A collaboration between University Pompeu Fabra, University of Oxford and Center for Music in the Brain at Aarhus University has shed new light on the nature of consciousness.

08.01.2021 | Hella Kastbjerg

Revisiting the Global Workspace orchestrating the hierarchical organisation of the human brain

The celebrations in the 250th anniversary of the birth of Ludwig van
Beethoven would not be the same without Herbert von Karajan's brilliant
performances conducting Beethoven's memorable symphonies. The execution
of any musical symphony is a hugely difficult task, demanding very
significant skills on the part of each individual musician – but perhaps
the most difficult task lies with the conductor who has to orchestrate
the musicians into making the music cohesively come alive and speak to
our deepest emotions.

In many ways the human brain is like an orchestra, where different
regions perform very different types of processing, such as in the
individual musician in the orchestra who needs to be able to read the
music, play their instrument and listen to the music produced. Still,
the role of the conductor is different, namely to coordinate and
orchestrate the output of each musician into a cohesive whole. Without a
conductor, the music invariably fails – as shown beautifully in
Fellini’s magisterial film "Prova d'orchestra" (eng. "Musical rehearsal").

It has been proposed that the human brain is similar to an orchestra in
that it is hierarchically organised but that there is unlikely to be
just a single conductor. Instead, in 1988 psychologist Bernard Baars
proposed the concept of a 'global workspace', where information is
integrated in a small group of 'conductors' before being broadcast to
the whole brain. This much celebrated theory proposes an elegant
solution to how hierarchical organisation allows the brain to
orchestrate function and behaviour by organising the flow of information
and the underlying computations necessary for survival. As such, this is
a theory of consciousness as pointed out by neuroscientists Stanislas
Dehaene and Jean-Pierre Changeux, who proposed the 'global neuronal
workspace' hypothesis where associative perceptual, motor, attention,
memory, and value areas interconnect to form a higher-level unified
space where information is broadly shared and broadcast back to
lower-level processors. Colloquially, the brain’s global workspace is
thus akin to a small core assembly of people in charge of an
organisation; in other words like a group of many Von Karajans leading a
musical orchestra.

Yet, until now it has not been known where and how this orchestration
takes place in the human brain. It is only with the new paper
"Revisiting the Global Workspace orchestrating the hierarchical
organisation of the human brain" published in the leading open-access
journal Nature Human Behaviour on Monday 4th of January 2021 that
researchers have discovered the existence of a functional 'rich club' of
brain regions incarnating this 'global workspace'. This radical new
discovery resulted from Profs Gustavo Deco and Morten L Kringelbach's
international collaboration between Center for Brain and Cognition at
University Pompeu Fabra, Barcelona (Spain) and Department of Psychiatry,
University of Oxford (UK) and Center for Music in the Brain, University
of Aarhus. Based on a large dataset of over 1000 human participants with
functional magnetic resonance imaging (fMRI) recordings, the findings
have shed new light on the nature of consciousness.

Prof Deco says: "To identify the global workspace, we determined the
information flow between brain regions by means of a normalised directed
transfer entropy framework applied to multimodal neuroimaging data a
large group of healthy participants. This revealed for the first time a
set of unique brain regions orchestrating information from perceptual,
long-term memory, evaluative and attentional systems across many
different tasks. Furthermore, we confirmed the causal significance and
robustness of our results by systematically lesioning a generative
whole-brain model".

Prof Kringelbach adds: "Our findings shed light on a major unsolved
challenging problem in neuroscience. While the results presented here
pertain to the global workspace of conscious task processing, future
work could use our framework to investigate other states such as sleep
and anaesthesia, allowing for a direct comparison with other theories of
consciousness. Equally, our framework could be used to investigate
unbalanced brain states in neuropsychiatric disorders and be used to
perturb and rebalance the model to identify novel optimal, causal paths
to health".  

The paper is avaiable here:

https://www.nature.com/articles/s41562-020-01003-6#citeas