In a nutshell: This finding will help work out the role of a mysterious sheet of brain cells, called the claustrum. Is it a brain “orchestrator”, helping create our seamless experience of the world? A traffic controller? Or something else entirely?

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The big picture

How the brain creates a single experience from many inputs — for example, when we think, read, drink a cup of tea, imagine, all at the same time — is still a mystery. It’s especially puzzling because information from different inputs spreads through the brain at different speeds.

About ten years ago, two neuroscientists suggested that the claustrum might be key, acting as a “orchestra conductor” of activity in the cortex, the crinkled outer brain that’s critical for impressive feats such as conscious thought and language.

“It lit a fire under a lot of people. The claustrum had been overlooked until then,” says David Reser, one of the authors of the paper here.

Reser and others went on to hypothesise an alternative job for the claustrum: traffic controller. In this role, the claustrum would help shift priority from, say, the networks in the cortex responding to the book on your lap, to the networks responding to the tiger creeping up behind you. These shifts would help determine subjective experience: peacefully reading, panicking because of the tiger.

Evidence for either the conductor or traffic controller role includes the claustrum’s shape and location: it is a bedsheet-thin sliver of cells that connects to practically every nook and cranny of the cortex. The research described in this paper shows a pattern to those connections, with the ones that go to parts of the cortex that deal with attention, planning and strategy being separate to those that go to parts that deal with movement and sensation.

Other clues come from what activates the claustrum. Listening to sad music —but only if it has lyrics. Being sexually aroused (if you are a man, but not a woman) — but only if you are also looking at sexually explicit images. Seeing a Chinese pictogram — but only if you also understand its meaning. This suggests the claustrum is helping bring together related brain activity from different inputs.

So, too, does the fact that the claustrum in often reduced in size in people who have abnormal experiences of consciousness, for example, in schizophrenia with delusions and visual hallucinations.

Next steps:
The claustrum’s complicated shape and thinness has made it difficult to study in the past. Studies like this create a map of the claustrum’s neural connections. Combined with increasingly powerful brain imagers, that will make it easier to work out the claustrum’s job by watching how its activity ebbs and flows in synchrony with activity in other parts of the brain as a person has different experiences.

Reser, D. H., Richardson, K. E., Montibeller, M. O., Zhao, S., Chan, J. M., Soares, J. G., Chaplin, T. A., Gattass, R., and Rosa, M. G. P. (2014). Claustrum projections to prefrontal cortex in the capuchin monkey (Cebus apella). Frontiers in Systems Neuroscience 8:123.

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