Novelty P3 elicited by the subject’s own name in comatose patients

Neuroimaging biomarkers for the diagnosis and prognosis of patients with disorders of consciousness

The progress in neuroimaging and electrophysiological techniques has shown substantial promise in improving the clinical assessment of disorders of consciousness (DOC). Through the examination of both stimulus-induced and spontaneous brain activity, numerous comprehensive investigations have explored variations in brain activity patterns among patients with DOC, yielding valuable insights for clinical diagnosis and prognostic purposes. Nonetheless, reaching a consensus on precise neuroimaging biomarkers for patients with DOC remains a challenge. Therefore, in this review, we begin by summarizing the empirical evidence related to neuroimaging biomarkers for DOC using various paradigms, including active, passive, and resting-state approaches, by employing task-based fMRI, resting-state fMRI (rs-fMRI), electroencephalography (EEG), and positron emission tomography (PET) techniques. Subsequently, we conducted a review of studies examining the neural correlates of consciousness in patients with DOC, with the findings holding potential value for the clinical application of DOC. Notably, previous research indicates that neuroimaging techniques have the potential to unveil covert awareness that conventional behavioral assessments might overlook. Furthermore, when integrated with various task paradigms or analytical approaches, this combination has the potential to significantly enhance the accuracy of both diagnosis and prognosis in DOC patients. Nonetheless, the stability of these neural biomarkers still needs additional validation, and future directions may entail integrating diagnostic and prognostic methods with big data and deep learning approaches.

Mismatch Negativity and P300 in the Diagnosis and Prognostic Assessment of Coma and Other Disorders of Consciousness

BACKGROUND

The objective of this study was to investigate the value of mismatch negativity (MMN) and P300 event-related potentials for discriminating the consciousness state and predicting improvement of consciousness at 6 months in patients with coma and other disorders of consciousness (DOC).

METHODS

We performed MMN and P300 on 42 patients with DOC with a mean onset time of 40.21 ± 19.43 days. These patients with DOC were categorized into coma, unresponsive wakefulness syndrome (UWS), minimal consciousness minus (MCS-), and minimal consciousness plus (MCS +) groups according to neurobehavioral assessment and the Coma Recovery Scale-Revised score. The primary outcome was the improvement of consciousness at 6 months in patients with DOC. We assessed the efficacy of MMN and P300 in quantitatively predicting the prognosis at 6 months and the capability of MMN and P300 parameters to differentiate between DOC.

RESULTS

At least one significant difference in either MMN or P300 parameters was displayed among the DOC groups, but not between the MCS- and MCS+ groups (significance level: 0.05). Both MMN and P300 amplitudes showed desirable predictive accuracy at 6 months, with areas under the curve (AUCs) of 0.859 and 0.856, respectively. The optimal thresholds for MMN and P300 amplitudes were 2.044 and 1.095 μV. However, the combined MMN-P300 amplitude showed better 6-month predictive accuracy (AUC 0.934, 95% confidence interval 0.860-1.000), with a sensitivity of 85% and a specificity of 90.9%.

CONCLUSIONS

MMN and P300 may help discriminate among coma, UWS, and MCS, but not between patients with MCS- and patients with MCS+ . The MMN amplitude, P300 amplitude, and especially combined MMN-P300 amplitude at 6 months may be interesting predictors of consciousness improvement at 6 months in patients with DOC.

TRIAL REGISTRATION

Chinese Clinical Trial Registry identifier ChiCTR2400083798.

Towards an electroencephalographic measure of awareness based on the reactivity of oscillatory macrostates to hearing a subject's own name

We proposed that the brain's electrical activity is composed of a sequence of alternating states with repeating topographic spectral distributions on scalp electroencephalogram (EEG), referred to as oscillatory macrostates. The macrostate showing the largest decrease in the probability of occurrence, measured as a percentage (reactivity), during sensory stimulation was labelled as the default EEG macrostate (DEM). This study aimed to assess the influence of awareness on DEM reactivity (DER). We included 11 middle cerebral artery ischaemic stroke patients with impaired awareness having a median Glasgow Coma Scale (GCS) of 6/15 and a group of 11 matched healthy controls. EEG recordings were carried out during auditory 1 min stimulation epochs repeating either the subject's own name (SON) or the SON in reverse (rSON). The DEM was identified across three SON epochs alternating with three rSON epochs. Compared with the patients, the DEM of controls contained more posterior theta activity reflecting source dipoles that could be mapped in the posterior cingulate cortex. The DER was measured from the 1 min quiet baseline preceding each stimulation epoch. The difference in mean DER between the SON and rSON epochs was measured by the salient EEG reactivity (SER) theoretically ranging from -100% to 100%. The SER was 12.4 ± 2.7% (Mean ± standard error of the mean) in controls and only 1.3 ± 1.9% in the patient group (P < 0.01). The patient SER decreased with the Glasgow Coma Scale. Our data suggest that awareness increases DER to SON as measured by SER.

Assessing mismatch negativity (MMN) and P3b within-individual sensitivity - A comparison between the local-global paradigm and two specialized oddball sequences

Mismatch negativity (MMN) and P3b are well known for their clinical utility. There exists no gold standard, however, for acquiring them as EEG markers of consciousness in clinical settings. This may explain why the within-individual sensitivity of MMN/P3b paradigms is often quite poor and why seemingly identical EEG markers can behave differently across Disorders of consciousness (DoC) studies. Here, we compare two traditional paradigms for MMN or P3b assessment with the recently more popular local-global paradigm that promises to assess MMN and P3b orthogonally within one oddball sequence. All three paradigms were administered to healthy participants (N = 15) with concurrent EEG. A clear MMN and local effect were found for 15/15 participants. The P3b and global effect were found for 14/15 and 13/15 participants, respectively. There were no systematic differences between the global effect and P3b. Indeed, P3b amplitude was highly correlated across paradigms. The local effect differed clearly from the MMN, however. It occurred earlier than MMN and was followed by a much more prominent P3a. The peak latencies and amplitudes were also not correlated across paradigms. Caution should therefore be exercised when comparing the local effect and MMN across studies. We conclude that the within-individual MMN sensitivity is adequate for both the local-global and a dedicated MMN paradigm. The within-individual sensitivity of P3b was lower than expected for both the local-global and a dedicated P3b paradigm, which may explain the often-low sensitivity of P3b paradigms in patients with DoC.

A Comprehensive Review and Practical Guide of the Applications of Evoked Potentials in Neuroprognostication After Cardiac Arrest

Cardiorespiratory arrest is a very common cause of morbidity and mortality nowadays, and many therapeutic strategies, such as induced coma or targeted temperature management, are used to reduce patient sequelae. However, these procedures can alter a patient's neurological status, making it difficult to obtain useful clinical information for the reliable estimation of neurological prognosis. Therefore, complementary investigations are conducted in the early stages after a cardiac arrest to clarify functional prognosis in comatose cardiac arrest survivors in the first few hours or days. Current practice relies on a multimodal approach, which shows its greatest potential in predicting poor functional prognosis, whereas the data and tools to identify patients with good functional prognosis remain relatively limited in comparison. Therefore, there is considerable interest in investigating alternative biological parameters and advanced imaging technique studies. Among these, somatosensory evoked potentials (SSEPs) remain one of the simplest and most reliable tools. In this article, we discuss the technical principles, advantages, limitations, and prognostic implications of SSEPs in detail. We will also review other types of evoked potentials that can provide useful information but are less commonly used in clinical practice (e.g., visual evoked potentials; short-, medium-, and long-latency auditory evoked potentials; and event-related evoked potentials, such as mismatch negativity or P300).

An EPR study of the cognitive processes underlying the impact of self-relevant information on emotional word processing

Using the event-related potentials (ERPs) technique, this study successively presented names (in either a supra- or subthreshold manner) and emotional words to examine how self-relevant cue (self-name) affects emotional word processing in word class judgment task (to determine whether an emotional word is a noun or adjective) and valence judgment task (to determine whether an emotional word is positive or negative). At the suprathreshold condition, self-relevant positive words elicited a more significant Early posterior negativity (EPN) than negative words only in the valence judgment task. In contrast, at the subthreshold condition, self-relevant negative words elicited an enhanced Late positive potential (LPP) than positive words only in the word class judgment task. These results indicate that self-relevant cue affects emotional word processing at both suprathreshold and subthreshold conditions; nevertheless, the effect manifests as self-positive bias at the suprathreshold condition and self-negative bias at the subthreshold condition. The experimental task modulates these dynamics.

Twenty-four-hour rhythmicities in disorders of consciousness are associated with a favourable outcome

Fluctuations of consciousness and their rhythmicities have been rarely studied in patients with a disorder of consciousness after acute brain injuries. 24-h assessment of brain (EEG), behaviour (eye-opening), and circadian (clock-controlled hormones secretion from urine) functions was performed in acute brain-injured patients. The distribution, long-term predictability, and rhythmicity (circadian/ultradian) of various EEG features were compared with the initial clinical status, the functional outcome, and the circadian rhythmicities of behaviour and clock-controlled hormones. Here we show that more physiological and favourable patterns of fluctuations are associated with a higher 24 h predictability and sharp up-and-down shape of EEG switches, reminiscent of the Flip-Flop model of sleep. Multimodal rhythmic analysis shows that patients with simultaneous circadian rhythmicity for brain, behaviour, and hormones had a favourable outcome. Finally, both re-emerging EEG fluctuations and homogeneous 24-h cycles for EEG, eye-opening, and hormones appeared as surrogates for preserved functionality in brainstem and basal forebrain, which are key prognostic factors for later improvement. While the recovery of consciousness has previously been related to a high short-term complexity, we suggest in this exploratory study the importance of the high predictability of the 24 h long-term generation of brain rhythms and highlight the importance of circadian body-brain rhythms in awakening.

Patients With Better Outcome Have Higher ERP Response to Emotional Auditory Stimuli

PURPOSE

Accuracy of outcome prognosis is one of the most important tasks of coma arousal therapy. Reactions toward sensory stimuli are the most significant predictor of conscience and cognitive functions restoration after a brain injury. A paradigm that includes ERP registration has the advantage of detailed stimuli processing visualization. The authors aimed to investigate perception and distinguishing of emotionally significant sounds (crying and laughter) in coma patients with different consciousness restoration prognosis.

METHODS

EEG was recorded in 24 comatose patients with different outcomes (scored with Glasgow Outcome Scale-Extended) and 32 healthy volunteers. The authors presented sounds of crying and laughter. ERPs for sound stimulation were calculated.

RESULTS

An analysis of the correlation of ERP components and Glasgow Outcome Scale-Extended score was performed. P200 (r = 0.6, P = 0.0014) and N200 amplitudes (r = -0.56, P = 0.0037) for emotional sounds correlated with the Glasgow Outcome Scale-Extended score. The significant differences of P300 and N400 amplitudes corresponded to differences of response between sounds of crying and laughter in subjects of the control group. Unlike the control group, comatose participants with good outcome produced similar electrical activity toward pleasant and unpleasant emotional stimuli.

CONCLUSIONS

Comatose patients with good outcome produced more prominent ERP for emotional sounds. Even the good outcome participants were unable to distinguish emotional sounds of different moods, which indicate the preservation of solely robust mechanisms of sound processing. N200 and P200 amplitudes for emotional stimuli correlated significantly with outcome prognosis in coma patients.

Discrepancies in the late auditory potentials of post-anoxic patients: watch out for focal brain lesions, a pilot retrospective study

AIMS

Late auditory evoked potentials, and notably mismatch negativity (MMN) and P3 responses, can be used as part of the multimodal prognostic evaluation in post-anoxic disorders of consciousness (DOC). MMN response preferentially stems from the temporal cortex and the arcuate fasciculus. Situations with discrepant evaluations, for example MMN absent but P3 present, are frequent and difficult to interpret. We hypothesize that discrepant MMN-/P3+ results could reflect a higher prevalence of lesions in MMN generating regions. This study presents correlations between neurophysiological and neuroradiological results.

METHODS

This retrospective study was conducted on 38 post-anoxic DOC patients. Brain lesions were analyzed on 3T MRI both anatomically and through computation of the local arcuate fasciculus fractional anisotropy values on Diffusion Tensor Imaging sequences. Neurophysiological data and outcome were also analyzed.

RESULTS

Our cohort included 8 MMN-/P3+, 7 MMN+/P3+, 21 MMN-/P3- and 2 MMN-/P3+ patients, assessed at a median delay of 20.5 days since cardiac arrest. Our results show that MMN-/P3+ patients tended to have fewer temporal and basal ganglia lesions than MMN-/P3- patients, and more than MMN+/P3+ patients (p-values for trend: p=0.02 for temporal and p=0.02 for basal ganglia lesions). There was a statistical difference across groups for mean fractional anisotropy values in the arcuate fasciculus (p=0.008). The percentage of patients regaining consciousness at three months in MMN-/P3+ patients was higher than in MMN-/P3- patients and lower than in MMN+/P3+ patients.

CONCLUSION

This study suggests that discrepancies in late auditory evoked potentials may be linked to focal post-anoxic brain lesions, visible on brain MRI.

Specific Neural Mechanisms of Self-Cognition and the Application of Brainprint Recognition

The important identity attribute of self-information presents unique cognitive processing advantages in psychological experiments and has become a research hotspot in psychology and brain science. The unique processing mode of own information has been widely verified in visual and auditory experiments, which is a unique neural processing method for own name, face, voice and other information. In the study of individual behavior, the behavioral uniqueness of self-information is reflected in the faster response of the human brain to self-information, the higher attention to self-information, and the stronger memory level of self-reference. Brain imaging studies have also presented the uniqueness of self-cognition in the brain. EEG studies have shown that self-information induces significant P300 components. fMRI and PET results show that the differences in self and non-self working patterns were located in the frontal and parietal lobes. In addition, this paper combines the self-uniqueness theory and brain-print recognition technology to explore the application of self-information in experimental design, channel combination strategy and identity feature selection of brainprints.

Auditory stimulation and deep learning predict awakening from coma after cardiac arrest

Assessing the integrity of neural functions in coma after cardiac arrest remains an open challenge. Prognostication of coma outcome relies mainly on visual expert scoring of physiological signals, which is prone to subjectivity and leaves a considerable number of patients in a 'grey zone', with uncertain prognosis. Quantitative analysis of EEG responses to auditory stimuli can provide a window into neural functions in coma and information about patients' chances of awakening. However, responses to standardized auditory stimulation are far from being used in a clinical routine due to heterogeneous and cumbersome protocols. Here, we hypothesize that convolutional neural networks can assist in extracting interpretable patterns of EEG responses to auditory stimuli during the first day of coma that are predictive of patients' chances of awakening and survival at 3 months. We used convolutional neural networks (CNNs) to model single-trial EEG responses to auditory stimuli in the first day of coma, under standardized sedation and targeted temperature management, in a multicentre and multiprotocol patient cohort and predict outcome at 3 months. The use of CNNs resulted in a positive predictive power for predicting awakening of 0.83 ± 0.04 and 0.81 ± 0.06 and an area under the curve in predicting outcome of 0.69 ± 0.05 and 0.70 ± 0.05, for patients undergoing therapeutic hypothermia and normothermia, respectively. These results also persisted in a subset of patients that were in a clinical 'grey zone'. The network's confidence in predicting outcome was based on interpretable features: it strongly correlated to the neural synchrony and complexity of EEG responses and was modulated by independent clinical evaluations, such as the EEG reactivity, background burst-suppression or motor responses. Our results highlight the strong potential of interpretable deep learning algorithms in combination with auditory stimulation to improve prognostication of coma outcome.

Infraclinical detection of voluntary attention in coma and post-coma patients using electrophysiology

OBJECTIVE

Early functional evaluation and prognosis of patients with disorders of consciousness is a major challenge that clinical assessments alone cannot solve. Objective measures of brain activity could help resolve this uncertainty. We used electroencephalogram at bedside to detect voluntary attention with a paradigm previously validated in healthy subjects.

METHODS

Using auditory-oddball sequences, our approach rests on detecting known attentional modulations of Event Related Potentials that reflect compliance with verbal instructions. Sixty-eight unresponsive patients were tested in their first year after coma onset (37 coma and 31 first year post-coma patients). Their evolution 6 months after the test was considered.

RESULTS

Fourteen of the 68 patients, showed a positive response. Nine were in a coma and 5 in a minimally conscious state (MCS). Except for one who died early, all responders evolved to exit-MCS within 6 months (93%), while 35 (65%) among non-responders only.

CONCLUSIONS

Among those patients for whom the outcome is highly uncertain, 21% responded positively to this simple but cognitively demanding test. Strikingly, some coma patients were among responders.

SIGNIFICANCE

The proposed paradigm revealed cognitive-motor dissociation in some coma patients. This ability to sustain attention on demand predicted awakening within 6 months and represents an immediately useful information for relatives and caregivers.

Prognostication after cardiac arrest: how EEG and evoked potentials may improve the challenge

About 80% of patients resuscitated from CA are comatose at ICU admission and nearly 50% of survivors are still unawake at 72 h. Predicting neurological outcome of these patients is important to provide correct information to patient's relatives, avoid disproportionate care in patients with irreversible hypoxic-ischemic brain injury (HIBI) and inappropriate withdrawal of care in patients with a possible favorable neurological recovery. ERC/ESICM 2021 algorithm allows a classification as "poor outcome likely" in 32%, the outcome remaining "indeterminate" in 68%. The crucial question is to know how we could improve the assessment of both unfavorable but also favorable outcome prediction. Neurophysiological tests, i.e., electroencephalography (EEG) and evoked-potentials (EPs) are a non-invasive bedside investigations. The EEG is the record of brain electrical fields, characterized by a high temporal resolution but a low spatial resolution. EEG is largely available, and represented the most widely tool use in recent survey examining current neuro-prognostication practices. The severity of HIBI is correlated with the predominant frequency and background continuity of EEG leading to "highly malignant" patterns as suppression or burst suppression in the most severe HIBI. EPs differ from EEG signals as they are stimulus induced and represent the summated activities of large populations of neurons firing in synchrony, requiring the average of numerous stimulations. Different EPs (i.e., somato sensory EPs (SSEPs), brainstem auditory EPs (BAEPs), middle latency auditory EPs (MLAEPs) and long latency event-related potentials (ERPs) with mismatch negativity (MMN) and P300 responses) can be assessed in ICU, with different brain generators and prognostic values. In the present review, we summarize EEG and EPs signal generators, recording modalities, interpretation and prognostic values of these different neurophysiological tools. Finally, we assess the perspective for futures neurophysiological investigations, aiming to reduce prognostic uncertainty in comatose and disorders of consciousness (DoC) patients after CA.

Objective Neurophysiologic Markers of Cognition After Pediatric Brain Injury

Background and Objectives

Following brain injury, clinical assessments of residual and emerging cognitive function are difficult and fraught with errors. In adults, recent American Academy of Neurology (AAN) practice guidelines recommend objective neuroimaging and neurophysiologic measures to support diagnosis. Equivalent measures are lacking in pediatrics-an especially great challenge due to the combined heterogeneity of both brain injury and pediatric development. Therefore, we aim to establish quantitative, clinically practicable measures of cognitive function following pediatric brain injury.

Methods

Participants with and without brain injury were aged 8-18 years, clinically classified according to cognitive recovery state: N = 8 in disorders of consciousness (DoC), N = 7 in confusional state, N = 19 cognitively impaired, and N = 13 typically developing uninjured controls. We prospectively measured electroencephalographic markers of sensory processing and attention in an auditory oddball paradigm, and of covert movement attempts in a command-following paradigm.

Results

In 3 participants with DoC, EEG markers of active attempted command following revealed cognitive function that clinical assessment had failed to detect. These same 3 individuals could also be distinguished from the rest of their group by 2 event-related potentials that correlate with sensory processing and orienting attention in the oddball paradigm. Considered across the whole participant group, magnitudes of these 2 ERP markers significantly increased as cognitive recovery progressed (ANOVA: each p < 0.001); viewed jointly, the 2 ERP markers cleanly delineated the 4 cognitive states.

Discussion

Despite heterogeneity of brain injuries and brain development, our objective EEG markers reflected cognitive recovery independent of motor function. Two of these markers required no active participation. Together, they allowed us to identify 3 individuals who meet the criteria for cognitive-motor dissociation. To diagnose, prognose, and track cognitive recovery accurately, such markers should be used in pediatrics.

Auditory event-related potentials based on name stimuli: A pilot study

In recent years, diagnostic studies of brain disorders based on auditory event-related potentials (AERP) have become a hot topic. Research showed that AERP might help to detect patient consciousness, especially using the subjects' own name (SON). In this study, we conducted a preliminary analysis of the brain response to Chinese name stimuli. Twelve subjects participated in this study. SONs were used as target stimuli for each trial. The names used for non-target stimuli were divided into three Chinese character names condition (3CC) and two Chinese characters names condition (2CC). Thus, each subject was required to be in active (silent counting) and passive mode (without counting) with four conditions [(passive, active) × (3CC, 2CC)]. We analyzed the spatio-temporal features for each condition, and we used SVM for target vs. non-target classification. The results showed that the passive mode under 3CC conditions showed a similar brain response to the active mode, and when 3CC was used as a non-target stimulus, the brain response induced by the target stimulus would have a better interaction than 2CC. We believe that the passive mode 3CC may be a good paradigm to replace the active mode which might need more attention from subjects. The results of this study can provide certain guidelines for the selection and optimization of the paradigm of auditory event-related potentials based on name stimulation.

Assessment of electroencephalography and event-related potentials in unresponsive patients with brain injury

OBJECTIVE

To investigate the predictors of clinical outcomes in unresponsive patients with acquired brain injuries.

METHODS

Patients with coma or disorders of consciousness were enrolled from August 2019 to March 2021. A retrospective analysis of demographics, etiology, clinical score, diagnosis, electroencephalography (EEG), and event-related potential (ERP) data from 1 week to 2 months after coma onset was conducted. Findings were assessed for predicting favorable outcomes at 6 months post-coma, and functional outcomes were determined using the Glasgow Outcome Scale-Extended (GOS-E).

RESULTS

Of 68 patients, 22 patients had a good neurological outcome at 6 months, while 11 died. Univariate analysis showed that motor response (Motor-R; p < 0.001), EEG pattern (p = 0.015), sleep spindles (p = 0.018), EEG reactivity (EEG-R; p < 0.001), mismatch negativity (MMN) amplitude at electrode Fz (FzMMNA; p = 0.001), P3a latency (p = 0.044), and P3a amplitude at electrode Cz (CzP3aA; p < 0.001) were significantly correlated with patient prognosis. Multivariable logistic regression analysis showed that FzMMNA, CzP3aA, EEG-R, and Motor-R were significant independent predictors of a favorable outcome. The sensitivity and specificity of FzMMNA (dichotomized at 1.16 μV) were 86.4% and 58.5%, and of CzP3aA (cut-off value 2.76 μV) were 90.9% and 70.7%, respectively. ERP amplitude (ERP-A), a combination of FzMMNA and CzP3aA, improved prediction accuracy, with an area under the receiver operating characteristic curve (AUC) of 0.884. A model incorporating Motor-R, EEG-R, and ERP-A yielded an outstanding predictive performance (AUC=0.921) for a favorable outcome.

CONCLUSION

ERP-A and the prognostic model resulted in the efficient prediction of a favorable outcome in unresponsive patients.

How brain-computer interface technology may improve the diagnosis of the disorders of consciousness: A comparative study

Objective

Clinical assessment of consciousness relies on behavioural assessments, which have several limitations. Hence, disorder of consciousness (DOC) patients are often misdiagnosed. In this work, we aimed to compare the repetitive assessment of consciousness performed with a clinical behavioural and a Brain-Computer Interface (BCI) approach.

Materials and methods

For 7 weeks, sixteen DOC patients participated in weekly evaluations using both the Coma Recovery Scale-Revised (CRS-R) and a vibrotactile P300 BCI paradigm. To use the BCI, patients had to perform an active mental task that required detecting specific stimuli while ignoring other stimuli. We analysed the reliability and the efficacy in the detection of command following resulting from the two methodologies.

Results

Over repetitive administrations, the BCI paradigm detected command following before the CRS-R in seven patients. Four clinically unresponsive patients consistently showed command following during the BCI assessments.

Conclusion

Brain-Computer Interface active paradigms might contribute to the evaluation of the level of consciousness, increasing the diagnostic precision of the clinical bedside approach.

Significance

The integration of different diagnostic methods leads to a better knowledge and care for the DOC.

P3b Does Not Reflect Perceived Contrasts

It has been shown that P3b is not a signature of perceptual awareness per se but is instead more closely associated with postperceptual processing (Cohen et al., 2020). Here, we seek to investigate whether human participants’ attentional states are different in the report and the no-report conditions. This difference in attentional states, if exists, may lead to degraded consciousness of the stimuli in the no-report condition, and it therefore remains unknown whether the disappearance of P3b is because of a lack of reportability or degraded consciousness. Results of our experiment 1 showed that participants did experience degraded contents of consciousness in the no-report condition. However, results of experiment 2 showed that the degraded contents of consciousness did not influence the amplitude of P3b. These findings strengthen the claim that P3b is not a signature of perceptual awareness but is associated with postperceptual processing.

Evoked and Event-Related Potentials as Biomarkers of Consciousness State and Recovery

SUMMARY

The definition of consciousness has been the subject of great interest for many scientists and philosophers. To better understand how evoked potentials may be identified as biomarkers of consciousness and recovery, the different theoretical models sustaining neural correlates of consciousness are reviewed. A multimodal approach can help to better predict clinical outcome in patients presenting with disorders of consciousness. Evoked potentials are inexpensive and easy-to-implement bedside examination techniques. Evoked potentials are an integral part of prognostic evaluation, particularly in cases of cognitive motor dissociation. Prognostic criteria are well established in postanoxic disorders of consciousness, especially postcardiac arrest but are less well determined in other etiologies. In the early examination, bilateral absence of N20 in disorder of consciousness patients is strongly associated with unfavorable outcome (i.e., death or unresponsive wakefulness syndrome) especially in postanoxic etiologies. This predictive value is lower in other etiologies and probably also in children. Both N20 and mismatch negativity are proven outcome predictors for acute coma. Many studies have shown that mismatch negativity and P3a are characterized by a high prognostic value for awakening, but some patients presenting unresponsive wakefulness syndrome also process a P3a. The presence of long-latency event-related potential components in response to stimuli is indicative of a better recovery. All neurophysiological data must be integrated within a multimodal approach combining repeated clinical evaluation, neuroimaging, functional imaging, biology, and neurophysiology combining passive and active paradigms.

How does self name influence the neural processing of emotional prosody? An ERP study

In this study, we investigated whether self-relevant information can accelerate the processing of emotional information. Our experiment, based on a passive auditory oddball paradigm, involved recording electroencephalography while participants listened to stimuli comprising their own names (ONs) and unfamiliar names (UNs) spoken with varying emotional prosody. At 220-300 ms, mismatch negativity (MMN) was more negative for ONs and angry prosody than for UNs and neutral prosody, respectively. These results suggest that attention is involuntarily attracted by ONs and emotional prosody, and that both types of information are given priority processing, even under pre-attentive conditions. Importantly, ONs with angry prosody induced more negative MMN than did similar UNs and ONs with neutral prosody, which indicates that the motivational significance embedded in angry prosody promotes the self-reference effect and, thus, involves more attention resources. At 300-500 ms, ONs triggered smaller P3a than did UNs, suggesting that less cognitive resources are required to process self-relevant information. These results suggest that self-relevant and emotional information of preferential processing interact with each other during the pre-attentive stage, with self-reference enhancing the processing of emotional information.

Eliciting and Recording Event Related Potentials (ERPs) in Behaviourally Unresponsive Populations: A Retrospective Commentary on Critical Factors

A consistent limitation when designing event-related potential paradigms and interpreting results is a lack of consideration of the multivariate factors that affect their elicitation and detection in behaviorally unresponsive individuals. This paper provides a retrospective commentary on three factors that influence the presence and morphology of long-latency event-related potentials—the P3b and N400. We analyze event-related potentials derived from electroencephalographic (EEG) data collected from small groups of healthy youth and healthy elderly to illustrate the effect of paradigm strength and subject age; we analyze ERPs collected from an individual with severe traumatic brain injury to illustrate the effect of stimulus presentation speed. Based on these critical factors, we support that: (1) the strongest paradigms should be used to elicit event-related potentials in unresponsive populations; (2) interpretation of event-related potential results should account for participant age; and (3) speed of stimulus presentation should be slower in unresponsive individuals. The application of these practices when eliciting and recording event-related potentials in unresponsive individuals will help to minimize result interpretation ambiguity, increase confidence in conclusions, and advance the understanding of the relationship between long-latency event-related potentials and states of consciousness.

Narrative Review: Quantitative EEG in Disorders of Consciousness

In this narrative review, we focus on the role of quantitative EEG technology in the diagnosis and prognosis of patients with unresponsive wakefulness syndrome and minimally conscious state. This paper is divided into two main parts, i.e., diagnosis and prognosis, each consisting of three subsections, namely, (i) resting-state EEG, including spectral power, functional connectivity, dynamic functional connectivity, graph theory, microstates and nonlinear measurements, (ii) sleep patterns, including rapid eye movement (REM) sleep, slow-wave sleep and sleep spindles and (iii) evoked potentials, including the P300, mismatch negativity, the N100, the N400 late positive component and others. Finally, we summarize our findings and conclude that QEEG is a useful tool when it comes to defining the diagnosis and prognosis of DOC patients.

Neural Evidence for Speech Processing Deficits During a Cocktail Party Scenario in Minimally and Low Verbal Adolescents and Young Adults with Autism

As demonstrated by the Cocktail Party Effect, a person's attention is grabbed when they hear their name in a multispeaker setting. However, individuals with autism (ASD) are commonly challenged in multispeaker settings and often do not respond to salient speech, including one's own name (OON). It is unknown whether neural responses during this Cocktail Party scenario differ in those with ASD and whether such differences are associated with expressive language or auditory filtering abilities. We measured neural responses to hearing OON in quiet and multispeaker settings using electroencephalography in 20 minimally or low verbal ASD (ASD-MLV), 27 verbally fluent ASD (ASD-V), and 27 neurotypical (TD) participants, ages 13-22. First, we determined whether TD's neural responses to OON relative to other names could be quantified with early frontal mismatch responses (MMRs) and late, slow shift parietal and frontal responses (LPPs/FNs). Second, we compared the strength of MMRs and LPPs/FNs across the three groups. Third, we tested whether participants with poorer auditory filtering abilities exhibited particularly weak neural responses to OON heard in a multispeaker setting. Our primary finding was that TDs and ASD-Vs, but not ASD-MLVs, had significant MMRs to OON in a multispeaker setting, and strength of LPPs positively correlated with auditory filtering abilities in those with ASD. These findings reveal electrophysiological correlates of auditory filtering disruption within a clinical population that has severe language and communication impairments and offer a novel neuroimaging approach to studying the Cocktail Party effect in neurotypical and clinical populations. Autism Res 2020, 13: 1828-1842. © 2020 International Society for Autism Research and Wiley Periodicals LLC. LAY SUMMARY: We found that minimally and low verbal adolescents and young adults with autism exhibit decreased neural responses to one's own name when heard in a multispeaker setting. In addition, decreased strength of neural responses in those with autism correlated with decreased auditory filtering abilities. We propose that these neural deficits may reflect the ineffective processing of salient speech in noisy settings and contribute to language and communication deficits observed in autism.

Electrophysiological and Neuroimaging Studies - During Resting State and Sensory Stimulation in Disorders of Consciousness: A Review

A severe brain injury may lead to a disorder of consciousness (DOC) such as coma, vegetative state (VS), minimally conscious state (MCS) or locked-in syndrome (LIS). Till date, the diagnosis of DOC relies only on clinical evaluation or subjective scoring systems such as Glasgow coma scale, which fails to detect subtle changes and thereby results in diagnostic errors. The high rate of misdiagnosis and inability to predict the recovery of consciousness for DOC patients have created a huge research interest in the assessment of consciousness. Researchers have explored the use of various stimulation and neuroimaging techniques to improve the diagnosis. In this article, we present the important findings of resting-state as well as sensory stimulation methods and highlight the stimuli proven to be successful in the assessment of consciousness. Primarily, we review the literature based on (a) application/non-use of stimuli (i.e., sensory stimulation/resting state-based), (b) type of stimulation used (i.e., auditory, visual, tactile, olfactory, or mental-imagery), (c) electrophysiological signal used (EEG/ERP, fMRI, PET, EMG, SCL, or ECG). Among the sensory stimulation methods, auditory stimulation has been extensively used, since it is easier to conduct for these patients. Olfactory and tactile stimulation have been less explored and need further research. Emotionally charged stimuli such as subject’s own name or narratives in a familiar voice or subject’s own face/family pictures or music result in stronger responses than neutral stimuli. Studies based on resting state analysis have employed measures like complexity, power spectral features, entropy and functional connectivity patterns to distinguish between the VS and MCS patients. Resting-state EEG and fMRI are the state-of-the-art techniques and have a huge potential in predicting the recovery of coma patients. Further, EMG and mental-imagery based studies attempt to obtain volitional responses from the VS patients and thus could detect their command-following capability. This may provide an effective means to communicate with these patients. Recent studies have employed fMRI and PET to understand the brain-activation patterns corresponding to the mental imagery. This review promotes our knowledge about the techniques used for the diagnosis of patients with DOC and attempts to provide ideas for future research.

Clinical and advanced neurophysiology in the prognostic and diagnostic evaluation of disorders of consciousness: review of an IFCN-endorsed expert group

The analysis of spontaneous EEG activity and evoked potentialsis a cornerstone of the instrumental evaluation of patients with disorders of consciousness (DoC). Thepast few years have witnessed an unprecedented surge in EEG-related research applied to the prediction and detection of recovery of consciousness after severe brain injury,opening up the prospect that new concepts and tools may be available at the bedside. This paper provides a comprehensive, critical overview of bothconsolidated and investigational electrophysiological techniquesfor the prognostic and diagnostic assessment of DoC.We describe conventional clinical EEG approaches, then focus on evoked and event-related potentials, and finally we analyze the potential of novel research findings. In doing so, we (i) draw a distinction between acute, prolonged and chronic phases of DoC, (ii) attempt to relate both clinical and research findings to the underlying neuronal processes and (iii) discuss technical and conceptual caveats.The primary aim of this narrative review is to bridge the gap between standard and emerging electrophysiological measures for the detection and prediction of recovery of consciousness. The ultimate scope is to provide a reference and common ground for academic researchers active in the field of neurophysiology and clinicians engaged in intensive care unit and rehabilitation.

Finally, Some Neurophysiologic Good News-Favorable Prognosis in Coma

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Clinical Research: Auditory Stimulation in the Disorders of Consciousness

Due to the complex situation of disorder of consciousness (DOC) patients, the assessment of conscious states of these patients has become a huge challenge for a long time (Laureys et al., 2010). At present, the main clinical diagnostic method to assess the conscious state of a DOC patient is the use of a relevant behavior scale like the Coma Recovery Scale-Revised (CRS-R). In this article, we will focus on auditory stimulation and select some representative auditory stimulus, like calling names and music stimulation, to discuss the function and application of the auditory stimulus in patients with DOC and provide guidance for future research.

Development of a point of care system for automated coma prognosis: a prospective cohort study protocol

INTRODUCTION

Coma is a deep state of unconsciousness that can be caused by a variety of clinical conditions. Traditional tests for coma outcome prediction are based mainly on a set of clinical observations. Recently, certain event-related potentials (ERPs), which are transient electroencephalogram (EEG) responses to auditory, visual or tactile stimuli, have been introduced as useful predictors of a positive coma outcome (ie, emergence). However, such tests require the skills of clinical neurophysiologists, who are not commonly available in many clinical settings. Additionally, none of the current standard clinical approaches have sufficient predictive accuracies to provide definitive prognoses.

OBJECTIVE

The objective of this study is to develop improved machine learning procedures based on EEG/ERP for determining emergence from coma.

METHODS AND ANALYSIS

Data will be collected from 50 participants in coma. EEG/ERP data will be recorded for 24 consecutive hours at a maximum of five time points spanning 30 days from the date of recruitment to track participants' progression. The study employs paradigms designed to elicit brainstem potentials, middle-latency responses, N100, mismatch negativity, P300 and N400. In the case of patient emergence, data are recorded on that occasion to form an additional basis for comparison. A relevant data set will be developed from the testing of 20 healthy controls, each spanning a 15-hour recording period in order to formulate a baseline. Collected data will be used to develop an automated procedure for analysis and detection of various ERP components that are salient to prognosis. Salient features extracted from the ERP and resting-state EEG will be identified and combined to give an accurate indicator of prognosis.

ETHICS AND DISSEMINATION

This study is approved by the Hamilton Integrated Research Ethics Board (project number 4840). Results will be disseminated through peer-reviewed journal articles and presentations at scientific conferences.

TRIAL REGISTRATION NUMBER

NCT03826407.

Prolonged exposure to highly rhythmic music affects brain dynamics and perception

Rhythmic stimulation is a powerful tool to improve temporal prediction and parsing of the auditory signal. However, for long duration of stimulation, the rhythmic and repetitive aspects of music have often been associated to a trance state. In this study we conceived an auditory monitoring task that allows tracking changes of psychophysical auditory thresholds. Participants performed the task while listening to rhythmically regular and an irregular (scrambled but spectrally identical) music that were presented with an intermittent (short) and continuous (long) type of stimulation. Results show that psychophysical auditory thresholds increase following a Continuous versus Intermittent stimulation and this is accompanied by a reduction of the amplitude of two event-related potentials to target stimuli. These effects are larger with regular music, thus do not simply derive from the duration of stimulation. Interestingly, they seem to be related to a frequency selective neural coupling as well as an increase of network connectivity in the alpha band between frontal and central regions. Our study shows that the idea that rhythmic presentation of sensory stimuli facilitates perception might be limited to short streams, while long, highly regular, repetitive and strongly engaging streams may have an opposite perceptual impact.

Evidence of P3a During Sleep, a Process Associated With Intrusions Into Consciousness in the Waking State

The present study examines processes associated with intrusions into consciousness during an unconscious state, natural sleep. The definition of sleep is still much debated. Almost all researchers agree that sleep onset represents a gradual loss of consciousness of the external environment. For sleep to be beneficial, it needs to remain as undisturbed as possible. Nevertheless, unlike other unconsciousness states, sleep is reversible. For purposes of survival, it is critical that the sleeper be able to “detect” and perhaps become conscious of highly relevant biological or personal information. Therefore, even in sleep, the brain must decide whether a new incoming stimulus is relevant and if so, may require an arousal to wakefulness, or whether it is irrelevant and can be gated to prevent disruption of sleep. Event-related potentials (ERPs) were used to measure the extent processing of auditory stimuli some of which elicited an ERP component, the P3a, in the waking state. The P3a is associated with processes resulting in the interruption of frontal central executive, leading to conscious awareness. Very little research has focused on the occurrence of the P3a during sleep. A multi-feature paradigm was used to examine the processing of a frequently occurring “standard” stimulus and six rarely occurring different “deviant” stimuli during wakefulness, NREM, and REM sleep. A P3a was elicited by novel environmental sounds and white noise bursts in the waking state, replicating previous studies. Other deviant stimuli (changes in pitch, intensity, duration) failed to do so. The ERPs indicated that processing of the stimuli that did not elicit a P3a in wakefulness were much inhibited during both NREM and REM sleep. Surprisingly, those deviants that did elicit a P3a in wakefulness continued to do so in stage N2 and REM sleep. The subject did not, however, awaken. These results suggest processes leading to consciousness in wakefulness may still remain active during sleep possibly allowing subjects to act on potentially highly relevant input. This may also explain how sleep can be reversed if the stimulus input is sufficiently critical.

Review of Abnormal Self-Knowledge in Major Depressive Disorder

Background: Major depressive disorder (MDD) is an affective disorder that is harmful to both physical and mental health. Abnormal self-knowledge, which refers to abnormal judgments about oneself, is a core symptom of depression. However, little research has summarized how and why patients with MDD differ from healthy individuals in terms of self-knowledge. Objective: To gain a better understanding of MDD, we reviewed previous studies that focused on the behavioral and neurological changes of self-knowledge in this illness. Main Findings: On the behavioral level, depressed individuals exhibited negative self-knowledge in an explicit way, while more heterogeneous patterns were reported in implicit results. On the neurological level, depressed individuals, as compared with non-depressed controls, showed abnormal self-referential processing in both early perception and higher cognitive processing phases during the Self-Referential Encoding Task. Furthermore, fMRI studies have reported aberrant activity in the medial prefrontal cortex area for negative self-related items in depression. These results revealed several behavioral features and brain mechanisms underlying abnormal self-knowledge in depression. Future Studies: The neural mechanism of implicit self-knowledge in MDD remains unclear. Future research should examine the importance of others' attitudes on the self-concept of individuals with MDD, and whether abnormal self-views may be modified through cognitive or pharmacological approaches. In addition, differences in abnormal self-knowledge due to genetic variation between depressed and non-depressed populations remain unconfirmed. Importantly, it remains unknown whether abnormal self-knowledge could be used as a specific marker to distinguish healthy individuals from those with MDD. Conclusion: This review extends our understanding of the relationship between self-knowledge and depression by indicating several abnormalities among individuals with MDD and those who are at risk for this illness.

A Machine Learning Framework for Automatic and Continuous MMN Detection With Preliminary Results for Coma Outcome Prediction

Mismatch negativity (MMN) is a component of the event-related potential (ERP) that is elicited through an odd-ball paradigm. The existence of the MMN in a coma patient has a good correlation with coma emergence; however, this component can be difficult to detect. Previously, MMN detection was based on visual inspection of the averaged ERPs by a skilled clinician, a process that is expensive and not always feasible in practice. In this paper, we propose a practical machine learning (ML) based approach for detection of MMN component, thus, improving the accuracy of prediction of emergence from coma. Furthermore, the method can operate on an automatic and continuous basis thus alleviating the need for clinician involvement. The proposed method is capable of the MMN detection over intervals as short as two minutes. This finer time resolution enables identification of waxing and waning cycles of a conscious state. An auditory odd-ball paradigm was applied to 22 healthy subjects and 2 coma patients. A coma patient is tested by measuring the similarity of the patient's ERP responses with the aggregate healthy responses. Because the training process for measuring similarity requires only healthy subjects, the complexity and practicality of training procedure of the proposed method are greatly improved relative to training on coma patients directly. Since there are only two coma patients involved with this study, the results are reported on a very preliminary basis. Preliminary results indicate we can detect the MMN component with an accuracy of 92.7% on healthy subjects. The method successfully predicted emergence in both coma patients when conventional methods failed. The proposed method for collecting training data using exclusively healthy subjects is a novel approach that may prove useful in future, unrelated studies where ML methods are used.

Task-free auditory EEG paradigm for probing multiple levels of speech processing in the brain

While previous studies on language processing highlighted several ERP components in relation to specific stages of sound and speech processing, no study has yet combined them to obtain a comprehensive picture of language abilities in a single session. Here, we propose a novel task-free paradigm aimed at assessing multiple levels of speech processing by combining various speech and nonspeech sounds in an adaptation of a multifeature passive oddball design. We recorded EEG in healthy adult participants, who were presented with these sounds in the absence of sound-directed attention while being engaged in a primary visual task. This produced a range of responses indexing various levels of sound processing and language comprehension: (a) P1-N1 complex, indexing obligatory auditory processing; (b) P3-like dynamics associated with involuntary attention allocation for unusual sounds; (c) enhanced responses for native speech (as opposed to nonnative phonemes) from ∼50 ms from phoneme onset, indicating phonological processing; (d) amplitude advantage for familiar real words as opposed to meaningless pseudowords, indexing automatic lexical access; (e) topographic distribution differences in the cortical activation of action verbs versus concrete nouns, likely linked with the processing of lexical semantics. These multiple indices of speech-sound processing were acquired in a single attention-free setup that does not require any task or subject cooperation; subject to future research, the present protocol may potentially be developed into a useful tool for assessing the status of auditory and linguistic functions in uncooperative or unresponsive participants, including a range of clinical or developmental populations.

Brain Network Studies in Chronic Disorders of Consciousness: Advances and Perspectives

Neuroimaging has opened new opportunities to study the neural correlates of consciousness, and provided additional information concerning diagnosis, prognosis, and therapeutic interventions in patients with disorders of consciousness. Here, we aim to review neuroimaging studies in chronic disorders of consciousness from the viewpoint of the brain network, focusing on positron emission tomography, functional MRI, functional near-infrared spectroscopy, electrophysiology, and diffusion MRI. To accelerate basic research on disorders of consciousness and provide a panoramic view of unconsciousness, we propose that it is urgent to integrate different techniques at various spatiotemporal scales, and to merge fragmented findings into a uniform "Brainnetome" (Brain-net-ome) research framework.

A framework for the extended monitoring of levels of cognitive function in unresponsive patients

Generally, prognostication of coma outcome currently combines behavioral, reflex, and possibly neuroimaging tests that are interpreted by an attending physician. Electroencephalography, particularly, event-related brain potentials (ERP) have received attention due to evidence demonstrating the positive predictive value of certain ERP including the mismatch negativity (MMN) and the P3a, for coma emergence. We describe a set of ERP paradigms designed to require and reflect increasing levels of cognitive processing with the added objective of determining the influence of each paradigm's context strength on its ability to elicit ERPs. These paradigms were then used without explicit instructions to participants to attend to the stimuli to determine which paradigms possessed sufficient context "strength" to elicit ERPs in the absence of active participation on the part of the subject; a circumstance often encountered in brain injury patients. These paradigms were then validated on two groups of adults-younger and older, and the difference due to active participation was validated on another group of younger adults. Results show that paradigms with stronger stimulus context features performed better than those with weaker contexts, and that older adults generally had significantly attenuated and delayed responses compared to younger adults. Based on these findings, it is recommended the use of the auditory oddball paradigm that includes novel stimuli to elicit the mismatch negativity and P300, and semantic violation sentences to elicit the N400. These findings also reinforce the procedure of instructing participants about the requirements of a protocol-regardless of the patient's diagnosis or apparent state-in order to help those who are able to attend to show the most robust responses possible.

Reducing the rate of misdiagnosis in patients with chronic disorders of consciousness: Is there a place for audiovisual stimulation?

BACKGROUND

The patients with chronic Disorders of Consciousness (DoC) mostly present with extremely challenging differential diagnosis. The advanced analysis of electroencephalographic (EEG) signals induced by brain stimulation paradigms may provide an appropriate approach to differentiate patients with DoC, besides the clinical assessment.

OBJECTIVE

This study was performed with an objective of identifying residual brain network perturbations following an innovative, non-invasive audiovisual stimulation protocol, which could be related to behavioral responsiveness in patients with DoC.

METHODS

The study comprised of ten healthy controls (HC), seven patients with Minimally Conscious State (MCS), and nine patients with Unresponsive Wakefulness Syndrome (UWS). Both synchronous as well as asynchronous transorbital and transauricolar alternating current were employed as stimuli and their effects were measured in terms of functional and effective connectivity.

RESULTS

A more noticeable deterioration of long range connectivity patterns were found in patients with UWS than in those with MCS, with an exception of two patients with UWS, who showed connectivity values similar to those of MCS patients.

CONCLUSION

The audiovisual stimulation paradigm used in the present study may be employed as a supportive bedside tool for improving the differential diagnosis in patients with DoC.

Patients with a severe prolonged Disorder of Consciousness can show classical EEG responses to their own name compared with others' names

Patients in Vegetative State (VS), also known as Unresponsive Wakefulness State (UWS) are deemed to be unaware of themselves or their environment. This is different from patients diagnosed with Minimally Conscious state (MCS), who can have intermittent awareness. In both states, there is a severe impairment of consciousness; these disorders are referred to as disorders of consciousness (DOC) and if the state is prolonged, pDOC. There is growing evidence that some patients who are behaviourally in VS/UWS can show neural activation to environmental stimuli and that this response can be detected using functional brain imaging (fMRI/PET) and electroencephalography (EEG). Recently, it has also been suggested that a more reliable detection of brain responsiveness and hence a more reliable differentiation between VS/UWS and MCS requires person-centred and person-specific stimuli, such as the subject's own name stimulus. In this study we obtained event related potential data (ERP) from 12 healthy subjects and 16 patients in pDOC, five of whom were in the VS/UWS and 11 in the Minimally Conscious State (MCS). We used as the ERP stimuli the subjects' own name, others' names and reversed other names. We performed a sensor level analysis using Statistical Parametric Mapping (SPM) software. Using this paradigm in 4 DOC patients (3 in MCS, and 1 in VS/UWS) we detected a statistically significant difference in EEG response to their own name versus other peoples' names with ERP latencies (~300 ms and ~700 ms post stimuli). Some of these differences were similar to those found in a control group of healthy subjects. This study shows the feasibility of using self-relevant stimuli such as a subject's own name for assessment of brain function in pDOC patients. This neurophysiological test is suitable for bed-side/hospital based assessment of pDOC patients. As it does not require sophisticated scanning equipment it can feasibly be used within a hospital or care setting to help professionals tailor medical and psycho-social management for patients.

The Clinical Diagnostic Utility of Electrophysiological Techniques in Assessment of Patients With Disorders of Consciousness Following Acquired Brain Injury: A Systematic Review

OBJECTIVE

To investigate the diagnostic utility of electrophysiological recordings during active cognitive tasks in detecting residual cognitive capacities in patients with disorders of consciousness (DoC) after severe acquired brain injury.

DESIGN

Systematic review of empirical research in MEDLINE, Embase, PsycINFO, and Cochrane from January 2002 to March 2016.

MAIN MEASURES

Data extracted included sample size, type of electrophysiological technique and task design, rate of cognitive responders, false negatives and positives, and excluded subjects from the study analysis. The Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) was used for quality appraisal of the retrieved literature.

RESULTS

Twenty-four studies examining electrophysiological signs of command-following in patients with DoC were identified. Sensitivity rates in healthy controls demonstrated variable accuracy across the studies, ranging from 71% to 100%. In patients with DoC, specificity and sensitivity rates varied in the included studies, ranging from 0% to 100%. Pronounced heterogeneity was found between studies regarding methodological approaches, task design, and procedures of analysis, rendering comparison between studies challenging.

CONCLUSION

We are still far from establishing precise recommendations for standardized electrophysiological diagnostic procedures in DoC, but electrophysiological methods may add supplemental diagnostic information of covert cognition in some patients with DoC.

Proving cortical death after vascular coma: Evoked potentials, EEG and neuroimaging

OBJECTIVES

Several studies have shown that bilateral abolition of somatosensory evoked potentials after a nontraumatic coma has 100% specificity for nonawakening with ethical consequences for active care withdrawal. We propose to evaluate the prognostic value of bilateral abolished cortical components of SEPs in severe vascular coma.

METHODS

A total of 144 comatose patients after subarachnoid haemorrhage were evaluated by multimodal evoked potentials (EPs); 7 patients presented a bilateral abolition of somatosensory and auditory EPs. Their prognosis value was interpreted with respect to brainstem auditory EPs, EEG, and structural imaging.

RESULTS

One patient emerged from vegetative state during follow-up; 6 patients did not return to consciousness. The main neurophysiological difference was a cortical reactivity to pain preserved in the patient who returned to consciousness. This patient had focal sub-cortical lesions, which could explain the abolition of primary cortical components by a bilateral deafferentation of somatosensory and auditory pathways.

CONCLUSIONS

This is the first report of a favourable outcome after a multimodal abolition of primary cortex EPs in vascular coma. For the 3 cases of vascular coma with preserved brainstem function, EEG reactivity and cortical EPs were abolished by a diffuse ischaemia close to cerebral anoxia.

SIGNIFICANCE

The complementarity of EPs, EEG, and imaging must be emphasised if therapeutic limitations are considered to avoid over-interpretation of the prognosis value of EPs.

Temporal Features of the Differentiation between Self-Name and Religious Leader Name among Christians: An ERP Study

Existing neuroimaging studies have shown that religion, as a subjective culture, can influence self-referential processing. However, the time course of this impact remains unclear. The present study examined how Christians process their own names, the name of their religious leader (i.e., Jesus), and a famous person’s name (i.e., Yao Ming). Behavioral and EEG data were recorded while the participants performed a name-color judgment task for these three names. The behavioral data showed no significant differences in reaction time or accuracy among the names. However, the ERP data showed that the P200 and P300 amplitudes elicited by the self-name and religious leader name were larger than those elicited by the famous name. Furthermore, the self-name also elicited a larger P300 amplitude than the religious leader name did. These results suggested that both the self-name and the religious leader name were processed preferentially due to their important social value for the self as compared to a generally famous name. Importantly, the dissociation between the self-name and the religious leader name was observed at a high-order cognitive stage, which might be attributed to their different roles in one’s self-concept.