Sequence Of Auditory Stimuli Research Articles

Changes in high-frequency neural inputs to muscles during movement cancellation

Objective.Cortical beta (13-30 Hz) and gamma (30-60 Hz) oscillations are prominent in the motor cortex and are known to be transmitted to the muscles despite their limited direct impact on force modulation. However, we currently lack fundamental knowledge about the saliency of these oscillations at spinal level. Here, we developed an experimental approach to examine the modulations in high-frequency inputs to motoneurons under different motor states while maintaining a stable force, thus constraining behaviour.Approach.Specifically, we acquired brain and muscle activity during a 'GO'/'NO-GO' task. In this experiment, the effector muscle for the task (tibialis anterior) was kept tonically active during the trials, while participants (N= 12) reacted to sequences of auditory stimuli by either keeping the contraction unaltered ('NO-GO' trials), or by quickly performing a ballistic contraction ('GO' trials). Motor unit (MU) firing activity was extracted from high-density surface and intramuscular electromyographic signals, and the changes in its spectral contents in the 'NO-GO' trials were analysed.Main results.We observed an increase in beta and low-gamma (30-45 Hz) activity after the 'NO-GO' cue in the MU population activity. These results were in line with the brain activity changes measured with electroencephalography. These increases in power occur without relevant alterations in force, as behaviour was restricted to a stable force contraction.Significance.We show that modulations in motor cortical beta and gamma rhythms are also present in muscles when subjects cancel a prepared ballistic action while holding a stable contraction in a 'GO'/'NO-GO' task. This occurs while force levels produced by the task effector muscle remain largely unaltered. Our results suggest that muscle recordings are informative also about motor states that are not force-control signals. This opens up new potential use cases of peripheral neural interfaces.

Pupil diameter as an indicator of sound pair familiarity after statistically structured auditory sequence

Inspired by recent findings in the visual domain, we investigated whether the stimulus-evoked pupil dilation reflects temporal statistical regularities in sequences of auditory stimuli. We conducted two preregistered pupillometry experiments (experiment 1, n = 30, 21 females; experiment 2, n = 31, 22 females). In both experiments, human participants listened to sequences of spoken vowels in two conditions. In the first condition, the stimuli were presented in a random order and, in the second condition, the same stimuli were presented in a sequence structured in pairs. The second experiment replicated the first experiment with a modified timing and number of stimuli presented and without participants being informed about any sequence structure. The sound-evoked pupil dilation during a subsequent familiarity task indicated that participants learned the auditory vowel pairs of the structured condition. However, pupil diameter during the structured sequence did not differ according to the statistical regularity of the pair structure. This contrasts with similar visual studies, emphasizing the susceptibility of pupil effects during statistically structured sequences to experimental design settings in the auditory domain. In sum, our findings suggest that pupil diameter may serve as an indicator of sound pair familiarity but does not invariably respond to task-irrelevant transition probabilities of auditory sequences.

Opposing serial dependencies revealed for sequences of auditory emotional stimuli.

Our percept of the world is not solely determined by what we perceive and process at a given moment in time, but also depends on what we processed recently. In the present study, we investigate whether the perceived emotion of a spoken sentence is contingent upon the emotion of an auditory stimulus on the preceding trial (i.e., serial dependence). Thereto, participants were exposed to spoken sentences that varied in emotional affect by changing the prosody that ranged from 'happy' to 'fearful'. Participants were instructed to rate the emotion. We found a positive serial dependence for emotion processing whereby the perceived emotion was biased towards the emotion on the preceding trial. When we introduced 'no-go' trials (i.e., no rating was required), we found a negative serial dependence when participants knew in advance to withhold their response on a given trial (Experiment 2) and a positive serial dependence when participants received the information to withhold their response after the stimulus presentation (Experiment 3). We therefore established a robust serial dependence for emotion processing in speech and introduce a methodology to disentangle perceptual from post-perceptual processes. This approach can be applied to the vast majority of studies investigating sequential dependencies to separate positive from negative serial dependence.

A-46 MMA Athletes Demonstrate Different Brain Vital Sign Profiles Compared to Matched Controls at “Baseline”

Abstract Purpose We compared objective brain vital sign metrics derived from event-related potentials (ERPs) of mixed martial arts (MMA) athletes and matched control participants. Methods We recorded 101 successful EEG scans from 12 MMA athletes (24.8 ± 2.6 yr) and 18 matched control participants (26.5±3.5 yr). For this analysis, only “baseline” scans were considered (n=30). “Baseline” was at least 90 days from a previous fight and 90 days (MMA) or 1 year (control) following medical clearance from a previously diagnosed concussion. We derived objective, clinical metrics (brain vital signs) from ERPs for auditory sensation (N100), basic attention (P300), and cognitive processing (N400) evoked while participants listen to a 6-minute auditory stimulus sequence. EEG data were processed using standard methods. N100, P300, and N400 amplitudes and latencies were manually identified on evoked potential waveforms by a blinded reviewer. Differences between groups at the waveform level were evaluated with a mass-univariate analysis using non-parametric resampling. Brain vital signs were compared across groups with a Kruskal-Wallis H-test for independent samples, with FDR correction for multiple comparisons. Results Mass-univariate waveform analyses showed significant differences (P < 0.05) between MMA athletes and controls in both P300 and N400 ERPs. The Kruskal-Wallis test identified a significant difference in N400 amplitude (H=7.04, P=.008, Padj=.047) between MMA athletes and controls. Conclusions MMA athletes demonstrate significant differences in “baseline” brain vital signs compared to controls, indicating that exposure to repetitive head impacts in MMA may be associated with subconcussive changes in brain function.

Variance aftereffect within and between sensory modalities for visual and auditory domains.

We can grasp various features of the outside world using summary statistics efficiently. Among these statistics, variance is an index of information homogeneity or reliability. Previous research has shown that visual variance information in the context of spatial integration is encoded directly as a unique feature, and currently perceived variance can be distorted by that of the preceding stimuli. In this study, we focused on variance perception in temporal integration. We investigated whether any variance aftereffects occurred in visual size and auditory pitch. Furthermore, to examine the mechanism of cross-modal variance perception, we also investigated whether variance aftereffects occur between different modalities. Four experimental conditions (a combination of sensory modalities of adaptor and test: visual-to-visual, visual-to-auditory, auditory-to-auditory, and auditory-to-visual) were conducted. Participants observed a sequence of visual or auditory stimuli perturbed in size or pitch with certain variance and performed a variance classification task before and after the variance adaptation phase. We found that in visual size, within modality adaptation to small or large variance, resulted in a variance aftereffect, indicating that variance judgments are biased in the direction away from that of the adapting stimulus. In auditory pitch, within modality adaptation to small variance caused variance aftereffect. For cross-modal combinations, adaptation to small variance in visual size resulted in variance aftereffect. However, the effect was weak, and variance aftereffect did not occur in other conditions. These findings indicate that the variance information of sequentially presented stimuli is encoded independently in visual and auditory domains.

Retrieving the structure of probabilistic sequences of auditory stimuli from EEG data

Using a new probabilistic approach we model the relationship between sequences of auditory stimuli generated by stochastic chains and the electroencephalographic (EEG) data acquired while 19 participants were exposed to those stimuli. The structure of the chains generating the stimuli are characterized by rooted and labeled trees whose leaves, henceforth called contexts, represent the sequences of past stimuli governing the choice of the next stimulus. A classical conjecture claims that the brain assigns probabilistic models to samples of stimuli. If this is true, then the context tree generating the sequence of stimuli should be encoded in the brain activity. Using an innovative statistical procedure we show that this context tree can effectively be extracted from the EEG data, thus giving support to the classical conjecture.

Tracking the Effects of Top-Down Attention on Word Discrimination Using Frequency-tagged Neuromagnetic Responses.

Discrimination of words from nonspeech sounds is essential in communication. Still, how selective attention can influence this early step of speech processing remains elusive. To answer that question, brain activity was recorded with magnetoencephalography in 12 healthy adults while they listened to two sequences of auditory stimuli presented at 2.17 Hz, consisting of successions of one randomized word (tagging frequency = 0.54 Hz) and three acoustically matched nonverbal stimuli. Participants were instructed to focus their attention on the occurrence of a predefined word in the verbal attention condition and on a nonverbal stimulus in the nonverbal attention condition. Steady-state neuromagnetic responses were identified with spectral analysis at sensor and source levels. Significant sensor responses peaked at 0.54 and 2.17 Hz in both conditions. Sources at 0.54 Hz were reconstructed in supratemporal auditory cortex, left superior temporal gyrus (STG), left middle temporal gyrus, and left inferior frontal gyrus. Sources at 2.17 Hz were reconstructed in supratemporal auditory cortex and STG. Crucially, source strength in the left STG at 0.54 Hz was significantly higher in verbal attention than in nonverbal attention condition. This study demonstrates speech-sensitive responses at primary auditory and speech-related neocortical areas. Critically, it highlights that, during word discrimination, top-down attention modulates activity within the left STG. This area therefore appears to play a crucial role in selective verbal attentional processes for this early step of speech processing.

Auditory and tactile frequency representations are co-embedded in modality-defined cortical sensory systems

Sensory information is represented and elaborated in hierarchical cortical systems that are thought to be dedicated to individual sensory modalities. This traditional view of sensory cortex organization has been challenged by recent evidence of multimodal responses in primary and association sensory areas. Although it is indisputable that sensory areas respond to multiple modalities, it remains unclear whether these multimodal responses reflect selective information processing for particular stimulus features. Here, we used fMRI adaptation to identify brain regions that are sensitive to the temporal frequency information contained in auditory, tactile, and audiotactile stimulus sequences. A number of brain regions distributed over the parietal and temporal lobes exhibited frequency-selective temporal response modulation for both auditory and tactile stimulus events, as indexed by repetition suppression effects. A smaller set of regions responded to crossmodal adaptation sequences in a frequency-dependent manner. Despite an extensive overlap of multimodal frequency-selective responses across the parietal and temporal lobes, representational similarity analysis revealed a cortical “regional landscape” that clearly reflected distinct somatosensory and auditory processing systems that converged on modality-invariant areas. These structured relationships between brain regions were also evident in spontaneous signal fluctuation patterns measured at rest. Our results reveal that multimodal processing in human cortex can be feature-specific and that multimodal frequency representations are embedded in the intrinsically hierarchical organization of cortical sensory systems.

Cognitive entrainment to isochronous rhythms is independent of both sensory modality and top-down attention

Abstract The anisochrony of a stimulus sequence was manipulated parametrically to investigate whether rhythmic entrainment is stronger in the auditory modality than in the visual modality (Experiment 1), and whether it relies on top-down attention (Experiment 2). In Experiment 1, participants had to respond as quickly as possible to a target presented after a sequence of either visual or auditory stimuli. The anisochrony of this sequence was manipulated parametrically, rather than in an all or none fashion; that is, it could range from smaller to larger deviations of the isochrony (0, 10, 20, 50, 100, 150 and 200 ms). We compared rhythmic entrainment patterns for auditory and visual modalities. Results showed a peak of entrainment for both isochrony and deviations of isochrony up to 50 ms (i.e., participants were equally fast both after the isochronous sequences and after 10, 20 and 50 ms deviations), suggesting that anisochronous sequences can also produce entrainment. Beyond this entrainment window, the reaction times became progressively slower. Surprisingly, no differences were found between the entrainment patterns for auditory and visual rhythms. In Experiment 2, we used a dual-task methodology by adding a working memory n-back task to the procedure of Experiment 1. Results did not show interference of the secondary task in either auditory or visual modalities, with participants showing the same entrainment pattern as in Experiment 1. These results suggest that rhythmic entrainment constitutes a cognitive process that occurs by default (automatically), regardless of the modality in which the stimuli are presented, and independent of top-down attention, to generate behavioural benefits.

Pre- and Post-Season Electroencephalography Measures of Brain Vital Signs in Youth Football Players

Amid growing concern of potential brain trauma caused by repetitive head impacts (RHI) in youth football, there is an emerging need to develop objective, physiologic assessments of brain function that can identify sub-concussive impairment. Electroencephalography (EEG) may be a viable tool to evaluate neurologic dysfunction associated with RHI. PURPOSE: To evaluate the neurophysiologic activity of youth football players in association with RHI. METHODS: EEG data were captured from nine middle school football players (13.1 ± 0.5 yr) before (PRE) and after (POST) one season using a portable 8-channel EEG cap with three electrodes (Fz, Cz and Pz) while subjects listened to an auditory stimulus sequence (~5 min). Amplitudes (A) and latencies (L) of event-related potentials (ERP) corresponding to auditory sensation (N100A, N100L), basic attention (P300A, P300L), and cognitive processing (N400A, N400L) were converted to normalized brain vital signs scores (0-100 scale). Larger ERP amplitudes equate to higher scores and delayed latencies equate to lower scores. RHI were measured during the season via accelerometry (Head Impact Telemetry System). EEG data from three subjects were of insufficient quality for analysis; thus, results were limited to the six remaining subjects. RESULTS: Scores for N400L decreased significantly (P = 0.031) from PRE (63.9 ± 7.6) to POST (38.2 ± 16.8). There were no significant changes in N100A (P = 0.971), N100L (P = 0.308), P300A (P = 0.562), P300L (P = 0.183), or N400A (P = 0.685) scores. On average, players sustained 134 ± 66 head impacts during the season. Head impact frequency was not significantly associated with any brain vital signs score (P = 0.169-0.783). CONCLUSION: In this small sample of youth football players, cognitive processing was delayed following a single season as measured by the significant reduction in N400 latency scores. However, this change was not associated with RHI incurred by the players. While these data should be interpreted with caution, they provide preliminary evidence for the potential value of using the brain vital signs framework to evaluate brain function and sub-concussive impairment in collision-sport athletes. This work was supported by a grant from the T. Denny Sanford Pediatric Collaborative Research Fund between Mayo Clinic and Sanford Health.

Serial dependence generalizes across different stimulus formats, but not different sensory modalities

Visual perception is thought to be supported by a stabilization mechanism integrating information over time, resulting in a systematic attractive bias in experimental contexts. Previous studies show that this effect, whereby a current stimulus appears more similar to the one previous to it, depends on attention, suggesting an active high-level mechanism that modulates perception. Here, we test the hypothesis that such a mechanism generalizes across different stimulus formats or sensory modalities, effectively abstracting from the low-level properties of the stimuli. Participants performed a numerosity discrimination task, with task-relevant dot-array stimuli preceded by a sequence of visual (flashes) or auditory (tones) stimuli encompassing different numerosities. Our results show a clear attractive bias induced by visual sequential numerosity affecting an array of simultaneously presented dots, thus operating across different stimulus formats. Conversely, auditory sequences did not affect the judgment on visual numerosities. Overall, our results demonstrate that serial dependence in numerosity perception operates according to the abstract representation of numerical magnitude of visual stimuli irrespective of their format. These results thus support the idea that a high-level mechanism mediates visual stability and continuity, which integrates relevant information over time irrespective of the low-level sensory properties of the stimuli.

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.

F153. NEUROMAGNETIC MISMATCH NEGATIVITY IN CLINICAL HIGH RISK AND FIRST-EPISODE PSYCHOSIS INDIVIDUALS

BackgroundAuditory mismatch negativity (MMN) and its magnetic counterpart (MMNm) are event-related potentials/fields elicited by violations of previously established auditory regularities (Näätänen et al. 2007). Reduced MMN amplitude is a robust finding in both medicated and unmedicated schizophrenia (ScZ) patients (for a review, see Umbricht & Krljes, 2005), potentially indicating impaired predictive processes (Sauer et al. 2017). Furthermore, several studies have examined MMN responses in individuals at clinical high risk for psychosis (CHR) and have found MMN deficits to be present already in this population, indicating that MMN is compromised before psychosis onset and could represent a marker of risk for psychosis development. However, not all studies have reported significant differences in MMN amplitude between clinical high risk and healthy individuals and there is evidence to suggest that MMN deficits are primarily observed in CHR individuals who transition to psychosis (Bodatsch et al., 2015).MethodsThe purpose of the present study is to investigate MEG recorded MMNm amplitude responses to both duration deviants and sound omissions in n = 90 CHR-individuals who were screened with the Schizophrenia Proneness Instrument and the Comprehensive Assessment of At Risk Mental States. N = 50 healthy controls served as a comparison group. We employed an auditory oddball paradigm in which three different sequences of auditory stimuli were presented binaurally at ~ 70 dB (150 ms SOA, 700 – 100 ms ISI). The standard sequence contained five identical tones (80 ms) and the deviant sequence contained four identical tones and one duration deviant tone (40 ms). In addition, an omission sequence which contained only four identical tones was included to examine auditory predictions. Participants were instructed to focus their attention away from the sounds and to perform a simple visual detection task. We analyzed MMNm responses to unpredictable deviant and omitted sounds in bsensor and source space. The linearly constrained minimum variance (LCMV) beamformer was used to identify the generators of the MMNm responses and to compute artefact-free source-level time-courses.ResultsConsistent with previous studies revealing MMN sources in auditory cortical areas, bilateral MMNm sources were localized in auditory cortices for both duration deviants and sound omissions. Our data show attenuated MMNm responses elicited by duration deviant sounds in CHR individuals compared to healthy controls.DiscussionTaken together, the study findings suggest that reduced MMNm amplitude is present before psychosis onset and reflects aberrant predictive processing rather than deficient stimulus-specific adaptation. Clinical follow-up measurements will be obtained to determine whether MMNm amplitudes are a potential biomarker for predicting onset of psychosis.

Parasympathetic activation enhanced by slow respiration modulates early auditory sensory gating.

Sensory gating is a preattentional mechanism to filter irrelevant information from the environment. It is typically reflected as a suppression of the event-related P50 component for successive sounds in the auditory modality. Although stress-induced sympathetic activation has been reported to disrupt P50 suppression, little is known about the modulatory effect of parasympathetic activation on early auditory sensory gating. We determined the parasympathetic effect on the magnetic P50 (P50m) suppression by controlling the respiratory rhythm and recording data simultaneously with magnetoencephalography and electrocardiography, using three successive click sounds as stimulus and ten normal individuals as study participants. The respiratory rhythm was guided by visual cues and set at 0.3, 0.25, or 0.2 Hz for distinct auditory stimulus sequence blocks. Heart rate variability analysis showed that slow respiration leads to significantly large high-frequency power, which is known as the parasympathetic index, whereas low-frequency/high-frequency ratio, known as the sympathetic index, did not differ with the respiratory rhythm. Although P50m suppression was observed in the left and right primary auditory areas for every respiratory condition, the left P50m intensity for the first sound was significantly decreased in the case of slow respiration, thereby indicating disruption of the left P50m suppression. Since background alpha oscillatory power, reflecting the arousal level, was similar for every respiratory rhythm, it is concluded that parasympathetic activation enhanced by slow respiration modulates P50m gating by reducing the initial neural sensitivity for an auditory input. Not only sympathetic but also parasympathetic effects should be considered in the evaluation of P50/P50m biomarkers.

The Dorsal Attention Network Reflects Both Encoding Load and Top-down Control during Working Memory.

The dorsal attention network is consistently involved in verbal and visual working memory (WM) tasks and has been associated with task-related, top-down control of attention. At the same time, WM capacity has been shown to depend on the amount of information that can be encoded in the focus of attention independently of top-down strategic control. We examined the role of the dorsal attention network in encoding load and top-down memory control during WM by manipulating encoding load and memory control requirements during a short-term probe recognition task for sequences of auditory (digits, letters) or visual (lines, unfamiliar faces) stimuli. Encoding load was manipulated by presenting sequences with small or large sets of memoranda while maintaining the amount of sensory stimuli constant. Top-down control was manipulated by instructing participants to passively maintain all stimuli or to selectively maintain stimuli from a predefined category. By using ROI and searchlight multivariate analysis strategies, we observed that the dorsal attention network encoded information for both load and control conditions in verbal and visuospatial modalities. Decoding of load conditions was in addition observed in modality-specific sensory cortices. These results highlight the complexity of the role of the dorsal attention network in WM by showing that this network supports both quantitative and qualitative aspects of attention during WM encoding, and this is in a partially modality-specific manner.

Auditory and Visual Sequence Learning in Humans and Monkeys using an Artificial Grammar Learning Paradigm

Language flexibly supports the human ability to communicate using different sensory modalities, such as writing and reading in the visual modality and speaking and listening in the auditory domain. Although it has been argued that nonhuman primate communication abilities are inherently multisensory, direct behavioural comparisons between human and nonhuman primates are scant. Artificial grammar learning (AGL) tasks and statistical learning experiments can be used to emulate ordering relationships between words in a sentence. However, previous comparative work using such paradigms has primarily investigated sequence learning within a single sensory modality. We used an AGL paradigm to evaluate how humans and macaque monkeys learn and respond to identically structured sequences of either auditory or visual stimuli. In the auditory and visual experiments, we found that both species were sensitive to the ordering relationships between elements in the sequences. Moreover, the humans and monkeys produced largely similar response patterns to the visual and auditory sequences, indicating that the sequences are processed in comparable ways across the sensory modalities. These results provide evidence that human sequence processing abilities stem from an evolutionarily conserved capacity that appears to operate comparably across the sensory modalities in both human and nonhuman primates. The findings set the stage for future neurobiological studies to investigate the multisensory nature of these sequencing operations in nonhuman primates and how they compare to related processes in humans.

Stimulus-Induced Rhythmic, Periodic, or Ictal Discharges in Coma-Incidence and Interrater Reliability of Continuous EEG After a Standard Stimulation Protocol: A Prospective Study.

Stimulus-induced rhythmic, periodic, or ictal discharges (SIRPIDs) are often seen during continuous electroencephalographic (cEEG) monitoring in coma. Given their uncertain clinical significance, our prospective study evaluated incidence of SIRPIDs in comatose patients in the neuroscience intensive care unit (NSICU) who underwent a standard stimulation protocol and defined interreader reliability for cEEG. Of 146 patients prospectively screened who underwent cEEG during a 6-month period, 53 patients were included and 93 patients were excluded. Our protocol used a sequence of auditory, mild tactile, and painful stimuli tested in a quiet room. Continuous electroencephalogram were then reviewed offline by blinded experts, with interrater agreement assessed by kappa statistic. By Pearson χ and Wilcoxon rank-sum tests, we then compared binary and numerical clinical features between those with and without SIRPIDs. Of 53 patients who underwent our protocol, one patient with a corrupt cEEG file was excluded. Traumatic brain injury was the most common diagnosis. Moderate interrater agreement was observed for 66 total stimulations: 20 patients (38.5%) had possible or definite SIRPIDs by minimum one reviewer. For 19 stimulations reviewed by a third reviewer, consensus was reached in 10 cases making the incidence of SIRPIDs 19.3% in our cohort. There was a moderate interrate agreement with kappa of 0.5 (95% confidence interval: 0.1, 0.7). Median intensive care unit stay was 15 days in patients with SIRPIDs versus 6.5 days in those without (P = 0.021). Our prospective study of SIRPIDs in the neuroscience intensive care unit found a 19% incidence by cEEG using a standard stimulation protocol, most often rhythmic delta activity, and showed a moderate interrater agreement.

Right hemisphere pitch-mismatch negativity reduction in patients with major depression: An MEG study

BackgroundThe mismatch negativity (MMN) component of the event-related potential and its magnetic counterpart, the MMNm, are generated by a mismatch between the physical features of a deviant stimulus and a neuronal sensory-memory trace produced by repetitive standard stimuli. Deficits in the MMN/MMNm have been reported in patients with major depression; however, the results are inconsistent. The present study investigated the pitch-MMNm in patients with major depression using whole-head 306-channel magnetoencephalography (MEG). MethodsTwenty patients with major depression and 36 healthy subjects participated in this study. Subjects were presented with two sequences of auditory stimuli. One consisted of 1000Hz standard signals (probability=90%) and 1200Hz deviant signals (probability=10%), while the other consisted of 1200Hz standard (90%) and 1000Hz deviant signals (10%). Event-related brain responses to standard tones were subtracted from responses to deviant tones. ResultsMajor depressive patients showed significantly reduced magnetic global field power (GFP) of MMNm in the right hemisphere (p=0.02), although no significant MMNm reduction was observed in the left hemisphere (p=0.81). Additionally, patients with major depression showed significantly earlier bilateral MMNm peak latencies (p=0.004). No significant associations were observed between MMNm variables and demographic data/clinical variables within the patients. LimitationsWe could not exclude the effects of antidepressants, mood stabilizers, or neuroleptics on the MMNm abnormalities found in patients with major depression. Sample size was also insufficient to permit subgroup analyses. ConclusionsPatients with major depression exhibited reduced GFP of MMNm in the right hemisphere. The present study suggested that patients with major depression may have right hemispheric dominant preattentive dysfunction.

Different spatio-temporal electroencephalography features drive the successful decoding of binaural and monaural cues for sound localization.

The human ability to localize sound is essential for monitoring our environment and helps us to analyse complex auditory scenes. Although the acoustic cues mediating sound localization have been established, it remains unknown how these cues are represented in human cortex. In particular, it is still a point of contention whether binaural and monaural cues are processed by the same or distinct cortical networks. In this study, participants listened to a sequence of auditory stimuli from different spatial locations while we recorded their neural activity using electroencephalography (EEG). The stimuli were presented over a loudspeaker array, which allowed us to deliver realistic, free-field stimuli in both the horizontal and vertical planes. Using a multivariate classification approach, we showed that it is possible to decode sound source location from scalp-recorded EEG. Robust and consistent decoding was shown for stimuli that provide binaural cues (i.e. Left vs. Right stimuli). Decoding location when only monaural cues were available (i.e. Front vs. Rear and elevational stimuli) was successful for a subset of subjects and showed less consistency. Notably, the spatio-temporal pattern of EEG features that facilitated decoding differed based on the availability of binaural and monaural cues. In particular, we identified neural processing of binaural cues at around 120ms post-stimulus and found that monaural cues are processed later between 150 and 200ms. Furthermore, different spatial activation patterns emerged for binaural and monaural cue processing. These spatio-temporal dissimilarities suggest the involvement of separate cortical mechanisms in monaural and binaural acoustic cue processing.

Auditory prediction errors as individual biomarkers of schizophrenia.

Schizophrenia is a complex psychiatric disorder, typically diagnosed through symptomatic evidence collected through patient interview. We aim to develop an objective biologically-based computational tool which aids diagnosis and relies on accessible imaging technologies such as electroencephalography (EEG). To achieve this, we used machine learning techniques and a combination of paradigms designed to elicit prediction errors or Mismatch Negativity (MMN) responses. MMN, an EEG component elicited by unpredictable changes in sequences of auditory stimuli, has previously been shown to be reduced in people with schizophrenia and this is arguably one of the most reproducible neurophysiological markers of schizophrenia.EEG data were acquired from 21 patients with schizophrenia and 22 healthy controls whilst they listened to three auditory oddball paradigms comprising sequences of tones which deviated in 10% of trials from regularly occurring standard tones. Deviant tones shared the same properties as standard tones, except for one physical aspect: 1) duration - the deviant stimulus was twice the duration of the standard; 2) monaural gap - deviants had a silent interval omitted from the standard, or 3) inter-aural timing difference, which caused the deviant location to be perceived as 90° away from the standards.We used multivariate pattern analysis, a machine learning technique implemented in the Pattern Recognition for Neuroimaging Toolbox (PRoNTo) to classify images generated through statistical parametric mapping (SPM) of spatiotemporal EEG data, i.e. event-related potentials measured on the two-dimensional surface of the scalp over time. Using support vector machine (SVM) and Gaussian processes classifiers (GPC), we were able classify individual patients and controls with balanced accuracies of up to 80.48% (p-values = 0.0326, FDR corrected) and an ROC analysis yielding an AUC of 0.87. Crucially, a GP regression revealed that MMN predicted global assessment of functioning (GAF) scores (correlation = 0.73, R2 = 0.53, p = 0.0006).