Vanderbilt University researchers have found evidence that awareness or consciousness results from widespread communication across sensory and association areas of the cortex — challenging previous hypotheses that changes in restricted areas of the brain were responsible for producing awareness.

“Identifying the fingerprints of consciousness in humans would be a significant advancement for basic and medical research, let alone its philosophical implications on the underpinnings of the human experience,” said René Marois, professor and chair of psychology at Vanderbilt University and senior author of the study.

“Many of the cognitive deficits observed in various neurological diseases may ultimately stem from changes in how information is communicated throughout the brain.”

The researchers used graph theory, a branch of mathematics concerned with explaining the interactive links between members of a complex network, such as social networks or flight routes, to characterize how connections between the various parts of the brain were related to awareness.

Their findings were published March 9 in the Proceedings of the National Academy of Sciences.

Whole-brain awareness

In the experiment, participants in a functional magnetic resonance imaging (fMRI) scanner were asked to detect a disk that was briefly flashed on a screen. In each trial, participants responded whether they were able to detect the target disk and how much confidence they had in their answer. Experimenters then compared the results of the high-confidence trials during which the target was detected to the trials when it was missed by participants. These were treated as “aware” and “unaware” trials, respectively.

They found that no one area or network of areas of the brain stood out as particularly more connected during awareness of the target; the whole brain appeared to become functionally more connected following reports of awareness.

“We know there are numerous brain networks that control distinct cognitive functions such as attention, language and control, with each node of a network densely interconnected with other nodes of the same network, but not with other networks,” Marois said. “Consciousness appears to break down the modularity of these networks, as we observed a broad increase in functional connectivity between these networks with awareness.”

The research suggests that consciousness is likely a product of this widespread communication, and that we can only report things that we have seen once they are being represented in the brain in this manner. Consciousness appears to be an emergent property of how information that needs to be acted upon gets propagated throughout the brain.

“We take for granted how unified our experience of the world is. We don’t experience separate visual and auditory worlds, it’s all integrated into a single conscious experience,” Godwin said. “This widespread cross-network communication makes sense as a mechanism by which consciousness gets integrated into that singular world.”

The research was funded by two National Institutes of Health grants.

Abstract of Breakdown of the brain’s functional network modularity with awareness

Neurobiological theories of awareness propose divergent accounts of the spatial extent of brain changes that support conscious perception. Whereas focal theories posit mostly local regional changes, global theories propose that awareness emerges from the propagation of neural signals across a broad extent of sensory and association cortex. Here we tested the scalar extent of brain changes associated with awareness using graph theoretical analysis applied to functional connectivity data acquired at ultra-high field while subjects performed a simple masked target detection task. We found that awareness of a visual target is associated with a degradation of the modularity of the brain’s functional networks brought about by an increase in intermodular functional connectivity. These results provide compelling evidence that awareness is associated with truly global changes in the brain’s functional connectivity.