Evoked Brain Potentials Research Articles

The effect of common parameters of bipolar stimulation on brain evoked potentials

ObjectiveTo identify optimal bipolar stimulation parameters for robust generation of brain evoked potentials (BEPs), namely the interelectrode distance (IED) and the intensity of stimulation (IS), in cortical and axonal stimulation. MethodsIn 15 patients who underwent awake surgery for brain tumor removal, BEPs were elicited at different values of IED and IS, respectively: 5 mm-5 mA, 5 mm-10 mA, and 10 mm-10 mA. The number of BEPs elicited by stimulation, as well as the delays and amplitudes of the N1 waves were compared between the different groups of stimulation parameters and according to the stimulated brain structure (cortical vs. axonal). ResultsThe amplitudes of N1 increased with the intensity of bipolar stimulation, either in cortical or axonal stimulation, while N1 peak delays were not affected by the stimulation parameters. Furthermore, axonal stimulation produced more N1s than cortical stimulation, with lower latencies. ConclusionsUnderstanding the relationship between stimulation parameters and BEP is of utmost importance to determine whether the generated N1 waves accurately reflect the underlying structural anatomy. Other factors, such as stimulation frequency or pulse width and shape, may also play a role and warrant further investigation. SignificanceThis study represents the first step in describing the influence of common bipolar stimulation parameters on robustness of BEPs by examining the impact of IED and IS on the N1 wave.

Potential Neurophysiological Markers of Combat-Related Post-Traumatic Stress Disorder: A Cross-Sectional Diagnostic Study.

Studies suggest that the components of brain-evoked potentials (EPs) may serve as biomarkers of the post-traumatic stress disorder (PTSD) caused by participation in combat operations; however, to date, research remains fragmented, with no studies that have attempted to combine different paradigms. In addition, the mismatch negativity component has not been studied in a Russian sample of veterans with PTSD. To identify objective neurophysiological markers of combat-related PTSD using the method of auditory-evoked potentials in active and passive listening paradigms. The study included a recording of auditory EPs in an oddball paradigm in three settings: 1) directed attention to auditory stimuli, 2) passive listening while viewing a neutral video sequence, and 3) viewing a video sequence associated with a traumatic event. Combatants diagnosed with PTSD (18 people) were compared with mentally healthy civilian volunteers (22 people). An increase in the latency period of the early components of auditory EP (N100 and P200), an increase in the amplitude of the P200 component to a deviant stimulus, and a decrease to a standard one in the active listening paradigm were established in the PTSD group. There were no significant differences in the parameters of the P300 component. The characteristics of mismatch negativity in the passive paradigm were revealed: an increase in the phenomenon amplitude, both when shown a video sequence associated with a traumatic event and when shown a neutral video sequence. A binary logistic regression model constructed using the selected parameters showed that the identified characteristics can potentially be considered as diagnostic markers of PTSD in combatants, as the classification accuracy stood at 87% (sensitivity - 81%, specificity - 91%). Potential neurophysiological markers of PTSD are the following: the amplitude and latency of early components of auditory EPs in the paradigm of directed attention to stimuli and the amplitude of mismatch negativity during passive attention.

The EEG N400 component as a marker of language acquisition and processing in cochlear implant users

Language processing can be measured objectively using late components in the evoked brain potential. The most established component in this area of research is the N400 component, a negativity that peaks at about 400 ms after stimulus onset with a centro-parietal maximum. It reflects semantic processing. Its presence, as well as its temporal and quantitative expression, allows to conclude about the quality of processing. It is therefore suitable for measuring speech comprehension in special populations, such as cochlear implant (CI) users. The following is an overview of the use of the N400 component as a tool for studying language processes in CI users. We present studies with adult CI users, where the N400 reflects the quality of speech comprehension with the new hearing device and we present studies with children where the emergence of the N400 component reflects the acquisition of their very first vocabulary.

Evoked Brain Potentials to Sound Offset in Humans in Conditions of Spatial Masking

Evoked Brain Potentials to Sound Offset in Humans in Conditions of Spatial Masking

Observing evoked brain potentials during facial neuromuscular electrical stimulation

Observing evoked brain potentials during facial neuromuscular electrical stimulation

A simple model of the attentional blink and its modulation by mental training.

The attentional blink (AB) effect is the reduced probability of reporting a second target (T2) that appears shortly after a first one (T1) within a rapidly presented sequence of distractors. The AB effect has been shown to be reduced following intensive mental training in the form of mindfulness meditation, with a corresponding reduction in T1-evoked P3b brain potentials. However, the mechanisms underlying these effects remain unknown. We propose a dynamical-systems model of the AB, in which attentional load is described as the response of a dynamical system to incoming impulse signals. Non-task related mental activity is represented by additive noise modulated by meditation. The model provides a parsimonious computational framework relating behavioral performance, evoked brain potentials and training through the concept of reduced mental noise.

N170 component analysis of single-trial EEG based on electrophysiological source imaging.

Event-related potentials (ERP) are brain-evoked potentials that reflect the neural activity of the brain. However, it is difficult to isolate the ERP components of our interest because single-trial EEG is disturbed by other signals, and the average ERP analysis in turn loses single-trial information. In this paper, we used electrophysiological source imaging (ESI) to analyze the N170 component of single-trial EEG triggered by face stimulation. The results show that ESI is feasible for the analysis of N170 and that there are left-right differences in the area of the fusiform gyrus associated with face stimulation in the brain. Clinical Relevance- Analysis of the N170 of single-trial EEG by ESI may help in the diagnosis of patients with prosopagnosia and may also help physicians clinically in determining whether the fusiform gyrus region is damaged.

Cardiac cycle and respiration phase affect responses to the conditioned stimulus in young adults trained in trace eyeblink conditioning.

Rhythms of breathing and heartbeat are linked to each other as well as to the rhythms of the brain. Our recent studies suggest that presenting conditioned stimulus during expiration or during the diastolic phase of the cardiac cycle facilitates neural processing of that stimulus and improves learning in a conditioning task. To date, it has not been examined whether using information from both respiration and cardiac cycle phases simultaneously allows even more efficient modulation of learning. Here, we studied whether the timing of the conditioned stimulus to different cardiorespiratory rhythm phase combinations affects learning in a conditioning task in healthy young adults. The results were consistent with previous reports: timing the conditioned stimulus to diastole during expiration was more beneficial for learning than timing it to systole during inspiration. Cardiac cycle phase seemed to explain most of this variation in learning at the behavioral level. Brain-evoked potentials (N1) elicited by the conditioned stimulus and recorded using electroencephalogram were larger when the conditioned stimulus was presented to diastole during expiration than when it was presented to systole during inspiration. Breathing phase explained the variation in the N1 amplitude. To conclude, our findings suggest that noninvasive monitoring of bodily rhythms combined with closed-loop control of stimulation can be used to promote learning in humans. The next step will be to test if performance can also be improved in humans with compromised cognitive ability, such as in older people with memory impairments.NEW & NOTEWORTHY We report, for the first time, that the rhythms of breathing and the beating of the heart have a phase combination that is indicative of a neural state beneficial for cognition. This suggests that bodily rhythms not only modulate cognition but that this phenomenon can also be noninvasively harnessed to improve learning in humans.

Auditory evoked brain potentials as markers of chronic effects of mild traumatic brain injury in mid-life

ObjectiveAuditory event-related potential (ERP) correlates of pre-dementia in late-life may also be sensitive to chronic effects of mild traumatic brain injury (mTBI) in mid-life. In addition to mTBI history, other clinical factors may also influence ERP measures of brain function. This study’s objective was to evaluate the relationship between mTBI history, auditory ERP metrics, and common comorbidities. MethodsERPs elicited during an auditory target detection task, psychological symptoms, and hearing sensitivity were collected in 152 combat-exposed veterans and service members, as part of a prospective observational cohort study. Participants, with an average age of 43.6 years, were grouped according to positive (n = 110) or negative (n = 42) mTBI history. Positive histories were subcategorized into repetitive mTBI (3 + ) (n = 40) or non-repetitive (1–2) (n = 70). ResultsPositive history of mTBI was associated with reduced N200 amplitude to targets and novel distractors. In participants with repetitive mTBI compared to non-repetitive and no mTBI, P50 was larger in response to nontargets and N100 was smaller in response to nontargets and targets. Changes in N200 were mediated by depression and anxiety symptoms and hearing loss, with no evidence of a supplementary direct mTBI pathway. ConclusionsAuditory brain function differed between the positive and negative mTBI groups, especially for repetitive injury, which implicated more basic, early auditory processing than did any mTBI exposure. Symptoms of internalizing psychopathology (depression and anxiety) and hearing loss are implicated in mTBI’s diminished brain responses to behaviorally relevant and novel stimuli. SignificanceA mid-life neurologic vulnerability conferred by mTBI, particularly repetitive mTBI, may be detectable using auditory brain potentials, and so auditory ERPs are a target for study of dementia risk in this population.

Neural excitability and sensory input determine intensity perception with opposing directions in initial cortical responses.

Perception of sensory information is determined by stimulus features (e.g., intensity) and instantaneous neural states (e.g., excitability). Commonly, it is assumed that both are reflected similarly in evoked brain potentials, that is, larger amplitudes are associated with a stronger percept of a stimulus. We tested this assumption in a somatosensory discrimination task in humans, simultaneously assessing (i) single-trial excitatory post-synaptic currents inferred from short-latency somatosensory evoked potentials (SEPs), (ii) pre-stimulus alpha oscillations (8-13 Hz), and (iii) peripheral nerve measures. Fluctuations of neural excitability shaped the perceived stimulus intensity already during the very first cortical response (at ~20 ms) yet demonstrating opposite neural signatures as compared to the effect of presented stimulus intensity. We reconcile this discrepancy via a common framework based on the modulation of electro-chemical membrane gradients linking neural states and responses, which calls for reconsidering conventional interpretations of brain potential magnitudes in stimulus intensity encoding.

Comprehensive analysis of the 5-HTTLPR allelic polymorphism effect on behavioral and neurophysiological indicators of executive control in people from different ethnic groups in Siberia

The allelic polymorphism of the serotonin transporter's gene 5-HTTLPR is considered as one of the factors determining an individual genetic predisposition to the development of a wide range of affective disorders, including depression. Many studies have shown that the climatic and social conditions of people's life can have a significant impact on the connections of 5-HTTLPR with the risk of depression. The stop-signal paradigm (SSP) is an experimental method allowing evaluating an individual ability to the self-control of behavior in a changing environment. In the SSP experiment, a subject should either press one of several buttons quickly after the appearance of the target stimuli or suppress the already started movement if an inhibitory signal follows the target stimulus. The aim of this study is a research of associations between the allelic the 5-HTTLPR polymorphism and the individual scores of the personal anxiety level, as well as the behavioral and neurophysiological indicators of the ability to self-control over motor reactions in the SSP. The study was conducted among people from three ethno-regional groups: healthy Caucasoids from Novosibirsk, the Mongoloid groups of the indigenous population of the Tuva Republic and Sakha Republic (Yakutia). Genetic, ethnographic, and psychological influences on an individual's ability to control motor responses were compared. The amplitude of the premotor peak of the evoked brain potential was used as a neurophysiological marker of the person's readiness to the execution of target-directed activity. It was revealed that the frequency of the S-allele polymorphism 5-HTTLPR was significantly higher for both mongoloid groups compared to the Caucasoids. The S/S genotype was associated with an increased level of personal anxiety and at the same time with a better ability to the self-control of behavior in the SSP experiment. Anxiety level, participants' sex, ethnicity, and allelic polymorphism 5-HTTLPR had a statistically significant effect on the amplitude of the premotor readiness potential recorded under the SSP conditions in the frontal and parietal-occipital cortical regions. Our data support the hypothesis that the S/S genotype of the 5-HTTLPR polymorphism may be associated with more success in adapting to the climatic conditions connected with high life risk in comparison to L/L and L/S genotypes.

Multisensory Processing Can Compensate for Top-Down Attention Deficits in Schizophrenia.

Studies on schizophrenia (SCZ) and aberrant multisensory integration (MSI) show conflicting results, which are potentially confounded by attention deficits in SCZ. To test this, we examined the interplay between MSI and intersensory attention (IA) in healthy controls (HCs) (N = 27) and in SCZ (N = 27). Evoked brain potentials to unisensory-visual (V), unisensory-tactile (T), or spatiotemporally aligned bisensory VT stimuli were measured with high-density electroencephalography, while participants attended blockwise to either visual or tactile inputs. Behaviorally, IA effects in SCZ, relative to HC, were diminished for unisensory stimuli, but not for bisensory stimuli. At the neural level, we observed reduced IA effects for bisensory stimuli over mediofrontal scalp regions (230-320 ms) in SCZ. The analysis of MSI, using the additive approach, revealed multiple phases of integration over occipital and frontal scalp regions (240-364 ms), which did not differ between HC and SCZ. Furthermore, IA and MSI effects were both positively related to the behavioral performance in SCZ, indicating that IA and MSI mutually facilitate bisensory stimulus processing. Multisensory processing could facilitate stimulus processing and compensate for top-down attention deficits in SCZ. Differences in attentional demands, which may be differentially compensated by multisensory processing, could account for previous conflicting findings on MSI in SCZ.

The Vagus Nerve Somatosensory-evoked Potential in Neural Disorders: Systematic Review and Illustrative Vignettes.

Objective. To review the scientific publications reporting vagal nerve somatosensory-evoked potential (VSEP) findings from individuals with brain disorders, and present novel physiological explanations on the VSEP origin. Methods. We did a systematic review on the papers reporting VSEP findings from individuals with brain disorders and their controls. We evaluated papers published from 2003 to date indexed in PubMed, Web of Science, and Scielo databases. We extracted the following information: number of patients and controls, type of neural disorder, age, gender, stimulating/recording and grounding electrodes as well as stimulus side, intensity, duration, frequency, and polarity. Information about physiological parameters, neurobiological variables, and correlation studies was also reviewed. Representative vignettes were included to add support to our conclusions. Results. The VSEP was studied in 297 patients with neural disorders such as Parkinson's disease (PD), Alzheimer's disease, vascular dementia, mild cognitive impairment, subjective memory impairment, major depression, and multiple sclerosis. Scalp responses marked as the VSEP showed high variability, low validity, and poor reproducibility. VSEP latencies and amplitudes did not correlate with disease duration, unified PD rating scale score, or heart function in PD patients nor with cerebrospinal fluid β amyloid, phosphor-τ, and cognitive tests from patients with mental disorders. Vignettes demonstrated that the VSEP was volume conduction propagating from muscles surrounding the scalp recording electrodes. Conclusion. The VSEP is not a brain-evoked potential of neural origin but muscle activity induced by electrical stimulation of the tragus region of the ear. This review and illustrative vignettes argue against assessing the parasympathetic system using the so-called VSEP.

Accuracy in Archery Shooting is linked to the Amplitude of the ERP N1 to the Snap of Clicker

An archer requires a well-balanced and highly reproducible release of the bowstring to attain high scores in competition. Recurve archers use a mechanical device called the “clicker” to check the draw length. The fall of the clicker that generates an auditory stimulus should evoke a response in the brain. The purpose of this study is to evaluate the event-related potentials during archery shooting as a response to the fall of the clicker. Fifteen high-level archers participated. An electro cap was placed on the archers’ scalps, and continuous EEG activity was recorded (digitized at 1000 Hz) and stored for off-line analysis. The EEG data were epoched beginning 200 ms before and lasting 800 ms after stimulus marker signals. An operational definition has been developed for classifying hits corresponding to hit and/or miss areas. The hit area enlarged gradually starting from the centre of the target (yellow: 10) to blue (6 score) by creating ten hit area indexes. It is found that the snap of the clicker during archery shooting evokes N1–P2 components of long-latency evoked brain potentials. N1 amplitudes are significantly higher in hit area than that of miss areas for the 2nd and 4th indexes with 95% confidence intervals and 90% confidence intervals for the 1st and 3rd indexes with 90% confidence intervals. We conclude that the fall of the clicker in archery shooting elicits an N1 response with higher amplitude. Although evoked potential amplitudes were higher in successful shots, their latencies were not significantly different from the unsuccessful ones.

Steady-state visual evoked potential and its applications in studying visual selective attention

Steady-state visual evoked potentials (SSVEP), an evoked brain potential, possesses the same frequency as periodic visual stimuli evoking potentials. It is extensively utilized in Brain-Computer Interface and human cognitive research. Moreover, the amplitude of SSVEP is sensitive to resources allocation of visual selective attention, and therefore can always serve as a corresponding electrophysiological indicator. In comparison with event-related potentials (ERPs) presented by P300 and N2pc, SSVEP index can be flexibly applied to a variety of paradigms and avoid errors caused by the brain lateralization as different items can be present in the center or in the same region of the view. Furthermore, SSVEP can reflect attention variation because of its continuity and sensibility to attention fluctuation. Besides, ERPs and SSVEP may reflect diverse attentive stages, and certain evidence suggests the attentive stage that SSVEP reflects is earlier compared with ERPs. Specifically, SSVEP may reflect the regulation that brain regions in charge of advanced cognitive function act on the visual cortex or the earlier stage of visual attention. Nevertheless, ERPs might reveal a later stage accomplished by brain regions responsible for higher-order cognitive processes such as the parietal lobe. In the study of visual selective attention, the frequency tagging is primarily employed to induce SSVEP. Visual stimuli are presented periodically at various frequencies to evoke SSVEP so that the stimuli are frequency tagged. We are able to figure out the allocation of attentive resources in those conditions by means of comparing SSVEP amplitude that the same stimulus evokes in a wide range of conditions. The frequency tagging is particularly appropriate to visual selective attention, especially feature-based and space-based attention. Benefiting from its accurate and sensitive reflection of attentive spatial distribution, SSVEP-based frequency tagging is widely adopted in space-based attention and directly proves the attention focus is shape-flexible and dividable but not always a solid circle. On the other hand, researchers developed the random dot kinematograms (RDK) paradigm for feature-based attention, which prolongs instantaneous feature-based attention process so that SSVEP can detect it. With RDK paradigm, researchers find strong evidence that feature-based attention does exist and has a global attentive activation. However, the other kind of visual selective attention, object-based attention, cannot be explored by frequency tagging because periodic flicker will be a highlighted feature so that participants will consider it as an object recognition marker and further destroy the integrity of the object. In the future, researchers can attempt to add emotion, reward and punishment, and working memory representations as research variables, or to build connections between feature-based attention and spatial-based attention in the process of using SSVEP to explore visual selective attention. In addition, the results of BCI algorithms for SSVEP have a potential for being a new visual selective attention index.

Methodological foundations of psychological reliability and professional suitability to work in dangerous conditions

The article discusses the experimental data obtained during the professional selection of persons in hazardous occupations. The high efficiency of sharing of eytracking and polygraph has been established. To determine the socio-psychological reliability, a computer program of evoked brain potentials can be used upon presentation of drug-related slides.

Pupil-Linked Arousal Responds to Unconscious Surprisal.

Pupil size under constant illumination reflects brain arousal state, and dilates in response to novel information, or surprisal. Whether this response can be observed regardless of conscious perception is still unknown. In the present study, male and female adult humans performed an implicit learning task across a series of three experiments. We measured pupil and brain-evoked potentials to stimuli that violated transition statistics but were not relevant to the task. We found that pupil size dilated following these surprising events, in the absence of awareness of transition statistics, and only when attention was allocated to the stimulus. These pupil responses correlated with central potentials, evoking an anterior cingulate origin. Arousal response to surprisal outside the scope of conscious perception points to the fundamental relationship between arousal and information processing and indicates that pupil size can be used to track the progression of implicit learning.SIGNIFICANCE STATEMENT Pupil size dilates following increase in mental effort, surprise, or more generally global arousal. However, whether this response arises as a conscious response or reflects a more fundamental mechanism outside the scrutiny of awareness is still unknown. Here, we demonstrate that unexpected changes in the environment, even when processed unconsciously and without being relevant to the task, lead to an increase in arousal levels as reflected by the pupillary response. Further, we show that the concurrent electrophysiological response shares similarities with mismatch negativity, suggesting the involvement of anterior cingulate cortex. All in all, our results establish novel insights about the mechanisms driving global arousal levels, and it provides new possibilities for reliably measuring unconscious processes.

New psychophysiologic approaches applied in occupational selection of candidates for dangerous professions

Introduction. In increased requirements to occupational and personal qualities of workers engaged into or applying for dangerous professions, effi ciency of occupational selection considerably depends on choice of methodic approaches adequate to the study objectives. Objective. To study psychophysiologic approaches to evaluation of social psychologic reliability and occupational fi tness of individuals with dangerous professions, for revealing prognostic facilities of new methods and for improving occupational selection for military and police offi cers. Materials and methods. Psychophysiologic studies used eye-tracker SMI-RED–250 and polygraph “Diana” and covered 201 candidates for service in various divisions of RF Investigating Committ ee. Major part of the examinees consisted of individuals aged under 30 years (134 males and 67 females). All the candidates had normal vision or corrected to normal one. Evoked brain potentials study covered 114 candidates for military service (2 females and 112 males) aged 17 to 52 years. According to polygraph study, 51.8% of the examinees demonstrated a risk factor of “drug use”. Results. Th e authors presented results of psychophysiologic studies of occupational fi tness in candidates for military and police service. Nowadays, polygraph study remains a reliable method to reveal reactions proving presence of concealed information. Using evoked brain potentials for disclosing individuals who conceal drug usage is an important procedure in security maintenance. Within a standard polygraph procedure, videooculography (eye-tracker) seems the most interesting. Th e studies covered possible use of evoked EEG potentials and eye-tracker along with polygraph study for personnel checkups. Conclusions. Occupational selection in individuals with dangerous professions obtained experimental data indicating high effi ciency of combined use of eye-tracking and polygraph, for diagnosis of social psychologic reliability one can use soft ware of evoked brain potentials with demonstration of drugs-associated slides.

Long-term use of a neural prosthesis in progressive paralysis

Brain–computer interfaces (BCIs) enable communication with others and allow machines or computers to be controlled in the absence of motor activity. Clinical studies evaluating neural prostheses in amyotrophic lateral sclerosis (ALS) patients have been performed; however, to date, no study has reported that ALS patients who progressed from locked-in syndrome (LIS), which has very limited voluntary movement, to a completely locked-in state (CLIS), characterized by complete loss of voluntary movements, were able to continue controlling neural prostheses. To clarify this, we used a BCI system to evaluate three late-stage ALS patients over 27 months. We employed steady-state visual evoked brain potentials elicited by flickering green and blue light-emitting diodes to control the BCI system. All participants reliably controlled the system throughout the entire period (median accuracy: 83.3%). One patient who progressed to CLIS was able to continue operating the system with high accuracy. Furthermore, this patient successfully used the system to respond to yes/no questions. Thus, this CLIS patient was able to operate a neuroprosthetic device, suggesting that the BCI system confers advantages for patients with severe paralysis, including those exhibiting complete loss of muscle movement.

Mental fatigue in central-field and peripheral-field steady-state visually evoked potential and its effects on event-related potential responses.

The steady-state visually evoked potential (SSVEP) is a natural response of the brain to visual stimulation at specific frequencies and is used widely for electroencephalography-based brain–computer interface (BCI) systems. Although the SSVEP is useful for its high level of decoding accuracy, visual fatigue from the repetitive visual flickering is an unavoidable problem. In addition, hybrid BCI systems that combine the SSVEP with the event-related potential (ERP) have been proposed recently. These hybrid BCI systems would improve the decoding accuracy; however, the competing effect by simultaneous presentation of the visual stimulus could possibly supervene the signal in the hybrid system. Nevertheless, previous studies have not sufficiently reported these problems of visual fatigue with SSVEP stimuli or the competing effect in the SSVEP+ERP system. In this study, two different experiments were designed to explore our claims. The first experiment evaluated the visual fatigue level and decoding accuracy for the different types of SSVEP stimuli, which were the peripheral-field SSVEP (pSSVEP) and the central-field SSVEP (cSSVEP). We report that the pSSVEP could reduce the visual fatigue level by avoiding direct exposure of the eye-retina to the flickering visual stimulus, while also delivering a decoding accuracy comparable to that of cSSVEP. The second experiment was designed to examine the competing effect of the SSVEP stimuli on ERP performance and vice versa. To do this, the visual stimuli of ERP and SSVEP were presented simultaneously as part of the BCI speller layout. We found a clear competing effect wherein the evoked brain potentials were influenced by the SSVEP stimulus and the band power at the target frequencies was also decreased significantly by the ERP stimuli. Nevertheless, these competing effects did not lead to a significant loss in decoding accuracy; their features preserved sufficient information for discriminating a target class. Our work is the first to evaluate the visual fatigue and competing effect together, which should be considered when designing BCI applications. Furthermore, our findings suggest that the pSSVEP is a viable substitution for the cSSVEP because of its ability to reduce the level of visual fatigue while maintaining a minimal loss of decoding accuracy.