Precuneus–Prefrontal Activity during Awareness of Visual Verbal Stimuli

doi:10.1006/ccog.2001.0509

Consciousness and Cognition

Volume 10, Issue 3, September 2001, Pages 356-365

https://doi.org/10.1006/ccog.2001.0509 Get rights and content

Abstract

Awareness is a personal experience, which is only accessible to the rest of world through interpretation. We set out to identify a neural correlate of visual awareness, using brief subliminal and supraliminal verbal stimuli while measuring cerebral blood flow distribution with H₂¹⁵O PET. Awareness of visual verbal stimuli differentially activated medial parietal association cortex (precuneus), which is a polymodal sensory cortex, and dorsolateral prefrontal cortex, which is thought to be primarily executive. Our results suggest participation of these higher order perceptual and executive cortical structures in visual verbal awareness.

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Citation Excerpt :
The first is the left precuneus, a key hub structure from the default mode network (DMN). The precuneus is engaged in self-related processing (Zhang and Chiang-shan, 2012), episodic memory (Ren et al., 2018), awareness and conscious information processing (Kjaer et al., 2001; Long et al., 2016; Vogt and Laureys, 2005). Also, it has been shown that patients with UWS having residual functional connectivity of DMN and external awareness networks might be misdiagnosed, since such functional connectivity is an indicator of covert consciousness (Naro et al., 2017).
Increasing evidence links disorders of consciousness (DOC) with disruptions in functional connectivity between distant brain areas. However, to which extent the balance of brain network segregation and integration is modified in DOC patients remains unclear. Using high-density electroencephalography (EEG), the objective of our study was to characterize the local and global topological changes of DOC patients' functional brain networks.
Resting state high-density-EEG data were collected and analyzed from 82 participants: 61 DOC patients recovering from coma with various levels of consciousness (EMCS (n = 6), MCS+ (n = 29), MCS- (n = 17) and UWS (n = 9)), and 21 healthy subjects (i.e., controls). Functional brain networks in five different EEG frequency bands and the broadband signal were estimated using an EEG connectivity approach at the source level. Graph theory-based analyses were used to evaluate their relationship with decreasing levels of consciousness as well as group differences between healthy volunteers and DOC patient groups.
Results showed that networks in DOC patients are characterized by impaired global information processing (network integration) and increased local information processing (network segregation) as compared to controls. The large-scale functional brain networks had integration decreasing with lower level of consciousness.
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Electromagnetic and transmitter manipulation have demonstrated that the network is not an epiphenomenon but instrumental in generation of self-awareness. Thus, transcranial magnetic stimulation (TMS) targeting the hubs impedes different aspects of self-awareness with a latency of 160 ms. The network is linked by ∼40 Hz oscillations and regulated by dopamine.
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^☆: The study was supported by the Danish Ministry of Social Affairs. The cyclotron, PET scanner, and MR scanner were donated by the John & Birthe Meyer Foundation. We thank the staff at the PET and cyclotron unit for extreme help and flexibility and Ole Norling, The Danish National Dictionary, for providing the word bank.

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Regular ArticlePrecuneus–Prefrontal Activity during Awareness of Visual Verbal Stimuli☆

Abstract

Current Opinion in Neurobiology

Neuroscience Letters

Neuroimage

Cognitive Brain Research

Cognitive Psychology

Cognitive Psychology

Frontoparietal cortical networks for directing attention and the eye to visual locations: Identical, independent, or overlapping neural systems?

Proceedings of the National Academy of Sciences of the USA

Are we aware of neural activity in primary visual cortex?

Nature

Imaging unconscious semantic priming

Nature

Regular Article
Precuneus–Prefrontal Activity during Awareness of Visual Verbal Stimuli☆