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OBJECTIVE: The P300 component of a sensory event-related potential is one of the major electrophysiological markers used to explore remnants of cognitive function in patients with disorders of consciousness (DoC). However, measuring the P300 in patients is complicated by significant inter-trial variability commonly observed in levels of arousal and awareness. To overcome this limitation, we analyzed single-trial modulation of power in the delta and theta frequency bands, which underlie the P300. METHODS: In a preliminary cross-sectional study using a 24-channel EEG and a passive own-name oddball paradigm, we analyzed event-related synchronization (ERS) across trials in the delta and theta bands in a sample of 10 control and 12 DoC subjects. RESULTS: In comparison to controls, DoC subjects presented a low percentage of trials where delta ERS was observed. In particular, coordinated modulation between delta and theta in response to the stimulus was absent, with a high percentage of trials where only theta ERS was observed. Further, we found a positive correlation between the percentage of epochs with delta ERS and the strength of the P300. CONCLUSIONS: Reduced modulation of spectral activity in the delta band in response to stimuli indicates a dissociation in the activity of the neural networks that oscillate in delta and theta ranges and contribute to the generation of the P300. SIGNIFICANCE: The reduction in spectral modulation observed in DoC provides a deeper understanding of neurophysiological dysfunction and the means to develop a more fine-grained marker of residual cognitive function in individual patients.

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Brain-injured patients may, with the assistance of life support, continue to perform basic bodily functions, but yet be deficient in wakefulness, awareness, decision making or other overt manifestations of consciousness. Here, we review two neurological states observed in brain injured patients with different degrees of brain impairment, the vegetative state (VS)and the minimally conscious state (MCS), and we discuss how these states are diagnosed through assessing patient behavioral responses during clinical examination. We consider howfunctional neuroimaging has revealed preserved cognitive capacities in patients that were supposed to be in the VS and has introduced a new diagnosis, cognitive motor dissociation.We review the GW Theory proposal that consciousness arises from functional connectivity (FC) of widely separated brain regions. We discuss how such high FC underlies the DefaultMode Network (DMN), a group of neural circuits that are active when an individual is not involved with external tasks and engages in introspective thinking. Finally, we discuss thefinding that the level of FC of the DMN is diminished in brain injured patients and the proposal that the level of residual DMN FC in brain injured patients is an index of their consciousness

Pacientes com lesão cerebral, quando assistidos, podem continuar a desempenhar funções fisiológicas básicas, mesmo estando com a vigília, a atenção, a capacidade de decisão e outras funções de consciência prejudicadas. Revisamos aqui dois níveis de distúrbio de consciência o estado vegetativo (VS) e o nível de consciência mínima (MCS), e discutimos como são diagnosticados através das respostas comportamentais durante o exame clínico. Abordamos como a neuroimagem funcional revelou capacidades cognitivas preservadas em pacientes supostamente em estado vegetativo, introduzindo um novo diagnóstico: a dissociação cognitivo-motora. Revisamos a proposta da Global Workspace (GW) teoria de que a consciência surge a partir de um alto grau de conectividade funcional (FC) entre áreas cerebrais distantes. Discutimos como esta alta conectividade é a base do Default Mode Network (DMN), uma rede neural ativada quando o indivíduo não está envolvido com tarefas externas e se volta para atividade mental introspectiva. Finalmente, discutimos os achados de redução do nível de FC no DMN em pacientes com lesão cerebral e a proposta de que o mesmo poderia ser um índice do nível de consciência nesses pacientes.

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RESUMO

Brain-injured patients may, with the assistance of life support, continue to perform basic bodily functions, but yet be deficient in wakefulness, awareness, decision making or other overt manifestations of consciousness. Here, we review two neurological states observed in brain injured patients with different degrees of brain impairment, the vegetative state (VS)and the minimally conscious state (MCS), and we discuss how these states are diagnosed through assessing patient behavioral responses during clinical examination. We consider howfunctional neuroimaging has revealed preserved cognitive capacities in patients that were supposed to be in the VS and has introduced a new diagnosis, cognitive motor dissociation.We review the GW Theory proposal that consciousness arises from functional connectivity (FC) of widely separated brain regions. We discuss how such high FC underlies the DefaultMode Network (DMN), a group of neural circuits that are active when an individual is not involved with external tasks and engages in introspective thinking. Finally, we discuss thefinding that the level of FC of the DMN is diminished in brain injured patients and the proposal that the level of residual DMN FC in brain injured patients is an index of their consciousness.(AU)

Pacientes com lesão cerebral, quando assistidos, podem continuar a desempenhar funções fisiológicas básicas, mesmo estando com a vigília, a atenção, a capacidade de decisão eoutras funções de consciência prejudicadas. Revisamos aqui dois níveis de distúrbio de consciência o estado vegetativo (VS) e o nível de consciência mínima (MCS), e discutimoscomo são diagnosticados através das respostas comportamentais durante o exame clínico. Abordamos como a neuroimagem funcional revelou capacidades cognitivas preservadas empacientes supostamente em estado vegetativo, introduzindo um novo diagnóstico: a dissociação cognitivo-motora. Revisamos a proposta da Global Workspace (GW) teoria de que a consciência surge a partir de um alto grau de conectividade funcional (FC) entre áreas cerebrais distantes. Discutimos como esta alta conectividade é a base do Default Mode Network (DMN), uma rede neural ativada quando o indivíduo não está envolvido com tarefas externas e se volta para atividade mental introspectiva. Finalmente, discutimos os achadosde redução do nível de FC no DMN em pacientes com lesão cerebral e a proposta de que o mesmo poderia ser um índice do nível de consciência nesses pacientes.(AU)

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Los desórdenes de la conciencia continúan fascinando a neurólogos, neurocientíficos y filósofos pero durante décadas no han sido objeto de estudios consistentes debido a su dificultad en el abordaje experimental. En los últimos años, un creciente número de grupos de investigación en neurociencias cognitivas están abordando el estudio de la neurofisiología de la conciencia desde una perspectiva experimental a pesar de la complejidad metodológica y epistemológica del tema. Aunque es difícil de describir la conciencia, ésta podría ser definida como una combinación entre la capacidad de estar en vigilia (wakefulness) y el hecho de estar consciente (awareness). Desde una perspectiva neurobiológica se ha propuesto que el sistema de la formación reticular ascendente y sus proyecciones talámicas serían críticos en modular el ciclo sueño vigilia y el alerta (wakefulness). La capacidad de darse cuenta conscientemente (awareness) sería una función de las redes neurales entre la corteza y el tálamo y el sistema córtico-cortical. Distintos modelos se han utilizado al atacar este difícil problema; estudios in vivo no invasivos, en personas conscientes con lesiones cerebrales, en animales y en personas en estados de conciencia disminuida. En este artículo revisamos la evidencia científica de los correlatos neurales de los procesos conscientes e inconscientes en diferentes estados de conciencia haciendo hincapié en pacientes en estado de conciencia disminuida.

Disorders of consciousness have captivated neurologists, neuroscientists, and philosophers for decades, but few consistent studies have been conducted on these conditions due to their difficult experimental approach. In recent years, an increasing number of cognitive neuroscience research groups have examined the physiology of consciousness from an experimental perspective, despite the methodological and epistemological complexities of the field. While describing consciousness can be challenging, a close definition must acknowledge a combination of wakefulness and awareness. Form a neurobiological standpoint; it has been argued that the ascending reticular system and its thalamic projections are critical in modulating awareness and wakefulness sleep cycles. Awareness may be a function of the neural networks within the cortex, the thalamus, and the cortico-cortical system. Different models have been employed to tackle this difficult problem, including non-invasive in vivo studies, examination of conscious patients with brain lesions, and studies on both animals and patients with disorders of consciousness. This article reviews the scientific evidence for the neural basis of conscious and unconscious processes in different states of consciousness, focusing on patients in the vegetative and minimally conscious state.

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