fMRI reveals large-scale network activation in minimally conscious patients

Classical conditioning in the vegetative and minimally conscious state

Pavlovian trace conditioning depends on the temporal gap between the conditioned and unconditioned stimuli. It requires, in mammals, functional medial temporal lobe structures and, in humans, explicit knowledge of the temporal contingency. It is therefore considered to be a plausible objective test to assess awareness without relying on explicit reports. We found that individuals with disorders of consciousness (DOCs), despite being unable to report awareness explicitly, were able to learn this procedure. Learning was specific and showed an anticipatory electromyographic response to the aversive conditioning stimulus, which was substantially stronger than to the control stimulus and was augmented as the aversive stimulus approached. The amount of learning correlated with the degree of cortical atrophy and was a good indicator of recovery. None of these effects were observed in control subjects under the effect of anesthesia (propofol). Our results suggest that individuals with DOCs might have partially preserved conscious processing, which cannot be mediated by explicit reports and is not detected by behavioral assessment.

Chronic consciousness disorders

Although philosophers and cognitive neuroscientists have struggled to define human consciousness, physicians can identify and assess its two clinical dimensions: wakefulness and awareness. A comatose patient has neither wakefulness nor awareness; a patient in a vegetative state has wakefulness without awareness; and a minimally conscious patient has both, but awareness is impaired. Syndromes of unconsciousness have established diagnostic criteria, but they encompass a spectrum of severity of brain damage and have indistinct boundaries. Functional neuroimaging using PET and fMRI have provided a new and complementary way to assess consciousness. Several recent provocative studies suggest that fMRI in unresponsive patients may detect evidence of conscious awareness when a careful neurological examination cannot. If these findings are verified by future studies, functional neuroimaging technologies will alter clinical practices concerning the diagnosis, classification, and prognosis of unconscious patients, and will lead to a greater understanding of the biology of human consciousness.

Cerebral response to speech in vegetative and minimally conscious states after traumatic brain injury

PRIMARY OBJECTIVE

To study cerebral response in a functional magnetic resonance imaging (fMRI) task of speech perception in a sample of patients in vegetative state (VS) and minimally conscious state (MCS) after traumatic brain injury.

METHODS

Three patients in VS, four patients in MCS and 19 healthy volunteers were enrolled for the study. All subjects underwent an fMRI task of passive listening of narratives played forward and backward, alternated with periods of silence. This study analysed cerebral response to language and to complex sound processing in the healthy subjects' group and in each patient, using SPM5.

RESULTS

One patient in VS and one in MCS showed cerebral responses to language and to complex sound very similar to those shown by the healthy volunteers. Two more patients, one in VS and one in MCS, showed significant responses to complex sound only. Finally, one patient in VS and one patient in MCS failed to show significant activation in response to either stimulus.

CONCLUSIONS

Some patients in VS and MCS can preserve cerebral responses to language and auditory stimuli. fMRI may be useful to identify these responses, which may pass unnoticed in a bedside examination.

Is there anybody in there? Detecting awareness in disorders of consciousness

The bedside detection of awareness in disorders of consciousness (DOC) caused by acquired brain injury is not an easy task. For this reason, differential diagnosis using neuroimaging and electrophysiological tools in search for objective markers of consciousness is being employed. However, such tools cannot be considered as diagnostic per se, but as assistants to the clinical evaluation, which, at present, remains the gold standard. Regarding therapeutic management in DOC, no evidence-based recommendations can be made in favor of a specific treatment. The present review summarizes clinical and paraclinical studies that have been conducted with neuroimaging and electrophysiological techniques in search of residual awareness in DOC. We discuss the medical, scientific and ethical implications that derive from these studies and we argue that, in the future, the role of neuroimaging and electrophysiology will be important not only for the diagnosis and prognosis of DOC but also in establishing communication with these challenging patients.

The problem of aphasia in the assessment of consciousness in brain-damaged patients

The assessment of the level and content of consciousness in brain-damaged patients relies to a large extent on behavioral assessment techniques. The limited behavioral repertoire displayed by vegetative and minimally conscious states requires the use of highly sensitive and reliable behavioral assessment methods, allowing the detection of subtle changes in behavior and associated level of consciousness. This situation is further complicated when patients with such disorders of consciousness have underlying deficits in the domain of communication functions, such as aphasia. The present paper examines the consequences of receptive and/or productive aphasia on the already limited behavioral repertoire presented in these patients and discusses a number of behavioral and neuroimaging assessment procedures designed to: (1) detect the presence of aphasia in patients with disorders of consciousness, and (2) reliably assess the level of consciousness of brain-damaged patients while taking into account the existence of receptive and/or expressive language deficits. The combined use of behavioral and neuroimaging assessment techniques appears to be particularly promising for disentangling impaired consciousness and aphasia.

Behavioral assessment in patients with disorders of consciousness: gold standard or fool's gold?

In the absence of "hard" neurophysiologic markers, the burden of proof for establishing conscious awareness in individuals who sustain severe brain injury lies in behavioral assessment. Because behavior represents indirect evidence of consciousness, reliance on behavioral markers presents significant challenges and may lead to misdiagnosis. Detection of conscious awareness is confounded by numerous factors including fluctuations in arousal level, difficulty differentiating reflexive or involuntary movement from intentional behavior, underlying sensory and motor impairments, and medication side effects. When an ambiguous behavior is observed, the onus falls to the clinician to determine where along the continuum of unconsciousness to consciousness, it lies. This paper (1) summarizes the current diagnostic criteria for coma, the vegetative state, and the minimally conscious state, (2) describes current behavioral assessment methods, (3) discusses the limitations of behavioral assessment techniques, (4) reviews recent applications of functional neuroimaging in the assessment of patients with disorders of consciousness, and (5) concludes with a case study that illustrates the disparity between behavioral and functional neuroimaging findings that may be encountered in this population.

Reaching across the abyss: recent advances in functional magnetic resonance imaging and their potential relevance to disorders of consciousness

Disorders of consciousness (DOC) raise profound scientific, clinical, ethical, and philosophical issues. Growing knowledge on fundamental principles of brain organization in healthy individuals offers new opportunities for a better understanding of residual brain function in DOCs. We here discuss new perspectives derived from a recently proposed scheme of brain organization underlying consciousness in healthy individuals. In this scheme, thalamo-cortical networks can be divided into two, often antagonistic, global systems: (i) a system of externally oriented, sensory-motor networks (the "extrinsic" system); and (ii) a system of inward-oriented networks (the "intrinsic" or default system). According to this framework, four distinct mental states would be possible that could be relevant for understanding DOCs. In normal healthy volunteers and locked-in syndrome patients, a state of high functionality of both the extrinsic and intrinsic or default systems is expected--associated with full awareness of environment and self. In this case, mental imagery tasks combined with fMRI can be used to detect covert awareness in patients that are unable to communicate. According to the framework, two complementary states of system imbalance are also possible, in which one system is in a hyperfunctional state, while the other is hypoactive. Extrinsic system hyperfunction is expected to lead to a state of total sensory-motor "absorption" or "lost self." In contrast, intrinsic or default system hyperfunction is expected to lead to a state of complete detachment from the external world. A state where both extrinsic and intrinsic systems are hypofunctional is predicted to lead to markedly impaired consciousness as seen in DOCs. Finally, we review the potential use of ultra-slow fluctuations in BOLD signal as a tool for assessing the functional integrity of extrinsic and intrinsic systems during "resting state" fMRI acquisitions. In particular, we discuss the potential provided by assessment of these slow spontaneous BOLD fluctuations as a novel tool in assessing the cognitive state and chances of recovery from brain pathologies underlying DOCs.

Neuroimaging and disorders of consciousness: envisioning an ethical research agenda

The application of neuroimaging technology to the study of the injured brain has transformed how neuroscientists understand disorders of consciousness, such as the vegetative and minimally conscious states, and deepened our understanding of mechanisms of recovery. This scientific progress, and its potential clinical translation, provides an opportunity for ethical reflection. It was against this scientific backdrop that we convened a conference of leading investigators in neuroimaging, disorders of consciousness and neuroethics. Our goal was to develop an ethical frame to move these investigative techniques into mature clinical tools. This paper presents the recommendations and analysis of a Working Meeting on Ethics, Neuroimaging and Limited States of Consciousness held at Stanford University during June 2007. It represents an interdisciplinary approach to the challenges posed by the emerging use of neuroimaging technologies to describe and characterize disorders of consciousness.

Neuroethics and neuroimaging: moving toward transparency

Without exaggeration, it could be said that we are entering a golden age of neuroscience. Informed by recent developments in neuroimaging that allow us to peer into the working brain at both a structural and functional level, neuroscientists are beginning to untangle mechanisms of recovery after brain injury and grapple with age-old questions about brain and mind and their correlates neural mechanisms and consciousness. Neuroimaging, coupled with new diagnostic categories and assessment scales are helping us develop a new diagnostic nosology about disorders of consciousness which will likely improve prognostication and suggest therapeutic advances. Historically such diagnostic refinement has yield therapeutic advances in medicine and there is no reason to doubt that this will be the case for disorders of consciousness, perhaps bringing relief to a marginalized population now on the periphery of the therapeutic agenda. In spite of this promise, the translation of research findings into the clinical context will be difficult. As we move from descriptive categories about disorders of consciousness, like the vegetative or minimally conscious states, to ones further specified by integrating behavioral and neuroimaging findings, humility not hubris should be the virtue that guides the ethical conduct of research and practice.

Types of brain dysfunction in critical illness

Cerebral dysfunction and injury in the ICU presents as focal neurologic deficits, seizures, coma, and delirium. These syndromes may result from a primary brain insult, such as stroke or trauma, but commonly are a complication of a systemic insult, such as cardiac arrest, hypoxemia, sepsis, metabolic derangements, and pharmacologic exposures. Many survivors of critical illness have cognitive impairment, which is believed to underlie the poor long-term functional status and quality of life observed in many critical illness survivors. Although progress has been made in characterizing the epidemiology of cerebral dysfunction in the ICU, more research is needed to elucidate underlying mechanisms that might represent targets for therapeutic intervention.

Central thalamic contributions to arousal regulation and neurological disorders of consciousness

This review focuses on the contributions of the central thalamus to normal mechanisms of arousal regulation and to neurological disorders of consciousness. Forebrain arousal is regulated by ascending influences from brainstem/basal forebrain neuronal populations ("arousal systems") and control signals descending from frontal cortical systems. These subcortical and cortical systems have converging projections to the central thalamus that emphasize their role in maintaining organized behavior during wakefulness. Central thalamic neurons appear to be specialized both anatomically and physiologically to support distributed network activity that maintains neuronal firing patterns across long-range cortico-cortical pathways and within cortico-striatopallidal-thalamocortical loop connections. Recruitment of central thalamic neurons occurs in response to increasing cognitive demand, stress, fatigue, and other perturbations that reduce behavioral performance. In addition, the central thalamus receives projections from brainstem pathways evolved to rapidly generate brief shifts of arousal associated with the appearance of salient stimuli across different sensory modalities. Through activation of the central thalamus, neurons across the cerebral cortex and striatum can be depolarized and their activity patterns selectively gated by descending or ascending signals related to premotor attention and alerting stimuli. Direct injury to the central thalamus or prominent deafferentation of these neurons as a result of complex, multifocal, brain insults are both associated with severe impairment of forebrain functional integration and arousal regulation. Interventions targeting neurons within the central thalamus may lead to rational therapeutic approaches to the treatment of impaired arousal regulation following nonprogressive brain injuries. A model accounting for present therapeutic strategies is proposed.

Neurostimulation and the minimally conscious state

Neurostimulation to restore cognitive and physical functions is an innovative and promising technique for treating patients with severe brain injury that has resulted in a minimally conscious state (MCS). The technique may involve electrical stimulation of the central thalamus, which has extensive projections to the cerebral cortex. Yet it is unclear whether an improvement in neurological functions would result in a net benefit for these patients. Quality-of-life measurements would be necessary to determine whether any benefit of neurostimulation outweighed any harm in their response to different degrees of cognitive and physical disability. These measures could also indicate whether the technique could be ethically justified and whether surrogates could give proxy consent to its use on brain-injured patients.

A case of locked-in syndrome complicated by central deafness

BACKGROUND

A 53-year-old male with a history of hypertension, diabetes mellitus, and factor V deficiency presented to an emergency room with progressively increasing headache, slurred speech, and left upper extremity weakness. Over the previous 3 months, he had been receiving warfarin for prophylaxis of deep venous thrombosis following knee surgery. After presentation and an initial period of coma, he became tetraplegic and anarthric, requiring intubation and ventilatory assistance.

INVESTIGATIONS

Neurological examination, CT scan, electroencephalogram, brainstem auditory and visual evoked potential studies, neuropsychological assessment and functional MRI studies.

DIAGNOSIS

Locked-in syndrome following ventral pontine hemorrhage, complicated by central deafness secondary to extension of the lesion to the inferior colliculus.

MANAGEMENT

Development of an augmentative communication system designed to exploit the patient's preserved cognitive and motor functions.

Mechanisms of neurologic failure in critical illness

Critical illness frequently is associated with neurologic failure that may involve the central and peripheral nervous systems. Central nervous system failure is associated with a spectrum of neurobehavioral changes including delirium, coma, and long-term cognitive dysfunction. Peripheral neurologic failure, or critical illness neuromuscular abnormalities, is suggested by diffuse arreflexic weakness and protracted respiratory insufficiency, and may also persist long after the acute hospitalization. While the burden of neurological disease complicating critical illness is considerable, preventive or therapeutic options are limited. This article provides an overview of research evaluating the relationship between critical illness and neurologic function, with a special emphasis on underlying mechanisms.

Functional MRI and other non-invasive imaging technologies: providing visual biomarkers for spinal cord structure and function after injury

Substantial progress has been made towards understanding the molecular basis for limited endogenous central nervous system (CNS) axonal growth after injuries such as spinal cord trauma. Realization of the potential benefit of therapeutic interventions requires methods to assess axonal growth and functional reorganization over time after neurological damage. Here, we discuss the technical challenges of analyzing and interpreting the effects of various interventions on CNS repair, specifically in the context of spinal cord injury. Evolving technologies such as functional magnetic resonance imaging and other non-invasive imaging techniques will be reviewed. These technologies should revolutionize our ability to track changes in both CNS structure and function.

Exploring impaired consciousness: the MRI approach

PURPOSE OF REVIEW

To summarize the application of advanced MRI sequences such as magnetic resonance spectroscopy, diffusion tensor imaging and functional MRI for the evaluation of patients with altered consciousness.

RECENT FINDINGS

Magnetic resonance spectroscopy, volumetry and diffusion tensor imaging have shown promising results in the evaluation of traumatic or anoxo-ischaemic brain lesions and can detect damage of the brainstem, basal ganglia and white matter tracts not visible on conventional sequences. A diffusion tensor imaging study has raised the possibility of detecting ongoing axonal regrowth many years after the initial injury in minimally conscious patients. Functional MRI studies have shown that a high level of brain activities, such as recognizing one's own name or imagining playing tennis, can be preserved in vegetative patients.

SUMMARY

The development of quantitative imaging could lead to a more objective evaluation of the extent of destruction or preservation of critical brain areas at the acute phase of brain injury, which could be integrated in multi-parametric decisional strategies for these patients. Functional imaging could help define borders between the various levels of altered consciousness and detect the presence of cryptic residual functions in vegetative or minimally conscious patients. This approach could eventually help determine the neurological outcome and make individual blueprints of the preserved brain activities in severely brain injured patients.

Dissociating speech perception and comprehension at reduced levels of awareness

We used functional MRI and the anesthetic agent propofol to assess the relationship among neural responses to speech, successful comprehension, and conscious awareness. Volunteers were scanned while listening to sentences containing ambiguous words, matched sentences without ambiguous words, and signal-correlated noise (SCN). During three scanning sessions, participants were nonsedated (awake), lightly sedated (a slowed response to conversation), and deeply sedated (no conversational response, rousable by loud command). Bilateral temporal-lobe responses for sentences compared with signal-correlated noise were observed at all three levels of sedation, although prefrontal and premotor responses to speech were absent at the deepest level of sedation. Additional inferior frontal and posterior temporal responses to ambiguous sentences provide a neural correlate of semantic processes critical for comprehending sentences containing ambiguous words. However, this additional response was absent during light sedation, suggesting a marked impairment of sentence comprehension. A significant decline in postscan recognition memory for sentences also suggests that sedation impaired encoding of sentences into memory, with left inferior frontal and temporal lobe responses during light sedation predicting subsequent recognition memory. These findings suggest a graded degradation of cognitive function in response to sedation such that "higher-level" semantic and mnemonic processes can be impaired at relatively low levels of sedation, whereas perceptual processing of speech remains resilient even during deep sedation. These results have important implications for understanding the relationship between speech comprehension and awareness in the healthy brain in patients receiving sedation and in patients with disorders of consciousness.

Behavioural improvements with thalamic stimulation after severe traumatic brain injury

Widespread loss of cerebral connectivity is assumed to underlie the failure of brain mechanisms that support communication and goal-directed behaviour following severe traumatic brain injury. Disorders of consciousness that persist for longer than 12 months after severe traumatic brain injury are generally considered to be immutable; no treatment has been shown to accelerate recovery or improve functional outcome in such cases. Recent studies have shown unexpected preservation of large-scale cerebral networks in patients in the minimally conscious state (MCS), a condition that is characterized by intermittent evidence of awareness of self or the environment. These findings indicate that there might be residual functional capacity in some patients that could be supported by therapeutic interventions. We hypothesize that further recovery in some patients in the MCS is limited by chronic underactivation of potentially recruitable large-scale networks. Here, in a 6-month double-blind alternating crossover study, we show that bilateral deep brain electrical stimulation (DBS) of the central thalamus modulates behavioural responsiveness in a patient who remained in MCS for 6 yr following traumatic brain injury before the intervention. The frequency of specific cognitively mediated behaviours (primary outcome measures) and functional limb control and oral feeding (secondary outcome measures) increased during periods in which DBS was on as compared with periods in which it was off. Logistic regression modelling shows a statistical linkage between the observed functional improvements and recent stimulation history. We interpret the DBS effects as compensating for a loss of arousal regulation that is normally controlled by the frontal lobe in the intact brain. These findings provide evidence that DBS can promote significant late functional recovery from severe traumatic brain injury. Our observations, years after the injury occurred, challenge the existing practice of early treatment discontinuation for patients with only inconsistent interactive behaviours and motivate further research to develop therapeutic interventions.

Self-consciousness in non-communicative patients

The clinical and para-clinical examination of residual self-consciousness in non-communicative severely brain damaged patients (i.e., coma, vegetative state and minimally conscious state) remains exceptionally challenging. Passive presentation of the patient's own name and own face are known to be effective attention-grabbing stimuli when clinically assessing consciousness at the patient's bedside. Event-related potential and functional neuroimaging studies using such self-referential stimuli are currently being used to disentangle the cognitive hierarchy of self-processing. We here review neuropsychological, neuropathological, electrophysiological and neuroimaging studies using the own name and own face paradigm obtained in conscious waking, sleep, pharmacological coma, pathological coma and related disorders of consciousness. Based on these results we discuss what we currently do and do not know about the functional significance of the neural network involved in "automatic" and "conscious" self-referential processing.

The use of functional MRI in traumatic brain injury diagnosis and treatment

Recent advances in MRI have provided the opportunity to map changes in hemodynamics that correspond to cognitive and sensory operations. These advances in noninvasive, low-risk, imaging environments have extended the traditional role of medical imaging into new domains that include investigations into the interplay between brain anatomy, physiology, and function. This interplay is mandatory for examination of the complex effects of diffuse damage caused by traumatic brain injury. Functional MRI (fMRI) provides relatively high-resolution indirect assessment of neuronal activity. Three main factors interact to affect the quality of fMRI data that is acquired: (1) MRI hardware, (2) the paradigm (or experimental) design, and (3) subject cooperation. This article focuses on paradigm design and subject cooperation.

Coma, delirium, and cognitive dysfunction in critical illness

Syndromes of global cerebral dysfunction that are associated with critical illness include acute disorders (eg, coma, delirium) and chronic processes (ie, cognitive impairment). These syndromes can result from direct cerebral injury; however, many cases develop as a complication of a systemic insult. Coma frequently evolves into phenomenologically distinct disorders of consciousness; it must be differentiated from conditions in which consciousness is preserved, as in the locked-in state. Advances have been made in defining, scoring, and delineating the epidemiology of cerebral dysfunction in the ICU, but research is needed to elucidate underlying mechanisms, with the goal of identifying targets for prevention and therapy.

Functional neuroimaging applications for assessment and rehabilitation planning in patients with disorders of consciousness

OBJECTIVE

To describe the theoretic framework, design, and potential clinical applications of functional neuroimaging protocols in patients with disorders of consciousness.

DATA SOURCES

Recent published literature and authors' own work.

STUDY SELECTION

Studies using functional neuroimaging techniques to investigate cognitive processing in patients diagnosed with vegetative and minimally conscious state.

DATA EXTRACTION

Not applicable.

DATA SYNTHESIS

Positron-emission tomography activation studies suggest that the vegetative state represents a global disconnection syndrome in which higher order association cortices are functionally disconnected from primary cortical areas. In contrast, patterns of activation in functional magnetic resonance imaging studies of patients in the minimally conscious state show preservation of large-scale cortical networks associated with language and visual processing.

CONCLUSIONS

Novel applications of functional neuroimaging in patients with disorders of consciousness may aid in differential diagnosis, prognostic assessment and identification of pathophysiologic mechanisms. Improvements in patient characterization may, in turn, provide new opportunities for restoration of function through interventional neuromodulation.

Cortical reorganization following intradigital tendon transfer

We distinguish between two models of adult cortical reorganization, adaptive and constant somatotopy, using functional magnetic resonance imaging maps corresponding to individual thumb and fourth-finger digits in a patient with a right-hand fourth digit tendon transfer that salvaged impaired function of the right thumb. Comparison of motor and sensory maps for both digits and both hands was consistent with a model of 'adaptive somatotopy' in which thumb control was taken over by regions adjacent to the fourth finger control cluster rather than at the presurgical lateral region as predicted by a model of 'constant somatotopy'. These findings are the first to demonstrate that rerouting of peripheral input, in the absence of brain injury, is sufficient to drive cortical reorganization resulting in recovery of lost motor function, and further suggest an adaptive mechanism associated with brain tissue engaged in intact motor functions.

When thoughts become action: an fMRI paradigm to study volitional brain activity in non-communicative brain injured patients

The assessment of voluntary behavior in non-communicative brain injured patients is often challenging due to the existence of profound motor impairment. In the absence of a full understanding of the neural correlates of consciousness, even a normal activation in response to passive sensory stimulation cannot be considered as proof of the presence of awareness in these patients. In contrast, predicted activation in response to the instruction to perform a mental imagery task would provide evidence of voluntary task-dependent brain activity, and hence of consciousness, in non-communicative patients. However, no data yet exist to indicate which imagery instructions would yield reliable single subject activation. The aim of the present study was to establish such a paradigm in healthy volunteers. Two exploratory experiments evaluated the reproducibility of individual brain activation elicited by four distinct mental imagery tasks. The two most robust mental imagery tasks were found to be spatial navigation and motor imagery. In a third experiment, where these two tasks were directly compared, differentiation of each task from one another and from rest periods was assessed blindly using a priori criteria and was correct for every volunteer. The spatial navigation and motor imagery tasks described here permit the identification of volitional brain activation at the single subject level, without a motor response. Volunteer as well as patient data [Owen, A.M., Coleman, M.R., Boly, M., Davis, M.H., Laureys, S., Pickard J.D., 2006. Detecting awareness in the vegetative state. Science 313, 1402] strongly suggest that this paradigm may provide a method for assessing the presence of volitional brain activity, and thus of consciousness, in non-communicative brain-injured patients.

Multimodal neuroimaging approaches to disorders of consciousness

Advances in neuroimaging techniques hold significant promise for improving understanding of disorders of consciousness arising from severe brain injuries. We review neuroimaging studies of the vegetative state (VS) and minimally conscious state (MCS), and findings in an unusual case of late emergence from MCS. Multimodal neuroimaging studies using positron emission tomography techniques, functional magnetic resonance imaging, and quantitative electroencephalography and magnetoencephalography quantify variations of residual cerebral activity across these patient populations. The results suggest models to distinguish the pathophysiologic basis of VS and MCS. Less clear are potential brain mechanisms underlying late recovery of communication in rare MCS patients. Diffusion tensor magnetic resonance imaging studies and recent experimental findings suggest that structural remodeling of the brain following severe injury may play a role in late functional recoveries. More generally, relatively long time courses of recovery following severe brain injury emphasize the need to develop markers for identifying patients who may harbor potential for further meaningful recovery. Introduction of neuroimaging into the clinical evaluation process will require developing frameworks for longitudinal assessments of cerebral function. Although limited in number, available studies already provide important insights into underlying brain mechanisms that may help guide development of such assessment strategies.

Measurements and models of cerebral function in the severely injured brain

We review the emerging applications of functional and structural neuroimaging techniques for the assessment of patients with disorders of consciousness. Measurements of brain function from patients in the vegetative state (VS) and minimally conscious state (MCS) are compared, and a conceptual organization is developed that suggests models of brain mechanisms associated with different functional levels of recovery. We emphasize developing strategies to place complex brain injuries on a more equal footing using global and regional quantification of resting or activated brain activity using functional imaging techniques alongside more detailed structural assessments of neuronal integrity and axonal connectivity now available. Preliminary studies from several investigative groups suggest that some MCS patients may harbor a functional reserve in the form of recruitable cerebral networks. These findings support developing systematic characterizations of the severely injured brain and suggest that some patients may benefit from improved diagnostic assessments.

Affirming the right to care, preserving the right to die: disorders of consciousness and neuroethics after Schiavo

In this article, I attempt to untangle some of the cultural, philosophical, and ethical currents that informed the Schiavo case. My objective is to better apprehend what the Schiavo case means for end-of-life care in general and to assert that our discourse about the ethical issues attendant to brain injury will be impoverished if we limit our discussions about disorders of consciousness solely to the vegetative state. If we ignore emerging developments in neuroscience that are helping to elucidate the nature of these disorders and fail to broaden the conversation about brain injury, beyond the unmitigated futility of the permanent vegetative state, we will imperil others who might improve and be helped. Through such efforts we can help mitigate the tragedy of the Schiavo case and overcome the rhetoric that marked the national discourse in March 2005. Once the complexity of disorders of consciousness is appreciated, rhetorical statements about a right to die or a right to life are exposed as being incompatible with the challenge of providing care to such patients. This is especially true as neuroscience brings greater diagnostic refinement to their assessment and management, a topic addressed in this article, which specifically focuses on the clinical and ethical implications of the recently described minimally conscious state. Instead of staking out ideological positions that do not meet the needs of patients or families, we should strive to both preserve the right to die for those who are beyond hope while affirming the right to care to those who might benefit from coming advances in neuroscience. If we can achieve that delicate balance, we will be able to transcend the partisan debate that shrouded the life and death of Theresa Marie Schiavo and begin to articulate a palliative neuroethics of care for those touched by severe brain injury and disorders of consciousness.

How should functional imaging of patients with disorders of consciousness contribute to their clinical rehabilitation needs?

PURPOSE OF REVIEW

We discuss the problems of evidence-based neurorehabilitation in disorders of consciousness, and recent functional neuroimaging data obtained in the vegetative state and minimally conscious state.

RECENT FINDINGS

Published data are insufficient to make recommendations for or against any of the neurorehabilitative treatments in vegetative state and minimally conscious state patients. Electrophysiological and functional imaging studies have been shown to be useful in measuring residual brain function in noncommunicative brain-damaged patients. Despite the fact that such studies could in principle allow an objective quantification of the putative cerebral effect of rehabilitative treatment in the vegetative state and minimally conscious state, they have so far not been used in this context.

SUMMARY

Without controlled studies and careful patient selection criteria it will not be possible to evaluate the potential of therapeutic interventions in disorders of consciousness. There also is a need to elucidate the neurophysiological effects of such treatments. Integration of multimodal neuroimaging techniques should eventually improve our ability to disentangle differences in outcome on the basis of underlying mechanisms and better guide our therapeutic options in the challenging patient populations encountered following severe acute brain damage.