Neuroimaging and the Vegetative State

Transcranial Magnetic Stimulation in Disorders of Consciousness: An Update and Perspectives

Disorders of consciousness (DOC) is a state in which consciousness is affected by brain injuries, leading to dysfunction in vigilance, awareness, and behavior. DOC encompasses coma, vegetative state, and minimally conscious state based on neurobehavioral function. Currently, DOC is one of the most common neurological disorders with a rapidly increasing incidence worldwide. Therefore, DOC not only impacts the lives of individuals and their families but is also becoming a serious public health threat. Repetitive transcranial magnetic stimulation (rTMS) can stimulate electrical activity using a pulsed magnetic field in the brain, with great value in the treatment of chronic pain, neurological diseases, and mental illnesses. However, the clinical application of rTMS in patients with DOC is debatable. Herein, we report the recent main findings of the clinical therapeutics of rTMS for DOC, including its efficacy and possible mechanisms. In addition, we discuss the potential key parameters (timing, location, frequency, strength, and secession of rTMS applications) that affect the therapeutic efficiency of rTMS in patients with DOC. This review may help develop clinical guidelines for the therapeutic application of rTMS in DOC.

Flowchart for Implementing Advanced Imaging and Electrophysiology in Patients With Disorders of Consciousness: To fMRI or Not to fMRI?

The American Academy of Neurology and the European Academy of Neurology have recognized, for the first time, the value of advanced neuroimaging and electrophysiology techniques (AIEs) in the context of diagnosing patients with a disorder of consciousness (DOC). This recognition is part of an important agenda of promoting evidence-based competency in the management of patients with DOC. Nonetheless, considering that these techniques (and the required knowledge) are seldom available outside of advanced medical centers, it is important to provide physicians with a framework for balancing risks and benefits and deciding, on a single patient basis, whether AIEs are suitable. This issue is all the more urgent considering that family members are increasingly aware of the use of AIEs in patients with DOC, pressure for these assessments is likely to increase in the context of ethical and clinical imperatives to meet standards of care, and pathways for reimbursement for such assessments in DOC are yet to be established. The new guidelines, however, provide no guiding principle for physicians to decide when such assessments are appropriate, a limitation that impedes their wide adoption. We address this important gap by proposing an easy to use algorithmic flowchart that is based on the new guidelines and can be used to determine the appropriateness of AIEs for any given patient with DOC and ensure that evidence-based best practices are being followed. We also provide a brief context for understanding the main categories of AIEs available to clinicians, their advantages, and their limitations.

The Mental Maxwell Relations: A Thermodynamic Allegory for Higher Brain Functions

The theoretical framework of classical thermodynamics unifies vastly diverse natural phenomena and captures once-elusive effects in concrete terms. Neuroscience confronts equally varied, equally ineffable phenomena in the mental realm, but has yet to unite or to apprehend them rigorously, perhaps due to an insufficient theoretical framework. The terms for mental phenomena, the mental variables, typically used in neuroscience are overly numerous and imprecise. Unlike in thermodynamics or other branches of physics, in neuroscience, there are no core mental variables from which all others formally derive and it is unclear which variables are distinct and which overlap. This may be due to the nature of mental variables themselves. Unlike the variables of physics, perhaps they cannot be interpreted as composites of a small number of axioms. However, it is well worth exploring if they can, as that would allow more parsimonious theories of higher brain function. Here we offer a theoretical exercise in the spirit of the National Institutes of Health Research Domain Criteria (NIH RDoC) Initiative and the Cognitive Atlas Project, which aim to remedy this state of affairs. Imitating classical thermodynamics, we construct a formal framework for mental variables, an extended analogy - an allegory - between mental and thermodynamic quantities. Starting with mental correlates of the physical indefinables length, time, mass or force, and charge, we pursue the allegory up to mental versions of the thermodynamic Maxwell Relations. The Maxwell Relations interrelate the thermodynamic quantities volume, pressure, temperature, and entropy and were chosen since they are easy to derive, yet capable of generating nontrivial, nonobvious predictions. Our "Mental Maxwell Relations" interlink the mental variables consciousness, salience, arousal, and distraction and make nontrivial, nonobvious statements about mental phenomena. The mental system thus constructed is internally consistent, in harmony with introspection, and respects the RDoC criteria of employing only psychologically valid constructs with some evidence of a brain basis. We briefly apply these concepts to the problem of decision-making and sketch how some of them might be tested empirically.

Toward a global and reproducible science for brain imaging in neurotrauma: the ENIGMA adult moderate/severe traumatic brain injury working group

The global burden of mortality and morbidity caused by traumatic brain injury (TBI) is significant, and the heterogeneity of TBI patients and the relatively small sample sizes of most current neuroimaging studies is a major challenge for scientific advances and clinical translation. The ENIGMA (Enhancing NeuroImaging Genetics through Meta-Analysis) Adult moderate/severe TBI (AMS-TBI) working group aims to be a driving force for new discoveries in AMS-TBI by providing researchers world-wide with an effective framework and platform for large-scale cross-border collaboration and data sharing. Based on the principles of transparency, rigor, reproducibility and collaboration, we will facilitate the development and dissemination of multiscale and big data analysis pipelines for harmonized analyses in AMS-TBI using structural and functional neuroimaging in combination with non-imaging biomarkers, genetics, as well as clinical and behavioral measures. Ultimately, we will offer investigators an unprecedented opportunity to test important hypotheses about recovery and morbidity in AMS-TBI by taking advantage of our robust methods for large-scale neuroimaging data analysis. In this consensus statement we outline the working group's short-term, intermediate, and long-term goals.

Consciousness among delta waves: a paradox?

A common observation in EEG research is that consciousness vanishes with the appearance of delta (1 - 4 Hz) waves, particularly when those waves are high amplitude. High amplitude delta oscillations are very frequently observed in states of diminished consciousness, including slow wave sleep, anaesthesia, generalised epileptic seizures, and disorders of consciousness such as coma and vegetative state. This strong correlation between loss of consciousness and high amplitude delta oscillations is thought to stem from the widespread cortical deactivation that occurs during the "down states" or troughs of these slow oscillations. Recently, however, many studies have reported the presence of prominent delta activity during conscious states, which casts doubt on the hypothesis that high amplitude delta oscillations are an indicator of unconsciousness. These studies include work in Angelman syndrome, epilepsy, behavioural responsiveness during propofol anaesthesia, postoperative delirium, and states of dissociation from the environment such as dreaming and powerful psychedelic states. The foregoing studies complement an older, yet largely unacknowledged, body of literature that has documented awake, conscious patients with high amplitude delta oscillations in clinical reports from Rett syndrome, Lennox-Gastaut syndrome, schizophrenia, mitochondrial diseases, hepatic encephalopathy, and nonconvulsive status epilepticus. At the same time, a largely parallel body of recent work has reported convincing evidence that the complexity or entropy of EEG and magnetoencephalogram or MEG signals strongly relates to an individual's level of consciousness. Having reviewed this literature, we discuss plausible mechanisms that would resolve the seeming contradiction between high amplitude delta oscillations and consciousness. We also consider implications concerning theories of consciousness, such as integrated information theory and the entropic brain hypothesis. Finally, we conclude that false inferences of unconscious states can be best avoided by examining measures of electrophysiological complexity in addition to spectral power.

The minimal self hypothesis

For millennia self has been conjectured to be necessary for consciousness. But scant empirical evidence has been adduced to support this hypothesis. Inconsistent explications of "self" and failure to design apt experiments have impeded progress. Advocates of phenomenological psychiatry, however, have helped explicate "self," and employed it to explain some psychopathological symptoms. In those studies, "self" is understood in a minimalist sense, sheer "for-me-ness." Unfortunately, explication of the "minimal self" (MS) has relied on conceptual analysis, and applications to psychopathology have been hermeneutic, allowing for many degrees of interpretive latitude. The result is that MS's current scientific status is analogous to that of the "atom," at the time when "atom" was just beginning to undergo transformation from a philosophical to a scientific concept. Fortunately, there is now an opportunity to promote a similar transformation for "MS." Discovery of the brain's Default Mode Network (DMN) opened the door to neuroimaging investigations of self. Taking the DMN and other forms of intrinsic activity as a starting point, an empirical foothold can be established, one that spurs experimental research and that enables extension of research into multiple phenomena. New experimental protocols that posit "MS" can help explain phenomena hitherto not thought to be related to self, thereby hastening development of a mature science of self. In particular, targeting phenomena wherein consciousness is lost and recovered, as in some cases of Unresponsive Wakefulness Syndrome (UWS), allow for design of neuroimaging probes that enable detection of MS during non-conscious states. These probes, as well as other experimental protocols applied to NREM Sleep, General Anesthesia (GA), and the waking state, provide some evidence to suggest that not only can self and consciousness dissociate, MS might be a necessary precondition for conscious experience. Finally, these findings have implications for the science of consciousness: it has been suggested that "levels of consciousness" (LoC) is not a legitimate concept for the science of consciousness. But because we have the conceptual and methodological tools with which to refine investigations of MS, we have the means to identify a possible foundation-a bifurcation point-for consciousness, as well as the means by which to measure degrees of distance from that foundation. These neuroimaging investigations of MS position us to better assess whether LoC has a role to play in a mature science of consciousness.

Subcortical atrophy correlates with the perturbational complexity index in patients with disorders of consciousness

BACKGROUND

The complexity of neurophysiological brain responses to direct cortical stimulation, referred to as the perturbational complexity index (PCI), has been shown able to discriminate between consciousness and unconsciousness in patients surviving severe brain injury as well as several other conditions (e.g., wake, dreamless sleep, sleep and ketamine dreaming, anesthesia).

OBJECTIVE

This study asks whether, in patients with a disorder of consciousness (DOC), the complexity of the neurophysiological response to cortical stimulation is preferentially associated with atrophy within specific brain structures.

METHODS

We perform a retrospective analysis of 40 DOC patients and correlate their maximal PCI to MR-based measurements of cortical thinning and subcortical atrophy.

RESULTS

PCI was systematically and inversely associated with the degree of local atrophy within the globus pallidus, a region previously linked to electrocortical and behavioral arousal. Conversely, we fail to detect any association between variance in cortical ribbon thickness and PCI.

CONCLUSION

These findings corroborate the previously reported association between pallidal atrophy and low behavioral arousal and suggest that this region's role in maintaining the overall balance of excitation and inhibition may critically affect the emergence of complex cortical interactions in chronic disorders of consciousness. This finding thus also suggests a target for potential neuromodulatory intervention in DOC patients.

Electrophysiological evidence of preserved hearing at the end of life

This study attempts to answer the question: “Is hearing the last to go?” We present evidence of hearing among unresponsive actively dying hospice patients. Individual ERP (MMN, P3a, and P3b) responses to deviations in auditory patterns are reported for conscious young, healthy control participants, as well as for hospice patients, both when the latter were conscious, and again when they became unresponsive to their environment. Whereas the MMN (and perhaps too the P3a) is considered an automatic response to auditory irregularities, the P3b is associated with conscious detection of oddball targets. All control participants, and most responsive hospice patients, evidenced a “local” effect (either a MMN, a P3a, or both) and some a “global” effect (P3b) to deviations in tone, or deviations in auditory pattern. Importantly, most unresponsive patients showed evidence of MMN responses to tone changes, and some showed a P3a or P3b response to either tone or pattern changes. Thus, their auditory systems were responding similarly to those of young, healthy controls just hours from end of life. Hearing may indeed be one of the last senses to lose function as humans die.

Brain-Based Binary Communication Using Spatiotemporal Features of fNIRS Responses

“Locked-in” patients lose their ability to communicate naturally due to motor system dysfunction. Brain-computer interfacing offers a solution for their inability to communicate by enabling motor-independent communication. Straightforward and convenient in-session communication is essential in clinical environments. The present study introduces a functional near-infrared spectroscopy (fNIRS)-based binary communication paradigm that requires limited preparation time and merely nine optodes. Eighteen healthy participants performed two mental imagery tasks, mental drawing and spatial navigation, to answer yes/no questions during one of two auditorily cued time windows. Each of the six questions was answered five times, resulting in five trials per answer. This communication paradigm thus combines both spatial (two different mental imagery tasks, here mental drawing for “yes” and spatial navigation for “no”) and temporal (distinct time windows for encoding a “yes” and “no” answer) fNIRS signal features for information encoding. Participants’ answers were decoded in simulated real-time using general linear model analysis. Joint analysis of all five encoding trials resulted in an average accuracy of 66.67 and 58.33% using the oxygenated (HbO) and deoxygenated (HbR) hemoglobin signal respectively. For half of the participants, an accuracy of 83.33% or higher was reached using either the HbO signal or the HbR signal. For four participants, effective communication with 100% accuracy was achieved using either the HbO or HbR signal. An explorative analysis investigated the differentiability of the two mental tasks based solely on spatial fNIRS signal features. Using multivariate pattern analysis (MVPA) group single-trial accuracies of 58.33% (using 20 training trials per task) and 60.56% (using 40 training trials per task) could be obtained. Combining the five trials per run using a majority voting approach heightened these MVPA accuracies to 62.04 and 75%. Additionally, an fNIRS suitability questionnaire capturing participants’ physical features was administered to explore its predictive value for evaluating general data quality. Obtained questionnaire scores correlated significantly (r = -0.499) with the signal-to-noise of the raw light intensities. While more work is needed to further increase decoding accuracy, this study shows the potential of answer encoding using spatiotemporal fNIRS signal features or spatial fNIRS signal features only.

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.

Bottom-Up and Top-Down Mechanisms of General Anesthetics Modulate Different Dimensions of Consciousness

There has been controversy regarding the precise mechanisms of anesthetic-induced unconsciousness, with two salient approaches that have emerged within systems neuroscience. One prominent approach is the “bottom up” paradigm, which argues that anesthetics suppress consciousness by modulating sleep-wake nuclei and neural circuits in the brainstem and diencephalon that have evolved to control arousal states. Another approach is the “top-down” paradigm, which argues that anesthetics suppress consciousness by modulating the cortical and thalamocortical circuits involved in the integration of neural information. In this article, we synthesize these approaches by mapping bottom-up and top-down mechanisms of general anesthetics to two distinct but inter-related dimensions of consciousness: level and content. We show how this explains certain empirical observations regarding the diversity of anesthetic drug effects. We conclude with a more nuanced discussion of how levels and contents of consciousness interact to generate subjective experience and what this implies for the mechanisms of anesthetic-induced unconsciousness.

Canadian perspectives on the clinical actionability of neuroimaging in disorders of consciousness

BACKGROUND

Acquired brain injury is a critical public health and socioeconomic problem in Canada, leaving many patients in vegetative, minimally conscious, or locked-in states, unresponsive and unable to communicate. Recent advances in neuroimaging research have demonstrated residual consciousness in a few exemplary patients with acquired brain injury, suggesting potential misdiagnosis and changes in prognosis. Such progress, in parallel with research using multimodal brain imaging technologies in recent years, has promising implications for clinical translation, notwithstanding the many challenges that impact health care and policy development. This study explored the perspectives of Canadian professionals with expertise either in neuroimaging research, disorders of consciousness, or both, on the potential clinical applications and implications of imaging technology.

METHODS

Twenty-two professionals from designated communities of neuroimaging researchers, ethicists, lawyers, and practitioners participated in semistructured interviews. Data were analyzed for emergent themes.

RESULTS

The five most dominant themes were: (1) validation and calibration of the methods; (2) informed consent; (3) burdens on the health care system; (4) implications for the Canadian health care system; and (5) possibilities for improved prognosis.

CONCLUSIONS

Movement of neuroimaging from research into clinical care for acquired brain injury will require careful consideration of legal and ethical issues alongside research reliability, responsible distribution of health care resources, and the interaction of technological capabilities with patient outcome.

Does Modafinil improve the level of consciousness for people with a prolonged disorder of consciousness? a retrospective pilot study

BACKGROUND AND AIM

Modafinil is best known as a sleep regulator among healthy individuals, but studies suggest that it reduces excessive daytime sleepiness in patients with brain injury. This retrospective pilot study evaluated the effectiveness of Modafinil for people with a prolonged disorder of consciousness and whether those with a traumatic brain injury did better than those with a non-traumatic brain injury.

METHOD

Twenty four prolonged disorder of consciousness patients who were prescribed Modafinil, were assessed at least four times both before and during treatment. The Coma Recovery Scale-Revised was used to determine if patients had a disorder of consciousness and the Wessex Head Injury Matrix was used to monitor behavior during baseline and treatment periods. Patients with a traumatic brain injury (N = 12) were compared with those with non-traumatic brain injury (N = 12). A chi-square test with significance at 0.05 was used and when frequencies were below 5 a Fisher's Exact Test was used.

RESULTS

Cognitive improvements were noted in domains of wakefulness, awareness, concentration, tracking and following commands. Significant differences were found for the whole group between baseline and Modafinil (x²=9.80; p = 0.002). Eleven of the 12 traumatic brain injury patients had higher Wessex Head Injury Matrix scores when on Modafinil (x²=8.33, p < 0.004). Six non-traumatic brain injury patients had higher scores with Modafinil, two had lower scores and four showed no change. There was no significant difference in the number of patients showing an increase compared to those showing a decrease (Fisher's exact test p = 0.29).

CONCLUSION

Modafinil appears to be beneficial for enhancing cognition in prolonged disorder of consciousness patients. Traumatic brain injury patients benefited more than non-traumatic brain injury patients. Implications for Rehabilitation People with prolonged disorders of consciousness are those in coma, a vegetative state or a minimally conscious state. Sensorimotor and neuromodulations (pharmacological and brain stimulation) are the available treatment strategies to this group. Modafinil promotes attention, concentration and maintains wakefulness in a patient with narcolepsy, obstructive sleep apnea and shift work sleep disorders. In a relatively small sample, this retrospective pilot study shows the effectiveness of Modafinil in conjunction with good care, suitable medications and multidisciplinary rehabilitation in enhancing arousal in prolonged disorders of consciousness patients.

TCD Diastolic Velocity Decay and Pulsatility Index Increment in PVS Cases

Background:

Functional neuroimaging has provided new insights for assessing cerebral function in persistent vegetative state patients (PVS). Compared to controls, positron emission tomography and single photon emission tomography have shown a substantial reduction of global brain cerebral glucose metabolism and perfusion in PVS. Doppler ultrasonography (TCD) assesses local blood flow velocity and direction in the proximal portions of large intracranial arteries; it is a noninvasive technique, and it can be carried out at the bedside. To date, few studies have applied TCD to study PVS.

Methods:

We assessed intracranial circulation by TCD in five PVS patients. The cause of brain insult was hypoxic encephalopathy in four cases, and the other suffered an embolic cerebral infarct causing a top of the basilar artery syndrome. The sample volume was set at 12 mm; power output and gain settings were maximized as needed. The temporal bone acoustic window was not suitable for intracranial vessel insonation in all patients. As an alternative, the internal carotid artery siphon was assessed by orbital insonation between 55-70 mm.

Results:

Systolic velocity was within a normal range, between 44 and 62 cm/second in all cases. However, the diastolic amplitude was reduced, as well as the end diastolic velocity, and the pulsatility index was increased in all patients.

Conclusions:

We conclude that TCD diastolic velocity decrement and PI augmentation in our cases might be related to uncoupling of cerebral blood flow and cerebral metabolic rate, arising from reduced cerebral glucose consumption and oxygen uptake, after extensive brain injury.

Global monitoring in the neurocritical care unit

Effective methods of monitoring the status of patients with neurological injuries began with non-invasive observations and evolved during the past several decades to include more invasive monitoring tools and physiologic measures. The monitoring paradigm continues to evolve, this time back toward the use of less invasive tools. In parallel, the science of monitoring began with the global assessment of the patient's neurological condition, evolved to focus on regional monitoring techniques, and with the advent of enhanced computing capabilities is now moving back to focus on global monitoring. The purpose of this session of the Second Neurocritical Care Research Conference was to collaboratively develop a comprehensive understanding of the state of the science for global brain monitoring and to identify research priorities for intracranial pressure monitoring, neuroimaging, and neuro-electrophysiology monitoring.

Coma recovery scale-r: variability in the disorder of consciousness

Background

Despite evidence from neuroimaging research, diagnosis and early prognosis in the vegetative (VS/UWS) and minimally conscious (MCS) states still depend on the observation of clinical signs of responsiveness. Multiple testing has documented a systematic variability during the day in the incidence of established signs of responsiveness. Spontaneous fluctuations of the Coma Recovery Scale-revised (CRS-r) scores are conceivable.

Methods

We retrospectively analyzed the CRS-r repeatedly administered to 7 VS/UWS and 12 MCS subjects undergoing systematic observation during a conventional 13 weeks. rehabilitation plan.

Results

The CRS-r global, visual and auditory scores were found higher in the morning than at the afternoon administration in both VS/UWS and MCS subgroups over the entire period of observation. The probability for a VS/UWS subject of being classified as MCS at the morning testing at least once during the 13 weeks. observation was as high as 30 %, i.e., compatible with the reported misdiagnosis rate between the two clinical conditions.

Conclusions

Multiple CRS-r testing is advisable to minimize the risk of misclassification; estimates of spontaneous variability could be used to characterize with greater accuracy patients with disorder of consciousness and possibly help optimize the rehabilitation plan.

Thalamo-frontal connectivity mediates top-down cognitive functions in disorders of consciousness

OBJECTIVE

We employed functional MRI (fMRI) to assess whether (1) patients with disorders of consciousness (DOC) retain the ability to willfully engage in top-down processing and (2) what neurophysiologic factors distinguish patients who can demonstrate this ability from patients who cannot.

METHODS

Sixteen volunteers, 8 patients in vegetative state (VS), 16 minimally conscious patients (MCS), and 4 exit from MCS (eMCS) patients were enrolled in a prospective cross-sectional fMRI study. Participants performed a target detection task in which they counted the number of times a (changing) target word was presented amidst a set of distractors.

RESULTS

Three of 8 patients diagnosed as being in a VS exhibited significant activations in response to the task, thereby demonstrating a state of consciousness. Differential activations across tasks were also observed in 6 MCS patients and 1 eMCS patient. A psycho-physiologic interaction analysis revealed that the main factor distinguishing patients who responded to the task from those who did not was a greater connectivity between the anterior section of thalamus and prefrontal cortex.

CONCLUSIONS

In our sample of patients, the dissociation between overt behavior observable in clinical assessments and residual cognitive faculties is prevalent among DOC patients (37%). A substantial number of patients, including some diagnosed with VS, can demonstrate willful engagement in top-down cognition. While neuroimaging data are not the same as observable behavior, this suggests that the mental status of some VS patients exceeds what can be appreciated clinically. Furthermore, thalamo-frontal circuits might be crucial to sustaining top-down functions.

Preservation of electroencephalographic organization in patients with impaired consciousness and imaging-based evidence of command-following

OBJECTIVE

Standard clinical characterization of patients with disorders of consciousness (DOC) relies on observation of motor output and may therefore lead to the misdiagnosis of vegetative state or minimally conscious state in patients with preserved cognition. We used conventional electroencephalographic (EEG) measures to assess a cohort of DOC patients with and without functional magnetic resonance imaging (fMRI)-based evidence of command-following, and correlated the findings with standard clinical behavioral evaluation and brain metabolic activity.

METHODS

We enrolled 44 patients with severe brain injury. Behavioral diagnosis was established using standardized clinical assessments. Long-term EEG recordings were analyzed to determine wakeful background organization and presence of elements of sleep architecture. A subset of patients had fMRI testing of command-following using motor imagery paradigms (26 patients) and resting brain metabolism measurement using (18) fluorodeoxyglucose positron emission tomography (31 patients).

RESULTS

All 4 patients with fMRI evidence of covert command-following consistently demonstrated well-organized EEG background during wakefulness, spindling activity during sleep, and relative preservation of cortical metabolic activity. In the entire cohort, EEG organization and overall brain metabolism showed no significant association with bedside behavioral testing, except in a few cases when EEG was severely abnormal.

INTERPRETATION

These findings suggest that conventional EEG is a simple strategy that complements behavioral and imaging characterization of DOC patients. Preservation of specific EEG features may be used to assess the likelihood of unrecognized cognitive abilities in severely brain-injured patients with very limited or no motor responses.

A neural network approach to fMRI binocular visual rivalry task analysis

The purpose of this study was to investigate whether artificial neural networks (ANN) are able to decode participants’ conscious experience perception from brain activity alone, using complex and ecological stimuli. To reach the aim we conducted pattern recognition data analysis on fMRI data acquired during the execution of a binocular visual rivalry paradigm (BR). Twelve healthy participants were submitted to fMRI during the execution of a binocular non-rivalry (BNR) and a BR paradigm in which two classes of stimuli (faces and houses) were presented. During the binocular rivalry paradigm, behavioral responses related to the switching between consciously perceived stimuli were also collected. First, we used the BNR paradigm as a functional localizer to identify the brain areas involved the processing of the stimuli. Second, we trained the ANN on the BNR fMRI data restricted to these regions of interest. Third, we applied the trained ANN to the BR data as a ‘brain reading’ tool to discriminate the pattern of neural activity between the two stimuli. Fourth, we verified the consistency of the ANN outputs with the collected behavioral indicators of which stimulus was consciously perceived by the participants. Our main results showed that the trained ANN was able to generalize across the two different tasks (i.e. BNR and BR) and to identify with high accuracy the cognitive state of the participants (i.e. which stimulus was consciously perceived) during the BR condition. The behavioral response, employed as control parameter, was compared with the network output and a statistically significant percentage of correspondences (p-value <0.05) were obtained for all subjects. In conclusion the present study provides a method based on multivariate pattern analysis to investigate the neural basis of visual consciousness during the BR phenomenon when behavioral indicators lack or are inconsistent, like in disorders of consciousness or sedated patients.

Knowledge of Partial Awareness in Disorders of Consciousness: Implications for Ethical Evaluations?

Recent results from neuroimaging appear to indicate that some patients in a vegetative state have partially intact awareness. These results may demonstrate misdiagnosis and suggest the need not only for alternative forms of treatment, but also for the reconsideration of end-of-life decisions in cases of disorders of consciousness. This article addresses the second consequence. First, I will discuss which aspects of consciousness may be involved in neuroimaging findings. I will then consider various factors relevant to ethical end-of-life decision-making, and analyse whether and to what extent the above consequence applies to these factors. It will be shown that knowledge of the existence of partial awareness in patients with disorders of consciousness only influences end-of-life decision-making if certain background assumptions are made.

Research and technology in neurocritical care

The daily practice of neurointensivists focuses on the recognition of subtle changes in the neurological examination, interactions between the brain and systemic derangements, and brain physiology. Common alterations such as fever, hyperglycemia, and hypotension have different consequences in patients with brain insults compared with patients of general medical illness. Various technologies have become available or are currently being developed. The session on "research and technology" of the first neurocritical care research conference held in Houston in September of 2009 was devoted to the discussion of the current status, and the research role of state-of-the art technologies in neurocritical patients including multi-modality neuromonitoring, biomarkers, neuroimaging, and "omics" research (proteomix, genomics, and metabolomics). We have summarized the topics discussed in this session. We have provided a brief overview of the current status of these technologies, and put forward recommendations for future research applications in the field of neurocritical care.

A learning assessment procedure as a test supplement for monitoring progress with two post-coma persons with a diagnosis of vegetative state

OBJECTIVE

Evaluating a learning assessment procedure for monitoring progress with two post-coma adults with a diagnosis of vegetative state.

METHOD

ABABCBCB and ABABCB designs were used for the two participants, with A representing baseline, B intervention and C control conditions. Participants' activation of an optic microswitch by eyelid closure produced stimulation during B phases.

RESULTS

One participant increased responding during B phases and decreased it during the C condition, suggesting a non-reflective minimal level of consciousness. She showed P300 and mismatch negativity responses and scored at the vegetative level on the Coma Recovery Scale-Revised (CRS-R). The other participant increased responding during the initial B phases without decline during the first (viable) part of the C condition, suggesting a pre-conscious level. He showed indistinct P300 and mismatch negativity responses and vegetative-level scores on the CRS-R.

CONCLUSION

Learning data seemed reconcilable with neurophysiological measures and more positive than CRS-R scores.

Visual cognition in disorders of consciousness: from V1 to top-down attention

What is it like to be at the lower boundaries of consciousness? Disorders of consciousness such as coma, the vegetative state, and the minimally conscious state are among the most mysterious and least understood conditions of the human brain. Particularly complicated is the assessment of residual cognitive functioning and awareness for diagnostic, rehabilitative, legal, and ethical purposes. In this article, we present a novel functional magnetic resonance imaging exploration of visual cognition in a patient with a severe disorder of consciousness. This battery of tests, first developed in healthy volunteers, assesses increasingly complex transformations of visual information along a known caudal to rostral gradient from occipital to temporal cortex. In the first five levels, the battery assesses (passive) processing of light, color, motion, coherent shapes, and object categories (i.e., faces, houses). At the final level, the battery assesses the ability to voluntarily deploy visual attention in order to focus on one of two competing stimuli. In the patient, this approach revealed appropriate brain activations, undistinguishable from those seen in healthy and aware volunteers. In addition, the ability of the patient to focus one of two competing stimuli, and switch between them on command, also suggests that he retained the ability to access, to some degree, his own visual representations.

Cognition in the vegetative state

Awake but not aware: This puzzling dissociation of the two central elements of consciousness defines the vegetative state. Traditionally, this condition has been believed to imply a brain with preserved hypothalamic and brainstem autonomic functions but with no capacity for cortical cognitive processes. As is discussed in this review, over a 20-year span neuroimaging techniques have clearly demonstrated that this characterization of patients in a vegetative state is incorrect. Contrary to the initial belief, the "vegetative" brain can retain several high-level aspects of cognitive functions, across sensory modalities, including language processing and learning dynamics. Nonetheless, the residual cognitive functions observed in vegetative patients might reflect intact but functionally disconnected cortical modules that do not give rise to the subjective feeling of phenomenological awareness.

Assessment of consciousness with electrophysiological and neurological imaging techniques

PURPOSE OF REVIEW

Brain MRI (diffusion tensor imaging and spectroscopy) and functional neuroimaging (PET, functional MRI, EEG and evoked potential studies) are changing our understanding of patients with disorders of consciousness encountered after coma such as the 'vegetative' or minimally conscious states.

RECENT FINDINGS

Increasing evidence from functional neuroimaging and electrophysiology demonstrates some residual cognitive processing in a subgroup of patients who clinically fail to show any response to commands, leading to the recent proposal of 'unresponsive wakefulness syndrome' as an alternative name for patients previously coined 'vegetative' or 'apallic'.

SUMMARY

Consciousness can be viewed as the emergent property of the collective behavior of widespread thalamocortical frontoparietal network connectivity. Data from physiological, pharmacological and pathological alterations of consciousness provide evidence in favor of this hypothesis. Increasing our understanding of the neural correlates of consciousness is helping clinicians to do a better job in terms of diagnosis, prognosis and finally treatment and drug development for these severely brain-damaged patients. The current challenge remains to continue translating this research from the bench to the bedside. Only well controlled large multicentric neuroimaging and electrophysiology studies will enable to identify which paraclinical diagnostic or prognostic test is necessary for our routine evidence-based assessment of individuals with disorders of consciousness.

Reductions of thalamic volume and regional shape changes in the vegetative and the minimally conscious states

The thalamus is known to play a key role in arousal regulation and support of human consciousness. Neuropathological studies have identified thalamic damage as one of the most common abnormalities present in the brains of patients who were in a vegetative state (VS) or a minimally-conscious state (MCS) state at the time of their deaths. Nonetheless, no in vivo studies of thalamic abnormalities in these patients have been conducted. Using high-resolution T1-weighted magnetic resonance images and a novel approach to shape analysis, we investigated thalamic global and regional changes in a sample of patients in a VS or an MCS. Group comparisons and correlations with clinical variables were performed for the total thalamic volume and for each surface vertex. Total thalamic volume was significantly lower in patients than in healthy volunteers. Shape analysis revealed significant bilateral regional atrophy in the dorso-medial body in patients compared to controls; this atrophy was more widespread in VS than in MCS patients. Lower thalamic volume was significantly correlated with worse Disability Rating Scale scores. Shape analysis suggested that the dorso-medial nucleus and the internal medullar lamina were the main regions responsible for this correlation. Our findings suggest that MCS and VS patients present different patterns of regional thalamic abnormalities, and that these differences partially explain their clinical profile.

Dissociations between behavioural and functional magnetic resonance imaging-based evaluations of cognitive function after brain injury

Functional neuroimaging methods hold promise for the identification of cognitive function and communication capacity in some severely brain-injured patients who may not retain sufficient motor function to demonstrate their abilities. We studied seven severely brain-injured patients and a control group of 14 subjects using a novel hierarchical functional magnetic resonance imaging assessment utilizing mental imagery responses. Whereas the control group showed consistent and accurate (for communication) blood-oxygen-level-dependent responses without exception, the brain-injured subjects showed a wide variation in the correlation of blood-oxygen-level-dependent responses and overt behavioural responses. Specifically, the brain-injured subjects dissociated bedside and functional magnetic resonance imaging-based command following and communication capabilities. These observations reveal significant challenges in developing validated functional magnetic resonance imaging-based methods for clinical use and raise interesting questions about underlying brain function assayed using these methods in brain-injured subjects.

An overview of intervention options for promoting adaptive behavior of persons with acquired brain injury and minimally conscious state

This paper presents an overview of the studies directed at helping post-coma persons with minimally conscious state improve their adaptive behavior. Twenty-one studies were identified for the 2000-2010 period (i.e., a period in which an intense debate has occurred about diagnostic, rehabilitative, prognostic, and ethical issues concerning people with severe acquired brain injury). Three of the 21 studies involved transcortical magnetic or deep brain stimulation. Six studies focused on the provision of multisensory stimulation or music therapy. The remaining 12 studies involved the use of response-related (contingent) stimulation and assistive technology. The outcomes of the studies, which were generally reported as positive, were discussed in terms of (a) the size (quantitative relevance) of the changes obtained, (b) the credibility/reliability of the changes, in light of the methodological conditions of the studies, and (c) the level of engagement and interaction involvement of the participants. Relevant issues for future research were also examined.

The Vegetative State: Life, Death and Consciousness

The three conditions that are traditionally defined as disorders of consciousness are the comatose state, the minimally conscious state and the vegetative state. Thirty years after the phrase was coined, the definition and management of patients in vegetative states continue to provoke debate. Recent advances in neuroimaging have cast doubt on the assertion that these patients are completely unaware of their environment. This article presents a case report and review of disorders of consciousness, their definition, prognosis and ethical issues in the management of patients.

Willful modulation of brain activity in disorders of consciousness

BACKGROUND

The differential diagnosis of disorders of consciousness is challenging. The rate of misdiagnosis is approximately 40%, and new methods are required to complement bedside testing, particularly if the patient's capacity to show behavioral signs of awareness is diminished.

METHODS

At two major referral centers in Cambridge, United Kingdom, and Liege, Belgium, we performed a study involving 54 patients with disorders of consciousness. We used functional magnetic resonance imaging (MRI) to assess each patient's ability to generate willful, neuroanatomically specific, blood-oxygenation-level-dependent responses during two established mental-imagery tasks. A technique was then developed to determine whether such tasks could be used to communicate yes-or-no answers to simple questions.

RESULTS

Of the 54 patients enrolled in the study, 5 were able to willfully modulate their brain activity. In three of these patients, additional bedside testing revealed some sign of awareness, but in the other two patients, no voluntary behavior could be detected by means of clinical assessment. One patient was able to use our technique to answer yes or no to questions during functional MRI; however, it remained impossible to establish any form of communication at the bedside.

CONCLUSIONS

These results show that a small proportion of patients in a vegetative or minimally conscious state have brain activation reflecting some awareness and cognition. Careful clinical examination will result in reclassification of the state of consciousness in some of these patients. This technique may be useful in establishing basic communication with patients who appear to be unresponsive.

Behavior in the Brain

Recent evidence has suggested that functional neuroimaging may play a crucial role in assessing residual cognition and awareness in brain injury survivors. In particular, brain insults that compromise the patient’s ability to produce motor output may render standard clinical testing ineffective. Indeed, if patients were aware but unable to signal so via motor behavior, they would be impossible to distinguish, at the bedside, from vegetative patients. Considering the alarming rate with which minimally conscious patients are misdiagnosed as vegetative, and the severe medical, legal, and ethical implications of such decisions, novel tools are urgently required to complement current clinical-assessment protocols. Functional neuroimaging may be particularly suited to this aim by providing a window on brain function without requiring patients to produce any motor output. Specifically, the possibility of detecting signs of willful behavior by directly observing brain activity (i.e., “brain behavior”), rather than motoric output, allows this approach to reach beyond what is observable at the bedside with standard clinical assessments. In addition, several neuroimaging studies have already highlighted neuroimaging protocols that can distinguish automatic brain responses from willful brain activity, making it possible to employ willful brain activations as an index of awareness. Certainly, neuroimaging in patient populations faces some theoretical and experimental difficulties, but willful, task-dependent, brain activation may be the only way to discriminate the conscious, but immobile, patient from the unconscious one.

Magnetic resonance spectroscopy and diffusion tensor imaging in coma survivors: promises and pitfalls

The status of comatose patient is currently established on the basis of the patient-exhibited behaviors. Clinical assessment is subjective and, in 40% of patients, fails to distinguish vegetative state (VS) from minimally conscious states (MCS). The technologic advances of magnetic resonance imaging (MRI) have dramatically improved our understanding of these altered states of consciousness. The role of neuroimaging in coma survivors has increased beyond the simple evaluation of morphological abnormalities. The development of 1H-MR spectroscopy (MRS) and diffusion tensor imaging (DTI) provide opportunity to evaluate processes that cannot be approached by current morphologic MRI sequences. They offer potentially unique insights into the histopathology of VS and MCS. The MRS is a powerful noninvasive imaging technique that enables the in vivo quantification of certain chemical compound or metabolites as N-acetylaspartate (NAA), Choline (Cho), and Creatine (Cr). These biomarkers explore neuronal integrity (NAA), cell membrane turnover (Cho), and cell energetic function (Cr). DTI is an effective and proved quantitative method for evaluating tissue integrity at microscopic level. It provides information about the microstructure and the architecture of tissues, especially the white matter. Various physical parameters can be extracted from this sequence: the fractional anisotropy (FA), a marker of white matter integrity; mean diffusivity (MD); and the apparent diffusion coefficient (ADC) which can differentiate cytotoxic and vasogenic edema. The most prominent findings with MRS and DTI performed in traumatic brain-injured (TBI) patients in subacute phase are the reduction of the NAA/Cr ratio in posterior pons and the decrease of mean infratentorial and supratentorial FA except in posterior pons that enables to predict unfavorable outcome at 1 year from TBI with up to 86% sensitivity and 97% specificity. This review will focus on the interest of comatose patients MRI multimodal assessment with MRS and DTI. It will emphasize the advantages and pitfalls of these techniques in particular in predicting the coma survivors' outcome.

A perturbational approach for evaluating the brain's capacity for consciousness

How do we evaluate a brain's capacity to sustain conscious experience if the subject does not manifest purposeful behaviour and does not respond to questions and commands? What should we measure in this case? An emerging idea in theoretical neuroscience is that what really matters for consciousness in the brain is not activity levels, access to sensory inputs or neural synchronization per se, but rather the ability of different areas of the thalamocortical system to interact causally with each other to form an integrated whole. In particular, the information integration theory of consciousness (IITC) argues that consciousness is integrated information and that the brain should be able to generate consciousness to the extent that it has a large repertoire of available states (information), yet it cannot be decomposed into a collection of causally independent subsystems (integration). To evaluate the ability to integrate information among distributed cortical regions, it may not be sufficient to observe the brain in action. Instead, it is useful to employ a perturbational approach and examine to what extent different regions of the thalamocortical system can interact causally (integration) and produce specific responses (information). Thanks to a recently developed technique, transcranial magnetic stimulation and high-density electroencephalography (TMS/hd-EEG), one can record the immediate reaction of the entire thalamocortical system to controlled perturbations of different cortical areas. In this chapter, using sleep as a model of unconsciousness, we show that TMS/hd-EEG can detect clear-cut changes in the ability of the thalamocortical system to integrate information when the level of consciousness fluctuates across the sleep-wake cycle. Based on these results, we discuss the potential applications of this novel technique to evaluate objectively the brain's capacity for consciousness at the bedside of brain-injured patients.

Executive functions in the absence of behavior: functional imaging of the minimally conscious state

One of the major challenges in the clinical evaluation of brain injury survivors is to comprehensively assess the level of preserved cognitive function in order to inform diagnostic decisions and suggest appropriate rehabilitation strategies. However, the limited (if any) capacity for producing behavior in some of these patients often limits the extent to which cognitive functions can be explored via standard bedside methods. We present a novel neuroimaging paradigm that allows the assessment of residual executive functions without requiring the patient to produce any behavioral output. In particular, we target processes such as active maintenance of information through time and willful adoption of "mind-sets" that have been proposed to require conscious awareness. Employing an fMRI block design paradigm, healthy volunteers were presented with a series of neutral (i.e., not emotionally salient) words, and alternatively instructed to listen to all the words, or to count the number of times a given target is repeated. Importantly, the perceptual stimulation in the passive listening and the counting tasks was carefully matched. Contrasted with passive listening, the counting task revealed a fronto-parietal network previously associated with target detection and working memory. Remarkably, when tested on this same procedure, a minimally conscious patient presented a highly similar pattern of activation. Furthermore, the activity in these regions appeared highly synchronous to the onset and offset of the counting blocks. Considering the close matching of sensory stimulation across the two tasks, these findings strongly suggest that the patient could willfully adopt differential "mind-sets" as a function of condition, and could actively maintain information across time. Neither cognitive function was apparent when the patient was (behaviorally) tested at the bedside. This paradigm thus exemplifies the potential for fMRI to explore high-level cognitive functions, and awareness, in the absence of any behavioral response.