Electroencephalographic Studies Research Articles

Ambivalence Is Better than Indifference: A Behavioral and Neurophysiological Assessment of Ambivalence in Online Environments

Information representations such as ratings and reviews play an important role in assisting users in making decisions in online environments. Prior information systems (IS) research has mostly focused on the role of extreme valence, i.e., the positivity/negativity of information, portrayed by such representations. Yet this bipolar approach discounts how the coexistence of positivity and negativity (i.e., ambivalence) or their absence (i.e., indifference) is formed and leads to distinct attentional processes and outcomes such as purchase decisions. We theorize how and why the valence of information projected through such representations may elicit mixed feelings and influence decision-making in online environments. We conducted four randomized controlled experiments, including an electroencephalography (EEG) study, to disentangle the influence of ambivalence and indifference on decision-making in an online shopping context. We found that ambivalence and indifference to online information distinctly influenced attention and purchase decisions relative to positivity and negativity. Our findings further suggest the inability of incumbent bipolar representations, such as the widely implemented star rating system, to capture the mixed feelings expressed in online content. We propose a bivariate intervention that overcomes the limitations of bipolar representations by not only discerning ambivalence from indifference but also amplifying purchase decisions for products with ambivalent information by at least 50%, compared to incumbent bipolar representations. Our findings advance ongoing research on the role of information valence in online environments and offer implications for practice.

Spotlight on Sleep Stage Classification Based on EEG.

The recommendations for identifying sleep stages based on the interpretation of electrophysiological signals (electroencephalography [EEG], electro-oculography [EOG], and electromyography [EMG]), derived from the Rechtschaffen and Kales manual, were published in 2007 at the initiative of the American Academy of Sleep Medicine, and regularly updated over years. They offer an important tool to assess objective markers in different types of sleep/wake subjective complaints. With the aims and advantages of simplicity, reproducibility and standardization of practices in research and, most of all, in sleep medicine, they have overall changed little in the way they describe sleep. However, our knowledge on sleep/wake physiology and sleep disorders has evolved since then. High-density electroencephalography and intracranial electroencephalography studies have highlighted local regulation of sleep mechanisms, with spatio-temporal heterogeneity in vigilance states. Progress in the understanding of sleep disorders has allowed the identification of electrophysiological biomarkers better correlated with clinical symptoms and outcomes than standard sleep parameters. Finally, the huge development of sleep medicine, with a demand for explorations far exceeding the supply, has led to the development of alternative studies, which can be carried out at home, based on a smaller number of electrophysiological signals and on their automatic analysis. In this perspective article, we aim to examine how our description of sleep has been constructed, has evolved, and may still be reshaped in the light of advances in knowledge of sleep physiology and the development of technical recording and analysis tools. After presenting the strengths and limitations of the classification of sleep stages, we propose to challenge the "EEG-EOG-EMG" paradigm by discussing the physiological signals required for sleep stages identification, provide an overview of new tools and automatic analysis methods and propose avenues for the development of new approaches to describe and understand sleep/wake states.

Neural correlates of statistical learning in developmental dyslexia: An electroencephalography study

The human brain extracts statistical regularities from the surrounding environment in a process called statistical learning. Behavioural evidence suggests that developmental dyslexia affects statistical learning. However, surprisingly few studies have assessed how developmental dyslexia affects the neural processing underlying this type of learning. We used electroencephalography to explore the neural correlates of an important aspect of statistical learning – sensitivity to transitional probabilities – in individuals with developmental dyslexia. Adults diagnosed with developmental dyslexia (n = 17) and controls (n = 19) were exposed to a continuous stream of sound triplets. Every so often, a triplet ending had a low transitional probability given the triplet’s first two sounds (“statistical deviants”). Furthermore, every so often a triplet ending was presented from a deviant location (“acoustic deviants”). We examined mismatch negativity elicited by statistical deviants (sMMN), and MMN elicited by location deviants (i.e., acoustic changes). Acoustic deviants elicited a MMN which was larger in the control group than in the developmental dyslexia group. Statistical deviants elicited a small, yet significant, sMMN in the control group, but not in the developmental dyslexia group. However, the difference between the groups was not significant. Our findings indicate that the neural mechanisms underlying pre-attentive acoustic change detection and implicit statistical auditory learning are both affected in developmental dyslexia.

(176) Unconscious Attention to Sexual Stimuli: An Electroencephalography Study Regarding the Role of Neuroticism and Sexual Excitation/Inhibition

Abstract Introduction Past research has shown that neuroticism is a higher-order vulnerability factor in developing and maintaining emotional disorders and is related to an increased risk of sexual dysfunction. In a recent study, neuroticism was found to impact the automatic attention towards sexual stimuli, but the influence of psychosexual dimensions on such cognitive processes is not fully established. Objective Our aim was to study the mediating role of sexual inhibition/excitation propensity in the relationship between neuroticism and automatic attention to sexual stimuli and also to identify the neuroelectric correlates of this process. Methods We studied 58 individuals (Mage = 23.63; SD = 0.97), who presented either high or low neuroticism levels in the NEO-Personality Inventory-Revised (NEO PI-R). Participants also completed the Sexual Inhibition/Excitation Scales (SIS/SES) and event-related potentials (ERP) P1, P2 and N2 were recorded during a modified oddball paradigm containing romantic and sexually explicit pictures. Using parallel mediation analyses, we simultaneously tested the mediating role of sexual inhibition/excitation in the relationship between neuroticism and each ERP of interest. Results Findings revealed an indirect effect of neuroticism on automatic attention, via SIS1, regardless of the type of stimuli. Such indirect effect was only significant for component N2, with increased amplitudes and earlier latencies in participants with high neuroticism. Effect sizes ranged from medium to large. Conclusions These results can be interpreted as a sign of an enhanced emotional response elicited by the exposure to the sexual content. Results also showed that neuroticism predicts sexual inhibition due to threat of performance failure (SIS1), but does not have an effect on sexual excitation (SES) or sexual inhibition due to threat of performance consequences (SIS2). Our findings suggest that automatic attentional mechanisms are closely related to personality and sexual-related domains, and support the relevance of studying non-conscious cognitive phenomena in the context of human sexual behaviour. Disclosure No

Dynamic electroencephalographic study of persons – mild COVID-19 convalescents

Background. The term “postcovid syndrome” is firmly entrenched in medical terminology, but many aspects of its clinical manifestations are not well understood. Aim. To establish the presence of the nature and severity of changes in the bioelectrical activity of the brain in COVID-19 survivors, as well as their relationship with the formed clinical neurological and neuropsychological syndromes during convalescence. Materials and methods. A dynamic study was conducted of 38 COVID-19 survivors returning to work. Neurophysiological studies were carried out using the EGI-GES-300 system (128 channels). The descriptive characteristics of electroencephalograms were built on the method of studying the spectral density of the electroencephalographic signal on the surface of the scalp, and the dynamic characteristics of the signal were studied by fixing electroencephalographic microstates, using the method of D. Lemmon and T. Kenning. Results and conclusions. In the study, a relatively new diagnostic technique for studying cognitive impairments based on the analysis of electroencephalographic microstates was implemented, which made it possible to identify signs of functional restructuring of the neuronal macronetworks of the brain and trace the characteristic adaptation of a person during the period of convalescence.

The effects of speech masking on neural tracking of acoustic and semantic features of natural speech

Listening environments contain background sounds that mask speech and lead to communication challenges. Sensitivity to slow acoustic fluctuations in speech can help segregate speech from background noise. Semantic context can also facilitate speech perception in noise, for example, by enabling prediction of upcoming words. However, not much is known about how different degrees of background masking affect the neural processing of acoustic and semantic features during naturalistic speech listening. In the current electroencephalography (EEG) study, participants listened to engaging, spoken stories masked at different levels of multi-talker babble to investigate how neural activity in response to acoustic and semantic features changes with acoustic challenges, and how such effects relate to speech intelligibility. The pattern of neural response amplitudes associated with both acoustic and semantic speech features across masking levels was U-shaped, such that amplitudes were largest for moderate masking levels. This U-shape may be due to increased attentional focus when speech comprehension is challenging, but manageable. The latency of the neural responses increased linearly with increasing background masking, and neural latency change associated with acoustic processing most closely mirrored the changes in speech intelligibility. Finally, tracking responses related to semantic dissimilarity remained robust until severe speech masking (−3 dB SNR). The current study reveals that neural responses to acoustic features are highly sensitive to background masking and decreasing speech intelligibility, whereas neural responses to semantic features are relatively robust, suggesting that individuals track the meaning of the story well even in moderate background sound.

Binaural acoustic stimulation in patients with Parkinson's disease.

Acoustic stimulation can improve motor symptoms in Parkinson's disease (PD) and might therefore represent a potential non-invasive treatment option. Scalp electroencephalography studies in healthy subjects indicate that specifically binaural beat stimulation (BBS) in the gamma frequency range is associated with synchronized cortical oscillations at 40 Hertz (Hz). Several studies suggest that oscillations in the gamma-frequency range (>30 Hz) serve a prokinetic function in PD. In this double-blind, randomized study, 25 PD patients were recruited. The study was conducted with (ON) and without dopaminergic medication (OFF). Each drug condition consisted of two phases (no stimulation and acoustic stimulation). The acoustic stimulation phase was divided into two blocks including BBS and conventional acoustic stimulation (CAS) as a control condition. For BBS, a modulated frequency of 35 Hz was used (left: 320 Hz; right: 355 Hz) and for CAS 340 Hz on both sides. We assessed effects on motor performance using Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and two validated commercially available portable devices (Kinesia ONE™ and Kinesia 360™) measuring motor symptoms such as dyskinesia, bradykinesia, and tremor. Repeated measures ANOVA revealed that BBS improved resting tremor on the side of the more affected limb in the OFF condition, as measured by wearables (F(2,48) = 3.61, p = 0.035). However, BBS did not exert a general positive effect on motor symptoms as assessed via MDS-UPDRS (F(2,48) = 1.00, p = 0.327). For CAS, we did not observe an improvement in specific symptoms but rather an overall beneficial effect on motor performance (MDS-UPDRS total score OFF medication: F(2,48) = 4.17, p = 0.021; wearable scores: F(2,48) = 2.46, p = 0.097). In this study, we found an improvement of resting tremor when applying BBS in the gamma frequency band OFF medication. Moreover, the positive effects of CAS underline the general positive potential for improvement of motor function by acoustically supported therapeutic approaches. However, more studies are needed to fully characterize the clinical relevance of BBS and to further optimize its ameliorating effects.

Measurement of craving among gamers with internet gaming disorder using repeated presentations of game videos: a resting-state electroencephalography study

BackgroundInternet gaming disorder (IGD) is receiving increasing attention owing to its effects on daily living and psychological function.MethodsIn this study, electroencephalography was used to compare neural activity triggered by repeated presentation of a stimulus in healthy controls (HCs) and those with IGD. A total of 42 adult men were categorized into two groups (IGD, n = 21) based on Y-IAT-K scores. Participants were required to watch repeated presentations of video games while wearing a head-mounted display, and the delta (D), theta (T), alpha (A), beta (B), and gamma (G) activities in the prefrontal (PF), central (C), and parieto-occipital (PO) regions were analyzed.ResultsThe IGD group exhibited higher absolute powers of DC, DPO, TC, TPO, BC, and BPO than HCs. Among the IGD classification models, a neural network achieves the highest average accuracy of 93% (5-fold cross validation) and 84% (test).ConclusionsThese findings may significantly contribute to a more comprehensive understanding of the neurological features associated with IGD and provide potential neurological markers that can be used to distinguish between individuals with IGD and HCs.

Between alpha and gamma oscillations: Neural signatures of linguistic predictions and listener's attention to speaker's communication intention

When listeners hear a message produced by their interlocutor, they can predict upcoming words thanks to the sentential context and their attention can be focused on the speaker's communication intention. In two electroencephalographical (EEG) studies, we investigated the oscillatory correlates of prediction in spoken-language comprehension and how they are modulated by the listener’s attention. Sentential contexts which were strongly predictive of a particular word were ended by a possessive adjective either matching the gender of the predicted word or not. Alpha, beta and gamma oscillations were studied as they were considered to play a crucial role in the predictive process. While evidence of word prediction was related to alpha fluctuations when listeners focused their attention on sentence meaning, changes in high-gamma oscillations were triggered by word prediction when listeners focused their attention on the speaker's communication intention. Independently of the endogenous attention to a level of linguistic information, the oscillatory correlates of word predictions in language comprehension were sensitive to the prosodic emphasis produced by the speaker at a late stage. These findings thus bear major implications for understanding the neural mechanisms that support predictive processing in spoken-language comprehension.

Monitoring Performance Monitors: Leveraging Neurocognitive Precision to Advance Illness Prevention

Previous sleep electroencephalography studies have detected abnormalities in sleep architecture and sleep spindle deficits in schizophrenia (SCZ), but the consistency of these results was not robust, which might be due to the small sample size and the influence of clinical factors such as the various medication therapies and symptom heterogeneity. This study aimed to regard auditory verbal hallucinations (AVHs) as a pointcut to downscale the heterogeneity of SCZ and explore whether some sleep architecture and spindle parameters were more severely impaired in SCZ patients with AVHs compared with those without AVHs.A total of 90 SCZ patients with AVHs, 92 SCZ patients without AVHs, and 91 healthy control subjects were recruited, and parameters of sleep architecture and spindle activities were compared between groups. The correlation between significant sleep parameters and clinical indicators was analyzed.Deficits of sleep spindle activities at prefrontal electrodes and intrahemispheric spindle coherence were observed in both AVH and non-AVH groups, several of which were more serious in the AVH group. In addition, deficits of spindle activities at central and occipital electrodes and interhemispheric spindle coherence mainly manifested accompanying AVH symptoms, most of which were retained in the medication-naive first-episode patients, and were associated with Auditory Hallucination Rating Scale scores.Our results suggest that the underlying mechanism of spindle deficits might be different between SCZ patients with and without AVHs. In the future, the sleep feature of SCZ patients with different symptoms and the influence of clinical factors, such as medication therapy, should be further illustrated.

Advancing Our Understanding of the Neural Basis of Attention-Deficit/Hyperactivity Disorder by Observing Longitudinal Changes in Resting-State Networks

Previous sleep electroencephalography studies have detected abnormalities in sleep architecture and sleep spindle deficits in schizophrenia (SCZ), but the consistency of these results was not robust, which might be due to the small sample size and the influence of clinical factors such as the various medication therapies and symptom heterogeneity. This study aimed to regard auditory verbal hallucinations (AVHs) as a pointcut to downscale the heterogeneity of SCZ and explore whether some sleep architecture and spindle parameters were more severely impaired in SCZ patients with AVHs compared with those without AVHs.A total of 90 SCZ patients with AVHs, 92 SCZ patients without AVHs, and 91 healthy control subjects were recruited, and parameters of sleep architecture and spindle activities were compared between groups. The correlation between significant sleep parameters and clinical indicators was analyzed.Deficits of sleep spindle activities at prefrontal electrodes and intrahemispheric spindle coherence were observed in both AVH and non-AVH groups, several of which were more serious in the AVH group. In addition, deficits of spindle activities at central and occipital electrodes and interhemispheric spindle coherence mainly manifested accompanying AVH symptoms, most of which were retained in the medication-naive first-episode patients, and were associated with Auditory Hallucination Rating Scale scores.Our results suggest that the underlying mechanism of spindle deficits might be different between SCZ patients with and without AVHs. In the future, the sleep feature of SCZ patients with different symptoms and the influence of clinical factors, such as medication therapy, should be further illustrated.

GCNs–FSMI: EEG recognition of mental illness based on fine-grained signal features and graph mutual information maximization

There is growing evidence that an increasing number of people suffer from mental illness, which seriously affects their quality of life. The study of electroencephalography (EEG) is becoming crucial for understanding the root causes of mental illnesses and preventing them proactively. However, most of the existing approaches are unable to comprehensively investigate the fine-grained EEG data of each channel and the correlations between the signals of each subject. This makes it difficult to establish associations between EEG and mental illnesses. To address this issue, this paper proposes a new method called GCNs–FSMI that combines fine-grained signals and graph mutual information maximization for EEG recognition of mental illness patients. This method integrates fine-grained EEG signals, graph mutual information maximization technology, and pre-trained graph convolutional neural networks (GCN) to explore high-level interactions of multi-channel EEG data between subjects, leading to more discriminative EEG feature representation. This is achieved by filtering the EEG signals on each channel into six frequency bands, calculating the average power of each frequency band, and combining them as fine-grained features of the nodes. Then, we splice the multi-channel EEG signals of a sample into a signal series and construct a network based on the Pearson correlation coefficient to represent the association between channels. After that, we perform pre-training and fine-tuning processes to further improve the EEG feature representations. We pre-train a three-layer GCN model, fix the first two layers of the model, and fine-tune the output layer (third layer) of the model through contrastive learning with graph mutual information maximization. Finally, we conduct several experiments to test the effectiveness of our GCNs–FSMI model. Experimental results on two real-world datasets demonstrate that the features learned by GCNs–FSMI improve the performance of downstream classifiers by 6% and 9%. Furthermore, our method outperformed state-of-the-art methods in classification accuracy. To the best of our knowledge, the GCNs–FSMI is the first EEG recognition method for patients with mental illness that uses fine-grained signals and graph mutual information maximization. Our method provides a new approach to diagnosing mental illness and processing multi-channel biological neural signal processing.

Differentiating mental health promotion effects of various bluespaces: An electroencephalography study

A growing body of literature suggests that visual contact with bluespace may benefit people's mental health. However, whether these benefits vary with the type of bluespace and length of contact duration is unclear. We addressed this critical knowledge gap by conducting a photograph-based experimental study to examine individual mental responses (n = 30) to three types of bluespace (Falling, Flowing, and Static bluespaces) and one control condition (Streetspaces).The participants were assigned to view four conditions in a random sequence in a laboratory. The effect of each condition on mental health was primarily measured through a portable electroencephalogram (EEG) device that continuously recorded brainwaves throughout each contact. We then administered the Restorative Components Scale (RCS) questionnaire as a secondary measure to the participants, who reported psychological states immediately after each contact.We have four main findings. First, visual contact with all three bluespaces yielded significantly greater mental health promotion effects than visual contact with streetspace. Second, the promotion effects of bluespaces varied, and the Falling bluespace was found to be the most beneficial type, as contact with it yielded the highest level of alpha brainwaves, the lowest level of beta brainwaves, and the highest score on the RCS questionnaire. Third, the type of environment appears to be the main factor, and contact duration appears to be the minor factor in explaining the differences in the mental health promotion effects. Finally, a 3-min contact with bluespaces is sufficient to promote mental health. We provide suggestions for future research into bluespaces and how bluespaces can be used to promote urban residents' mental health and well-being.

Perceptual echoes as travelling waves may arise from two discrete neuronal sources

Growing evidence suggests that travelling waves are functionally relevant for cognitive operations in the brain. Several electroencephalography (EEG) studies report on a perceptual alpha-echo, representing the brain response to a random visual flicker, propagating as a travelling wave across the cortical surface. In this study, we ask if the propagating activity of the alpha-echo is best explained by a set of discrete sources mixing at the sensor level rather than a cortical travelling wave. To this end, we presented participants with gratings modulated by random noise and simultaneously acquired the ongoing MEG. The perceptual alpha-echo was estimated using the temporal response function linking the visual input to the brain response. At the group level, we observed a spatial decay of the amplitude of the alpha-echo with respect to the sensor where the alpha-echo was the largest. Importantly, the propagation latencies consistently increased with the distance. Interestingly, the propagation of the alpha-echoes was predominantly centro-lateral, while EEG studies reported mainly posterior-frontal propagation. Moreover, the propagation speed of the alpha-echoes derived from the MEG data was around 10 m/s, which is higher compared to the 2 m/s reported in EEG studies. Using source modelling, we found an early component in the primary visual cortex and a phase-lagged late component in the parietal cortex, which may underlie the travelling alpha-echoes at the sensor level. We then simulated the alpha-echoes using realistic EEG and MEG forward models by placing two sources in the parietal and occipital cortices in accordance with our empirical findings. The two-source model could account for both the direction and speed of the observed alpha-echoes in the EEG and MEG data. Our results demonstrate that the propagation of the perceptual echoes observed in EEG and MEG data can be explained by two sources mixing at the scalp level equally well as by a cortical travelling wave. Importantly, these findings should not be directly extrapolated to intracortical recordings, where travelling waves gradually propagate at a sub-millimetre scale.

Contingent negative variation to tactile stimuli - differences in anticipatory and preparatory processes between participants with and without blindness.

People who are blind demonstrate remarkable abilities within the spared senses and compensatory enhancement of cognitive skills, underscored by substantial plastic reorganization in relevant neural areas. However, little is known about whether people with blindness form top-down models of the world on short timescales more efficiently to guide goal-oriented behavior. This electroencephalography study investigates this hypothesis at the neurophysiological level, focusing on contingent negative variation (CNV) as a marker of anticipatory and preparatory processes prior to expected events. In sum, 20 participants with blindness and 27 sighted participants completed a classic CNV task and a memory CNV task, both containing tactile stimuli to exploit the expertise of the former group. Although the reaction times in the classic CNV task did not differ between groups, participants who are blind reached higher performance rates in the memory task. This superior performance co-occurred with a distinct neurophysiological profile, relative to controls: greater late CNV amplitudes over central areas, suggesting enhanced stimulus expectancy and motor preparation prior to key events. Controls, in contrast, recruited more frontal sites, consistent with inefficient sensory-aligned control. We conclude that in more demanding cognitive contexts exploiting the spared senses, people with blindness efficiently generate task-relevant internal models to facilitate behavior.

Post-Concussion Symptoms, Cognition and Brain Connectivity in an Australian Undergraduate Population: A Quantitative Electroencephalography Study

An estimated 99 in 100,000 people experience a traumatic brain injury (TBI), with 85% being mild (mTBI) in nature. The Post-Concussion Symptom Scale (PCSS), is a reliable and valid measure of post-mTBI symptoms; however, diagnostic specificity is challenging due to high symptom rates in the general population. Understanding the neurobiological characteristics that distinguish high and low PCSS raters may provide further clarification on this phenomenon. To explore the neurobiological characteristics of post-concussion symptoms through the association between PCSS scores, brain network connectivity (using quantitative electroencephalography; qEEG) and cognition in undergraduates. high PCSS scorers will have (1) more network dysregulation and (2) more cognitive dysfunction compared to the low PCSS scorers. A sample of 40 undergraduates were divided into high and low PCSS scorers. Brain connectivity was measured using qEEG, and cognition was measured via neuropsychological measures of sustained attention, inhibition, immediate attention, working memory, processing speed and inhibition/switching. Contrary to expectations, greater frontoparietal network dysregulation was seen in the low PCSS score group (p = 0.003). No significant difference in cognitive dysfunction was detected between high and low PCSS scorers. Post-hoc analysis in participants who had experienced mTBI revealed greater network dysregulation in those reporting a more recent mTBI. Measuring post-concussion symptoms alone is not necessarily informative about changes in underlying neural mechanisms. In an exploratory subset analysis, brain network dysregulation appears to be greater in the early post-injury phase compared to later. Further analysis of underlying PCSS constructs and how to measure these in a non-athlete population and clinical samples is warranted.

Neurophysiological Parameters in Patients after Coronary Bypass Grafing Depending on the Success of Rehabilitation Using the Dual Task Method

The impact of cognitive rehabilitation using the method of dual tasks on the neurophysiological parameters of patients with postoperative cognitive dysfunction (POCD) in the early postoperative period of coronary artery bypass grafting (CABG) under cardiopulmonary bypass was analyzed. The study included 96 male CABG patients. All the patients underwent a detailed neuropsychological and electroencephalographic study before and after CABG. At 2–3 days after surgery, POCD was diagnosed all patients, and they were randomly divided into two groups: with training (n = 54) and without training (n = 42). Starting from 3–4 days of the postoperative period, a daily course of cognitive training was carried out using a dual task (simultaneous performance of the cognitive and physical components). The POCD diagnosis was repeated at the end of the training course (8–11 days). It was found that patients who successfully completed the training (with no POCD at 8–11 days) demonstrated a decrease of the theta-1 power, while in all patients with POCD these indicators increased compared to preoperative data. The topographic features of theta1 rhythm changes were found in the left parietal areas of the cortex, which may indicate impaired perfusion in these regions of the brain.

Electroencephalographic study of the Error Related Negativity in patients suffering from treatment-resistant obsessive-compulsive disorder

IntroductionThe physiopathology of patients with treatment-resistant obsessive-compulsive disorder (OCD) may differ from that of treatment-responsive patients. Cognitive evoked potentials may be one of the ways to detect these differences. The error-related negativity (ERN) is an electrophysiological correlate of error detection during the execution of a motor task, which is larger in patients with OCD than in typical people. According to the literature, the ERN could vary according the patients’ treatment-resistance.ObjectivesThe main goal of this study was to assess whether the ERN, which begins 20 ms before the motor response and reaches its maximum 80 ms later, was different between non-resistant and highly resistant OCD patients.MethodsForty-seven OCD patients and their age- and gender-matched controls were asked to perform a flanker task while the potentials evoked by their motor responses were recorded. For each participant, the difficulty of the task was adjusted to get an error rate of about 20%. Treatment-resistance was evaluated using Pallanti and Quercioli’s (Prog Neuropsychopharmacol Biol Psychiatry 2006; 30 400-412) resistance scales.ResultsIn all participants, response errors evoked an ERN at fronto-central electrodes [Fz, FCz, red and green lines on the figure], whereas the negativity was absent or smaller for correct responses (black and blue lines on the figure, both ps < .01). As expected, the ERN of OCD patients was consistently larger and of longer duration than that of control participants (compare the green and blue lines with the red and black ones, respectively). Interestingly, the amplitude of the potentials evoked by correct responses at central and centro-parietal electrodes on the left side of the brain [C5, C3, CP5] was significantly less negative in treatment-resistant patients (all ps < .05). In control participants, the ERN recorded at fronto-central electrodes were followed by a positive wave which reached its maximum between 170 and 270 ms after the response, and was larger after errors than after correct response. In OCD patients in contrast, this positive wave was absent whether the response was correct or not.Image:ConclusionsThe significant correlation observed between OCD patients’ treatment resistance and the potential evoked by correct responses on the left side of the brain suggest that this potential could be used as a marker of treatment-resistance. The absence in OCD patients of the positive wave that follows the ERN in control participants suggests that OCD patients were not fully aware of whether or not their response was correct.Disclosure of InterestNone Declared

Cortical sources of electroencephalographic alpha rhythms related to the anticipation and experience of mirror visual feedback-induced illusion of finger movements.

Mirror visual feedback (MVF) technique consists in placing a mirror in a person's body midline to induce the illusion of bilateral synchronous movements of the limbs during actual unilateral movements. A recent electroencephalographical (EEG) study demonstrated that MVF-induced illusion was related to the event-related desynchronization (ERD) of alpha (8-12 Hz) rhythms (cortical activation) at the central and parietal scalp electrodes ipsilateral to the unilateral right finger movements. In the present study, we re-analyzed those data to localize the cortical sources of alpha ERD during the anticipation and experience of the MVF-induced illusion of index finger movements. To this aim, the exact Low-Resolution Brain Electromagnetic Tomography freeware was used for the estimation of the cortical sources of the alpha ERD. Results showed that as compared to the condition without MVF, the MVF condition was characterized by greater (p< .01, uncorrected) alpha ERD sources in right frontopolar areas during the anticipation of the MVF-induced illusion of left movements. The MVF condition was also characterized by greater (p< .05, corrected) alpha ERD sources in right premotor, primary somatomotor, and posterior inferior parietal areas during both the anticipation and experience of that MVF-induced illusion. These findings suggest that the MVF-induced illusory experience of left finger movements may be due to dynamic changes in alpha ERD in associative, premotor, somatomotor, and visuomotor frontal-parietal areas located in the hemisphere contralateral to the mirrored motor acts.

POSTICTAL TODD’S PARALYSIS AS A MANIFESTATION OF POSTTRAUMATIC ENCEPHALOPATHY AND A “MASK” OF STROKE: CLINICAL OBSERVATION

Todd's paralysis is rare phenomenon, but its identification is of key diagnostic and therapeutic value. The authors present a clinical observation of post-traumatic encephalopathy accompanied by Todd's paralysis. The main differential diagnostic criteria for post-traumatic encephalopathy with cerebral paroxysms in the form of Todd's paralysis and stroke syndromes have been identified: closed craniocerebral injury in history; epileptiform paroxysms; a clear connection between epileptic seizures and trauma; characteristic "scarcity" of the clinical picture; stereotype paroxysms and rapid regression of symptoms; electroencephalographic study; absence of significant pathological changes on magnetic resonance tomo- and angiography; dissociation between the presence of a neurological deficit and magnetic resonance neuroimaging data; cumulated clinical analysis.