in the human brain. Despite their extensive use in biological, cognitive, and clinical neuroscience, there are no guidelines for how to appropriately power ERP studies using these components. In the present study, we investigated how the number of trials, number of participants, effect magnitude, and study design influenced statistical power. Using Monte Carlo simulations of ERP data from a passive listening task, we determined the probability of finding a statistically significant effect in 58,900 experiments repeated 1,000 times each. We found that as the number of trials, number of participants, and effect magnitude increased, so did statistical power. We also found that increasing the number of trials had a bigger effect on statistical power for within-subject designs than for between-subject designs, and that within-subject designs required a smaller number of trials and participants to provide the same level of statistical power for a given effect magnitude than between-subject designs. These results show that it is important to carefully consider these factors when designing ERP studies, rather than relying on tradition or anecdotal evidence. To improve the robustness and reproducibility of ERP research, we have built an online statistical power calculator (https://bradleynjack.shinyapps.io/ErpPowerCalculator), which we hope will allow researchers to estimate the statistical power of previous studies, as well as help them design appropriately-powered studies in the future.

"What" and "when" predictions modulate auditory processing in a mutually congruent manner

Introduction

Extracting regularities from ongoing stimulus streams to form predictions is crucial for adaptive behavior. Such regularities exist in terms of the content of the stimuli and their timing, both of which are known to interactively modulate sensory processing. In real-world stimulus streams such as music, regularities can occur at multiple levels, both in terms of contents (e.g., predictions relating to individual notes vs. their more complex groups) and timing (e.g., pertaining to timing between intervals vs. the overall beat of a musical phrase). However, it is unknown whether the brain integrates predictions in a manner that is mutually congruent (e.g., if "beat" timing predictions selectively interact with "what" predictions falling on pulses which define the beat), and whether integrating predictions in different timing conditions relies on dissociable neural correlates.

Methods

To address these questions, our study manipulated "what" and "when" predictions at different levels - (local) interval-defining and (global) beat-defining - within the same stimulus stream, while neural activity was recorded using electroencephalogram (EEG) in participants (N = 20) performing a repetition detection task.

Results

Our results reveal that temporal predictions based on beat or interval timing modulated mismatch responses to violations of "what" predictions happening at the predicted time points, and that these modulations were shared between types of temporal predictions in terms of the spatiotemporal distribution of EEG signals. Effective connectivity analysis using dynamic causal modeling showed that the integration of "what" and "when" predictions selectively increased connectivity at relatively late cortical processing stages, between the superior temporal gyrus and the fronto-parietal network.

Discussion

Taken together, these results suggest that the brain integrates different predictions with a high degree of mutual congruence, but in a shared and distributed cortical network. This finding contrasts with recent studies indicating separable mechanisms for beat-based and memory-based predictive processing.

Various aspects of hearing loss in newborns: A narrative review

Hearing loss is considered the most common birth defect. The estimated prevalence of moderate and severe hearing loss in a normal newborn is 0.1%-0.3%, while the prevalence is 2%-4% in newborns admitted to the newborn intensive care unit. Neonatal hearing loss can be congenital (syndromic or non-syndromic) or acquired such as ototoxicity. In addition, the types of hearing loss can be conductive, sensorineural, or mixed. Hearing is vital for the acquisition of language and learning. Therefore, early detection and prompt treatment are of utmost importance in preventing the unwanted sequel of hearing loss. The hearing screening program is mandatory in many nations, especially for high-risk newborns. An automated auditory brainstem response test is used as a screening tool in newborns admitted to the newborn intensive care unit. Moreover, genetic testing and screening for cytomegalovirus in newborns are essential in identifying the cause of hearing loss, particularly, mild and delayed onset types of hearing loss. We aimed to update the knowledge on the various aspects of hearing loss in newborns with regard to the epidemiology, risk factors, causes, screening program, investigations, and different modalities of treatment.

Objective Detection of Tinnitus Based on Electrophysiology

Tinnitus, a common disease in the clinic, is associated with persistent pain and high costs to society. Several aspects of tinnitus, such as the pathophysiology mechanism, effective treatment, objective detection, etc., have not been elucidated. Any change in the auditory pathway can lead to tinnitus. At present, there is no clear and unified mechanism to explain tinnitus, and the hypotheses regarding its mechanism include auditory plasticity theory, cortical reorganization theory, dorsal cochlear nucleus hypothesis, etc. Current theories on the mechanism of tinnitus mainly focus on the abnormal activity of the central nervous system. Unfortunately, there is currently a lack of objective diagnostic methods for tinnitus. Developing a method that can detect tinnitus objectively is crucial, only in this way can we identify whether the patient really suffers from tinnitus in the case of cognitive impairment or medical disputes and the therapeutic effect of tinnitus. Electrophysiological investigations have prompted the development of an objective detection of tinnitus by potentials recorded in the auditory pathway. However, there is no objective indicator with sufficient sensitivity and specificity to diagnose tinnitus at present. Based on recent findings of studies with various methods, possible electrophysiological approaches to detect the presence of tinnitus have been summarized. We analyze the change of neural activity throughout the auditory pathway in tinnitus subjects and in patients with tinnitus of varying severity to find available parameters in these methods, which is helpful to further explore the feasibility of using electrophysiological methods for the objective detection of tinnitus.

Event-Related Potential Evidence for Involuntary Consciousness During Implicit Memory Retrieval

Classical notion claims that a memory is implicit if has nothing to do with consciousness during the information retrieval from storage, or is otherwise explicit. Here, we demonstrate event-related potential evidence for involuntary consciousness during implicit memory retrieval. We designed a passive oddball paradigm for retrieval of implicit memory in which an auditory stream of Shepard tones with musical pitch interval contrasts were delivered to the subjects. These contrasts evoked a mismatch negativity response, which is an event-related potential and a neural marker of implicit memory, in the subjects with long-term musical training, but not in the subjects without. Notably, this response was followed by a salient P3 component which implies involvement of involuntary consciousness in the implicit memory retrieval. Finally, source analysis of the P3 revealed moving dipoles from the frontal lobe to the insula, a brain region closely related to conscious attention. Our study presents a case of involvement of involuntary consciousness in the implicit memory retrieval and suggests a potential challenge to the classical definition of implicit memory.

Effects of the glycine transporter-1 inhibitor iclepertin (BI 425809) on sensory processing, neural network function, and cognition in animal models related to schizophrenia

N-methyl-D-aspartate (NMDA) receptor hypofunction leading to neural network dysfunction is thought to play an important role in the pathophysiology of cognitive impairment associated with schizophrenia (CIAS). Increasing extracellular concentrations of the NMDA receptor co-agonist glycine through inhibition of glycine transporter-1 (GlyT1) has the potential to treat CIAS by improving cortical network function through enhanced glutamatergic signaling. Indeed, the novel GlyT1 inhibitor iclepertin (BI 425809) improved cognition in a recent clinical study in patients with schizophrenia. The present study tested the ability of iclepertin to reverse MK-801-induced deficits in auditory sensory processing and cortical network function using electroencephalography (EEG) to measure auditory event-related potentials (AERP) and 40 Hz auditory steady-state response (ASSR). In addition, improvements in memory performance with iclepertin were evaluated using the T-maze spontaneous alternation test in MK-801-treated mice and the social recognition test in naïve rats. Iclepertin reversed MK-801-induced deficits in the AERP readouts N1 amplitude and N1 gating, as well as 40 Hz ASSR power and inter-trial coherence. Additionally, iclepertin significantly attenuated an MK-801-induced increase in basal gamma power. Furthermore, iclepertin reversed MK-801-induced working memory deficits in mice and improved social recognition memory performance in rats. Overall, this study demonstrates that inhibition of GlyT1 is sufficient to attenuate MK-801-induced deficits in translatable EEG parameters relevant to schizophrenia. Moreover, iclepertin showed memory-enhancing effects in rodent cognition tasks, further demonstrating the potential for GlyT1 inhibition to treat CIAS. Significance Statement Despite the significant patient burden caused by cognitive impairment associated with schizophrenia, there are currently no approved pharmacotherapies. In this preclinical study, the novel glycine transporter inhibitor iclepertin (BI 425809) reversed sensory processing deficits and neural network dysfunction evoked by inhibition of N-methyl-D-aspartate (NMDA) receptors, and enhanced working memory performance and social recognition in rodents. These findings support previous clinical evidence for the pro-cognitive effects of iclepertin.

Neurophysiology in psychosis: The quest for disease biomarkers

Psychotic disorders affect 3% of the population at some stage in life, are a leading cause of disability, and impose a great economic burden on society. Major breakthroughs in the genetics of psychosis have not yet been matched by an understanding of its neurobiology. Biomarkers of perception and cognition obtained through non-invasive neurophysiological tools, especially EEG, offer a unique opportunity to gain mechanistic insights. Techniques for measuring neurophysiological markers are inexpensive and ubiquitous, thus having the potential as an accessible tool for patient stratification towards early treatments leading to better outcomes. In this paper, we review the literature on neurophysiological markers for psychosis and their relevant disease mechanisms, mainly covering event-related potentials including P50/N100 sensory gating, mismatch negativity, and the N100 and P300 waveforms. While several neurophysiological deficits are well established in patients with psychosis, more research is needed to study neurophysiological markers in their unaffected relatives and individuals at clinical high risk. We need to harness EEG to investigate markers of disease risk as key steps to elucidate the aetiology of psychosis and facilitate earlier detection and treatment.

Sound omission related brain responses in children

Action is an important way for children to learn about the world. Recent theories suggest that action is inherently accompanied by the sensory prediction of its effects. Such predictions can be revealed by rarely omitting the expected sensory consequence of the action, resulting in an omission response that is observable in the EEG. Although prediction errors play an important role in models of learning and development, little is known about omission-related brain responses in children. This study used a motor-auditory omission paradigm, testing a group of 6-8-year-old children and an adult group (N = 31 each). In an identity-specific condition, the sound coupled to the motor action was predictable, while in an identity unspecific condition the sound was unpredictable. Results of a temporal principal component analysis revealed that sound-related brain responses underlying the N1-complex differed considerably between age groups. Despite these developmental differences, omission responses (oN1) were similar between age groups. Two subcomponents of the oN1 were differently affected by specific and unspecific predictions. Results demonstrate that children, independent from the maturation of sound processing mechanisms, can implement specific and unspecific predictions as flexibly as adults. This supports theories that regard action and prediction error as important drivers of cognitive development.

Early Schizophrenia and Bipolar Disorder Patients Display Reduced Neural Prepulse Inhibition

BACKGROUND

Altered sensorimotor gating has been demonstrated by Prepulse Inhibition (PPI) tests in patients with psychosis. Recent advances in signal processing methods allow assessment of neural PPI through electroencephalogram (EEG) recording during acoustic startle response measures (classic muscular PPI). Simultaneous measurements of muscular (eye-blink) and neural gating phenomena during PPI test may help to better understand sensorial processing dysfunctions in psychosis. In this study, we aimed to assess simultaneously muscular and neural PPI in early bipolar disorder and schizophrenia patients.

METHOD

Participants were recruited from a population-based case-control study of first episode psychosis. PPI was measured using electromyography (EMG) and EEG in pulse alone and prepulse + pulse with intervals of 30, 60, and 120 ms in early bipolar disorder (n = 18) and schizophrenia (n = 11) patients. As control group, 15 socio-economically matched healthy subjects were recruited. All subjects were evaluated with Rating Scale, Hamilton Rating Scale for Depression, and Young Mania Rating Scale questionnaires at recruitment and just before PPI test. Wilcoxon ranked sum tests were used to compare PPI test results between groups.

RESULTS

In comparison to healthy participants, neural PPI was significantly reduced in PPI 30 and PPI60 among bipolar and schizophrenia patients, while muscular PPI was reduced in PPI60 and PPI120 intervals only among patients with schizophrenia.

CONCLUSION

The combination of muscular and neural PPI evaluations suggested distinct impairment patterns among schizophrenia and bipolar disorder patients. Simultaneous recording may contribute with novel information in sensory gating investigations.

The Development and Neurophysiological Assessment of Newborn Auditory Cognition: A Review of Findings and Their Application

This review article introduces the basic principles of infants' neurophysiology, while summarizing the core knowledge of the anatomical structure of the auditory pathway, and presents previous findings on newborns' neural speech processing and suggests their possible applications for clinical practice. In order to tap into the functioning of the auditory pathway in newborns, recent approaches have employed electrophysiological techniques that measure electrical activity of the brain. The neural processing of an incoming auditory stimulus is objectively reflected by means of auditory event-related potentials. The newborn's nervous system processes the incoming sound, and the associated electrical activity of the brain is measured and extracted as components characterized by amplitude, latency, and polarity. Based on the parameters of event-related potentials, it is possible to assess the maturity of a child's brain, or to identify a pathology that needs to be treated or mitigated. For instance, in children with a cochlear implant, auditory event-related potentials are employed to evaluate an outcome of the implantation procedure and to monitor the development of hearing. Event-related potentials turn out to be an irreplaceable part of neurodevelopmental care for high-risk children e.g., preterm babies, children with learning disabilities, autism and many other risk factors.

Cortical Auditory Evoked Potentials in Cognitive Impairment and Their Relevance to Hearing Loss: A Systematic Review Highlighting the Evidence Gap

Background: Alzheimer’s disease (AD) is the most prevalent cause of dementia which affects a growing number of people worldwide. Early identification of people at risk to develop AD should be prioritized. Hearing loss is considered an independent potentially modifiable risk factor for accelerated cognitive decline and dementia in older adults. The main outcome of interest of this review is the alteration of Cortical Auditory Evoked Potential (CAEP) morphology in an AD or mild cognitive impairment (MCI) population with and without hearing loss.

Methods: Two investigators independently and systematically searched publications regarding auditory processing on a cortical level in people with cognitive impairment (MCI or AD) with and without hearing loss. Only articles which mentioned at least one auditory elicited event-related potential (ERP) component and that were written in English or Dutch were included. Animal studies were excluded. No restrictions were imposed regarding publication date. The reference list of potential sources were screened for additional articles.

Results: This systematic review found no eligible articles that met all inclusion criteria. Therefore, no results were included, resulting in an empty systematic review.

Conclusion: In general, dysfunction – being either from cognitive or auditory origin – reduces CAEP amplitudes and prolongs latencies. Therefore, CAEPs may be a prognostic indicator in the early stages of cognitive decline. However, it remains unclear which CAEP component alteration is due to cognitive impairment, and which is due to hearing loss (or even both). In addition, vestibular dysfunction – associated with hearing loss, cognitive impairment and AD – may also alter CAEP responses. Further CAEP studies are warranted, integrating cognitive, hearing, and vestibular evaluations.

Vestibular-Evoked Cerebral Potentials

The human vestibular cortex has mostly been approached using functional magnetic resonance imaging and positron emission tomography combined with artificial stimulation of the vestibular receptors or nerve. Few studies have used electroencephalography and benefited from its high temporal resolution to describe the spatiotemporal dynamics of vestibular information processing from the first milliseconds following vestibular stimulation. Evoked potentials (EPs) are largely used to describe neural processing of other sensory signals, but they remain poorly developed and standardized in vestibular neuroscience and neuro-otology. Yet, vestibular EPs of brainstem, cerebellar, and cortical origin have been reported as early as the 1960s. This review article summarizes and compares results from studies that have used a large range of vestibular stimulation, including natural vestibular stimulation on rotating chairs and motion platforms, as well as artificial vestibular stimulation (e.g., sounds, impulsive acceleration stimulation, galvanic stimulation). These studies identified vestibular EPs with short latency (<20 ms), middle latency (from 20 to 50 ms), and late latency (>50 ms). Analysis of the generators (source analysis) of these responses offers new insights into the neuroimaging of the vestibular system. Generators were consistently found in the parieto-insular and temporo-parietal junction-the core of the vestibular cortex-as well as in the prefrontal and frontal areas, superior parietal, and temporal areas. We discuss the relevance of vestibular EPs for basic research and clinical neuroscience and highlight their limitations.

Detecting Connected Consciousness During Propofol-Induced Anesthesia Using EEG Based Brain Decoding

Connected consciousness refers to the state when external stimuli can enter into the stream of our consciousness experience. Emerging evidence suggests that although patients may not respond behaviorally to external stimuli during anesthesia, they may be aware of their surroundings. In this work, we investigated whether EEG based brain decoding could be used for detecting connected consciousness in the absence of behavioral responses during propofol infusion. A total of 14 subjects participated in our experiment. Subjects were asked to discriminate two types of auditory stimuli with a finger press during an ultraslow propofol infusion. We trained an EEG based brain decoding model using data collected in the awakened state using the same auditory stimuli and tested the model on data collected during the propofol infusion. The model provided a correct classification rate (CCR) of [Formula: see text]% when subjects were able to respond to the stimuli during the propofol infusion. The CCR dropped to [Formula: see text]% when subjects ceased responding and further decreased to [Formula: see text]% when we increased the propofol concentration by another 0.2 [Formula: see text]g/ml. After terminating the propofol infusion, we observed that the CCR rebounded to [Formula: see text]% before the subjects regained consciousness. With the classification results, we provided evidence that loss of consciousness is a gradual process and may progress from full consciousness to connected consciousness and then to disconnected consciousness.

Selective attention modulates neural envelope tracking of informationally masked speech in healthy older adults

Speech understanding in noisy situations is compromised in old age. This study investigated the energetic and informational masking components of multi‐talker babble noise and their influence on neural tracking of the speech envelope in a sample of healthy older adults. Twenty‐three older adults (age range 65–80 years) listened to an audiobook embedded in noise while their electroencephalogram (EEG) was recorded. Energetic masking was manipulated by varying the signal‐to‐noise ratio (SNR) between target speech and background talkers and informational masking was manipulated by varying the number of background talkers. Neural envelope tracking was measured by calculating temporal response functions (TRFs) between speech envelope and EEG. Number of background talkers, but not SNR modulated the amplitude of an earlier (around 50 ms time lag) and a later (around 300 ms time lag) peak in the TRFs. Selective attention, but not working memory or peripheral hearing additionally modulated the amplitude of the later TRF peak. Finally, amplitude of the later TRF peak was positively related to accuracy in the comprehension task. The results suggest that stronger envelope tracking is beneficial for speech‐in‐noise understanding and that selective attention is an important ability supporting speech‐in‐noise understanding in multi‐talker scenes.

Persistence of Neuronal Alterations in Alcohol-Dependent Patients at Conclusion of the Gold Standard Withdrawal Treatment: Evidence From ERPs

Background: One of the main challenges for clinicians is to ensure that alcohol withdrawal treatment is the most effective possible after discharge. To address this issue, we designed a pilot study to investigate the efficacy of the rehabilitation treatment on the main stages of information processing, using an electroencephalographic method. This topic is of main importance as relapse rates after alcohol withdrawal treatment remain very high, indicating that established treatment methods are not fully effective in all patients in the long run. Method: We examined in alcohol-dependent patients (ADP) the effects of the benzodiazepine-based standard detoxification program on event-related potential components at incoming (D0) and completion (D15) of the treatment, using tasks of increasing difficulty (with and without workload) during an auditory oddball target paradigm. Untreated non-alcohol-dependent-volunteers were used as matching controls. Results: At D0, ADP displayed significantly lower amplitude for all ERP components in both tasks, as compared to controls. At D15, this difference disappeared for the amplitude of the N1 component during the workload-free task, as well as the amplitude of the P3b for both tasks. Meanwhile, the amplitude of the N2 remained lower in both tasks for ADP. At D0, latencies of N2 and P3b in both task conditions were longer in ADP, as compared to controls, whilst the latency of N1 was unchanged. At D15, the N2 latency remained longer for the workload condition only, whereas the P3b latency remained longer for the workload-free task only. Conclusion: The present pilot results provide evidence for a persistence of impaired parameters of ERP components, especially the N2 component. This suggests that neural networks related to attention processing remain dysfunctional. Longitudinal long-term follow-up of these patients is mandatory for further assessment of a link between ERP alterations and a later risk of relapse.

Systematic review and meta-analysis of late auditory evoked potentials as a candidate biomarker in the assessment of tinnitus

Subjective tinnitus, the perception of sound in the absence of any sound source, is routinely assessed using questionnaires. The subjective nature of these tools hampers objective evaluation of tinnitus presence, severity and treatment effects. Late auditory evoked potentials (LAEPs) might be considered as a potential biomarker for assessing tinnitus complaints. Using a multivariate meta-analytic model including data from twenty-one studies, we determined the LAEP components differing systematically between tinnitus patients and controls. Results from this model indicate that amplitude of the P300 component is lower in tinnitus patients (standardized mean difference (SMD) = -0.83, p < 0.01), while latency of this component is abnormally prolonged in this population (SMD = 0.97, p < 0.01). No other investigated LAEP components were found to differ between tinnitus and non-tinnitus subjects. Additional sensitivity analyses regarding differences in experimental conditions confirmed the robustness of these results. Differences in age and hearing levels between the two experimental groups might have a considerable impact on LAEP outcomes and should be carefully considered in future studies. Although we established consistent differences in the P300 component between tinnitus patients and controls, we could not identify any evidence that this component might covary with tinnitus severity. We conclude that out of several commonly assessed LAEP components, only the P300 can be considered as a potential biomarker for subjective tinnitus, although more research is needed to determine its relationship with subjective tinnitus measures. Future trials investigating experimental tinnitus therapies should consider including P300 measurements in the evaluation of treatment effect.

Neural Substrates of Tinnitus in an Auditory Brainstem Implant Patient: A Preliminary Molecular Imaging Study Using H2 15 O-PET Including a 5-year Follow-up of Auditory Performance and Tinnitus Perception

INTRODUCTION

It was previously demonstrated that tinnitus due to profound unilateral hearing loss can be treated by the use of electrical stimulation via a cochlear implant (CI) with long-lasting positive effects. In cases where patients are not suitable for cochlear implantation due to aplasia/hypoplasia, cochlear malformations etc., an auditory brainstem implant (ABI) may be a solution. While auditory performance with ABI is well investigated, it is currently unknown whether stimulation through ABI also renders tinnitus reduction in patients with incapacitating tinnitus. The current case study reports on the subjective tinnitus perception during a 5-year follow-up period. In addition, a first H2O PET imaging study in an ABI patient is carried out revealing underlying neural substrates of tinnitus.

METHODS

A 56-year-old male single-sided deaf patient with incapacitating tinnitus received an ABI after insufficient auditory performances and only minor tinnitus reduction with CI. Audiological follow-up was carried out during a 5-year follow-up period comprising pure-tone audiometry, speech-in-quiet testing, speech-in-noise testing, tinnitus questionnaires (tinnitus questionnaire and numeric rating scale) and the HISQUI19 questionnaire. To investigate the neural substrates of tinnitus in this subject, H2O PET tomography scans were acquired in three different conditions: 1) ABI switched off which was considered as the resting-state measurement rendering the loudest possible tinnitus for the patient (ABI OFF); 2) ABI switched on causing a small suppression of tinnitus due to electrical stimulation (ABI ON); 3) ABI switched on and 70 dB SPL white noise presented directly to the external audio processor through a direct audio cable providing the maximum tinnitus suppression for the patient (NOISE).

RESULTS

Subjectively the patient reported a significant tinnitus reduction after implantation which remained stable over time with a decrease in tinnitus questionnaire from grade 4 to grade 2 and a 50% reduction in the numeric rating scale (from 8 to 4) during the 5-year period. Comparing the ABI OFF and ABI ON conditions, significant increase in regional cerebral blood flow (rCBF) was observed in brain areas involved in the salience network showing already suppression of tinnitus only by electrical stimulation in the absence of auditory stimuli. The NOISE condition showed relatively decreased rCBF in the insula (as well as in the orbitofrontal cortex) as compared with the ABI OFF condition. Abnormally activated areas comprising the salience network may have been significantly suppressed by the NOISE condition both by acoustic and electrical stimulations of the auditory pathway. Moreover, the NOISE condition showed significantly decreased rCBF in the parahippocampus as compared with the ABI OFF condition. This finding supports the idea of distinct tinnitus generators depending on the amount of hearing loss.

CONCLUSION

The reduction of tinnitus in the current ABI subject may be attributable to partial peripheral reafferentation-induced deactivation of the parahippocampus-based tinnitus generator as well as the salience network. Further validation is required by the use of a follow-up study with a larger number of subjects.

Spectral fingerprints of correct vestibular discrimination of the intensity of body accelerations

Perceptual decision-making is a complex task that requires multiple processing steps performed by spatially distinct brain regions interacting in order to optimize perception and motor response. Most of our knowledge on these processes and interactions were derived from unimodal stimulations of the visual system which identified the lateral intraparietal area and the posterior parietal cortex as critical regions. Unlike the visual system, the vestibular system has no primary cortical areas and it is associated with separate multisensory areas within the temporo-parietal cortex with the parieto-insular vestibular cortex, PIVC, being the core region. The aim of the presented experiment was to investigate the transition from sensation to perception and to reveal the main structures of the cortical vestibular system involved in perceptual decision-making. Therefore, an EEG analysis was performed in 35 healthy subjects during linear whole-body accelerations of different intensities on a motor-driven motion platform (hexapod). We used a discrimination task in order to judge the intensity of the accelerations. Furthermore, we manipulated the expectation of the upcoming stimulus by indicating the probability (25%, 50%, 75%, 100%) of the motion direction. The analysis of the vestibular evoked potentials (VestEPs) showed that the decision-making process leads to a second positive peak (P2b) which was not observed in previous task-free experiments. The comparison of the estimated neural generators of the P2a and P2b components showed significant activity differences in the anterior cingulus, the parahippocampal and the middle temporal gyri. Taking into account the time courses of the P2 components, the physical properties of the stimuli, and the responses given by the subjects we conclude that the P2b likely reflects the transition from the processing of sensory information to perceptual evaluation. Analyzing the decision-uncertainty reported by the subjects, a persistent divergence of the time courses starting at 188 ​ms after the acceleration was found at electrode Pz. This finding demonstrated that meta-cognition by means of confidence estimation starts in parallel with the decision-making process itself. Further analyses in the time-frequency domain revealed that a correct classification of acceleration intensities correlated with an inter-trial phase clustering at electrode Cz and an inter-site phase clustering of theta oscillations over frontal, central, and parietal cortical areas. The sites where the phase clustering was observed corresponded to core decision-making brain areas known from neuroimaging studies in the visual domain.

Decoding across sensory modalities reveals common supramodal signatures of conscious perception

An increasing number of studies highlight common brain regions and processes in mediating conscious sensory experience. While most studies have been performed in the visual modality, it is implicitly assumed that similar processes are involved in other sensory modalities. However, the existence of supramodal neural processes related to conscious perception has not been convincingly shown so far. Here, we aim to directly address this issue by investigating whether neural correlates of conscious perception in one modality can predict conscious perception in a different modality. In two separate experiments, we presented participants with successive blocks of near-threshold tasks involving subjective reports of tactile, visual, or auditory stimuli during the same magnetoencephalography (MEG) acquisition. Using decoding analysis in the poststimulus period between sensory modalities, our first experiment uncovered supramodal spatiotemporal neural activity patterns predicting conscious perception of the feeble stimulation. Strikingly, these supramodal patterns included activity in primary sensory regions not directly relevant to the task (e.g., neural activity in visual cortex predicting conscious perception of auditory near-threshold stimulation). We carefully replicate our results in a control experiment that furthermore show that the relevant patterns are independent of the type of report (i.e., whether conscious perception was reported by pressing or withholding a button press). Using standard paradigms for probing neural correlates of conscious perception, our findings reveal a common signature of conscious access across sensory modalities and illustrate the temporally late and widespread broadcasting of neural representations, even into task-unrelated primary sensory processing regions.

The First 250 ms of Auditory Processing: No Evidence of Early Processing Negativity in the Go/NoGo Task

Past evidence of an early Processing Negativity in auditory Go/NoGo event-related potential (ERP) data suggests that young adults proactively process sensory information in two-choice tasks. This study aimed to clarify the occurrence of Go/NoGo Processing Negativity and investigate the ERP component series related to the first 250 ms of auditory processing in two Go/NoGo tasks differing in target probability. ERP data related to each task were acquired from 60 healthy young adults (M = 20.4, SD = 3.1 years). Temporal principal components analyses were used to decompose ERP data in each task. Statistical analyses compared component amplitudes between stimulus type (Go vs. NoGo) and probability (High vs. Low). Neuronal source localisation was also conducted for each component. Processing Negativity was not evident; however, P1, N1a, N1b, and N1c were identified in each task, with Go P2 and NoGo N2b. The absence of Processing Negativity in this study indicated that young adults do not proactively process targets to complete the Go/NoGo task and/or questioned Processing Negativity’s conceptualisation. Additional analyses revealed stimulus-specific processing as early as P1, and outlined a complex network of active neuronal sources underlying each component, providing useful insight into Go and NoGo information processing in young adults.

Sensory and Cognitive Components of Auditory Processing in Individuals With Tinnitus

Purpose The main purpose of the study is to explore the auditory selective attention abilities (using event-related potentials) and the neuronal oscillatory activity in the default mode network sites (using electroencephalogram [EEG]) in individuals with tinnitus. Method Auditory selective attention was measured using P300, and the resting state EEG was assessed using the default mode function analysis. Ten individuals with continuous and bothersome tinnitus along with 10 age- and gender-matched control participants underwent event-related potential testing and 5 min of EEG recording (at wakeful rest). Results Individuals with tinnitus were observed to have larger N1 and P3 amplitudes along with prolonged P3 latency. The default mode function analysis revealed no significant oscillatory differences between the groups. Conclusion The current study shows changes in both the early sensory and late cognitive components of auditory processing. The change in the P3 component is suggestive of selective auditory attention deficit, and the sensory component (N1) suggests an altered bottom-up processing in individuals with tinnitus.

Literature overview on P3 measurement as an objective measure of auditory performance in post-lingually deaf adults with a cochlear implant

Objective: Cochlear implantation results in restoration of hearing, potential cortical reorganisation and the reallocation of attentional resources to the auditory system. Hence, the distorted cortical activity of patients with profound sensorineural hearing loss may be partially reversed. The measurement of auditory event-related potentials (ERPs) forms a promising electrophysiological evaluation of the central auditory nervous system. In particular, the P3 component is hypothesised to be a differential indicator of subjective auditory discrimination. This overview discusses the association between the cortical P3 component and the performance on auditory tests in post-lingually deaf adults using a CI. Moreover, the current article proposes important guidelines on eliciting, recording and analysing ERPs in CI users.Design: The literature search was conducted in PubMed.Study sample: Articles were included if they focussed on the relationship between P3 and auditory performance of an adult CI population.Results: The higher-order processing of speech in quiet and in noise of adult CI users is correlated with the ERP components, including the P3, shedding light on neurophysiological foundations for auditory performance differences.Conclusions: There is a need for replicating studies with larger sample sizes to fully comprehend the relationship between P3 and the auditory performance of CI users.

Sequential dual-site High-Definition transcranial Direct Current Stimulation (HD-tDCS) treatment in chronic subjective tinnitus: study protocol of a double-blind, randomized, placebo-controlled trial

Background

Chronic tinnitus is a highly prevalent symptom, with many patients reporting considerable effects of tinnitus on quality of life. No clear evidence-based treatment options are currently available. While counseling-based methods are valuable in some cases, they are not sufficiently effective for all tinnitus patients. Neuromodulation techniques such as high-definition transcranial direct current stimulation (HD-tDCS) are proposed to have positive effects on tinnitus severity but, to date, these effects have not been proven conclusively. The proposed trial will investigate the hypothesis that chronic tinnitus patients receiving HD-tDCS will report a positive effect on the impact of tinnitus on daily life, as compared to patients receiving sham stimulation.

Methods

This study proposes a randomized, double-blind, placebo-controlled trial with parallel group design. A total of 100 chronic tinnitus patients will be randomly allocated to an experimental group or a sham group, with allocation stratified according to gender and tinnitus severity. Patient and researcher will be blinded to the patient’s allocation. Patients will undergo six sessions of sequential dual-site HD-tDCS of the left temporal area and the right dorsolateral prefrontal cortex. Evaluations will take place at baseline, immediately following treatment, and at three and six months after the start of the therapy. The primary outcome measure is the change in Tinnitus Functional Index (TFI) score. Secondary outcome measures include audiological measurements, cortical auditory evoked potentials, the Repeatable Battery for the Assessment of Neuropsychological Status adjusted for hearing-impaired individuals (RBANS-H), and supplementary questionnaires probing tinnitus severity and additional symptoms. By use of a linear regression model, the effects of HD-tDCS compared to sham stimulation will be assessed.

Discussion

The objective of this study is to evaluate whether HD-tDCS can reduce the impact of tinnitus on daily life in chronic tinnitus patients. To date, published trials on the effects of HD-tDCS on tinnitus suffer from a lack of standardization and few randomized controlled trials exist. The proposed study will be the first adequately powered trial to investigate the effects of sequential dual-site HD-tDCS on tinnitus severity.

Trial registration

ClinicalTrials.gov, NCT03754127. Registered on 22 November 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3594-y) contains supplementary material, which is available to authorized users.

Learning to Expect: Predicting Sounds During Movement Is Related to Sensorimotor Association During Listening

Sensory experiences, such as sound, often result from our motor actions. Over time, repeated sound-producing performance can generate sensorimotor associations. However, it is not clear how sensory and motor information are associated. Here, we explore if sensory prediction is associated with the formation of sensorimotor associations during a learning task. We recorded event-related potentials (ERPs) while participants produced index and little finger-swipes on a bespoke device, generating novel sounds. ERPs were also obtained as participants heard those sounds played back. Peak suppression was compared to assess sensory prediction. Additionally, transcranial magnetic stimulation (TMS) was used during listening to generate finger-motor evoked potentials (MEPs). MEPs were recorded before and after training upon hearing these sounds, and then compared to reveal sensorimotor associations. Finally, we explored the relationship between these components. Results demonstrated that an increased positive-going peak (e.g., P2) and a suppressed negative-going peak (e.g., N2) were recorded during action, revealing some sensory prediction outcomes (P2: p = 0.050, ηp2 = 0.208; N2: p = 0.001, ηp2 = 0.474). Increased MEPs were also observed upon hearing congruent sounds compared with incongruent sounds (i.e., associated to a finger), demonstrating precise sensorimotor associations that were not present before learning (Index finger: p < 0.001, ηp2 = 0.614; Little finger: p < 0.001, ηp2 = 0.529). Consistent with our broad hypotheses, a negative association between the MEPs in one finger during listening and ERPs during performance of the other was observed (Index finger MEPs and Fz N1 action ERPs; r = −0.655, p = 0.003). Overall, data suggest that predictive mechanisms are associated with the fine-tuning of sensorimotor associations.

Changes in Event-Related Potentials Underlying Coma Recovery in Patients with Large Left Hemispheric Infarction

<strong>BACKGROUND</strong> The aim of this study was to investigate changes in event-related potentials (ERPs) between coma and awakening in patients with large left hemispheric infarction (left LHI). <strong>MATERIAL AND METHODS</strong> Ten patients with left LHI who suffered coma and survived to awaken were enrolled in this study. The eye-opening subscore of the Glasgow Coma Scale (GCS) was used to assess the extent of patients' arousal. ERPs elicited by the passive oddball paradigm were collected during coma and awakening states, respectively. Peak latencies, peak amplitudes, topography, and time-frequency information of P1, N1, P2, and mismatch negativity (MMN) were compared between the 2 sessions. <strong>RESULTS</strong> No significant differences in the peak amplitudes and peak latencies of P1 and N1, but significantly greater P2 amplitude with shorter latency in left hemisphere and midline was shown in the awakening state compared with that in coma. A marked shift of P2 topography in response to deviant tones was also seen, from the right centro-parieto-frontal areas during coma to left frontal-midline areas during awakening. MMN waveforms were not detected in 6/10 patients during the coma state, but these 6 patients all recovered to awakening. Evoked oscillations in bilateral hemisphere were profoundly inhibited during the coma state, with poor inter-trial phase synchronization, while obvious activities with broader frequency ranges and consistent inter-trial phase synchronization were observed during awakening state, and different frequency activities were distributed in distinct brain regions. <strong>CONCLUSIONS</strong> P2 may be a central index of coma recovery and a component of the arousal system. Changes in time-frequency information could provide more information during coma recovery, perhaps including some cognitive processing of the sensory stimulus.

Electrophysiological changes in auditory evoked potentials in rats with salicylate-induced tinnitus

Early-response auditory evoked potentials (AEPs) in humans are significantly altered in tinnitus. These changes are closely related to that seen in animals, leading to new approaches to study tinnitus based on objective parameters. The purpose of this study was to characterize the AEPs in animals with tinnitus, by assessing early to late latency responses. For behavioral evaluation, rats were trained using positive reinforcement to press a lever in the presence of an auditory stimulus and to not press during silence. The auditory brainstem response (ABR), middle latency response (MLR) and auditory late latency response (LLR) were correlated to the false-positive responses (pressing the lever during silence), after oral administrations of Sodium Salicylate (SS, 350 mg/kg). In the present study, SS significantly increased the hearing thresholds and reduced ABR peak I amplitudes across the frequency range (4-32 kHz). In contrast, increased amplitudes were observed for several peaks in ABR, MLR, and LLR. Moreover, reduced ABR latencies in response to 8, 16 and 24 kHz tone bursts were observed after SS administration. Similarly, the central evaluation also revealed significantly reduced latencies in MLR and LLR during SS administration. In contrast, increased latencies were observed for ABR latencies in response to 32 kHz tone bursts, and at the P1-N1 component of LLR. Correlational analysis revealed that latencies and amplitudes of peaks II and IV (8 and 16 kHz) of ABR, and N2 latency and P2-N2 amplitude of LLR were associated with behavioral tinnitus. We suggest that AEPs can be used in the rat to evaluate the reduced sensory input and the increased central gain in SS-induced tinnitus, as well as reduced latencies (8-16 kHz) to distinguish between hearing loss and tinnitus.

Clinical neurophysiology of neurologic rehabilitation

Clinical neurophysiologic testing provides valuable support in predicting outcome in the setting of disorders of consciousness (DOC), including coma and traumatic brain injury (TBI). Electroencephalography (EEG) and evoked potentials (EP) are simple to apply, inexpensive, safe, and available in most rehabilitation facilities. This chapter reviews the use of EEG and EP in postanoxic coma and TBI. Bilateral absence of cortical somatosensory evoked potentials (SSEP) may be regarded as a predictor of poor outcome in hypoxic brain damage. Flash VEP may be useful to differentiate between good and poor outcome. In addition, low EEG frequencies, burst suppression, and isoelectric EEG patterns prognosticate poor outcomes in hypoxic brain damage. While a loss of cortical SSEP is generally regarded as a negative prognostic sign in the acute phase of hypoxic brain damage, absence of cortical SSEP responses is not necessarily associated with poor outcome in TBI. Event-related potentials (ERPs) can provide support in outcome prediction. In particular, the N100, mismatch negativity, P300, and N400 may improve accuracy of outcome prediction DOC of different etiologies. Some evidence suggests that ERPs may be superior to SSEP in predicting functional and DOC outcomes (Lew et al., 2003). ERPs are measured brain responses resulting from specific cognitive tasks, sensory stimulation, or planned motor activity.

Genetic Association between Alzheimer's Disease Risk Variant of the PICALM Gene and Auditory Event-Related Potentials in Aging

Aging and genetic predisposition are major risk factors in age-related neurodegenerative disorders. The most common neurodegenerative disorder is Alzheimer's disease (AD). Genome-wide association studies (GWAS) have identified statistically significant association of the PICALM rs3851179 polymorphism with AD. The PICALM G allele increases the risk of AD, while the A allele has a protective effect. We examined the association of the PICALM rs3851179 polymorphism with parameters of the P3 component of auditory event-related potentials (ERPs) in 87 non-demented volunteers (age, 19-77 years) subdivided into two cohorts younger and older than 50 years of age. We found statistically significant association between the AD risk variant PICALM GG and increase in the P3 latency in subjects over 50 years old. The age-dependent increase in the P3 latency was more pronounced in the PICALM GG carriers than in the carriers of the PICALM AA and PICALM AG genotypes. The observed PICALM-associated changes in the neurophysiological processes indicate a decline in the information processing speed with aging due, probably, to neuronal dysfunction and subclinical neurodegeneration of the neuronal networks in the hippocampus and the frontal and parietal cortical areas. Such changes were less pronounced in the carriers of the PICALM gene A allele, which might explain the protective effect of this allele in the cognitive decline and AD development.

Accessing knowledge of the 'here and now': a new technique for capturing electromagnetic markers of orientation processing

OBJECTIVE

The ability to orient with respect to the current context (e.g. current time or location) is crucial for daily functioning, and is used to measure overall cognitive health across many frontline clinical assessments. However, these tests are often hampered by their reliance on verbal probes (e.g. 'What city are we in?') in evaluating orientation. Objective, physiology-based measures of orientation processing are needed, but no such measures are currently in existence. We report the initial development of potential brainwave-based markers of orientation processing as characterized using electroencephlography (EEG) and magnetoencephalography (MEG).

APPROACH

An auditory stimulus sequence embedded with words corresponding to orientation-relevant (i.e. related to the 'here and now') and orientation-irrelevant (i.e. unrelated to the current context) conditions was used to elicit orientation processing responses. EEG/MEG data, in concert with clinical assessments, were collected from 29 healthy adults. Analysis at sensor and source levels identified and characterized neural signals related to orientation processing.

MAIN RESULTS

Orientation-irrelevant stimuli elicited increased negative amplitude in EEG-derived event-related potential (ERP) waveforms during the 390-570 ms window (p  <  0.05), with cortical activations across the left frontal, temporal, and parietal regions. These effects are consistent with the well-known N400 response to semantic incongruence. In contrast, ERP responses to orientation-relevant stimuli exhibited increased positive amplitude during the same interval (p  <  0.05), with activations across the bilateral temporal and parietal regions. Importantly, these differential responses were robust at the individual level, with machine-learning classification showing high accuracy (89%), sensitivity (0.88) and specificity (0.90).

SIGNIFICANCE

This is the first demonstration of a neurotechnology platform that elicits, captures, and evaluates electrophysiological markers of orientation processing. We demonstrate neural responses to orientation stimuli that are validated across EEG and MEG modalities and robust at the individual level. The extraction of physiology-based markers through this technique may enable improved objective brain functional evaluation in clinical applications.

Influence of Audiovisual Training on Horizontal Sound Localization and Its Related ERP Response

The objective was to investigate the influence of audiovisual training on horizontal sound localization and the underlying neurological mechanisms using a combination of psychoacoustic and electrophysiological (i.e., event-related potential, ERP) measurements on sound localization. Audiovisual stimuli were used in the training group, whilst the control group was trained using auditory stimuli only. Training sessions were undertaken once per day for three consecutive days. Sound localization accuracy was evaluated daily after training, using psychoacoustic tests. ERP responses were measured on the first and last day of tasks. Sound localization was significantly improved in the audiovisual training group when compared to the control group. Moreover, a significantly greater reduction in front-back confusion ratio for both trained and untrained angles was found between pre- and post-test in the audiovisual training group. ERP measurement showed a decrease in N1 amplitude and an increase in P2 amplitude in both groups. However, changes in late components were only found in the audiovisual training group, with an increase in P400 amplitude and decrease in N500 amplitude. These results suggest that the interactive effect of audiovisual localization training is likely to be mediated at a relatively late cognitive processing stage.

Cortical Areas Associated With Mismatch Negativity: A Connectivity Study Using Propofol Anesthesia

Auditory mismatch negativity (MMN) is an event-related potential (ERP) waveform induced by rare deviant stimuli that occur in a stream of regular auditory stimuli. The generators of MMN are believed to include several different cortical regions like the bilateral temporal and the right inferior frontal gyrus (IFG). However, exact cortical regions associated with MMN remain controversial. In this study, we compared the number of long-distance connections induced by the standard and deviant stimuli during awake state and propofol anesthesia state to identify the cortical areas associated with the generation of MMN. In awake state, we find that deviant stimuli synchronize more information between the right frontal and temporal than standard stimuli. Moreover, we find that the deviant stimuli in awake state activate the bilateral frontal, central areas, the left temporal and parietal areas as compared to the anesthesia state, whereas the standard stimuli do not. These results suggest that, in addition to the bilateral temporal and the right IFG, the bilateral frontal and centro-parietal regions also contribute to the generation of MMN.

Conservative therapy for the treatment of patients with somatic tinnitus attributed to temporomandibular dysfunction: study protocol of a randomised controlled trial

BACKGROUND

Tinnitus is a highly prevalent symptom affecting 10-15% of the adult population. It often affects patient quality of life and frequently causes distress. When subjective tinnitus can be elicited by the somatosensory system of the cervical spine or temporomandibular area it is termed somatic tinnitus. The first aim of the current study is to investigate the effect of the best evidence conservative temporomandibular disorder (TMD) treatment on tinnitus in patients with co-existence of tinnitus and TMD or oral parafunctions compared to no treatment. The second aim is to identify a subgroup of patients with tinnitus that benefits from the conservative temporomandibular joint treatment.

METHODS AND DESIGN

This study is a randomised controlled trial with a delayed treatment design. Patients with a TMD (TMD pain screener ≥ 3 points) or oral parafunctions (such as clenching and bruxism), who are suffering from moderate to severe subjective tinnitus (Tinnitus Functional Index (TFI) between 25 and 90 points), will be recruited from the tertiary tinnitus clinic of the University Hospital of Antwerp, Edegem, Belgium. Patients will be excluded in case of clear otological or neurological causes of the tinnitus, progressive middle ear pathology, intracranial pathology, traumatic cervical spine or temporomandibular injury in the past 6 months, severe depression as diagnosed by a psychologist, tumours, previous surgery in the orofacial area, substance abuse that may affect the outcome measures, any contra-indication for physical therapy treatment directed to the orofacial area or when they received TMD treatment in the past 2 months. After screening for eligibility, baseline data among which scores on the TFI, tinnitus questionnaire (TQ), mean tinnitus loudness as measured with visual analogue scale (VAS), TMD pain screener, and a set of temporomandibular joint tests will be collected. Patients will be randomised in an early-start group and in a delayed-start group of therapy by 9 weeks. Patients will receive conservative TMD treatment with a maximum of 18 sessions within 9 weeks. At baseline (week 0), at the start of therapy (weeks 0 or 9), 9 weeks after therapy (weeks 9 or 18), and at follow-up (weeks 18 or 27) data from the TFI, TQ, VAS mean tinnitus loudness and the TMD pain screener will be collected.

DISCUSSION

Herein, we aim to improve the quality of care for patients with tinnitus attributed to TMD or oral parafunctions. By evaluating the effect of state-of-the-art TMD treatment on tinnitus complaints, we can investigate the usefulness of TMD treatment in patients with somatic tinnitus.

TRIAL REGISTRATION

3 July 2017, version 1 of the protocol, ClinicalTrials.gov NCT03209297 .

Auditory Predictive Coding across Awareness States under Anesthesia: An Intracranial Electrophysiology Study

The systems-level mechanisms underlying loss of consciousness (LOC) under anesthesia remain unclear. General anesthetics suppress sensory responses within higher-order cortex and feedback connections, both critical elements of predictive coding hypotheses of conscious perception. Responses to auditory novelty may offer promise as biomarkers for consciousness. This study examined anesthesia-induced changes in auditory novelty responses over short (local deviant [LD]) and long (global deviant [GD]) time scales, envisioned to engage preattentive and conscious levels of processing, respectively. Electrocorticographic recordings were obtained in human neurosurgical patients (3 male, 3 female) from four hierarchical processing levels: core auditory cortex, non-core auditory cortex, auditory-related, and PFC. Stimuli were vowel patterns incorporating deviants within and across stimuli (LD and GD). Subjects were presented with stimuli while awake, and during sedation (responsive) and following LOC (unresponsive) under propofol anesthesia. LD and GD effects were assayed as the averaged evoked potential and high gamma (70-150 Hz) activity. In the awake state, LD and GD effects were present in all recorded regions, with averaged evoked potential effects more broadly distributed than high gamma activity. Under sedation, LD effects were preserved in all regions, except PFC. LOC was accompanied by loss of LD effects outside of auditory cortex. By contrast, GD effects were markedly suppressed under sedation in all regions and were absent following LOC. Thus, although the presence of GD effects is indicative of being awake, its absence is not indicative of LOC. Loss of LD effects in higher-order cortical areas may constitute an alternative biomarker of LOC.SIGNIFICANCE STATEMENT Development of a biomarker that indexes changes in the brain upon loss of consciousness (LOC) under general anesthesia has broad implications for elucidating the neural basis of awareness and clinical relevance to mechanisms of sleep, coma, and disorders of consciousness. Using intracranial recordings from neurosurgery patients, we investigated changes in the activation of cortical networks involved in auditory novelty detection over short (local deviance) and long (global deviance) time scales associated with sedation and LOC under propofol anesthesia. Our results indicate that, whereas the presence of global deviance effects can index awareness, their loss cannot serve as a biomarker for LOC. The dramatic reduction of local deviance effects in areas beyond auditory cortex may constitute an alternative biomarker of LOC.

Processing of auditory novelty across the cortical hierarchy: An intracranial electrophysiology study

Under the predictive coding hypothesis, specific spatiotemporal patterns of cortical activation are postulated to occur during sensory processing as expectations generate feedback predictions and prediction errors generate feedforward signals. Establishing experimental evidence for this information flow within cortical hierarchy has been difficult, especially in humans, due to spatial and temporal limitations of non-invasive measures of cortical activity. This study investigated cortical responses to auditory novelty using the local/global deviant paradigm, which engages the hierarchical network underlying auditory predictive coding over short ('local deviance'; LD) and long ('global deviance'; GD) time scales. Electrocorticographic responses to auditory stimuli were obtained in neurosurgical patients from regions of interest (ROIs) including auditory, auditory-related and prefrontal cortex. LD and GD effects were assayed in averaged evoked potential (AEP) and high gamma (70-150 Hz) signals, the former likely dominated by local synaptic currents and the latter largely reflecting local spiking activity. AEP LD effects were distributed across all ROIs, with greatest percentage of significant sites in core and non-core auditory cortex. High gamma LD effects were localized primarily to auditory cortex in the superior temporal plane and on the lateral surface of the superior temporal gyrus (STG). LD effects exhibited progressively longer latencies in core, non-core, auditory-related and prefrontal cortices, consistent with feedforward signaling. The spatial distribution of AEP GD effects overlapped that of LD effects, but high gamma GD effects were more restricted to non-core areas. High gamma GD effects had shortest latencies in STG and preceded AEP GD effects in most ROIs. This latency profile, along with the paucity of high gamma GD effects in the superior temporal plane, suggest that the STG plays a prominent role in initiating novelty detection signals over long time scales. Thus, the data demonstrate distinct patterns of information flow in human cortex associated with auditory novelty detection over multiple time scales.

Probing Electrophysiological Indices of Perceptual Awareness across Unisensory and Multisensory Modalities

The neural underpinnings of perceptual awareness have been extensively studied using unisensory (e.g., visual alone) stimuli. However, perception is generally multisensory, and it is unclear whether the neural architecture uncovered in these studies directly translates to the multisensory domain. Here, we use EEG to examine brain responses associated with the processing of visual, auditory, and audiovisual stimuli presented near threshold levels of detectability, with the aim of deciphering similarities and differences in the neural signals indexing the transition into perceptual awareness across vision, audition, and combined visual-auditory (multisensory) processing. More specifically, we examine (1) the presence of late evoked potentials (∼>300 msec), (2) the across-trial reproducibility, and (3) the evoked complexity associated with perceived versus nonperceived stimuli. Results reveal that, although perceived stimuli are associated with the presence of late evoked potentials across each of the examined sensory modalities, between-trial variability and EEG complexity differed for unisensory versus multisensory conditions. Whereas across-trial variability and complexity differed for perceived versus nonperceived stimuli in the visual and auditory conditions, this was not the case for the multisensory condition. Taken together, these results suggest that there are fundamental differences in the neural correlates of perceptual awareness for unisensory versus multisensory stimuli. Specifically, the work argues that the presence of late evoked potentials, as opposed to neural reproducibility or complexity, most closely tracks perceptual awareness regardless of the nature of the sensory stimulus. In addition, the current findings suggest a greater similarity between the neural correlates of perceptual awareness of unisensory (visual and auditory) stimuli when compared with multisensory stimuli.

Fifty years of microneurography: learning the language of the peripheral sympathetic nervous system in humans

As a primary component of homeostasis, the sympathetic nervous system enables rapid adjustments to stress through its ability to communicate messages among organs and cause targeted and graded end organ responses. Key in this communication model is the pattern of neural signals emanating from the central to peripheral components of the sympathetic nervous system. But what is the communication strategy employed in peripheral sympathetic nerve activity (SNA)? Can we develop and interpret the system of coding in SNA that improves our understanding of the neural control of the circulation? In 1968, Hagbarth and Vallbo (Hagbarth KE, Vallbo AB. Acta Physiol Scand 74: 96-108, 1968) reported the first use of microneurographic methods to record sympathetic discharges in peripheral nerves of conscious humans, allowing quantification of SNA at rest and sympathetic responsiveness to physiological stressors in health and disease. This technique also has enabled a growing investigation into the coding patterns within, and cardiovascular outcomes associated with, postganglionic SNA. This review outlines how results obtained by microneurographic means have improved our understanding of SNA outflow patterns at the action potential level, focusing on SNA directed toward skeletal muscle in conscious humans.