Recent research suggests that there's no one location in the brain that causes consciousness, pointing to a network phenomenon. However, tracing the various linkages between regions in the brain networks that give rise to awareness and wakefulness has been elusive.
A new approach using functional MRI, an imaging technique that allows you to see and measure brain activity through changes in blood flow over time, provides new insight into how we describe and study conscious states.
When it comes to consciousness, these dimensions can include 1) arousability, that is, the ability of the brain to be awake; 2) awareness, or what we actually experience, like the redness of a rose; and 3) sensory organization, or how sights and sounds and feelings become woven together to create our seamless conscious experience.
Typically, brain imaging studies assess discrete, well-defined brain areas. To understand this, consider the state of Colorado on a map of the United States. It has very clear boundaries in an almost rectangular shape.
However, the borders separating, for example, Colorado and Wyoming, are arbitrary. By contrast, looking at the topology of the mountains across Colorado and Wyoming give you a more informative, natural view of the region. The investigators did something very similar in this neuroimaging study: instead of looking at clearly defined brain regions, they investigated the topology or gradients across brain regions.
To develop a map of these so-called cortical gradients of consciousness, the team used fMRI data from study participants who were awake, anesthetized, in a form of coma, or who had psychiatric diagnoses such as schizophrenia.
The team was then able to arrange recordings from 400 different brain regions into gradients and compare how they change in relation to these states or diagnoses. They found three cortical gradients that seemed to align with the dimensions of consciousness, including arousability, awareness, and sensory organization.
