The aptly-named ‘hard problem’ of consciousness: why do we experience? Why do we perceive colours and sounds? Why do we feel emotions?

On the surface, we can track the mechanical basis of all these sensations. We can look at a network of firing neurons and say, “there, that’s the perception of the colour red”. But we can’t explain how that links to our actual experience of the colour red. We currently have no neurobiological or physical explanation for how subjective experience results from complex systems of neurons.

It seems as if there is no reason why subjective perception would have evolved in us. We just don’t need it. To escape a predator, I just need my brain to recognize a rustle in the bushes and make my legs move. To stop at a red light, I just need my neurons doing their jobs of recognizing the colour red, and pushing on the brake pedal. Where does my subjective perception of these events actually matter? On the surface, I am no different from a robot.

One of the discoverers of the structure of DNA, Francis Crick, became interested in this ‘hard problem’ of consciousness. Just before his death he wrote a manuscript with Cristof Koch, suggesting that one area of the brain was particularly important for generating consciousness. This area, called the claustrum (meaning ‘hidden away’), is a thin strip of neurons that sits deep within the centre of the brain. It sends out connections to many areas of the brain, and receives many back. In particular, it connects areas of the brain known to have important roles in aspects of perception: vision, movement and hearing.

Brain imaging studies have shown that the claustrum is activated when participants perform tasks requiring multiple senses. Crick and Koch’s theory is that the claustrum sits amidst all our many perceptions of the outside world and binds them all together, creating one coherent consciousness. In their words, they see the claustrum as a conductor of an orchestra; all the individual sections need to play in synchrony for the overall result to make any sense.

What might happen if we shut down the claustrum? If we lose the conductor of the orchestra of consciousness?

Amazingly, there’s a psychedelic drug that does just that. Salvia divinorum is a herb that’s been used in traditional healing rituals for centuries. Its main psychoactive compound, Salvinorin A, binds to receptors in the claustrum and shuts it down. So what happens when consciousness is released from the control of the claustrum?

One study of individuals’ reports of the Salvia psychedelic experience found that users lose their sense of body ownership and lose perception of the outside world. This is typical of many psychedelics; losing the sense-of-self, commonly known as ‘ego dissolution’. Another typical experience is the merging of senses, or synaesthesia; hearing light or feeling sound. Perhaps without the control of the claustrum, consciousness becomes unregulated and unusual connections are made. Although Salvia is the only psychedelic with a confirmed link to the claustrum, it’s likely that other psychedelics alter this consciousness conduit.

Many skeptics will argue that understanding the claustrum will not bring us any closer to answering the hard problem of consciousness. Although the claustrum may bind our perceptions together, we still can’t pinpoint the link between our physical brains and subjective experience.

Maybe the hard problem is something that can’t be answered with science at all. Maybe subjective experience is an epiphenomenon, a byproduct of matter, which by definition can’t be measured or viewed.

For the moment, we continue to use science to try and understand the mind; and the claustrum may be an important stepping stone on our way to solving the hard problem.