Despite an extraordinary array of scientific discoveries advancing our understanding of the human body, we still know remarkably little about the brain in general, and the nature of consciousness in particular. Setting aside centuries of philosophizing over what actually defines a conscious mind, neuroscientists are only now grappling with how our brains generate conscious awareness.

The goal of this new research was to try to identify a variety of neural signatures that can effectively indicate the presence of consciousness. This could, for example, allow doctors to differentiate conscious and unconscious patients suffering from brain injuries in cases where individuals are unable to communicate.

The research involved over 150 subjects, who were studied using functional magnetic resonance imaging (fMRI). Some subjects scanned were patients in diagnosed vegetative states, while others were healthy individuals. The researchers ultimately discovered four specific neural activity patterns that could distinguish a person's place on a spectrum from conscious to unconscious.

The most complex pattern identified dynamic communication across 42 different brain regions. This highly active pattern of long-distance, brain-wide coordination was primarily seen in healthy, awake and aware subjects. At the other end of the spectrum, the fourth, and least complex pattern reflected fewer long-distance connections in the brain. This pattern was often seen in completely vegetative patients.

Interestingly, the research revealed many subjects fluctuated between different neural patterns. For example, some subjects in vegetative states did indicate brief flashes of more complex neural activity, similar to the most active pattern. This implies that some vegetative, and seemingly unconscious patients may enter brief states of consciousness. This active conscious pattern was primarily activated in vegetative patients after they were asked to mentally picture an image or activity.

Subjects were also scanned while sedated with the general anesthetic propofol. In that completely sedated state any complex neural patterning disappeared, with both healthy and vegetative subjects displaying the least active neural pattern.

"Importantly, this complex pattern disappeared when patients were under deep anesthesia, confirming that our methods were indeed sensitive to the patients' level of consciousness and not their general brain damage or external responsiveness," writes Davinia Fernández-Espejo, one of the authors on the study.

The most immediate outcome from this research is the promise of offering doctors, and families, a better way to understand whether a completely non-responsive patient is still capable of conscious thought. Another promising prospect arising from this research is the suggestion that consciousness could be artificially altered using methods that force the brain into generating different neural signatures.

"In the future it might be possible to develop ways to externally modulate these conscious signatures and restore some degree of awareness or responsiveness in patients who have lost them, for example by using non-invasive brain stimulation techniques such as transcranial electrical stimulation," suggests Fernández-Espejo.

The new research was published in the journal Science Advances.