Usefulness of standard EEG in predicting the outcome of patients with disorders of consciousness after anoxic coma

Prognosis of consciousness disorders in the intensive care unit

Assessments of consciousness are a critical part of prognostic algorithms for critically ill patients suffering from severe brain injuries. There have been significant advances in the field of coma science over the past two decades, providing clinicians with more advanced and precise tools for diagnosing and prognosticating disorders of consciousness (DoC). Advanced neuroimaging and electrophysiological techniques have vastly expanded our understanding of the biological mechanisms underlying consciousness, and have helped identify new states of consciousness. One of these, termed cognitive motor dissociation, can predict functional recovery at 1 year post brain injury, and is present in up to 15-20% of patients with DoC. In this chapter, we review several tools that are used to predict DoC, describing their strengths and limitations, from the neurological examination to advanced imaging and electrophysiologic techniques. We also describe multimodal assessment paradigms that can be used to identify covert consciousness and thus help recognize patients with the potential for future recovery and improve our prognostication practices.

Conventional and Investigational Approaches Leveraging Clinical EEG for Prognosis in Acute Disorders of Consciousness

Prediction of recovery of consciousness after severe brain injury is difficult and limited by a lack of reliable, standardized biomarkers. Multiple approaches for analysis of clinical electroencephalography (EEG) that shed light on prognosis in acute severe brain injury have emerged in recent years. These approaches fall into two major categories: conventional characterization of EEG background and quantitative measurement of resting state or stimulus-induced EEG activity. Additionally, a small number of studies have associated the presence of electrophysiologic sleep features with prognosis in the acute phase of severe brain injury. In this review, we focus on approaches for the analysis of clinical EEG that have prognostic significance and that could be readily implemented with minimal additional equipment in clinical settings, such as intensive care and intensive rehabilitation units, for patients with acute disorders of consciousness.

Neural reactivity parameters of awareness predetermine one-year survival in patients with disorders of consciousness

Objective: The current investigation evaluated the sensitivity of neural-reactivity markers of awareness versus standard clinical assessments in predicting 1-year survival in nonresponsive-awake patients with disorders of consciousness (DOC).Methods: Pre-attentive auditory mismatch-negativity (MMN) event-related potentials (ERP's), globally induced electroencephalography (EEG) spectral power following verbal command, and clinical parameters were assessed. The study included 10 patients with DOC with mixed etiology and 10 healthy controls (HC) at baseline. The clinical status of patients with DOC was reassessed after 1 year.Results: Unlike baseline clinical assessment scores, baseline MMN amplitudes of non-survivors and induced theta-power following verbal-command clearly distinguished the non-surviving patients versus surviving patients. Baseline MMN peak-amplitude latencies in survivors with DOC were significantly related to clinical outcome over a 1-year period.Conclusion: Current findings underscore the increased sensitivity of EEG-reactivity markers of awareness versus standard clinical scores in predicting 1-year clinical outcome and survival in patients with DOC. Further longitudinal research in larger DOC samples is needed to confirm the prognostic-reliability, and validity of neural reactivity parameters of awareness in patients with DOC. Current finding may have implications for clinical care and medical-legal decisions in unresponsive-awake patients, and could assist clinicians to predict their survival up to 1 year from admission.

Cervical Spinal Cord Stimulation for the Vegetative State: A Preliminary Result of 12 Cases

OBJECTIVES

Data on the treatment of the vegetative state (VS) with cervical spinal cord stimulation (cSCS) are limited and prognostic factors are inconclusive. In this study, we present our experience of treating 12 VS patients with cSCS and discuss the prognostic factors.

METHODS

Twelve VS patients were enrolled. Preoperative assessments included CT/MRI, PET, brainstem auditory evoked potentials (BAEPs), somatosensory evoked potentials (SEPs), and electroencephalogram (EEG). cSCS surgeries were performed at West China Hospital. The electrode was implanted in the epidural space of the C2-4 vertebrae. Levels of consciousness were evaluated based on the Coma Recovery Scale-Revised (CRS-R) at baseline and during follow-up.

RESULTS

The average follow-up was 11.1 months. The average CRS-R score at the last evaluation was 10.8, which was significantly improved compared with the baseline score (6.25). Five patients achieved responsive outcomes (three recovered and two evolved to a minimally conscious state) and seven achieved unresponsive outcomes (six remained in VS and one died). Age, preoperative CRS-R score, the interval between acute comatose injury and cSCS, and the Vth wave of BAEPs did not differ significantly between the responsive group and the unresponsive group. Appearance of the N20 of SEPs and multifocal abnormalities on CT/MRI and PET were significantly associated with a better outcome, while the etiology of ischemia and anoxia (IAA) was significantly associated with a poor outcome.

CONCLUSIONS

cSCS should be a glimmer of hope for VS patients. Patients whose N20 is elicited or whose CT/MRI or PET demonstrates multifocal abnormalities are more likely to benefit from cSCS, whereas those with an IAA etiology have a lower likelihood of recovery after cSCS.

A Systematic Review and Meta-Analysis of the Relationship Between Brain Data and the Outcome in Disorders of Consciousness

A systematic search revealed 68 empirical studies of neurophysiological [EEG, event-related brain potential (ERP), fMRI, PET] variables as potential outcome predictors in patients with Disorders of Consciousness (diagnoses Unresponsive Wakefulness Syndrome [UWS] and Minimally Conscious State [MCS]). Data of 47 publications could be presented in a quantitative manner and systematically reviewed. Insufficient power and the lack of an appropriate description of patient selection each characterized about a half of all publications. In more than 80% studies, neurologists who evaluated the patients' outcomes were familiar with the results of neurophysiological tests conducted before, and may, therefore, have been influenced by this knowledge. In most subsamples of datasets, effect size significantly correlated with its standard error, indicating publication bias toward positive results. Neurophysiological data predicted the transition from UWS to MCS substantially better than they predicted the recovery of consciousness (i.e., the transition from UWS or MCS to exit-MCS). A meta-analysis was carried out for predictor groups including at least three independent studies with N > 10 per predictor per improvement criterion (i.e., transition to MCS versus recovery). Oscillatory EEG responses were the only predictor group whose effect attained significance for both improvement criteria. Other perspective variables, whose true prognostic value should be explored in future studies, are sleep spindles in the EEG and the somatosensory cortical response N20. Contrary to what could be expected on the basis of neuroscience theory, the poorest prognostic effects were shown for fMRI responses to stimulation and for the ERP component P300. The meta-analytic results should be regarded as preliminary given the presence of numerous biases in the data.

Longitudinal Dynamics of 3-Dimensional Components of Selfhood After Severe Traumatic Brain Injury: A qEEG Case Study

In this report, we describe the case of a patient who sustained extremely severe traumatic brain damage with diffuse axonal injury in a traffic accident and whose recovery was monitored during 6 years. Specifically, we were interested in the recovery dynamics of 3-dimensional components of selfhood (a 3-dimensional construct model for the complex experiential selfhood has been recently proposed based on the empirical findings on the functional-topographical specialization of 3 operational modules of brain functional network responsible for the self-consciousness processing) derived from the electroencephalographic (EEG) signal. The analysis revealed progressive (though not monotonous) restoration of EEG functional connectivity of 3 modules of brain functional network responsible for the self-consciousness processing, which was also paralleled by the clinically significant functional recovery. We propose that restoration of normal integrity of the operational modules of the self-referential brain network may underlie the positive dynamics of 3 aspects of selfhood and provide a neurobiological mechanism for their recovery. The results are discussed in the context of recent experimental studies that support this inference. Studies of ongoing recovery after severe brain injury utilizing knowledge about each separate aspect of complex selfhood will likely help to develop more efficient and targeted rehabilitation programs for patients with brain trauma.

Changes in Standard Electroencephalograms Parallel Consciousness Improvements in Patients With Unresponsive Wakefulness Syndrome

OBJECTIVE

To identify changes in the standard electroencephalograms (EEGs) of patients with unresponsive wakefulness syndrome (UWS) who did or did not recover consciousness 6 months after admission to a rehabilitation department.

DESIGN

Prospective cohort study.

SETTING

Unit for severe acquired brain injuries.

PARTICIPANTS

Consecutive patients with UWS (N=28).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

EEG amplitude (reduced or normal), dominant frequency (alpha, theta, or delta), and reactivity (absent or present) were scored at admission and 6 months later. The cumulative Amplitude-Frequency-Reactivity score was evaluated. Clinical assessments were made using the Coma Recovery Scale-Revised.

RESULTS

Sixteen (57.1%) of the 28 patients with UWS recovered consciousness after 6 months, while 12 patients (42.9%) did not recover consciousness. EEG improvements occurred in 14 patients with consciousness recovery (87.5%) and 2 patients without consciousness recovery (16.7%) only. Improvements in EEG dominant frequency (from the theta to the alpha band or from the delta to the theta band), reappearance of EEG reactivity, and Amplitude-Frequency-Reactivity score increase (P<.01) differentiated patients with consciousness improvement from those without consciousness improvement. Six months after admission for rehabilitation, patients with EEG improvements showed higher Coma Recovery Scale-Revised scores than did those without EEG changes (P<.01).

CONCLUSIONS

Most patients who emerge from UWS demonstrate improvement in basic EEG characteristics over time. EEG changes in patients with UWS may aid in the timely recognition of patients transitioning into a minimally conscious state.

Long-Term (Six Years) Clinical Outcome Discrimination of Patients in the Vegetative State Could be Achieved Based on the Operational Architectonics EEG Analysis: A Pilot Feasibility Study

Electroencephalogram (EEG) recordings are increasingly used to evaluate patients with disorders of consciousness (DOC) or assess their prognosis outcome in the short-term perspective. However, there is a lack of information concerning the effectiveness of EEG in classifying long-term (many years) outcome in chronic DOC patients. Here we tested whether EEG operational architectonics parameters (geared towards consciousness phenomenon detection rather than neurophysiological processes) could be useful for distinguishing a very long-term (6 years) clinical outcome of DOC patients whose EEGs were registered within 3 months post-injury. The obtained results suggest that EEG recorded at third month after sustaining brain damage, may contain useful information on the long-term outcome of patients in vegetative state: it could discriminate patients who remain in a persistent vegetative state from patients who reach a minimally conscious state or even recover a full consciousness in a long-term perspective (6 years) post-injury. These findings, if confirmed in further studies, may be pivotal for long-term planning of clinical care, rehabilitative programs, medical-legal decisions concerning the patients, and policy makers.

The Chief Role of Frontal Operational Module of the Brain Default Mode Network in the Potential Recovery of Consciousness from the Vegetative State: A Preliminary Comparison of Three Case Reports

It has been argued that complex subjective sense of self is linked to the brain default-mode network (DMN). Recent discovery of heterogeneity between distinct subnets (or operational modules - OMs) of the DMN leads to a reconceptualization of its role for the experiential sense of self. Considering the recent proposition that the frontal DMN OM is responsible for the first-person perspective and the sense of agency, while the posterior DMN OMs are linked to the continuity of 'I' experience (including autobiographical memories) through embodiment and localization within bodily space, we have tested in this study the hypothesis that heterogeneity in the operational synchrony strength within the frontal DMN OM among patients who are in a vegetative state (VS) could inform about a stable self-consciousness recovery later in the course of disease (up to six years post-injury). Using EEG operational synchrony analysis we have demonstrated that among the three OMs of the DMN only the frontal OM showed important heterogeneity in VS patients as a function of later stable clinical outcome. We also found that the frontal DMN OM was characterized by the process of active uncoupling (stronger in persistent VS) of operations performed by the involved neuronal assemblies.

Brain-computer interfaces for patients with disorders of consciousness

The disorders of consciousness refer to clinical conditions that follow a severe head injury. Patients diagnosed as in a vegetative state lack awareness, while patients diagnosed as in a minimally conscious state retain fluctuating awareness. However, it is a challenge to accurately diagnose these disorders with clinical assessments of behavior. To improve diagnostic accuracy, neuroimaging-based approaches have been developed to detect the presence or absence of awareness in patients who lack overt responsiveness. For the small subset of patients who retain awareness, brain-computer interfaces could serve as tools for communication and environmental control. Here we review the existing literature concerning the sensory and cognitive abilities of patients with disorders of consciousness with respect to existing brain-computer interface designs. We highlight the challenges of device development for this special population and address some of the most promising approaches for future investigations.

Standard EEG in diagnostic process of prolonged disorders of consciousness

OBJECTIVE

This cross-sectional study assessed the ability of standard EEG in distinguishing vegetative state (VS) from minimally conscious state plus (MCS+) or MCS minus (MCS-), and to correlate EEG features with aetiology and level of responsiveness assessed by Coma Recovery Scale-Revised (CRS-R).

METHODS

We analyzed background EEG activity and EEG reactivity to eye opening and closing and to tactile, acoustic, nociceptive stimuli and Intermittent Photic Stimulation (IPS) in 73 inpatients (VS=37, MCS-=11, MCS+=25), with traumatic (n=21), vascular (n=25) or anoxic (n=27) aetiology.

RESULTS

All patients, but one, showed abnormal background activity. EEG abnormalities were more severe in VS than in MCS+ or MCS-, and in anoxic than other aetiologies. MCS+ patients with normal or Mildly Abnormal background activity showed higher scores on CRS-R than patients with moderate to severe EEG abnormalities. Reactivity to IPS, and acoustic stimuli was significantly more frequent in MCS+ and MCS- than in VS patients.

CONCLUSIONS

EEG features differ between VS and MCS- or MCS+ patients and can provide evidence of relative sparing of thalamocortical connections in MCS+ patients. In anoxic patients EEG organization is more severely impaired and provides less discriminative diagnostic information.

SIGNIFICANCE

Conventional EEG can help clinicians to disentangle VS from MCS patients.

EEG epileptiform abnormalities at admission to a rehabilitation department predict the risk of seizures in disorders of consciousness following a coma

BACKGROUND

Seizures affect about a quarter of patients with disorders of consciousness (DOC) after a coma.

AIMS

We investigated whether the presence of epileptiform abnormalities (EAs) in the electroencephalogram (EEG) of patients with DOC may predict the occurrence of seizures. Moreover, we evaluated whether EAs have a prognostic role in these patients.

METHODS

This was a retrospective single-center cohort study of patients hospitalized between January 2005 and December 2014 in a rehabilitation department (mean time from acute brain injury: 46.1 days). We analyzed 30-minute EEGs at admittance for 112 patients with unresponsive wakefulness syndrome (UWS) or in a minimally conscious state (MCS), then compared occurrence of seizures over the following three months across patients with absent, unilateral, and bilateral EAs (generalized or bilateral independent). Outcomes at three months were assessed in the same groups using the Coma Recovery Scale Revised.

RESULTS

Epileptiform abnormalities were observed in 38 patients (33.9%). Of these, 25 were unilateral, and 13 were bilateral. Seizures occurred in 84.6% of patients with bilateral EAs, which was significantly higher than in patients without EAs (10.8%, p<0.001) or with unilateral EAs (24%, p=0.001). The presence of EAs was not related to etiology or different DOC and did not significantly affect outcomes at three months.

CONCLUSIONS

Patients with EAs at admission to a rehabilitation department have an increased risk of seizures. Specifically, most patients with bilateral EAs had seizures within the following 3 months. Evaluation of EAs in EEGs of patients with DOC may give valuable information in the management of antiepileptic drug treatment.

Prospective Cohort Study Evaluating the Prognostic Value of Simple EEG Parameters in Postanoxic Coma

We prospectively studied early bedside standard EEG characteristics in 61 acute postanoxic coma patients. Five simple EEG features, namely, isoelectric, discontinuous, nonreactive to intense auditory and nociceptive stimuli, dominant delta frequency, and occurrence of paroxysms were classified yes or no. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and area under the receiver operating characteristic curve (AUC) of each of these variables for predicting an unfavorable outcome, defined as death, persistent vegetative state, minimally conscious state, or severe neurological disability, as assessed 1 year after coma onset were computed as well as Synek's score. The outcome was unfavorable in 56 (91.8%) patients. Sensitivity, specificity, PPV, NPV, and AUC of nonreactive EEG for predicting an unfavorable outcome were 84%, 80%, 98%, 31%, and 0.82, respectively; and were all very close to the ones of Synek score>3, which were 82%, 80%, 98%, 29%, and 0.81, respectively. Specificities for predicting an unfavorable outcome were 100% for isoelectric, discontinuous, or dominant delta activity EEG. These 3 last features were constantly associated to unfavorable outcome. Absent EEG reactivity strongly predicted an unfavorable outcome in postanoxic coma, and performed as accurate as a Synek score>3. Analyzing characteristics of some simple EEG features may easily help nonneurophysiologist physicians to investigate prognostic issue of postanoxic coma patient. In this study (a) discontinuous, isoelectric, or delta-dominant EEG were constantly associated with unfavorable outcome and (b) nonreactive EEG performed prognostic as accurate as a Synek score>3.

Repetitive transcranial magnetic stimulation improves consciousness disturbance in stroke patients: A quantitative electroencephalography spectral power analysis

Repetitive transcranial magnetic stimulation is a noninvasive treatment technique that can directly alter cortical excitability and improve cerebral functional activity in unconscious patients. To investigate the effects and the electrophysiological changes of repetitive transcranial magnetic stimulation cortical treatment, 10 stroke patients with non-severe brainstem lesions and with disturbance of consciousness were treated with repetitive transcranial magnetic stimulation. A quantitative electroencephalography spectral power analysis was also performed. The absolute power in the alpha band was increased immediately after the first repetitive transcranial magnetic stimulation treatment, and the energy was reduced in the delta band. The alpha band relative power values slightly decreased at 1 day post-treatment, then increased and reached a stable level at 2 weeks post-treatment. Glasgow Coma Score and JFK Coma Recovery Scale-Revised score were improved. Relative power value in the alpha band was positively related to Glasgow Coma Score and JFK Coma Recovery Scale-Revised score. These data suggest that repetitive transcranial magnetic stimulation is a noninvasive, safe, and effective treatment technology for improving brain functional activity and promoting awakening in unconscious stroke patients.

EEG predictors of outcome in patients with disorders of consciousness admitted for intensive rehabilitation

OBJECTIVE

This study examined the prognostic value of standard EEG in patients with unresponsive wakefulness syndrome (UWS) or in a minimally conscious state (MCS).

METHODS

EEGs recorded at admission in 106 patients with UWS or in a MCS were analyzed retrospectively. EEG amplitude, dominant frequency, and reactivity to stimuli were correlated to patient outcomes according to the Coma Recovery Scale Revised (CRS-R). In 101 patients, data were integrated to generate a novel Amplitude-Frequency-Reactivity (AFR) scale, with scores ranging from 3 to 7.

RESULTS

Patients with reduced amplitudes showed less improvement in CRS-R scores at 3 months compared to patients with normal amplitudes. Delta, theta, and alpha frequencies were associated with the least, intermediate, and the greatest improvement in CRS-R scores, respectively. Patients with EEG reactivity showed greater improvements in CRS-R scores than patients without reactivity. The AFR scores for these patients were correlated with outcomes.

CONCLUSIONS

Reduced EEG amplitudes and delta frequencies correlated with worse clinical outcomes, while alpha frequencies and reactivity correlated with better outcomes. AFR scores allowed more delineated descriptions of outcomes in patients with normal amplitude, theta frequency, and no reactivity.

SIGNIFICANCE

Standard EEG descriptors are related to the 3-month outcomes in patients with disorders of consciousness.

Hypnotic induction is followed by state-like changes in the organization of EEG functional connectivity in the theta and beta frequency bands in high-hypnotically susceptible individuals

Altered state theories of hypnosis posit that a qualitatively distinct state of mental processing, which emerges in those with high hypnotic susceptibility following a hypnotic induction, enables the generation of anomalous experiences in response to specific hypnotic suggestions. If so then such a state should be observable as a discrete pattern of changes to functional connectivity (shared information) between brain regions following a hypnotic induction in high but not low hypnotically susceptible participants. Twenty-eight channel EEG was recorded from 12 high susceptible (highs) and 11 low susceptible (lows) participants with their eyes closed prior to and following a standard hypnotic induction. The EEG was used to provide a measure of functional connectivity using both coherence (COH) and the imaginary component of coherence (iCOH), which is insensitive to the effects of volume conduction. COH and iCOH were calculated between all electrode pairs for the frequency bands: delta (0.1–3.9 Hz), theta (4–7.9 Hz) alpha (8–12.9 Hz), beta1 (13–19.9 Hz), beta2 (20–29.9 Hz) and gamma (30–45 Hz). The results showed that there was an increase in theta iCOH from the pre-hypnosis to hypnosis condition in highs but not lows with a large proportion of significant links being focused on a central-parietal hub. There was also a decrease in beta1 iCOH from the pre-hypnosis to hypnosis condition with a focus on a fronto-central and an occipital hub that was greater in high compared to low susceptibles. There were no significant differences for COH or for spectral band amplitude in any frequency band. The results are interpreted as indicating that the hypnotic induction elicited a qualitative change in the organization of specific control systems within the brain for high as compared to low susceptible participants. This change in the functional organization of neural networks is a plausible indicator of the much theorized “hypnotic-state.”

Significance of multiple neurophysiological measures in patients with chronic disorders of consciousness

OBJECTIVE

The aim of this study was to verify the value of multiple neurophysiological tests in classifying disorders of consciousness (DOCs) in patients in a chronic vegetative or minimal consciousness state categorised on the basis of the Coma Recovery Scale (CRS).

METHODS

The study included 142 patients, all of whom underwent long (18h) EEG-polygraphic recordings including one night. The EEG was scored using the Synek scale and sleep patterns using an arbitrary scale. Absolute total power and relative EEG power were evaluated in different frequency bands. Multimodal evoked potentials (EPs), including auditory event-related potentials, were also evaluated and scored.

RESULTS

The most information came from the combined multimodal EPs and sleep EEG scores. A two-step cluster analysis based on the collected information allowed a satisfactory evaluation of DOC severity. Spectral EEG properties seemed to be significantly related to DOC classes and CRS scores, but did not seem to make any significant additional contribution to DOC classification.

CONCLUSIONS

Multiple electrophysiological evaluations based on EEG, sleep polygraphic recordings and multimodal EPs are helpful in assessing DOC severity and residual functioning in patients with chronic DOCs.

SIGNIFICANCE

Simple electrophysiological measures that can be easily applied at patients' bedsides can significantly contribute to the recognition of DOC severity in chronic patients surviving a severe brain injury.

Dissociation of vegetative and minimally conscious patients based on brain operational architectonics: factor of etiology

Discrimination between patients in vegetative (VS) and minimally conscious state (MCS) is currently based upon the behavioral gold standard. Behavioral assessment remains equivocal and difficult to interpret as evidence for the presence or absence of consciousness, resulting in possible clinical misdiagnosis in such patients. Application of an operational architectonics (OA) strategy to electroencephalogram (EEG) analysis reveals that absence of consciousness in patients in VS is paralleled by significant impairment in overall EEG operational architecture compared to patients in MCS: neuronal assemblies become smaller, their life span shortened, and they became highly unstable and functionally disconnected (desynchronized). However, in a previous study, patients with different brain damage etiologies were intermixed. Therefore, the goal of the present study was to investigate whether the application of OA methodology to EEG could reliably dissociate patients in VS and MCS independent of brain damage etiology. We conclude that the observed EEG OA structure impairment in patients in VS and partial preservation in patients in MCS is a marker of consciousness/unconsciousness rather than physiological damage. Results of this study may have neuroscientific, clinical, and ethical implications.

A range of antiepileptic drugs do not affect the recovery of consciousness in vegetative and minimally conscious states

Since most antiepileptic drugs (AEDs) have cognitive effects, the aim of this study was to evaluate the influence of AED therapy on the recovery of consciousness in 103 consecutive patients in a vegetative or minimally conscious state (VS, MCS). The levels of cognitive functioning (LCF) score was retrospectively compared after a three-month period of rehabilitation between patients who were medicated (n=54) and patients who were not medicated (n=49) with AEDs. Mean LCF scores in AED-medicated and nonmedicated patients were 2.2±0.7 and 2.3±0.8 at admission and 3.8±2.2 and 3.7±2.1 after three months, respectively (p values>0.05). These results did not change when we compared patients with the same etiology separately, with the same disorder of consciousness only, or patients treated with only one or more than one AED. In conclusion, AEDs did not affect the recovery of consciousness in a large cohort of patients in a VS or MCS following an acute brain injury.

Clinical review: neuromonitoring - an update

Critically ill patients are frequently at risk of neurological dysfunction as a result of primary neurological conditions or secondary insults. Determining which aspects of brain function are affected and how best to manage the neurological dysfunction can often be difficult and is complicated by the limited information that can be gained from clinical examination in such patients and the effects of therapies, notably sedation, on neurological function. Methods to measure and monitor brain function have evolved considerably in recent years and now play an important role in the evaluation and management of patients with brain injury. Importantly, no single technique is ideal for all patients and different variables will need to be monitored in different patients; in many patients, a combination of monitoring techniques will be needed. Although clinical studies support the physiologic feasibility and biologic plausibility of management based on information from various monitors, data supporting this concept from randomized trials are still required.

Prognostic Value of Resting-State Electroencephalography Structure in Disentangling Vegetative and Minimally Conscious States

Background. Patients in a vegetative state pose problems in diagnosis, prognosis, and treatment. Currently, no prognostic markers predict the chance of recovery, which has serious consequences, especially in end-of-life decision making. Objective. We aimed to assess an objective measurement of prognosis using advanced electroencephalography (EEG). Methods. EEG data (19 channels) were collected in 14 patients who were diagnosed to be persistently vegetative based on repeated clinical evaluations at 3 months following brain damage. EEG structure parameters (amplitude, duration, and variability within quasi-stationary segments, as well as the spatial synchrony between such segments and the strength of this synchrony) were used to predict recovery of consciousness 3 months later. Results. The number and strength of cortical functional connections between EEG segments were higher in patients who recovered consciousness ( P < .05 to P < .001) compared with those who did not recover. Linear regression analysis confirms that EEG structure parameters are capable of predicting ( P = .0025) recovery of consciousness 6 months postinjury, whereas the same analysis failed to significantly predict patient outcome based on aspects of their clinical history alone ( P = .629) or conventional EEG spectrum power ( P = .473). Conclusions. The result of this preliminary study demonstrates that structural strategy of EEG analysis is better suited for providing prognosis of consciousness recovery than existing methods of clinical assessment and of conventional EEG. Our results may be a starting point for developing reliable prognosticators in patients who are in a vegetative state, with the potential to improve their day-to-day management, quality of life, and access to early interventions.

The value of spontaneous EEG oscillations in distinguishing patients in vegetative and minimally conscious states

OBJECTIVE

The value of spontaneous electroencephalography (EEG) oscillations in distinguishing patients in vegetative state (VS) and minimally conscious states (MCS) was studied.

METHODS

We quantified dynamic repertoire of EEG oscillations in resting condition with closed eyes in patients in VS and MCS. The exact composition of EEG oscillations was assessed by the probability-classification analysis of short-term EEG spectral patterns.

RESULTS

The probability of delta, theta, and slow-alpha oscillations occurrence was smaller for patients in MCS than for VS. Additionally, only patients in MCS demonstrated fast-alpha oscillation occurrence. Depending on the type and composition of EEG oscillations, the probability of their occurrence was either etiology dependent or independent. The probability of EEG oscillations occurrence differentiated brain injuries with different etiologies.

CONCLUSIONS

Spontaneous EEG oscillations have a potential value in distinguishing patients in VS and MCS.

SIGNIFICANCE

This work may have implications for clinical care, rehabilitative programs, and medical-legal decisions in patients with impaired consciousness states following coma due to acute brain injuries.

HIGHLIGHTS

The probability of delta, theta, and slow-alpha oscillations occurrence was smaller and the probability of fast-alpha oscillations occurrence was higher for patients in MCS than for patients in VS. The probability of EEG oscillations occurrence differentiated brain injuries with different etiologies. Spontaneous EEG has a potential value in distinguishing patients in VS and MCS.

Brain-derived neurotrophic factor (Val66Met) polymorphism does not influence recovery from a post-traumatic vegetative state: a blinded retrospective multi-centric study

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that influences neuronal plasticity throughout life. Emergence from a vegetative state (VS) after a traumatic brain injury (TBI) implies that the brain undergoes plastic changes. A common polymorphism in the BDNF gene--BDNF Val66Met (referred to herein as BDNF(Met))--impairs cognitive function in healthy subjects. The aim of this study was to determine whether the BDNF(Met) polymorphism plays a role in the recovery of consciousness and cognitive functions in patients in a VS after a TBI. Fifty-three patients in a VS 1 month after a TBI were included in the study and genotyped for the BDNF(Met) polymorphism. Scores of levels of cognitive functioning (LCF) at 1, 3, 6, and 12 months post-TBI were retrospectively compared in patients without (Val group), and with (Met group), the BDNF(Met) polymorphism. The BDNF(Met) polymorphism was detected in 20 out of the 53 patients. The mean LCF scores in the Val and Met groups were 1.6±0.5 and 1.4±0.5 at 1 month, 2.3±0.7 and 2.5±1.2 at 3 months, 3.3±1.7 and 3.5±1.7 at 6 months, and 4±1.9 and 3.9±1.8 at 12 months, respectively (p>0.05). The percentages of patients in the Val and Met groups who emerged from the VS were 36.4% and 30% at 3 months, 66.3% and 70% at 6 months, and 70% and 87.5% at 12 months (p>0.05), respectively. These findings provide evidence that the BDNF(Met) polymorphism is not involved in cognitive improvement in patients with a VS following TBI. Future studies should focus on the role of other BDNF polymorphisms in the recovery from a VS.

DMN Operational Synchrony Relates to Self-Consciousness: Evidence from Patients in Vegetative and Minimally Conscious States

The default mode network (DMN) has been consistently activated across a wide variety of self-related tasks, leading to a proposal of the DMN’s role in self-related processing. Indeed, there is limited fMRI evidence that the functional connectivity within the DMN may underlie a phenomenon referred to as self-awareness. At the same time, none of the known studies have explicitly investigated neuronal functional interactions among brain areas that comprise the DMN as a function of self-consciousness loss. To fill this gap, EEG operational synchrony analysis [1, 2] was performed in patients with severe brain injuries in vegetative and minimally conscious states to study the strength of DMN operational synchrony as a function of self-consciousness expression. We demonstrated that the strength of DMN EEG operational synchrony was smallest or even absent in patients in vegetative state, intermediate in patients in minimally conscious state and highest in healthy fully self-conscious subjects. At the same time the process of ecoupling of operations performed by neuronal assemblies that comprise the DMN was highest in patients in vegetative state, intermediate in patients in minimally conscious state and minimal in healthy fully self-conscious subjects. The DMN’s frontal EEG operational module had the strongest decrease in operational synchrony strength as a function of selfconsciousness loss, when compared with the DMN’s posterior modules. Based on these results it is suggested that the strength of DMN functional connectivity could mediate the strength of self-consciousness expression. The observed alterations similarly occurred across EEG alpha, beta1 and beta2 frequency oscillations. Presented results suggest that the EEG operational synchrony within DMN may provide an objective and accurate measure for the assessment of signs of self-(un)consciousness in these challenging patient populations. This method therefore, may complement the current diagnostic procedures for patients with severe brain injuries and, hence, the planning of a rational rehabilitation intervention.