More potential in statistical analyses of event-related potentials: a mixed regression approach

Habituation to pain: self-report, electroencephalography, and functional magnetic resonance imaging in healthy individuals. A scoping review and future recommendations

ABSTRACT

Habituation to pain is a fundamental learning process and important adaption. Yet, a comprehensive review of the current state of the field is lacking. Through a systematic search, 63 studies were included. Results address habituation to pain in healthy individuals based on self-report, electroencephalography, or functional magnetic resonance imaging. Our findings indicate a large variety in methods, experimental settings, and contexts, making habituation a ubiquitous phenomenon. Habituation to pain based on self-report studies shows a large influence of expectations, as well as the presence of individual differences. Furthermore, widespread neural effects, with sometimes opposing effects in self-report measures, are noted. Electroencephalography studies showed habituation of the N2-P2 amplitude, whereas functional magnetic resonance imaging studies showed decreasing activity during painful repeated stimulation in several identified brain areas (cingulate cortex and somatosensory cortices). Important considerations for the use of terminology, methodology, statistics, and individual differences are discussed. This review will aid our understanding of habituation to pain in healthy individuals and may lead the way to improving methods and designs for personalized treatment approaches in chronic pain patients.

Towards Optimization of Oscillatory Stimulation During Sleep

BACKGROUND

Oscillatory rhythms during sleep, such as slow oscillations (SOs) and spindles and, most importantly, their coupling, are thought to underlie processes of memory consolidation. External slow oscillatory transcranial direct current stimulation (so-tDCS) with a frequency of 0.75 Hz has been shown to improve this coupling and memory consolidation; however, effects varied quite markedly between individuals, studies, and species. In this study, we aimed to determine how precisely the frequency of stimulation must match the naturally occurring SO frequency in individuals to best improve SO-spindle coupling. Moreover, we systematically tested stimulation durations necessary to induce changes.

MATERIALS AND METHODS

We addressed these questions by comparing so-tDCS with individualized frequency to standardized frequency of 0.75 Hz in a within-subject design with 28 older participants during napping while stimulation train durations were systematically varied between 30 seconds, 2 minutes, and 5 minutes.

RESULTS

Stimulation trains as short as 30 seconds were sufficient to modulate the coupling between SOs and spindle activity. Contrary to our expectations, so-tDCS with standardized frequency indicated stronger aftereffects regarding SO-spindle coupling than individualized frequency. Angle and variance of spindle maxima occurrence during the SO cycle were similarly modulated.

CONCLUSIONS

In sum, short stimulation trains were sufficient to induce significant changes in sleep physiology, allowing for more trains of stimulation, which provides methodological advantages and possibly even larger behavioral effects in future studies. Regarding individualized stimulation frequency, further options of optimization need to be investigated, such as closed-loop stimulation, to calibrate stimulation frequency to the SO frequency at the time of stimulation onset.

CLINICAL TRIAL REGISTRATION

The Clinicaltrials.gov registration number for the study is NCT04714879.

An Agent-First Preference in a Patient-First Language During Sentence Comprehension

The language comprehension system preferentially assumes that agents come first during incremental processing. While this might reflect a biologically fixed bias, shared with other domains and other species, the evidence is limited to languages that place agents first, and so the bias could also be learned from usage frequency. Here, we probe the bias with electroencephalography (EEG) in Äiwoo, a language that by default places patients first, but where sentence-initial nouns are still locally ambiguous between patient or agent roles. Comprehenders transiently interpreted nonhuman nouns as patients, eliciting a negativity when disambiguation was toward the less common agent-initial order. By contrast and against frequencies, human nouns were transiently interpreted as agents, eliciting an N400-like negativity when the disambiguation was toward patient-initial order. Consistent with the notion of a fixed property, the agent bias is robust against usage frequency for human referents. However, this bias can be reversed by frequency experience for nonhuman referents.

Losses resulting from deliberate exploration trigger beta oscillations in frontal cortex

We examined the neural signature of directed exploration by contrasting MEG beta (16-30 Hz) power changes between disadvantageous and advantageous choices in the two-choice probabilistic reward task. We analyzed the choices made after the participants have learned the probabilistic contingency between choices and their outcomes, i.e., acquired the inner model of choice values. Therefore, rare disadvantageous choices might serve explorative, environment-probing purposes. The study brought two main findings. Firstly, decision making leading to disadvantageous choices took more time and evidenced greater large-scale suppression of beta oscillations than its advantageous alternative. Additional neural resources recruited during disadvantageous decisions strongly suggest their deliberately explorative nature. Secondly, an outcome of disadvantageous and advantageous choices had qualitatively different impact on feedback-related beta oscillations. After the disadvantageous choices, only losses-but not gains-were followed by late beta synchronization in frontal cortex. Our results are consistent with the role of frontal beta oscillations in the stabilization of neural representations for selected behavioral rule when explorative strategy conflicts with value-based behavior. Punishment for explorative choice being congruent with its low value in the reward history is more likely to strengthen, through punishment-related beta oscillations, the representation of exploitative choices consistent with the inner utility model.

Pupil dilation and response slowing distinguish deliberate explorative choices in the probabilistic learning task

This study examined whether pupil size and response time would distinguish directed exploration from random exploration and exploitation. Eighty-nine participants performed the two-choice probabilistic learning task while their pupil size and response time were continuously recorded. Using LMM analysis, we estimated differences in the pupil size and response time between the advantageous and disadvantageous choices as a function of learning success, i.e., whether or not a participant has learned the probabilistic contingency between choices and their outcomes. We proposed that before a true value of each choice became known to a decision-maker, both advantageous and disadvantageous choices represented a random exploration of the two options with an equally uncertain outcome, whereas the same choices after learning manifested exploitation and direct exploration strategies, respectively. We found that disadvantageous choices were associated with increases both in response time and pupil size, but only after the participants had learned the choice-reward contingencies. For the pupil size, this effect was strongly amplified for those disadvantageous choices that immediately followed gains as compared to losses in the preceding choice. Pupil size modulations were evident during the behavioral choice rather than during the pretrial baseline. These findings suggest that occasional disadvantageous choices, which violate the acquired internal utility model, represent directed exploration. This exploratory strategy shifts choice priorities in favor of information seeking and its autonomic and behavioral concomitants are mainly driven by the conflict between the behavioral plan of the intended exploratory choice and its strong alternative, which has already proven to be more rewarding.

A Functional Coupling of Brain and Behavior During Social Categorization of Faces

Considerable research has focused on how people derive information about others' social category memberships from their faces. Theoretical models posit that early extraction of task-relevant information from a face should determine the efficiency with which that face is categorized, but evidence supporting this idea has been elusive. Here, we used a novel trial-level data analytic approach to examine the relationship between two event-related potential components-the P2, indexing early attention to category-relevant information, and the P3, indexing stimulus evaluation-and the speed of overt categorization judgments. As predicted, a larger face-elicited P2 on a particular trial was associated with faster overt race or gender categorization of that face. Moreover, this association was mediated by P3 latency, indicating that extraction of more category-relevant information early in processing facilitated stimulus evaluation. These findings support continuous flow models of information processing and the long-theorized functional significance of face-elicited neurophysiological responses for social categorization.

Anxiety increases sensitivity to errors and negative feedback over time

Anxiety is characterized by sensitivity to negative external and internal information, apparent both in symptoms (e.g., hypervigilance and worry) and neural performance monitoring measures (i.e., feedback- and error-related negativity (FRN and ERN)). Here we examine whether anxiety is associated with persistent neural sensitivity to negative performance markers reflected in both the FRN and ERN (n = 273). Higher anxiety was associated with larger responses to both negative feedback and errors as the task progressed compared to those with lower anxiety particularly in women, suggesting that anxiety makes reactions to negative cues more persistent. Similar hypotheses were investigated for depression, which is associated with similar negative cognitive biases and deficits in reward-related processing, but results were mixed. Together, the findings identify variation over time-in-task as an overlooked dimension by which FRN and ERN may serve as a biomarker of anxiety but suggest that depression is not consistently related to performance monitoring.

Using multilevel models for the analysis of event-related potentials

Multilevel modeling (MLM) is becoming increasingly accessible and popular in the analysis of event-related potentials (ERPs). In this article, we review the benefits of MLM for analyzing psychophysiological data, which often contains repeated observations within participants, and introduce some of the decision-making points in the analytic process, including how to set up the data set, specify the model, conduct hypothesis tests, and visualize the model estimates. We highlight how the use of MLM can extend the types of theoretical questions that can be answered using ERPs, including investigations of how ERPs vary meaningfully across trials within a testing session. We also address reporting practices and provide tools to calculate effect sizes and simulate power curves. Ultimately, we hope this review contributes to emerging best practices for the use of MLM with psychophysiological data.

Selective adaptation in sentence comprehension: Evidence from event-related brain potentials

In this study, two event-related potential experiments were conducted to investigate whether readers adapt their expectations to morphosyntactically (Experiment 1) or semantically (Experiment 2) anomalous sentences when they are repeatedly exposed to them. To address this issue, we experimentally manipulated the probability of occurrence of grammatical sentences and syntactically and semantically anomalous sentences through experiments. For the low probability block, anomalous sentences were presented less frequently than grammatical sentences (with a ratio of 1 to 4), while they were presented as frequently as grammatical sentences in the equal probability block. Experiment 1 revealed a smaller P600 effect for morphosyntactic violations in the equal probability block than in the low probability block. Linear mixed-effects models were used to examine how the size of the P600 effect changed as the experiment went along. The results showed that the smaller P600 effect of the equal probability block resulted from an amplitude's decline in morphosyntactically violated sentences over the course of the experiment, suggesting an adaptation to morphosyntactic violations. In Experiment 2, semantically anomalous sentences elicited a larger N400 effect than their semantically natural counterparts regardless of probability manipulation. Little evidence was found in favour of adaptation to semantic violations in that the processing cost associated with the N400 did not decrease over the course of the experiment. Therefore, a dynamic aspect of language-processing system was demonstrated in this study. We will discuss why the language-processing system shows a selective adaptation to morphosyntactic violations.

Simultaneous tracking of psychophysical detection thresholds and evoked potentials to study nociceptive processing

Measuring altered nociceptive processing involved in chronic pain is difficult due to a lack of objective methods. Potential methods to characterize human nociceptive processing involve measuring neurophysiological activity and psychophysical responses to well-defined stimuli. To reliably measure neurophysiological activity in response to nociceptive stimulation using EEG, synchronized activation of nerve fibers and a large number of stimuli are required. On the other hand, to reliably measure psychophysical detection thresholds, selection of stimulus amplitudes around the detection threshold and many stimulus-response pairs are required. Combining the two techniques helps in quantifying the properties of nociceptive processing related to detected and non-detected stimuli around the detection threshold.The two techniques were combined in an experiment including 20 healthy participants to study the effect of intra-epidermal electrical stimulus properties (i.e. amplitude, single- or double-pulse and trial number) on the detection thresholds and vertex potentials. Generalized mixed regression and linear mixed regression were used to quantify the psychophysical detection probability and neurophysiological EEG responses, respectively.It was shown that the detection probability is significantly modulated by the stimulus amplitude, trial number, and the interaction between stimulus type and amplitude. Furthermore, EEG responses were significantly modulated by stimulus detection and trial number. Hence, we successfully demonstrated the possibility to simultaneously obtain information on psychophysical and neurophysiological properties of nociceptive processing. These results warrant further investigation of the potential of this method to observe altered nociceptive processing.

Group penalized generalized estimating equation for correlated event-related potentials and biomarker selection

Background

Event-related potentials (ERP) data are widely used in brain studies that measure brain responses to specific stimuli using electroencephalogram (EEG) with multiple electrodes. Previous ERP data analyses haven’t accounted for the structured correlation among observations in ERP data from multiple electrodes, and therefore ignored the electrode-specific information and variation among the electrodes on the scalp. Our objective was to evaluate the impact of early adversity on brain connectivity by identifying risk factors and early-stage biomarkers associated with the ERP responses while properly accounting for structured correlation.

Methods

In this study, we extend a penalized generalized estimating equation (PGEE) method to accommodate structured correlation of ERPs that accounts for electrode-specific data and to enable group selection, such that grouped covariates can be evaluated together for their association with brain development in a birth cohort of urban-dwelling Bangladeshi children. The primary ERP responses of interest in our study are N290 amplitude and the difference in N290 amplitude.

Results

The selected early-stage biomarkers associated with the N290 responses are representatives of enteric inflammation (days of diarrhea, MIP1b, retinol binding protein (RBP), Zinc, myeloperoxidase (MPO), calprotectin, and neopterin), systemic inflammation (IL-5, IL-10, ferritin, C Reactive Protein (CRP)), socioeconomic status (household expenditure), maternal health (mother height) and sanitation (water treatment).

Conclusions

Our proposed group penalized GEE estimator with structured correlation matrix can properly model the complex ERP data and simultaneously identify informative biomarkers associated with such brain connectivity. The selected early-stage biomarkers offer a potential explanation for the adversity of neurocognitive development in low-income countries and facilitate early identification of infants at risk, as well as potential pathways for intervention.

Trial registration

The related clinical study was retrospectively registered with https://doi.org/ClinicalTrials.gov, identifier NCT01375647, on June 3, 2011.

From movement to action: An EEG study into the emerging sense of agency in early infancy

Research into the developing sense of agency has traditionally focused on sensitivity to sensorimotor contingencies, but whether this implies the presence of a causal action-effect model has recently been called into question. Here, we investigated whether 3- to 4.5-month-old infants build causal action-effect models by focusing on behavioral and neural measures of violation of expectation. Infants had time to explore the causal link between their movements and audiovisual effects before the action-effect contingency was discontinued. We tested their ability to predict the consequences of their movements and recorded neural (EEG) and movement measures. If infants built a causal action-effect model, we expected to observe their violation of expectation in the form of a mismatch negativity (MMN) in the EEG and an extinction burst in their movement behavior after discontinuing the action-effect contingency. Our findings show that the group of infants who showed an MMN upon cessation of the contingent effect demonstrated a more pronounced limb-specific behavioral extinction burst, indicating a causal action-effect model, compared to the group of infants who did not show an MMN. These findings reveal that, in contrast to previous claims, the sense of agency is only beginning to emerge at this age.

Analysis Of Nociceptive Evoked Potentials During Multi-Stimulus Experiments Using Linear Mixed Models

Neural processing of sensory stimuli can be studied using EEG by estimation of the evoked potential using the averages of large sets of trials. However, it is not always possible to include all stimulus parameters in a conventional analysis, since this would lead to an insufficient amount of trials to obtain the evoked potential by averaging. Linear mixed models use dependencies within the data to combine information from all data for the estimation of the evoked potential. In this work, it is shown that in multi-stimulus EEG data the quality of an evoked potential estimate can be improved by using a linear mixed model. Furthermore, the linear mixed model effectively deals with correlation between parameters in the data and reveals the influence of individual stimulus parameters.

Relation of depression symptoms to sustained reward and loss sensitivity

Depression is characterized by altered sensitivity to rewards, with recent evidence suggesting that the ability to sustain responses to rewards across long experimental tasks is diminished. Most work on sustained reward responsiveness has taken a categorical approach and focused on major depressive disorder. However, impairments in reward sensitivity are also found at lower levels of symptom severity and may be relevant for understanding basic mechanisms linking reward processing abnormalities to depression. The current study took a dimensional approach to examine the relation between depression symptoms and sustained reward responsiveness by examining how early neural responses to rewards and losses change over a short time course (i.e., during the experiment). In a sample of 45 unselected undergraduates, changes in the amplitude of the reward positivity (RewP) and feedback negativity (FN) were examined over the course of a simple gambling task using multilevel modeling. Amplitude of the RewP was sustained and amplitude of the FN increased during the task. Unlike prior work focused on clinical populations, depression symptoms in this unselected sample were associated with enhanced RewP and FN responding over the course of the task. Results echo prior work that underscores the importance of examining changes in response to reward across trials and further suggests that sustained responses to both rewards and losses vary in relation to symptom level.

Neural and behavioral effects of regulating emotional responses to errors during an implicit racial bias task

Affect regulation plays a key role in several theories of racial bias reduction. Here, we tested whether engaging in emotion regulation strategies while performing an implicit racial bias task (Weapons Identification Task; WIT) would alter neural and behavioral manifestations of bias. Participants either suppressed or reappraised in a positive light the distress associated with making errors during the WIT, while an electroencephalogram (EEG) was recorded. We hypothesized that engaging in emotion regulation strategies would reduce the distress associated with making errors indicative of bias, resulting in smaller error-related negativity (ERN) amplitude during errors and increased expression of racial bias. Results of within-subjects comparisons (Experiment 1) generally supported these predictions. However, when emotion regulation strategies were manipulated between subjects (Experiment 2) there was no effect of suppression or reappraisal on bias expression. Across both experiments, engaging in emotion regulation led to larger ERNs for errors occurring on Black- relative to White-primed trials. In addition, a number of significant order effects were observed, indicating important differences in the effects of engaging in emotion regulation strategies when those strategies are attempted in participants' first versus second block of trials. No such order effects were evident when a second trial block was completed with no emotion regulation instructions. Findings are discussed in terms of the need for greater specificity in experimental tests of emotion regulation on error processing and cognitive performance.

Robust and Gaussian spatial functional regression models for analysis of event-related potentials

Event-related potentials (ERPs) summarize electrophysiological brain response to specific stimuli. They can be considered as correlated functions of time with both spatial correlation across electrodes and nested correlations within subjects. Commonly used analytical methods for ERPs often focus on pre-determined extracted components and/or ignore the correlation among electrodes or subjects, which can miss important insights, and tend to be sensitive to outlying subjects, time points or electrodes. Motivated by ERP data in a smoking cessation study, we introduce a Bayesian spatial functional regression framework that models the entire ERPs as spatially correlated functional responses and the stimulus types as covariates. This novel framework relies on mixed models to characterize the effects of stimuli while simultaneously accounting for the multilevel correlation structure. The spatial correlation among the ERP profiles is captured through basis-space Matérn assumptions that allow either separable or nonseparable spatial correlations over time. We induce both adaptive regularization over time and spatial smoothness across electrodes via a correlated normal-exponential-gamma (CNEG) prior on the fixed effect coefficient functions. Our proposed framework includes both Gaussian models as well as robust models using heavier-tailed distributions to make the regression automatically robust to outliers. We introduce predictive methods to select among Gaussian vs. robust models and models with separable vs. non-separable spatiotemporal correlation structures. Our proposed analysis produces global tests for stimuli effects across entire time (or time-frequency) and electrode domains, plus multiplicity-adjusted pointwise inference based on experiment-wise error rate or false discovery rate to flag spatiotemporal (or spatio-temporal-frequency) regions that characterize stimuli differences, and can also produce inference for any prespecified waveform components. Our analysis of the smoking cessation ERP data set reveals numerous effects across different types of visual stimuli.

Presaccadic EEG activity predicts visual saliency in free-viewing contour integration

While viewing a scene, the eyes are attracted to salient stimuli. We set out to identify the brain signals controlling this process. In a contour integration task, in which participants searched for a collinear contour in a field of randomly oriented Gabor elements, a previously established model was applied to calculate a visual saliency value for each fixation location. We studied brain activity related to the modeled saliency values, using coregistered eye tracking and EEG. To disentangle EEG signals reflecting salience in free viewing from overlapping EEG responses to sequential eye movements, we adopted generalized additive mixed modeling (GAMM) to single epochs of saccade-related EEG. We found that, when saliency at the next fixation location was high, amplitude of the presaccadic EEG activity was low. Since presaccadic activity reflects covert attention to the saccade target, our results indicate that larger attentional effort is needed for selecting less salient saccade targets than more salient ones. This effect was prominent in contour-present conditions (half of the trials), but ambiguous in the contour-absent condition. Presaccadic EEG activity may thus be indicative of bottom-up factors in saccade guidance. The results underscore the utility of GAMM for EEG-eye movement coregistration research.

Temporal dynamics of reactive cognitive control as revealed by event-related brain potentials

Reactive cognitive control refers to a complementary set of cognitive operations by which individuals monitor for and detect the presence of goal-interfering conflict (i.e., conflict monitoring/evaluation) and, subsequently, initiate attention-focusing and response selection processes to bolster goal-directed action in the face of such conflict (regulative control). The purpose of the current study was to characterize the nature of conflict adaptation in both components of this dynamic process across sequences of trials and, more broadly, across time as participants complete a cognitive control task. Fifty-two young adults completed a standard arrow flanker task while behavioral and ERP data were recorded. Multilevel modeling of sequences of compatible and incompatible trials over time showed that, whereas response time data demonstrated a typical conflict adaptation effect throughout the task, N2 and frontal slow wave (FSW) indices of conflict monitoring and regulative control, respectively, demonstrated significant conflict adaptation only during the early part of the task. Moreover, although differential change in N2 and FSW over time suggested that conflict monitoring and regulative control were dissociable, a reciprocal relation between them was maintained throughout the task and was not present in a component theoretically unrelated to conflict adaptation (visual attention-related N1). Findings are discussed in terms of compensatory processes that help to maintain goal-directed performance even as control-related neural responses become fatigued.

Does pain hypervigilance further impact the lack of habituation to pain in individuals with chronic pain? A cross-sectional pain ERP study

AIM

In chronic pain, habituation is believed to be impaired, and pain hypervigilance can enhance the pain experience. The goal of this study was to determine whether pain hypervigilance further worsens habituation of event-related potentials, measured in a pain-rating protocol of 25 painful somatosensory electrical stimuli, in patients with chronic pain.

METHODS

Pain hypervigilance was assessed with the Pain Vigilance Awareness Questionnaire and analyzed using the event-related fixed interval areas multilevel technique, which enables one to study within-session habituation. In a cohort of 111 participants, 33 reported chronic pain. This chronic pain group was compared with 33 pain-free individuals, matched for age and sex.

RESULTS

The relationship between pain status and habituation was not moderated by pain hypervigilance. Chronic pain status affected linear habituation and dishabituation (quadratic function) from 220 to 260 ms for nearly all electrodes, and from 580 to 640 ms for frontal electrodes. The effect of pain hypervigilance on habituation was observed primarily from 480 to 820 ms poststimulus for right-sided and central electrodes.

CONCLUSION

Pain hypervigilance and chronic pain independently influence habituation to painful stimuli - although not synergistically. To confirm that these effects are mediated by separate pathways, further research is required, in which electroencephalography is combined with other modalities with adequate spatial resolution, such as functional magnetic resonance imaging.

Using trial-level data and multilevel modeling to investigate within-task change in event-related potentials

EEG data, and specifically the ERP, provide psychologists with the power to examine quickly occurring cognitive processes at the native temporal resolution at which they occur. Despite the advantages conferred by ERPs to examine processes at different points in time, ERP researchers commonly ignore the trial-to-trial temporal dimension by collapsing across trials of similar types (i.e., the signal averaging approach) because of constraints imposed by repeated measures ANOVA. Here, we present the advantages of using multilevel modeling (MLM) to examine trial-level data to investigate change in neurocognitive processes across the course of an experiment. Two examples are presented to illustrate the usefulness of this technique. The first demonstrates decreasing differentiation in N170 amplitude to faces of different races across the course of a race categorization task. The second demonstrates attenuation of the ERN as participants commit more errors within a task designed to measure implicit racial bias. Although the examples presented here are within the realm of social psychology, the use of MLM to analyze trial-level EEG data has the potential to contribute to a number of different theoretical domains within psychology.

Pain Processing in a Social Context and the Link with Psychopathic Personality Traits-An Event-Related Potential Study

Empathy describes the ability to understand another person's feelings. Psychopathy is a disorder that is characterized by a lack of empathy. Therefore, empathy and psychopathy are interesting traits to investigate with respect to experiencing and observing pain. The present study aimed to investigate pain empathy and pain sensitivity by measuring event-related potentials (ERPs) extracted from the ongoing EEG in an interactive setup. Each participant fulfilled subsequently the role of "villain" and "victim". In addition, mode of control was modulated resulting in four different conditions; passive villain, active villain, active victim and passive victim. Response-, visual- and pain ERPs were compared between the four conditions. Furthermore, the role of psychopathic traits in these outcomes was investigated. Our findings suggested that people experience more conflict when hurting someone else than hurting themselves. Furthermore, our results indicated that self-controlled pain was experienced as more painful than uncontrolled pain. People that scored high on psychopathic traits seemed to process and experience pain differently. According to the results of the current study, social context, attention and personality traits seem to modulate pain processing and the empathic response to pain in self and others. The within-subject experimental design described here provides an excellent approach to further unravel the influence of social context and personality traits on social cognition.

The iterative nature of person construal: Evidence from event-related potentials

Recently, a dynamic-interactive model of person construal (DI model) has been proposed, whereby the social categories a person represents are determined on the basis of an iterative integration of bottom-up and top-down influences. The current study sought to test this model by leveraging the high temporal resolution of event-related brain potentials (ERPs) as 65 participants viewed male faces that varied by race (White vs Black), fixating either between the eyes or on the forehead. Within face presentations, the effect of fixation, meant to vary bottom-up visual input, initially was large but decreased across early latency neural responses identified by a principal components analysis (PCA). In contrast, the effect of race, reflecting a combination of top-down and bottom-up factors, initially was small but increased across early latency principal components. These patterns support the DI model prediction that bottom-up and top-down processes are iteratively integrated to arrive at a stable construal within 230 ms. Additionally, exploratory multilevel modeling of single trial ERP responses representing a component linked to outgroup categorization (the P2) suggests change in effects of the manipulations over the course of the experiment. Implications of the findings for the DI model are considered.

The Relation between Infant Covert Orienting, Sustained Attention and Brain Activity

This study used measures of event-related potentials (ERPs) and cortical source analysis to examine the effect of covert orienting and sustained attention on 3- and 4.5-month-old infants' brain activity in a spatial cueing paradigm. Cortical source analysis was conducted with current density reconstruction using realistic head models created from age-appropriate infant MRIs. The validity effect was found in the P1 ERP component that was greater for valid than neutral trials in the electrodes contralateral to the visual targets when the stimulus onset asynchrony (SOA) was short. Cortical source analysis revealed greater current density amplitude around the P1 peak latency in the contralateral inferior occipital and ventral temporal regions for valid than neutral and invalid trials. The processing cost effect was found in the N1 ERP component that was greater for neutral than invalid trials in the short SOA condition. This processing cost effect was also shown in the current density amplitude around the N1 peak latency in the contralateral inferior and middle occipital and middle and superior temporal regions. Infant sustained attention was found to modulate infants' brain responses in covert orienting by enhancing the P1 ERP responses and current density amplitude in their cortical sources during sustained attention. These findings suggest that the neural mechanisms that underpin covert orienting already exist in 3- to 4.5-month-old, and they could be facilitated by infant sustained attention.

Impact of early life adversity on EMG stress reactivity of the trapezius muscle

Human and animal research indicates that exposure to early life adversity increases stress sensitivity later in life. While behavioral markers of adversity-induced stress sensitivity have been suggested, physiological markers remain to be elucidated. It is known that trapezius muscle activity increases during stressful situations. The present study examined to what degree early life adverse events experienced during early childhood (0-11 years) and adolescence (12-17 years) moderate experimentally induced electromyographic (EMG) stress activity of the trapezius muscles, in an experimental setting. In a general population sample (n = 115), an anticipatory stress effect was generated by presenting a single unpredictable and uncontrollable electrical painful stimulus at t = 3 minutes. Subjects were unaware of the precise moment of stimulus delivery and its intensity level. Linear and nonlinear time courses in EMG activity were modeled using multilevel analysis. The study protocol included 2 experimental sessions (t = 0 and t = 6 months) allowing for examination of reliability.Results show that EMG stress reactivity during the stress paradigm was consistently stronger in people with higher levels of early life adverse events; early childhood adversity had a stronger moderating effect than adolescent adversity. The impact of early life adversity on EMG stress reactivity may represent a reliable facet that can be used in both clinical and nonclinical studies.

Experimental Sleep Restriction Facilitates Pain and Electrically Induced Cortical Responses

STUDY OBJECTIVES

Sleep restriction (SR) has been hypothesized to sensitize the pain system. The current study determined whether experimental sleep restriction had an effect on experimentally induced pain and pain-elicited electroencephalographic (EEG) responses.

DESIGN

A paired crossover study.

INTERVENTION

Pain testing was performed after 2 nights of 50% SR and after 2 nights with habitual sleep (HS).

SETTING

Laboratory experiment at research center.

PARTICIPANTS

Self-reported healthy volunteers (n = 21, age range: 18-31 y).

MEASUREMENTS AND RESULTS

Brief high-density electrical stimuli to the forearm skin produced pinprick-like pain. Subjective pain ratings increased after SR, but only in response to the highest stimulus intensity (P = 0.018). SR increased the magnitude of the pain-elicited EEG response analyzed in the time-frequency domain (P = 0.021). Habituation across blocks did not differ between HS and SR. Event-related desynchronization (ERD) was reduced after SR (P = 0.039). Pressure pain threshold of the trapezius muscle region also decreased after SR (P = 0.017).

CONCLUSION

Sleep restriction (SR) increased the sensitivity to pressure pain and to electrically induced pain of moderate, but not low, intensity. The increased electrical pain could not be explained by a difference in habituation. Increased response magnitude is possibly related to reduced processing within the somatosensory cortex after partial SR.

Neural systems mediating processing of sound units of language distinguish recovery versus persistence in stuttering

BACKGROUND

Developmental stuttering is a multi-factorial disorder. Measures of neural activity while children processed the phonological (language sound unit) properties of words have revealed neurodevelopmental differences between fluent children and those who stutter. However, there is limited evidence to show whether the neural bases of phonological processing can be used to identify stuttering recovery status. As an initial step, we aimed to determine if differences in neural activity during phonological processing could aid in distinguishing children who had recovered from stuttering and those whose stuttering persisted.

METHODS

We examined neural activity mediating phonological processing in forty-three 7-8 year old children. Groups included children who had recovered from stuttering (CWS-Rec), those whose stuttering persisted (CWS-Per), and children who did not stutter (CWNS). All children demonstrated normal non-verbal intelligence and language skills. Electroencephalograms were recorded as the children listened to pairs of pseudo-words (primes-targets) that either rhymed or did not. Behavioral rhyme judgments along with peak latency and mean amplitude of the N400s elicited by prime and target stimuli were examined.

RESULTS

All the groups were very accurate in their rhyme judgments and displayed a typical ERP rhyme effect, characterized by increased N400 amplitudes over central parietal sites for nonrhyming targets compared to rhyming targets. However, over anterior electrode sites, an earlier onset of the N400 for rhyming compared to non-rhyming targets, indexing phonological segmentation and rehearsal, was observed in the CWNS and CWS-Rec groups. This effect occurred bilaterally for the CWNS, was greater over the right hemisphere in the CWS-Rec, and was absent in the CWS-Per.

CONCLUSIONS

These results are the first to show that differences in ERPs reflecting phonological processing are marked by atypical lateralization in childhood even after stuttering recovery and more pronounced atypical neural patterns for the children whose stuttering persisted. Despite comparable language and phonological skills as revealed by standardized tests, the neural activity mediating phonological segmentation and rehearsal differentiated 7-8 year old children whose stuttering persisted from those who had recovered from stuttering and typically developing peers.

The Influence of Perceived Stress on Cortical Reactivity: A Proof-Of-Principle Study

The aim of this study was to investigate how perceived stress may affect electroencephalographical (EEG) activity in a stress paradigm in a sample of 76 healthy participants. EEG activity was analyzed using multilevel modeling, allowing estimation of nested effects (EEG time segments within subjects). The stress paradigm consisted of a 3-minute pre-stimulus stress period and a 2-minute post-stimulus phase. At t=3 minutes, a single electrical stimulus was delivered. Participants were unaware of the precise moment of stimulus delivery and its intensity level. In the EEG time course of alpha activity, a stronger increase was observed during the post-stimulus period as compared to the pre-stimulus period. An opposite time course effect was apparent for gamma activity. Both effects were in line with a priori expectations and support the validity of this experimental EEG-stress paradigm. Secondly, we investigated whether interaction effects of stress and coping, as measured with the Perceived Stress Scale-10 questionnaire (PSS-10), could be demonstrated. A higher perceived stress score was accompanied by a greater increase in delta- and theta-activity during the post-stimulus phase, compared to low scores. In contrast, low coping capacity was associated with a stronger decrease in slow beta, fast beta and gamma activity during the post-stimulus phase. The results of the present article may be interpreted as proof-of-principle that EEG stress-related activity depends on the level of subjectively reported perceived stress. The inclusion of psychosocial variables measuring coping styles as well as stress-related personality aspects permits further examination of the interconnection between mind and body and may inform on the process of transformation from acute to chronic stress.

Does habituation differ in chronic low back pain subjects compared to pain-free controls? A cross-sectional pain rating ERP study reanalyzed with the ERFIA multilevel method

The objective of the present study was to investigate cortical differences between chronic low back pain (CLBP) subjects and pain-free controls with respect to habituation and processing of stimulus intensity. The use of a novel event-related fixed-interval areas (ERFIA) multilevel technique enables the analysis of event-related electroencephalogram (EEG) of the whole post stimulus range at a single trial level. This technique makes it possible to disentangle the cortical processes of habituation and stimulus intensity.In a cross-sectional study, 78 individuals with CLBP and 85 pain-free controls underwent a rating paradigm of 150 nonpainful and painful somatosensory electrical stimuli. For each trial, the entire epoch was partitioned into 20-ms ERFIAs, which acted as dependent variables in a multilevel analysis. The variability of each consecutive ERFIA period was modeled with a set of predictor variables, including 3 forms of habituation and stimulus intensity.Seventy-six pain-free controls and 65 CLBP subjects were eligible for analysis. CLBP subjects showed a significantly decreased linear habituation at 340 to 460 ms in the midline electrodes and C3 (Ps < .05) and had a significantly more pronounced dishabituation for the regions of 400 to 460 ms and 800 to 820 ms for all electrodes, except for T3 and T4 (Ps < .05). No significant group differences for stimulus intensity processing were observed.In this study, group differences with respect to linear habituation and dishabituation were demonstrated. By means of the ERFIA multilevel technique, habituation effects were found in a broad post stimulus range and were not solely limited to peaks. This study suggests that habituation may be a key mechanism involved in the transition process to chronic pain. Future studies with a longitudinal design are required to solve this issue.

Modeling nonlinear relationships in ERP data using mixed-effects regression with R examples

In the analysis of psychological and psychophysiological data, the relationship between two variables is often assumed to be a straight line. This may be due to the prevalence of the general linear model in data analysis in these fields, which makes this assumption implicitly. However, there are many problems for which this assumption does not hold. In this paper, we show that, in the analysis of event-related potential (ERP) data, the assumption of linearity comes at a cost and may significantly affect the inferences drawn from the data. We demonstrate why the assumption of linearity should be relaxed and how to model nonlinear relationships between ERP amplitudes and predictor variables within the familiar framework of generalized linear models, using regression splines and mixed-effects modeling.

Experimentally induced stress validated by EMG activity

Experience of stress may lead to increased electromyography (EMG) activity in specific muscles compared to a non-stressful situation. The main aim of this study was to develop and validate a stress-EMG paradigm in which a single uncontrollable and unpredictable nociceptive stimulus was presented. EMG activity of the trapezius muscles was the response of interest. In addition to linear time effects, non-linear EMG time courses were also examined. Taking into account the hierarchical structure of the dataset, a multilevel random regression model was applied. The stress paradigm, executed in N = 70 subjects, consisted of a 3-minute baseline measurement, a 3-minute pre-stimulus stress period and a 2-minute post-stimulus phase. Subjects were unaware of the precise moment of stimulus delivery and its intensity level. EMG activity during the entire experiment was conform a priori expectations: the pre-stimulus phase showed a significantly higher mean EMG activity level compared to the other two phases, and an immediate EMG response to the stimulus was demonstrated. In addition, the analyses revealed significant non-linear EMG time courses in all three phases. Linear and quadratic EMG time courses were significantly modified by subjective anticipatory stress level, measured just before the start of the stress task. Linking subjective anticipatory stress to EMG stress reactivity revealed that subjects with a high anticipatory stress level responded with more EMG activity during the pre-stimulus stress phase, whereas subjects with a low stress level showed an inverse effect. Results suggest that the stress paradigm presented here is a valid test to quantify individual differences in stress susceptibility. Further studies with this paradigm are required to demonstrate its potential use in mechanistic clinical studies.

Introducing the event related fixed interval area (ERFIA) multilevel technique: a method to analyze the complete epoch of event-related potentials at single trial level

In analyzing time-locked event-related potentials (ERPs), many studies have focused on specific peaks and their differences between experimental conditions. In theory, each latency point after a stimulus contains potentially meaningful information, regardless of whether it is peak-related. Based on this assumption, we introduce a new concept which allows for flexible investigation of the whole epoch and does not primarily focus on peaks and their corresponding latencies. For each trial, the entire epoch is partitioned into event-related fixed-interval areas under the curve (ERFIAs). These ERFIAs, obtained at single trial level, act as dependent variables in a multilevel random regression analysis. The ERFIA multilevel method was tested in an existing ERP dataset of 85 healthy subjects, who underwent a rating paradigm of 150 painful and non-painful somatosensory electrical stimuli. We modeled the variability of each consecutive ERFIA with a set of predictor variables among which were stimulus intensity and stimulus number. Furthermore, we corrected for latency variations of the P2 (260 ms). With respect to known relationships between stimulus intensity, habituation, and pain-related somatosensory ERP, the ERFIA method generated highly comparable results to those of commonly used methods. Notably, effects on stimulus intensity and habituation were also observed in non-peak-related latency ranges. Further, cortical processing of actual stimulus intensity depended on the intensity of the previous stimulus, which may reflect pain-memory processing. In conclusion, the ERFIA multilevel method is a promising tool that can be used to study event-related cortical processing.