A new Johns Hopkins study, looking at how psilocybin influences a mysterious brain region called the claustrum, is just one of several compelling recent articles shining a light on how our brains generate our experience of consciousness.
In 2004, Francis Crick, one of the 20th century’s greatest scientific minds, died of colon cancer. Crick was best known for describing the structure of DNA in the 1950s with collaborator James Watson, but over the last couple of decades of his life his research focused on perhaps the biggest scientific question of them all: how does our brain generate what we consider to be consciousness?
The last paper Crick ever penned homed in on a small and still relatively mysterious brain region called the claustrum. Co-authored with Christof Koch, Crick was reportedly still editing the manuscript in hospital the day he died. Subsequently published in 2005, the paper presented a novel hypothesis – the claustrum may be key to our experience of consciousness, unifying and co-ordinating disparate brain areas to help generate our singular experience.
“The claustrum is a thin, irregular, sheet-like neuronal structure hidden beneath the inner surface of the neocortex in the general region of the insula,” wrote Crick and Koch in the landmark paper. “Its function is enigmatic. Its anatomy is quite remarkable in that it receives input from almost all regions of cortex and projects back to almost all regions of cortex.”
The extraordinarily unique way the claustrum connects different brain regions fascinated Crick. While some researchers had previously suggested the claustrum could potentially be the brain’s epicenter of consciousness, Crick and Koch presented a different analogy to describe the role of this mysterious brain region.
“We think that a more appropriate analogy for the claustrum is that of a conductor coordinating a group of players in the orchestra, the various cortical regions,” the pair wrote. “Without the conductor, the players can still play but they fall increasingly out of synchrony with each other. The result is a cacophony of sounds.”
It’s like a highway
A new study, published in the journal Current Biology, is describing in unprecedented detail how the claustrum communicates with other brain regions. The project, an international collaboration between researchers in Sweden and Singapore, somewhat backs up Crick’s “consciousness conductor” hypothesis, revealing the claustrum is less like a singular hub for cortical inputs and more like a collection of specialized synaptic pathways connecting specific cortical regions.
“We found that the synaptic connectivity between the cortex and claustrum is in fact organized into functional connectivity modules, much like the European route E4 highway or the underground system,” says Gilad Silberberg, lead author on the study, from the Karolinska Institutet.
Another recent and even more focused study zoomed in on the claustrum’s role in coordinating slow-wave brain activity. A team from Japan’s RIKEN Center for Brain Science generated a transgenic mouse model in which they could artificially activate neurons in the claustrum through optogenetic light stimulation.
… it is so exciting that we are getting closer to linking specific brain connections and actions with the ultimate puzzle of consciousness.
The research discovered slow-wave activity across a number of brain regions increased in tandem with neural firing in the claustrum. Slow-wave brain activity is most often linked to a key period of sleep associated with memory consolidation and synaptic homeostasis.
“We think the claustrum plays a pivotal role in triggering the down states during slow-wave activity, through its widespread inputs to many cortical areas,” says Yoshihiro Yoshihara, team leader on the new RIKEN research. “The claustrum is a coordinator of global slow-wave activity, and it is so exciting that we are getting closer to linking specific brain connections and actions with the ultimate puzzle of consciousness.”
So, if increased claustrum activity seems to orchestrate a kind of synchronized slowing down of brain activity across a number of different cortical regions, what happens when claustrum activity is suppressed?