Central Scalp Regions Research Articles

Improving Tracking of Selective Attention in Hearing Aid Users: The Role of Noise Reduction and Nonlinearity Compensation.

Hearing impairment (HI) disrupts social interaction by hindering the ability to follow conversations in noisy environments. While hearing aids (HAs) with noise reduction (NR) partially address this, the "cocktailparty problem" persists, where individuals struggle to attend to specific voices amidst background noise. This study investigated how NR and an advanced signal processing method for compensating for nonlinearities in EEG signals can improve neural speech processing in HI listeners. Participants wore hearing aids with NR, either activated or deactivated, while focusing on target speech amidst competing masker speech and background noise. Analysis focused on temporal response functions to assess neural tracking of relevant target and masker speech. Results revealed enhanced neural responses (N1 and P2) to target speech, particularly in frontal and central scalp regions, when NR was activated. Additionally, a novel method compensated for nonlinearities in EEG data, leading to improved signal-to-noise ratio (SNR) and potentially revealing more precise neural tracking of relevant speech. This effect was most prominent in the left-frontal scalp region. Importantly, NR activation significantly improved the effectiveness of this method, leading to stronger responses and reduced variance in EEG data and potentially revealing more precise neural tracking of relevant speech. This study provides valuable insights into the neural mechanisms underlying NR benefits and introduces a promising EEG analysis approach sensitive to NR effects, paving the way for potential improvements in HAs.Significance Statement Understanding how hearing aids (HAs) with noise reduction (NR) improve selective auditory attention in noisy environments is crucial for future advancements. This study investigated the neural effects of NR in hearing-impaired listeners using EEG. We observed significantly enhanced neural responses (N1 and P2 peaks) to target speech with NR activated, suggesting improved speech tracking in frontal and central scalp regions. The advanced signal processing method also compensated for nonlinearities in EEG data, improving the signal-to-noise ratio (SNR) and revealing more precise neural tracking, particularly in the left-frontal scalp region. This study sheds light on the neural mechanisms behind NR benefits and introduces a promising EEG analysis method sensitive to NR effects, paving the way for optimizing future HAs.

Contribution of Scalp Regions to Machine Learning-Based Classification of Dementia Utilizing Resting-State qEEG Signals.

This study aims to investigate using eyes-open (EO) and eyes-closed (EC) resting-state EEG data to diagnose cognitive impairment using machine learning methods, enhancing timely intervention and cost-effectiveness in dementia research. A total of 890 participants aged 40-90 were included in the study, comprising 269healthy controls (HC), 356 individuals with mild cognitive impairment (MCI), and 265 with Alzheimer's disease (AD) from a cohort study. Resting-state EEG (rEEG) signals were recorded and transformed into relative power spectral density (PSD) data for analysis. The processed PSD data, representing 19 scalp regions, were then input into a Random Forest (RF) machine learning classifier to identify distinctive EEG patterns across the groups. Statistical comparisons between the groups were conducted using one-way ANOVA, applied to the relative PSD features extracted from the EEG data, to assess significant differences in EEG activity across the diagnostic categories. The study found that rEEG-based categorization effectively differentiates between cognitively impaired individuals and healthy individuals. The EO rEEG achieved the highest performance metrics across various models. For HC vs MCI (combined hemisphere), the accuracy, sensitivity, specificity, and AUC were 92%, 99%, 83%, and 96%, respectively. For HC vs AD (parietal, temporal, occipital), these metrics were 95%, 96%, 94%, and 99%. The HC vs CASE (MCI + AD) (combined hemisphere) results were 90%, 99%, 73%, and 92%. The metrics for HC vs MCI vs AD (frontal, parietal, temporal) were 89%, 88%, 94%, and 96%. The study demonstrates that EO rEEG can effectively distinguish between cognitive impairment and healthy states, leading to early diagnosis, cost-effective treatment, and better clinical outcomes for dementia patients. EO and EC rEEG models trained with relative PSD, particularly from parietal, temporal, occipital, and central scalp regions, can significantly assist clinicians in practice.

Corticomotor Plasticity Underlying Priming Effects of Motor Imagery on Force Performance.

The neurophysiological processes underlying the priming effects of motor imagery (MI) on force performance remain poorly understood. Here, we tested whether the priming effects of embedded MI practice involved short-term changes in corticomotor connectivity. In a within-subjects counterbalanced experimental design, participants (n = 20) underwent a series of experimental sessions consisting of successive maximal isometric contractions of elbow flexor muscles. During inter-trial rest periods, we administered MI, action observation (AO), and a control passive recovery condition. We collected electromyograms (EMG) from both agonists and antagonists of the force task, in addition to electroencephalographic (EEG) brain potentials during force trials. Force output was higher during MI compared to AO and control conditions (both p < 0.01), although fatigability was similar across experimental conditions. We also found a weaker relationship between triceps brachii activation and force output during MI and AO compared to the control condition. Imaginary coherence topographies of alpha (8-12 Hz) oscillations revealed increased connectivity between EEG sensors from central scalp regions and EMG signals from agonists during MI, compared to AO and control. Present results suggest that the priming effects of MI on force performance are mediated by a more efficient cortical drive to motor units yielding reduced agonist/antagonist coactivation.

Identifying Individuals With Mild Cognitive Impairment Using Working Memory-Induced Intra-Subject Variability of Resting-State EEGs.

Individuals with mild cognitive impairment (MCI) are at high risk of developing into dementia (e. g., Alzheimer's disease, AD). A reliable and effective approach for early detection of MCI has become a critical challenge. Although compared with other costly or risky lab tests, electroencephalogram (EEG) seems to be an ideal alternative measure for early detection of MCI, searching for valid EEG features for classification between healthy controls (HCs) and individuals with MCI remains to be largely unexplored. Here, we design a novel feature extraction framework and propose that the spectral-power-based task-induced intra-subject variability extracted by this framework can be an encouraging candidate EEG feature for the early detection of MCI. In this framework, we extracted the task-induced intra-subject spectral power variability of resting-state EEGs (as measured by a between-run similarity) before and after participants performing cognitively exhausted working memory tasks as the candidate feature. The results from 74 participants (23 individuals with AD, 24 individuals with MCI, 27 HC) showed that the between-run similarity over the frontal and central scalp regions in the HC group is higher than that in the AD or MCI group. Furthermore, using a feature selection scheme and a support vector machine (SVM) classifier, the between-run similarity showed encouraging leave-one-participant-out cross-validation (LOPO-CV) classification performance for the classification between the MCI and HC (80.39%) groups and between the AD vs. HC groups (78%), and its classification performance is superior to other widely-used features such as spectral powers, coherence, and the complexity estimated by Katz's method extracted from single-run resting-state EEGs (a common approach in previous studies). The results based on LOPO-CV, therefore, suggest that the spectral-power-based task-induced intra-subject EEG variability extracted by the proposed feature extraction framework has the potential to serve as a neurophysiological feature for the early detection of MCI in individuals.

Infants exposed to antibiotics after birth have altered recognition memory responses at one month of age.

Background:Neonatal exposure to antibiotics, in the absence of infection, results in abnormal learning and memory in animals and is linked to changes in gut microbes. The relevance of early-life antibiotic exposure to brain function in humans is not known.Methods:Recognition memory was assessed at 1 month of age in 15 term-born infants exposed to antibiotics (with negative cultures) and 57 unexposed infants using event-related potentials (ERPs). Linear regression analysis, adjusting for covariates, was employed to compare groups with respect to ERP features representing early stimulus processing (P2 amplitude) and discrimination between mother and stranger voices.Results:Infants exposed to antibiotics exhibited smaller P2 amplitudes for both voice conditions (p = 0.001), with greatest reductions observed for mother’s voice in frontal and central scalp regions (p < 0.04). Infants exposed to antibiotics showed larger P2 amplitudes to stranger’s as compared to mother’s voice, a reversal of the typical response exhibited by unexposed infants. Abnormal ERP responses did not consistently correlate with increased inflammatory cytokines within the antibiotic-exposed group.Conclusion:Otherwise healthy infants exposed to antibiotics soon after birth demonstrated altered auditory processing and recognition memory responses, supporting the possibility of a microbiota-gut-brain axis in humans during early life.

Gating by inhibition during top-down control of willed attention

ABSTRACTIn natural settings, the control of attention may be influenced both by external information as well as internal decision-making processes driven by intent (e.g. free will). In past studies of spatial attention, we and others have developed experimental paradigms that permit individuals to choose where to direct their attention on a trial-by-trial basis in the absence of instructive external cues – we term this willed attention. Here we investigate the electrophysiological correlates of willed attention by recording EEG activity when subjects decided to focus covert attention on one of two lateralized target locations versus when they decided to maintain attention at fixation. Independent of the direction of attention, decisions to attend, relative to decisions not to attend, resulted in significant increases in both frontal theta (4–7 Hz) power and central alpha (8–13 Hz) power. We found that focusing spatial attention, as indexed by occipital alpha lateralization was predicted across subjects by the decision-related alpha increases over central scalp regions, but not changes in frontal theta power. This finding is interpreted in terms of the Gating by Inhibition model, where the central alpha EEG signals reflect cortical inhibition of decision processes that lead to the expression of willed attention.

Comparison of DP3 Signals Evoked by Comfortable 3D Images and 2D Images \u2014 an Event-Related Potential Study using an Oddball Task

The horizontal binocular disparity is a critical factor for the visual fatigue induced by watching stereoscopic TVs. Stereoscopic images that possess the disparity within the ‘comfort zones’ and remain still in the depth direction are considered comfortable to the viewers as 2D images. However, the difference in brain activities between processing such comfortable stereoscopic images and 2D images is still less studied. The DP3 (differential P3) signal refers to an event-related potential (ERP) component indicating attentional processes, which is typically evoked by odd target stimuli among standard stimuli in an oddball task. The present study found that the DP3 signal elicited by the comfortable 3D images exhibits the delayed peak latency and enhanced peak amplitude over the anterior and central scalp regions compared to the 2D images. The finding suggests that compared to the processing of the 2D images, more attentional resources are involved in the processing of the stereoscopic images even though they are subjectively comfortable.

The impact of physical activity on motor preparation in young adults

Regular physical activity benefits brain health and function. Physical activity performed by young adults is declining. However, the influence of diminished physical activity on cognitive performance and motor preparation in young adults remains unclear. This study measured changes in behavior and brain activity during preparation and performance of simple (SRT) and choice (CRT) reaction time tasks in less and more physically active young adults. Electromyograms were obtained from left and right first dorsal interossei muscles. Midline and hemisphere-specific electroencephalograms were analyzed from frontal and central scalp regions in 11 less- and 11 more-active participants. Physical activity level was assessed by questionnaire (IPAQ). Reaction and premotor times were slower for SRT and CRT tasks in less active participants. No statistically significant difference in contingent negative variation (CNV) amplitude was present between groups. Hemisphere-specific CNV amplitude over frontal scalp regions was evident for both less and more active participants for right hand SRT, whereas only the more active group showed hemisphere-specific CNVs for left hand SRT. Decreased levels of physical activity in young adults may be detrimental for cognitive processing and motor function measured by reaction time and changes in brain activity.

Functional Hubs in Mild Cognitive Impairment

We investigate how hubs of functional brain networks are modified as a result of mild cognitive impairment (MCI), a condition causing a slight but noticeable decline in cognitive abilities, which sometimes precedes the onset of Alzheimer's disease. We used magnetoencephalography (MEG) to investigate the functional brain networks of a group of patients suffering from MCI and a control group of healthy subjects, during the execution of a short-term memory task. Couplings between brain sites were evaluated using synchronization likelihood, from which a network of functional interdependencies was constructed and the centrality, i.e. importance, of their nodes was quantified. The results showed that, with respect to healthy controls, MCI patients were associated with decreases and increases in hub centrality respectively in occipital and central scalp regions, supporting the hypothesis that MCI modifies functional brain network topology, leading to more random structures.

Altered neurophysiological responses to emotional faces discriminate children with ASD, ADHD and ASD + ADHD

There are high rates of overlap between autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD). Emotional impairment in the two disorders, however, has not been directly compared using event-related potentials (ERPs) that are able to measure distinct temporal stages in emotional processing. The N170 and N400 ERP components were measured during presentation of emotional face stimuli to boys with ASD (n=19), ADHD (n=18), comorbid ASD+ADHD (n=29) and typically developing controls (n=26). Subjects with ASD (ASD/ASD+ADHD) displayed reduced N170 amplitude across all stimuli, particularly for fearful versus neutral facial expressions. Conversely, subjects with ADHD (ADHD/ASD+ADHD) demonstrated reduced modulation of N400 amplitude by fearful expressions in parietal scalp regions and happy facial expressions in central scalp regions. These findings indicate a dissociation between disorders on the basis of distinct stages of emotion processing; while children with ASD show alterations at the structural encoding stage, children with ADHD display abnormality at the contextual processing stage. The comorbid ASD+ADHD group presents as an additive condition with the unique deficits of both disorders. This supports the use of objective neural measurement of emotional processing to delineate pathophysiological mechanisms in complex overlapping disorders.

Reduced P3a amplitudes in antipsychotic naïve first-episode psychosis patients and individuals at clinical high-risk for psychosis

Event related potentials (ERP) associated with early sensory information processing have been proposed as possible vulnerability markers for psychosis. Compared to other ERPs reported in schizophrenia research, like Mismatch Negativity (MMN), little is known about P3a, an ERP related to novelty detection. The aim of this study was to analyze the MMN-P3a complex in 20 antipsychotic naïve first-episode psychosis patients (FEP), 23 antipsychotic naïve individuals at clinical high-risk for psychosis (CHR) and 24 healthy controls. The MMN-P3a amplitudes and latencies were obtained during a passive auditory mismatch frequency deviant ERP paradigm and analyzed in frontal and central scalp regions. There were no significant differences in MMN amplitude between groups. There was a significant group difference in P3a due to reduced amplitude (F[2,64] = 3.7, p = 0.03) in both CHR and FEP groups (Mean difference (MD) = 0.39, p = 0.04 and MD = 0.49, p = 0.02, respectively) compared to the control group and this effect was most prominent on the right side (Group × laterality effect: MD = 0.57, p < 0.01 and MD = 0.58, p < 0.01, respectively). No significant differences were observed for MMN or P3a latencies between groups. Although a P3a decrement in chronic schizophrenia and FEP has been previously reported, our results suggest that this novelty detection impairment is present even in pre-psychosis stages in antipsychotic naïve subjects. This study supports the evidence that P3a could represent a neurophysiological vulnerability marker for the development of psychosis.

Neural indices of spoken word processing in background multi-talker babble

Objective: To evaluate the impact of multi-talker babble on cortical event-related potentials (ERPs), specifically the N400, in a spoken semantic priming paradigm. Design: Participants listened in quiet and with background babble to word triplets, evaluating whether the third word was related to the preceding words. A temporo-spatial principal component analysis was conducted on ERPs to the first and second words (S1 and S2), processed without an overt behavioral response. One factor corresponded to the N400 and revealed greater processing negativity for unrelated as compared to related S2s in quiet and in babble. Study sample: Twelve young adults with normal hearing. Results: Background babble had no significant impact on the N400 in the posterior region but increased neural processing negativity at anterior and central regions during the same timeframe. This differential processing negativity in babble occurred in response to S2 but not S1. Furthermore, background babble impacted processing negativity for related S2s more than unrelated S2s. Conclusions: Results suggest that speech processing in a modestly degraded listening environment alters neural activity associated with auditory working memory, attention, and semantic processing in anterior and central scalp regions.SumarioObjetivo: Evaluar el impacto del balbuceo de múltiples hablantes en los potenciales corticales relacionados con eventos (ERP), específicamente el N400, en un paradigma de habla de base semántica. Diseño: Los participantes escucharon en silencio y con balbuceo de fondo, tripletas de palabras, para evaluar si la tercera palabra estaba relacionada con las palabras precedentes. Se realizó el análisis témporo-espacial del componente principal sobre los ERPs, en las palabras primera y segunda (S1 y S2), procesadas sin una respuesta conductual manifiesta. Un factor correspondió al N400 y reveló una negatividad de procesamiento para la no relacionada, en comparación con la S2 relacionada, tanto en silencio como con balbuceo. Muestra de Estudio: Doce adultos jóvenes con audición normal. Resultados: El balbuceo de fondo no tiene un impacto significativo en el N400 en la región posterior pero aumentó la negatividad de procesamiento en las regiones anterior y central durante el mismo marco temporal. Esta diferente negatividad diferencial de procesamiento con balbuceo, ocurrió en respuesta a S2 pero no a S1. Más aún, el balbuceo de fondo impactó la negatividad de procesamiento para las S2 relacionadas, más que para las S2 no relacionadas. Conclusiones: Los resultados sugieren que el procesamiento del lenguaje en un ambiente de escucha modestamente degradado, altera la actividad neural asociada con la memoria auditiva activa, la atención y el procesamiento semántico en las regiones anterior y central de la cabeza.

Think to Move: a Neuromagnetic Brain-Computer Interface (BCI) System for Chronic Stroke

Stroke is a leading cause of long-term motor disability among adults. Present rehabilitative interventions are largely unsuccessful in improving the most severe cases of motor impairment, particularly in relation to hand function. Here we tested the hypothesis that patients experiencing hand plegia as a result of a single, unilateral subcortical, cortical or mixed stroke occurring at least 1 year previously, could be trained to operate a mechanical hand orthosis through a brain-computer interface (BCI). Eight patients with chronic hand plegia resulting from stroke (residual finger extension function rated on the Medical Research Council scale=0/5) were recruited from the Stroke Neurorehabilitation Clinic, Human Cortical Physiology Section of the National Institute for Neurological Disorders and Stroke (NINDS) (n=5) and the Clinic of Neurology of the University of Tübingen (n=3). Diagnostic MRIs revealed single, unilateral subcortical, cortical or mixed lesions in all patients. A magnetoencephalography-based BCI system was used for this study. Patients participated in between 13 to 22 training sessions geared to volitionally modulate micro rhythm amplitude originating in sensorimotor areas of the cortex, which in turn raised or lowered a screen cursor in the direction of a target displayed on the screen through the BCI interface. Performance feedback was provided visually in real-time. Successful trials (in which the cursor made contact with the target) resulted in opening/closing of an orthosis attached to the paralyzed hand. Training resulted in successful BCI control in 6 of 8 patients. This control was associated with increased range and specificity of mu rhythm modulation as recorded from sensors overlying central ipsilesional (4 patients) or contralesional (2 patients) regions of the array. Clinical scales used to rate hand function showed no significant improvement after training. These results suggest that volitional control of neuromagnetic activity features recorded over central scalp regions can be achieved with BCI training after stroke, and used to control grasping actions through a mechanical hand orthosis.

Topography of spectral EEG and late VEP components in patients with benign rolandic epilepsy of childhood.

We studied 11 patients (7-15 years of age) with benign rolandic epilepsy of childhood. Spontaneous EEG and flash evoked potentials were recorded from 19 channels. Following visual stimulation, five of the patients displayed a late sustained component over temporal and central scalp regions (mean latency: 194.8 ms). The occurrence of this component was related to the spectra of spontaneous EEG and clinical parameters. Significant topographical differences were observed between the EEG amplitude spectra of patients with and without a N200 component. The effects were most evident in the lower alpha (7.5-9.5 Hz) and beta band (13-15 Hz) when temporal, parietal and occipital regions of the left and right hemisphere were compared. There was also a tendency that children without N200 displayed more hypersynchroneous activity in the spontaneous EEG than children with N200. This suggests a protective role of focal interictal spikes, and probably coincides with a benign prognosis of epilepsy.

Stimulus and response ERP analyses of a two-level reaction time task.

Higher cognitive processes include the ability to reliably transform sensory or mnemonic information. These processes either occur automatically or they are consciously controlled. To compare these two types of information processing, we developed a reaction time task that requires either a rule operation or else a direct sensory association. We were interested in evaluating the brain's electrical activity corresponding to both tasks, using event-related potentials (ERPs). In order to gain complete insight into the electrical activity of a stimulus-response segment, we analyzed the ERPs corresponding to the processing of the stimulus and the ERPs corresponding to the preparation of the response. To complete the analysis, we also evaluated the lateralized readiness potential (LRP) matched to the stimulus and to the response onset. Compared with the sensory association task, rule operation generated a higher negative potential field at frontocentral scalp areas in a latency range of 312-512 ms after the stimulus. In contrast, the LRP showed a negative component in the sensory association task which was absent during the rule operation; the latency of the difference was in the range 374-532 ms after the stimulus. The ERP component obtained by the response onset analysis was more negative in the rule condition up to a latency of -214 ms before the generation of the movement; the effect was localized at frontal and central scalp regions. We failed to find any significant difference in the LRP matched to the response onset. These results suggest that the brain computation of the rule operation takes place approximately in the middle of the stimulus-response time interval and that it is an additive process to the sensory association response.

Human Cortical Electroencephalography (EEG) Rhythms during the Observation of Simple Aimless Movements: A High-Resolution EEG Study

In the present high-resolution electroencephalographic (EEG) study, we computed event-related desynchronization and synchronization (ERD/ERS) of α (about 10 Hz) and β (about 20 Hz) rhythms in association with the execution (with visual feedback) and observation of brisk unilateral right and left aimless finger movements. A first scope was to test the topographical “functional equivalence” of cortical rhythmicity related to movement execution and observation, which would represent an ideal cortical observation/execution matching system. A second scope was to evaluate the hypothesis of a left or right hemisphere prevalence of the cortical rhythmicity related to the movement observation compared to the movement execution. EEG (128 electrodes) was recorded in 10 healthy right-handed volunteers. Surface Laplacian estimation spatially enhanced EEG data over a MRI-constraint head model. Under both conditions, ERD peaked during the movement execution or observation and was replaced by a ERS “rebound” or “recovery,” which peaked during the postevent period. Topographical results are in favor of a “functional equivalence” (i.e., similar ERD/ERS values in magnitude and timing) of α and β rhythmicity in central scalp regions overlying premotor/primary sensorimotor cortex. On the contrary, the functional equivalence of α rhythmicity was negligible (i.e., different ERD/ERS values in magnitude and timing) in parietal–occipital scalp regions overlying posterior parietal and parieto-occipital cortex, which could be the neural substrate to distinguish among the own motor intensions and others' aimless movements (i.e., visuomotor transformation integrated with sensorimotor, postural, and kinematics representations). Finally, the pattern of hemispherical cortical rhythmicity did not support a “simple concentration” of movement observation functions in the left or right hemisphere.

Hemispheric differences in the neural processing of stimulus location and type: Effects of selective attention on visual evoked potentials

Hemispheric differences in a negative brain potential associated with selectively attending the location and type of stimulation were investigated. The earlier portion of this negativity (between 125 and 222 msec after stimulation) was associated with attending the location of the stimulus. It was symmetrical in the central scalp regions but was greater in the hemisphere contralateral to the attended visual field in the posterior scalp region. The later portion of this negativity (from 222 to 272 msec after stimulation) primarily was associated with attending one of the different types of stimuli presented at a given location and was greater over the left posterior regions of the scalp. These results were interpreted in relationship to the time-course of different types of information processing in the left and right hemispheres.

Somatosensory far field potentials: Studies in normal subjects and patients with multiple sclerosis

Somatosensory evoked potentials to median nerve stimulation which arise in subcortical structures were recorded from the scalp of 15 normal subjects and 26 patients with definite multiple sclerosis (McAlpine's criteria) in non-cephalic reference leads. In normal subjects, these subcortical events consisted of 3 positive potentials which were distributed widely over the scalp and were of similar amplitude at all scalp recording locations. In some subjects, these potentials were followed by another positive potential which was recorded predominantly over frontal central scalp regions. These potentials were followed by a larger negative potential which was most prominent over the somesthetic cortex contralateral to the side of stimulation. This negative potential is thought to reflect the arrival of the afferent volley in cerebral cortical elements. The criteria for abnormality in the patient group were (a) absence of components consistently recorded in normal subjects, (b) statistically significant component peak latency differences in patients compared to normal subjects, and (c) statistically significant differences in the amplitudes of the third positive and first negative potentials to stimulation of the left median nerve as compared with right median nerve stimulation. The response in all but one of the patients was judged to be abnormal. Absent components were observed in 17 patients, prolonged peak latency differences in 13 patients and component amplitude measurements were abnormal in 3 patients. Sequential recordings obtained in 5 of 9 patients revealed loss of components or latency changes. Evoked potential abnormalities were often found in the absence of either brain stem signs or clinically evident disturbances of specific sensory systems.