Residual cognitive function in comatose, vegetative and minimally conscious states

in Current Opinion In Neurology (2005), 18(6), 726-733

Purpose of review The clinical evaluation of cognition in non-communicative severely brain-damaged patients is inherently difficult. In addition to novel behavioural 'consciousness-scales', the role of ... [more ▼]

Purpose of review The clinical evaluation of cognition in non-communicative severely brain-damaged patients is inherently difficult. In addition to novel behavioural 'consciousness-scales', the role of para-clinical markers of consciousness, such as event related potentials and functional neuroimaging is reviewed. Recent findings New behavioural scales for vegetative and minimally conscious patients have been shown to reduce diagnostic error but regrettably remain underused in clinical routine. Electrophysiological studies have confirmed their role in estimating outcome and possibly cognition. Several recent functional neuroimaging studies have shown residual cortical function in undeniably vegetative patients. This cortical activation, however, seems limited to primary 'low-level' areas and does not imply 'higher-order' integration, considered necessary for conscious perception. Minimally conscious patients show large-scale high-order cerebral activation, apparently dependent upon the emotional relevance of the stimulation. Summary Careful clinical assessment of putative 'conscious behaviour' in vegetative and minimally conscious patients is the first requirement for their proper diagnosis and management. Complementary functional neuroimaging and electrophysiological studies will have a major impact on future clinical decision making and may guide selective therapeutic options. At present, more experimental evidence and the elucidation of methodological and ethical controversies are awaited prior to their routine clinical use. [less ▲]

Death, unconsciousness and the brain

in Nature Reviews Neuroscience (2005), 6(11), 899-909

The concept of death has evolved as technology has progressed. This has forced medicine and society to redefine its ancient cardiorespiratory centred diagnosis to a neurocentric diagnosis of death. The ... [more ▼]

The concept of death has evolved as technology has progressed. This has forced medicine and society to redefine its ancient cardiorespiratory centred diagnosis to a neurocentric diagnosis of death. The apparent consensus about the definition of death has not yet appeased all controversy. Ethical, moral and religious concerns continue to surface and include a prevailing malaise about possible expansions of the definition of death to encompass the vegetative state or about the feared bias of formulating criteria so as to facilitate organ transplantation. [less ▲]

Involvement of both prefrontal and inferior parietal cortex in dual-task performance

in Cognitive Brain Research (2005), 24(2), 237-251

This PET study explored the neural substrate of both dual-task management and integration task using single tasks that are known not to evoke any prefrontal activation. The paradigm included two simple ... [more ▼]

This PET study explored the neural substrate of both dual-task management and integration task using single tasks that are known not to evoke any prefrontal activation. The paradigm included two simple (visual and auditory) discrimination tasks, a dual task and an integration task (requiring simultaneous visual and auditory discrimination), and baseline tasks (passive viewing and hearing). Data were analyzed using SPM99. As predicted, the comparison of each single task to the baseline task showed no activity in prefrontal areas. The comparison of the dual task to the single tasks demonstrated left-sided foci of activity in the frontal gyrus (BA 9/46, BA 10/47 and BA 6), inferior parietal gyrus (BA 40), and cerebellum. By reference to previous neuroimaging studies, BA 9/46 was associated with the coordinated manipulation of simultaneously presented information, BA 10/47 with selection processes, BA 6 with articulatory rehearsal, and BA 40 with attentional shifting. Globally similar regions were found for the integration task, except that the inferior parietal gyrus was not recruited. These results confirm the hypothesis that the left prefrontal cortex is implicated in dual-task performance. Moreover, the involvement of a parietal area in the dual task is in keeping with the hypothesis that a parieto-frontal network sustains executive functioning. [less ▲]

Modulation of brain activity during phonological familiarization

in Brain & Language (2005), 92(3), 320-331

We measured brain activity in 12 adults for the repetition of auditorily presented words and nonwords, before and after repeated exposure to their phonological form. The nonword phoneme combinations were ... [more ▼]

We measured brain activity in 12 adults for the repetition of auditorily presented words and nonwords, before and after repeated exposure to their phonological form. The nonword phoneme combinations were either of high (HF) or low (LF) phonotactic frequency. After familiarization, we observed, for both word and nonword conditions, decreased activation in the left posterior superior temporal gyrus, in the bilateral temporal pole and middle temporal gyri. At the same time, interaction analysis showed that the magnitude of decrease of activity in bilateral posterior temporal lobe was significantly smaller for LF nonwords, relative to words and HF nonwords. Decrease of activity in this area also correlated with the size of behavioral familiarization effects for LF nonwords. The results show that the posterior superior temporal gyrus plays a fundamental role during phonological learning. Its relationship to sublexical and lexical phonological processing as well as to phonological short-term memory is discussed. (c) 2004 Elsevier Inc. All rights reserved. [less ▲]

Time-of-day modulations of rCBF response in functional brain imaging studies: a meta-analysis

in NeuroImage (2005), 26(Suppl. 1),

Neural mechanisms involved in the detection of our first name : A combined ERPs and PET study

in Neuropsychologia (2005), 43(1), 12-19

In everyday social interactions, hearing our own first name captures our attention and gives rise to a sense of self-awareness, since it is one of the most socially self related stimulus. In the present ... [more ▼]

In everyday social interactions, hearing our own first name captures our attention and gives rise to a sense of self-awareness, since it is one of the most socially self related stimulus. In the present study, we combined ERPs and PET scan methods to explore the cerebral mechanisms underlying the detection of our own name. While categorical analyses of PET data failed to reveal significant results, we found that the amplitude of the P3 component, elicited when hearing one's own name, correlates with regional cerebral blood changes in right superior temporal sulcus, precuneus and medial prefrontal cortex. Additionally, the latter was more correlated to the P3 obtained for the subject's name compared to that obtained for other first names. These results suggest that the medial prefrontal cortex plays the most prominent role in self-processing. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

The cognitive modulation of pain: hypnosis- and placebo-induced analgesia.

in Progress in Brain Research (2005), 150

Nowadays, there is compelling evidence that there is a poor relationship between the incoming sensory input and the resulting pain sensation. Signals coming from the peripheral nervous system undergo a ... [more ▼]

Nowadays, there is compelling evidence that there is a poor relationship between the incoming sensory input and the resulting pain sensation. Signals coming from the peripheral nervous system undergo a complex modulation by cognitive, affective, and motivational processes when they enter the central nervous system. Placebo- and hypnosis-induced analgesia form two extreme examples of how cognitive processes may influence the pain sensation. With the advent of modern brain imaging techniques, researchers have started to disentangle the brain mechanisms involved in these forms of cognitive modulation of pain. These studies have shown that the prefrontal and anterior cingulate cortices form important structures in a descending pathway that modulates incoming sensory input, likely via activation of the endogenous pain modulatory structures in the midbrain periaqueductal gray. Although little is known about the receptor systems involved in hypnosis-induced analgesia, studies of the placebo response suggest that the opiodergic and dopaminergic systems play an important role in the mediation of the placebo response. [less ▲]

Human cognition during REM sleep and the activity profile within frontal and parietal cortices: a reappraisal of functional neuroimaging data

in Progress in Brain Research (2005), 150(Boundaries of Consciousness: Neurobiology and Neuropathology), 219-227

In this chapter, we aimed at further characterizing the functional neuroanatomy of the human rapid eye movement (REM) sleep at the population level. We carried out a meta-analysis of a large dataset of ... [more ▼]

In this chapter, we aimed at further characterizing the functional neuroanatomy of the human rapid eye movement (REM) sleep at the population level. We carried out a meta-analysis of a large dataset of positron emission tomography (PET) scans acquired during wakefulness, slow wave sleep and REM sleep, and focused especially on the brain areas in which the activity diminishes during REM sleep. Results show that quiescent regions are confined to the inferior and middle frontal cortex and to the inferior parietal lobule. Providing a plausible explanation for some of the features of dream reports, these findings may help in refining the concepts, which try to account for human cognition during REM sleep. In particular, we discuss the significance of these results to explain the alteration in executive processes, episodic memory retrieval and self representation during REM sleep dreaming as well as the incorporation of external stimuli into the dream narrative. [less ▲]

Two Aspects of Impaired Consciousness in Alzheimer's Disease

in Progress in Brain Research (2005), 150(Boundaries of Consciousness: Neurobiology and Neuropathology), 287-98

Alzheimer's disease (AD) is a degenerative dementia characterized by different aspects of impaired consciousness. For example, there is a deficit of controlled processes that require conscious processing ... [more ▼]

Alzheimer's disease (AD) is a degenerative dementia characterized by different aspects of impaired consciousness. For example, there is a deficit of controlled processes that require conscious processing of information. Such an impairment is indexed by decreased performances at controlled cognitive tasks, and it is related to reduced brain metabolic activity in a network of frontal, posterior associative, and limbic regions. Another aspect of impaired consciousness is that AD patients show variable levels of anosognosia concerning their cognitive deficits. A discrepancy score between patient's and caregiver's assessment of cognitive functions is one of the most frequently used measures of anosognosia. A high discrepancy score has been related to impaired activity in the superior frontal sulcus and the parietal cortex in AD. Anosognosia for cognitive deficits in AD could be partly explained by impaired metabolism in parts of networks subserving self-referential processes (e.g., the superior frontal sulcus) and perspective-taking (e.g., the temporoparietal junction). We hypothesize that these patients are impaired in the ability to see themselves with a third-person perspective (i.e., being able to see themselves as other people see them). [less ▲]

Zerebrale Funktionen bei hirngeschädigten Patienten. Was bedeuten Koma, "vegetative state“, "minimally conscious state“, "Locked-in-Syndrom“ und Hirntod?

in Anaesthesist (2004), 53(12), 1195-1202

Comatose, vegetative, minimally conscious or locked-in patients represent a problem in terms of diagnosis, prognosis, treatment and everyday management at the intensive care unit. The evaluation of ... [more ▼]

Comatose, vegetative, minimally conscious or locked-in patients represent a problem in terms of diagnosis, prognosis, treatment and everyday management at the intensive care unit. The evaluation of possible cognitive functions in these patients is difficult because voluntary movements may be very small, inconsistent and easily exhausted. Functional neuroimaging cannot replace the clinical assessment of patients with altered states of consciousness. Nevertheless, it can describe objectively how deviant from normal the cerebral activity is and its regional distribution at rest and under various conditions of stimulation. The quantification of brain activity differentiates patients who sometimes only differ by a brief and incomplete blink of an eye. In the present paper, we will first try to define consciousness as it can be assessed at the patient's bedside. We then review the major clinical entities of altered states of consciousness encountered in the intensive care unit. Finally, we discuss the functional neuroanatomy of these conditions as assessed by positron emission tomography (PET) scanning. [less ▲]