Human consciousness is supported by dynamic complex patterns of brain signal coordination.

Adopting the framework of brain dynamics as a cornerstone of human consciousness, we determined whether dynamic signal coordination provides specific and generalizable patterns pertaining to conscious and unconscious states after brain damage. A dynamic pattern of coordinated and anticoordinated functional magnetic resonance imaging signals characterized healthy individuals and minimally conscious patients. The brains of unresponsive patients showed primarily a pattern of low interareal phase coherence mainly mediated by structural connectivity, and had smaller chances to transition between patterns. The complex pattern was further corroborated in patients with covert cognition, who could perform neuroimaging mental imagery tasks, validating this pattern's implication in consciousness. Anesthesia increased the probability of the less complex pattern to equal levels, validating its implication in unconsciousness. Our results establish that consciousness rests on the brain's ability to sustain rich brain dynamics and pave the way for determining specific and generalizable fingerprints of conscious and unconscious states.

Relationship between etiology and covert cognition in the minimally conscious state.

OBJECTIVES: Functional neuroimaging has shown that the absence of externally observable signs of consciousness and cognition in severely brain-injured patients does not necessarily indicate the true absence of such abilities. However, relative to traumatic brain injury, nontraumatic injury is known to be associated with a reduced likelihood of regaining overtly measurable levels of consciousness. We investigated the relationships between etiology and both overt and covert cognitive abilities in a group of patients in the minimally conscious state (MCS). METHODS: Twenty-three MCS patients (15 traumatic and 8 nontraumatic) completed a motor imagery EEG task in which they were required to imagine movements of their right-hand and toes to command. When successfully performed, these imagined movements appear as distinct sensorimotor modulations, which can be used to determine the presence of reliable command-following. The utility of this task has been demonstrated previously in a group of vegetative state patients. RESULTS: Consistent and robust responses to command were observed in the EEG of 22% of the MCS patients (5 of 23). Etiology had a significant impact on the ability to successfully complete this task, with 33% of traumatic patients (5 of 15) returning positive EEG outcomes compared with none of the nontraumatic patients (0 of 8). CONCLUSIONS: The overt behavioral signs of awareness (measured with the Coma Recovery Scale-Revised) exhibited by nontraumatic MCS patients appear to be an accurate reflection of their covert cognitive abilities. In contrast, one-third of a group of traumatically injured patients in the MCS possess a range of high-level cognitive faculties that are not evident from their overt behavior.

Multimodal neuroimaging in patients with disorders of consciousness showing "functional hemispherectomy".

Beside behavioral assessment of patients with disorders of consciousness, neuroimaging modalities may offer objective paraclinical markers important for diagnosis and prognosis. They provide information on the structural location and extent of brain lesions (e.g., morphometric MRI and diffusion tensor imaging (DTI-MRI) assessing structural connectivity) but also their functional impact (e.g., metabolic FDG-PET, hemodynamic fMRI, and EEG measurements obtained in "resting state" conditions). We here illustrate the role of multimodal imaging in severe brain injury, presenting a patient in unresponsive wakefulness syndrome (UWS; i.e., vegetative state, VS) and in a "fluctuating" minimally conscious state (MCS). In both cases, resting state FDG-PET, fMRI, and EEG showed a functionally preserved right hemisphere, while DTI showed underlying differences in structural connectivity highlighting the complementarities of these neuroimaging methods in the study of disorders of consciousness.

Alteración de la conectividad cerebral en pacientes con traumatismo cráneoencefálico grave crónico. Un estudio mediante imágenes de tensor de difusión / Impairment of cerebral connectivity in patients with chronic and severe brain injury. A diffussion tensor imaging study

Objetivo: Investigar las alteraciones de la conectividad estructural y sus relación clínica en pacientes con traumatismo cráneo-encefálico (TCE) de larga evolución. Método: Se estudiaron 30 pacientes con TCE grave y una evolución de entre 2 y 7 años desde el accidente, estratificados según edad, sexo y educación con una muestra de 20 sujetos control. Ambas muestras fueron sometidas a una exploración neuropsicológica y de imágenes de tensor de difusión (ITD). Resultados: Los pacientes mostraron una afectación generalizada de ambas medidas de ITD que correlacionó de forma significativa con la amnesia postraumática (p<0,001) para la anisotropía fraccional (AF) y para la difusividad media (DM) (p<0,001). Además, los valores de AF global correlacionaron con la velocidad de procesamiento de la información y con la retención a largo plazo de la lista de palabras de Rey. Los mapas de AF mostraron correlaciones de la velocidad del procesamiento con los fascículos asociativos y de la memoria declarativa con el cuerpo calloso y los fascículos longitudinales superiores. Conclusión: La ITD puede evidenciar alteraciones de la conectividad cerebral tras largos periodos de evolución en los TCE graves que explican parte de las secuelas neuropsicológicas persistentes en memoria y velocidad de procesamiento (AU)

Objetive: To investigate the structural connectivity alterations and their clinical and neuropsychological correlates in patients with chronic traumatic brain injury (TBI). Method: 30 patients with chronic and severe TBI and 20 healthy controls matched by age and years of education were scanned. Patients’ time post-injury ranged from 2 to 7 years. Neuropsychological assessement and diffusion tensor imaging (DTI) were performed Results: Whole brain DTI analysis showed a global decrease in fractional anisotropy (FA) and a global increase in mean diffusivity (MD) in the patient group that correlated with post-traumatic amnesia (r= 0,75, P=<0.001 for FA and r= 0.69 P=<0.001 for MD). FA also correlated with information processing speed and long-term memory assessed by the Rey Auditory Verbal Learning Test. FA maps showed these correlations to be widespread in the case of information processing speed, and localized to the splenium of the corpus callosum and longitudinal fasciculi in the case of memory functions. Conclusion: DTI is a technique that allows the detection of long-term white matter changes. These changes may explain the persistent memory and processing speed deficits (AU)