Intrinsic Brain Activity in Altered States of Consciousness

Abstract

Spontaneous brain activity has recently received increasing interest in the neuroimaging community. However, the value of resting-state studies to a better understanding of brain-behavior relationships has been challenged. That altered states of consciousness are a privileged way to study the relationships between spontaneous brain activity and behavior is proposed, and common resting-state brain activity features observed in various states of altered consciousness are reviewed. Early positron emission tomography studies showed that states of extremely low or high brain activity are often associated with unconsciousness. However, this relationship is not absolute, and the precise link between global brain metabolism and awareness remains yet difficult to assert. In contrast, voxel-based analyses identified a systematic impairment of associative frontoparieto-cingulate areas in altered states of consciousness, such as sleep, anesthesia, coma, vegetative state, epileptic loss of consciousness, and somnambulism. In parallel, recent functional magnetic resonance imaging studies have identified structured patterns of slow neuronal oscillations in the resting human brain. Similar coherent blood oxygen level-dependent (BOLD) systemwide patterns can also be found, in particular in the default-mode network, in several states of unconsciousness, such as coma, anesthesia, and slow-wave sleep. The latter results suggest that slow coherent spontaneous BOLD fluctuations cannot be exclusively a reflection of conscious mental activity, but may reflect default brain connectivity shaping brain areas of most likely interactions in a way that transcends levels of consciousness, and whose functional significance remains largely in the dark.

Brain functional integration decreases during propofol-induced loss of consciousness

“…Results show that deep sedation was associated with reduced interactions between all these associative cortices. This finding suggests that coherent integration among frontoparietal cortices is important in the generation of conscious perception (Boly et al, 2008;Dehaene et al, 2006;Rees et al, 2002). However, as indicated by a larger decrease in IDPC, the functional interactions of parietal areas were deteriorated to a significantly larger extent than those of frontal or temporal areas.…”

BOLD correlates of EEG topography reveal rapid resting-state network dynamics

“…The latter is supported by the fact that the main nodes of the DMN are already present at birth (Fransson et al, 2007) and that they form the main nodes of the structural core of the cerebral cortex (Hagmann et al, 2008). Moreover, the DMN can also be identified in sleep and coma (Boly et al, 2008) and the anesthetized monkey (Vincent et al, 2007).…”

Functional connectivity MRI in infants: Exploration of the functional organization of the developing brain

“…RSNs incorporating higher order functional systems and primary sensory systems have been identified in pediatric and adult subjects during different levels of sleep, under anesthesia, and in coma, indicating correlations are not obliterated by these conditions (Kiviniemi, Jauhiainen et al 2000; Kiviniemi, Haanpaa et al 2005; Fukunaga, Horovitz et al 2006; Redcay, Kennedy et al 2007; Boly, Phillips et al 2008; Greicius, Kiviniemi et al 2008; Horovitz, Fukunaga et al 2008; Horovitz, Braun et al 2009; Larson-Prior, Zempel et al 2009; Martuzzi, Ramani et al 2010; Mhuircheartaigh, Rosenorn-Lanng et al 2010). However, effects of level of arousal on neural network detection remains incompletely understood, with correlation strength modulated in a network specific manner by state (Greicius, Kiviniemi et al 2008; Horovitz, Braun et al 2009; Mhuircheartaigh, Rosenorn-Lanng et al 2010).…”