Consciousness supporting networks

Abstract

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. Author's personal copy In most cases authors Consciousness supporting networksAthena Demertzi, Andrea Soddu and Steven LaureysFunctional neuroimaging shows that patients with disorders of consciousness exhibit disrupted system-level functional connectivity. Unresponsive/''vegetative state'' patients preserve wakefulness networks of brainstem and basal forebrain but the cerebral networks accounting for external perceptual awareness and internal self-related mentation are disrupted. Specifically, the 'external awareness' network encompassing lateral fronto-temporo-parietal cortices bilaterally, and the 'internal awareness' network including midline anterior cingulate/mesiofrontal and posterior cingulate/ precuneal cortices, are functionally disconnected. By contrast, patients in minimally conscious state 'minus', who show nonreflex behaviors, are characterized by right-lateralized recovery of the external awareness network. Similarly, patients who evolve to minimally conscious state 'plus' and respond to commands recover the dominant left-lateralized language network. Now, the use of active experimental paradigms targeting at detecting motor-independent signs of awareness or even establishing communication with these patients, challenge these two clinical boundaries. Such advances are naturally accompanied by legitimate neuroscientific and ethical queries demanding our attention on the medical implementations of this new knowledge. What is 'minimally conscious'?At present there is no generally accepted definition of consciousness [1]. As clinicians, we will reduce the complexity of this term and define consciousness operationally, separating two main components: wakefulness and awareness [2]. Wakefulness has been shown to critically depend upon the functional integrity of subcortical arousal systems over 50 years ago [(e.g., see 3)]. The level of wakefulness can be estimated by simple behavioral criteria based on eye opening ranging from absent, over stimulus-induced to spontaneous sustained eye opening.For instance, every night when falling asleep, we experience a decrease of the level of wakefulness up to the point we lose awareness of our environment. Awareness is more difficult to define and more challenging to assess behaviorally [4]. We have recently proposed to reduce the phenomenological complexity of awareness into two further components: external awareness, namely everything we perceive through our senses (what we see, hear, feel, smell and taste), and internal awareness or stimulusindependent thoughts. Interestingly, the switch between the external and internal milieu was found not only to characterize overt...

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“…3); this finding is also consistent with the mesocircuit model and comparable to a tendency for the more anterior prefrontal cortical regions to demonstrate reduced blood flow under anesthesia, sleep, and even early awakening sleep inertia (34,35). Collectively, these findings support a mechanistic link between the key role of the posterior medial complex in outcomes of DOCs (36), restoration of normal resting metabolic activity (33), and restoration of anterior forebrain mesocircuit function via activity of the c-TH (13,14).…”

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“…95 The DMN was shown to be absent in brain death, 96 but still partially preserved in VS, [97][98][99] probably reflecting residual structural connectivity. 93 At the group level, resting-state network activity revealed reduced interhemispheric connectivity 100 and correlated with levels of consciousness in patients with DOC ( Figure 2). 97 At the single-patient level, however, it fails to reliably distinguish VS from MCS, and contamination by motion or other artefacts can impede the identification of true neuronal activity.…”

“…91,92 Recording of spontaneous fluctuations in BOLD fMRI activity under unstimulated conditions has identified various functional networks, some of which are thought to represent conscious cognitive activity. 71,93,94 The best-studied network is the default mode network (DMN) encompassing the posterior and anterior cortical midline structures, which are considered to be involved in stimulus-independent thought, mind-wandering and self-consciousness. 95 The DMN was shown to be absent in brain death, 96 but still partially preserved in VS, [97][98][99] probably reflecting residual structural connectivity.…”

Assessment of Patient Comfort During Palliative Sedation: Is it always Reliable?

“…Studies based on neuroimaging and electroencephalography have found evidence to support the integrated information theory. This theory states that consciousness depends on the brain's capacity to sustain complex patterns of internal communication [39,40]. Hence, if we are able to measure communication between different brain areas, this may be an indication of the degree of consciousness.…”