Rev Neuroscience
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We have reviewed the literature on transcranial magnetic stimulation studies in patients with brain death, coma, vegetative, minimally conscious, and locked-in states. Transcranial magnetic stimulation permits non-invasive study of brain excitability and may extend our understanding of the underlying mechanisms of these disorders. However, use of this technique in severe brain damage remains methodologically ill-defined and must be further validated prior to clinical application in these challenging patients.
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The diagnosis and management of patients with persistent vegetative (PVS) and minimally conscious (MCS) states entail powerful medical, ethical and legal debates. The recent description of the MCS highlights the crucial role of unexpected and well-documented recoveries of cognitive functions. ⋯ We present a review on this topic, emphasizing the clinical and neuroimaging assessment of these states, with some of our recent results in this area. We conclude that the development of rehabilitation techniques for patients with PVS and others suffering long-lasting effects of brain injury is a crucial challenge for actual and future generations of neuroscientists.
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Review Historical Article
Networks of conscious experience: computational neuroscience in understanding life, death, and consciousness.
We demonstrate brain locations appearing to correlate with consciousness, but not being directly responsible for it. Technology reveals that brain activity is associated with consciousness but is not equivalent to it. We examine how consciousness occurs at critical levels of complexity. ⋯ There is no threshold or rationale specified; rather, consciousness 'just happens'. Consciousness then involves an awareness of what we are sensing or experiencing and some ability to control or coordinate voluntary actions. These issues of life, death, and consciousness are discussed in the context of Mike, the headless chicken, who survived for 18 months, and in the context of consciousness with high degrees of intellectual and cognitive function in a congenitally anencephalic brain; additionally, in the reanimation work of Soviet scientists in the 1920-30s, and in auditory sentence processing in patients in comatose, vegetative, and minimally conscious states.
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There exists much controversy in providing an effective definition of human death, largely due to the lack of a rigorous separation and ordered formulation of three distinct elements: a universally accepted definition of death, the medical criterion (anatomical substrata) for determining that death has occurred, and the tests to prove that the criterion has been satisfied. The papers herein review medical standards, philosophical arguments, neurophysiological knowledge, behavioural and cognitive theory and the legal ramifications of the brain-oriented standards of death (whole brain, brainstem and higher brain). The papers examine the notion of connectivities and networks of conscious experience in order to formulate an effective definition of death, based on the basic physiopathological mechanisms of consciousness. ⋯ The thread of the arguments is the basis for a standard of human death that includes consciousness as the most important function of the body, because it provides the capacity for integrating the functions of the body. The notion of consciousness as the ultimate integrative function is more consistent with the biologically-based systems than the more philosophically-based notions of personhood. Both sides of the argument are presented herein.
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The clinical criteria for brain death consist of the demonstration of the absence of any clinical sign of encephalic activity. Confirmatory testing is usually not required for the diagnosis of brain death, except in some special situations that Spanish law details. In these situations demonstrating cerebral circulatory arrest (CCA) by cerebral flow studies is necessary to support the diagnosis of brain death. ⋯ TCD is a useful method for detecting CCA and therefore can be used to confirm brain death in a clinically brain-dead patient. The presence of reverberating flow, systolic spikes or absence of flow in the basilar and both middle cerebral arteries observed in two examinations is highly specific for the prediction of CCA and brain death in all patients.