The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology


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English Includes bibliographical references and index. Description based on online resource; title from PDF title page ebrary, viewed September 3, Bibliography Electronic books. Illustrated text. Summary The second edition of The Neurology of Consciousness is a comprehensive update of this ground-breaking work on human consciousness, the first book in this area to summarize the neuroanatomical and functional underpinnings of consciousness by emphasizing a lesional approach offered by the study of neurological patients. Since the publication of the first edition in , new methodologies have made consciousness much more accessible scientifically, and, in particular, the study of disorders, disruptions, and disturbances of consciousness has added tremendously to our understanding of the biolo.

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University of Liverpool Library. University of Manchester Library. University of Oxford Libraries. Queen Margaret University Library. Sheffield Hallam University Library. Theoretical frameworks combining all this progress surpass the functional localization of self-related cognition and suggest a dynamic system-level approach to the phenomenological complexity of subjectivity.

Importantly for non-communicating patients suffering from disorders of consciousness, the clinical translation of these technologies will allow medical professionals and families to better comprehend these disorders and plan efficient medical management for these patients. The scientific study of consciousness dictates that there is an intimate relationship between the mind and the brain Feinberg, ; John, ; Freeman, ; Tononi and Laureys, ; Fingelkurts et al. Nevertheless, besides several attempts to define it, consciousness remains a difficult term to describe and different people may think differently about it Demertzi et al.

Here, we will define consciousness in an operational manner, namely consciousness is what is lost during dreamless sleep Tononi, As such, consciousness is a matter of both waking states and experience, so that the less awake we get the less aware we become of our surroundings and ourselves. Based on this definition, patients in coma are not conscious because they cannot be awakened. The linear relationship between wakefulness and awareness is violated in cases of severely brain-damaged patients who are in a vegetative state VS and minimally conscious state MCS.

On the other hand, patients in MCS show fluctuating signs of awareness and non-reflex behaviors, such as visual pursuit and command following Giacino et al. Importantly, in both clinical conditions patients remain unable to communicate with their environment in a functional manner.

Damasio and Meyer, We think that the study of patients with disorders of consciousness offers a unique lesion approach to tackle the necessary neural correlates of self-consciousness. As these patients are not able to communicate or show high-level cognitive function, we will here refer to self-consciousness as to its basic expression. In other words, as self-detection, namely when an organism can respond to stimuli with which is directly implicated or modify its behavior in ways which imply awareness of its own actions Zeman, Therefore, we will here focus on studies employing these neuroimaging methods to study residual self-consciousness in patients with disorders of consciousness.

To date, such functional neuroimaging studies point to the critical recruitment of anterior and posterior midline cerebral areas in experimental paradigms employing self-referential stimuli. Activation of these midline regions is further observed during resting state conditions in healthy volunteers.

This has led to the suggestion of a link between resting state activity and unconstraint self-related mentation. We will review these studies in patients and healthy controls, discuss the involvement of midline areas to the notion of self in patients and will propose that self-related cognition might be a matter of a system-level dynamic activity rather than activation of specific brain areas.

Clinicians are offered with various clinical scales to detect sings of awareness at the bedside Majerus et al. Nonetheless, it is not only a certain behavior that needs to be detected, but the way this is assessed seems to be equally important. For example, when visual pursuit was tested by means of a moving object, a moving person, and a moving mirror, more patients tracked their image in the mirror compared the other two stimuli and were hence considered as in a MCS Vanhaudenhuyse et al.

Similarly, to score sound localization with the Coma Recovery Scale-Revised, patients need to orient their head or eyes toward the source of the sound. To what degree, however, can one claim that these paradigms also reflect the, indirect, assessment of residual self-consciousness in this non-communicating clinical population?

If the cerebral pattern is indistinguishable between the two groups, then one has good reasons to believe that the extracted statistical maps reflect the same construct Owen, Naturally, there are emerging legitimate concerns about the degree of confidence one can have on functional neuroimaging results, especially in the absence of subjective reports e. In addition, our limited understanding of the dynamic neural complexity underlying consciousness and its resistance to quantification in the absence of communication Seth et al.

Nevertheless, the use of these technologies have shed light on the gray zones between the different clinical entities of consciousness and have revealed that not all patients can be considered unresponsive Laureys and Boly, ; Gantner et al. For example, fMRI has been used to assist the diagnosis of patients with disorders of consciousness Coleman et al.

Due to the difficulty to control voluntary eye-opening of patients, most neuroimaging studies employing self-referential stimuli restrict to the auditory modality Table 1. Although caution should be paid on the accurate behavioral evaluation of these patients with standardized tools, like the Coma Recovery Scale-Revised Table 1 , there are cases of unresponsive patients where functional neuroimaging can precede the clinic e.

Taken together, these studies suggest that when activity of the anterior midline areas is recruited using the own name paradigm, this can work as prognostic marker for a review, see Di et al. Table 1. Apart from activation studies utilizing self-referential stimuli, increasing attention has been paid to spontaneous brain activity and its significance to self-related cognition.

During resting state, a set of brain areas encompassing precuneus, medial prefrontal cortex and bilateral temporo-parietal junctions have been shown to work by default, when subjects do not perform any task Gusnard and Raichle, This default mode network DMN of areas in healthy controls has been related to internally oriented cognitive content, such as self-referential or social cognition, mind-wandering, and autobiographical memory recall e.

Such intrinsic cerebral activity also seems to be implicated in consciousness processes. For example, in brain death, where all brainstem reflexes are lost parallel to continuous cessation of respiration, functional connectivity in the DMN is absent Boly et al. Coma patients show no identifiable fMRI DMN connectivity and in those patients where such connectivity can be detected may indicate subsequent recovery of consciousness Norton et al. It has been further proposed that deactivation of the DMN is supposed to reflect interruptions of introspective processes.

Taken together, studies of spontaneous activity in patients suggest that changes in the DMN functional connectivity could suggest modified self-related conscious mentation. Indeed, it has been suggested that in normal waking conditions, resting state activity in the posterior cingulate, and frontal areas accounts for self-referential thoughts Whitfield-Gabrieli et al.

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Therefore, it could be inferred that decreased connectivity in these midline regions of the DMN reflects, at least to certain degree, restricted abilities for self-referential processing in patients with disorders of consciousness. Figure 1. Of note is that patients who have emerged from the minimally conscious state who yet experience confusion and amnesia syndromes show metabolic dysfunction only in the posterior cingulate and adjacent retrosplenial cortex but not in the lateral frontoparietal network see text.

Finally, fully conscious yet severely paralyzed patients with locked-in syndrome do not show metabolic impairment in any of these areas, suggesting a critical involvement of midline regions in supporting self-related cognition figure adapted from Thibaut et al. Previous studies showed that these two systems are of a competing character in the sense that they can disturb or even interrupt each other e.

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The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology by Steven Laureys

Such anticorrelated pattern is also illustrated in activation studies on motor performance Fox et al. We have recently proposed that these two systems may account for the phenomenological complexity of awareness. Interestingly, the switch between the external and internal milieu was found not only to characterize overt behavioral reports but also had a cerebral correlate Vanhaudenhuyse et al. Conversely, subjective ratings for external awareness correlated with the activity of lateral fronto-parieto-temporal regions.

The Neurology of Consciousness

These findings highlight that the anticorrelated pattern between the internal and external awareness system is of functional relevance to conscious cognition. Indeed, in an altered conscious state like hypnosis, where subjects report awareness alterations but remain fully responsive, hypnosis-related reductions in functional connectivity were shown in the external awareness system parallel to subjective ratings of increased sense of dissociation from the environment and reduced intensity of thoughts about external events Demertzi et al.

Similar reductions in external awareness systems have been also shown for non-responsive conditions, such as deep sleep and anesthesia for a review, see Heine et al. Recent PET data indicate that recovery of MCS patients seems to be accompanied by a right-lateralized recovery of the external awareness network whereas the presence of command following, defining the MCS plus Bruno et al.

Similar results have been observed in slow wave sleep and general anesthesia for review, see Boveroux et al. Interestingly, these findings are also confirmed in transient dissociative states of unresponsive wakefulness, such as absence seizures, complex partial seizures, or sleepwalking — all characterized by preserved automatic reflex motor behavior in the absence of response to commands and showing transient impaired activity in these fronto-temporo-parietal associative areas Laureys, ; Blumenfeld, According to a suggested framework taking the external and internal awareness systems into account, two complementary states of system imbalance are possible, where one system can be in a hyperfunctional state, while the other is hypoactive.

A state where both extrinsic and intrinsic systems are hypofunctional is predicted to lead to markedly impaired consciousness as seen in disorders of consciousness Soddu et al. A more recent proposal, adopting a similar system-level approach, points to the functional separation of the dorsal and ventral subcomponents of the posterior cingulate cortex PCC : the ventral PCC appears to be highly integrated within the DMN, and is involved in internally directed cognition e.

The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology
The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology
The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology
The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology
The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology
The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology
The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology
The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology
The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology

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