Theoretical Models of Consciousness: A Scoping Review

Abstract

The amount of knowledge on human consciousness has created a multitude of viewpoints and it is difficult to compare and synthesize all the recent scientific perspectives. Indeed, there are many definitions of consciousness and multiple approaches to study the neural correlates of consciousness (NCC). Therefore, the main aim of this article is to collect data on the various theories of consciousness published between 2007-2017 and to synthesize them to provide a general overview of this topic. To describe each theory, we developed a thematic grid called the dimensional model, which qualitatively and quantitatively analyzes how each article, related to one specific theory, debates/analyzes a specific issue. Among the 1130 articles assessed, 85 full texts were included in the prefinal step. Finally, this scoping review analyzed 68 articles that described 29 theories of consciousness. We found heterogeneous perspectives in the theories analyzed. Those with the highest grade of variability are as follows: subjectivity, NCC, and the consciousness/cognitive function. Among sub-cortical structures, thalamus, basal ganglia, and the hippocampus were the most indicated, whereas the cingulate, prefrontal, and temporal areas were the most reported for cortical ones also including the thalamo-cortical system. Moreover, we found several definitions of consciousness and 21 new sub-classifications.

Keywords: cognition; consciousness; consciousness definition; consciousness theory; neural correlates; subjectivity.

Figure 1

Prisma flow diagram.

Figure 2

Graphic representation of the number of articles found for each theory in the period analyzed. ADT: apical dendrite theory; AIM: activation/information/mode-synthesis hypothesis; ART: adaptive resonance theory; AST: attention schema theory; COI: cross-order integration theory of consciousness; CP: centrencephalic proposal; CCS: consciousness state space model; DCT: dynamic core theory; EM/CEMI: electromagnetic field hypothesis/consciousness electromagnetic Information field theory; GWT: global workspace theory; GNW: global neural workspace; HOT/FOR: higher order theories of consciousness/first order representational theory; IIT: integrated information theory; LRMB: layered reference model of the brain; MCTT: memory consciousness and temporality theory; NIH: network inhibition hypothesis; PFT: passive frame theory; PToC: psychological theory of consciousness. Q theories—Orch OR: orchestrated objective reduction theory; single particle consciousness hypothesis; quantum no-go theorems; the three layer model; Koehler’s mathematical approach; timeless and spaceless; the four-dimensional Einstein; RPT: radical plasticity thesis; SPC: semantic pointer competition theory of consciousness; Agnati et al.; Bieberich’s; Damasio; Gelepithis’s; Gurwitsch’s; Min’s; O’Doherty’s; Rejikumar’s. The Mesocircuit hypothesis is not abbreviated.

Figure 3

Graphic representation of the maximum scores obtained in the six dimensions analyzed by each theory. The figures depicted the scores achieved by each theory (displayed in alphabetical order) in each dimension of the dimensional model. We considered the maximum score for each theory among the articles belonging to it. The y-axis represents the scores ranging from 0 to 5. D1 refers to the neural correlates of consciousness dimension. D2 refers to the association between consciousness and other cognitive functions dimension. D3 refers to translation from theory to clinical practice dimension. D4 refers to the quantitative measures of consciousness dimension. D5 refers to consciousness, sensory processes, and the autonomic nervous system dimension. D6 refers to the subjectivity dimension.