(Warning: neuroscience weeds)
I’ve discussed global workspace theories (GWT) before, the idea that consciousness is content making it into a global workspace available to a vast array of specialty processes. More specifically, through a neural competitive process, the content excites key hub areas, which then broadcast it to the rest of the specialty systems throughout the cerebral cortex.
A key question is where these hub areas might be. Strictly speaking, in Bernard Baars’ original conception, the location of the workspace is the entire thalamo-cortical system. But often discussion of where the workspace might be is in terms of where the core broadcast hubs are located. Baars, at one time, thought it might be in the midbrain and thalamus complex, although the data hasn’t seemed to bear that out. Stanislas Dehaene, in his global neuronal workspace variant, saw the prefrontal cortex and parietal regions as likely candidates.
A new paper in Nature claims to have narrowed down the locations by studying the flow of information across the brain using a new technique they call NDTE (normalized directed transfer entropy). They use this technique to identify a set of regions they refer to as FRIC:
For this purpose, we propose the concept of a ‘functional rich club’ (FRIC) as the core set of regions, an array of functional hubs that are characterized by a tendency to be more densely functionally connected among themselves than to other brain regions from where they receive integrative information.
So what are the locations of these regions? The results are somewhat surprising:
The GW was found to consist of a core subset of brain regions including the precuneus, posterior and isthmus cingulate, nucleus accumbens, putamen, hippocampus and amygdala.
The first two regions are cortical ones, locations inside the midline area between the cerebral hemispheres, and overall part of the parietal regions. The rest are all subcortical, although part of the forebrain, and heavily interconnected with cortical regions. I find the absence of the thalamus and prefrontal cortex here somewhat striking. The authors go on to mention what the functional roles of these regions are thought to be:
This core functional ‘club’ of integrative brain regions is consistent with the original proposal by Dehaene and Changeux15, which suggests that the global neuronal workspace must integrate past and present through focusing and evaluation. Indeed, Dehaene and Changeux proposed that associative perceptual, motor, attention, memory and value areas interconnect to form a higher-level unified space. For the integration of the past, the hippocampus has been shown to play a key role in many aspects of memory (see, for example, refs. 44,45,46). Similarly, the evaluation of value has been shown to involve the nucleus accumbens (see, for example, refs. 47,48,49), putamen (see, for example, refs. 49,50) and amygdala (see, for example, refs. 49,51,52,53,54). The integration of the past, present and future by processing and attending perceptual information has been strongly associated with the precuneus (see, for example, refs. 55,56,57) and the posterior and isthmus cingulate cortices (see, for example, refs. 49,57,58,59,60). Interestingly, the functions of the precuneus have also been shown to be compromised in coma and vegetative state61.
So, assuming these results hold up, we have an idea of where the central regions of the workspace may reside. (Given that this was published in Nature and likely heavily peer reviewed, I have no particular reason to think they won’t hold up, but this is science and replication will be crucial.) Even if the GWT turns out to be wrong, it seems evident that these regions will need to have crucial roles in whatever theory, or more likely collection of theories, does eventually turn out to be right.
What do you think of these results?