In my previous posts, I've looked at a lot of potential medical applications of Salvia; but now I want to return to the consciousness-altering effects of the plant. After all, when this entheogen was first discovered, it was being used in a religious context by the Mazatecs of Central America (Valdes et al. 1983). Salvia divinorum was grown in highly guarded groves, with shamans and their initiates drinking it in a tea and chewing the leaves. These highly religious rituals were intended to induce visions of angels; hence the local name for the plant, "ska Maria Pastora", meaning "leaves of Mary the shepherdess". Modern recreational use of Salvia, commonly through smoking dried leaf, is often motivated by a desire to explore an altered state of consciousness or induce a spiritual epiphany (Baggott et al. 2010). This means that people separated by generations, cultures and continents have used Salvia for its consciousness-altering properties.

Salvia's effects on consciousness are so profound and unusual that scientists have started using them to study the nature of consciousness. Here I'll give an overview of a popular theory of how consciousness is organised in the brain, and how the effects of Salvia on consciousness lend support to this theory.

The claustrum; a conductor of consciousness

Figure 1: Claustrum Location

Figure 1: Location of the claustrum.The claustrum is a thin sheet that sits near the centre of the brain, and receives inputs from many important brain areas such as the prefrontal, motor and visual cortices.

Francis Crick is best known for his contributions to the discovery of the molecular structure of DNA; but in his later life he became interested in neurobiology and consciousness. Just before his death he wrote a manuscript with Cristof Koch, suggesting that one area of the brain was particularly important for coordinating consciousness (Crick and Koch 2005). This area, called the claustrum, sits deep within the centre of the brain, a thin strip comprising a very small fraction of total brain volume (figure 1). In fact, its name means "hidden away". It is thought to have an important role in consciousness because it sends out connections to many areas of the brain, and receives many back. In particular, its connections are sent to and received from areas of the brain known to have important roles in aspects of perception, like the visual, motor and auditory cortices. Brain imaging studies in humans have shown that the claustrum is activated when participants perform tasks requiring multiple sensory inputs. Crick and Koch's theory, therefore, is that the claustrum sits amidst all our many perceptions of the outside world and binds them all together with our thoughts to create 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.

The problem, say Crick & Koch, is that no one has yet managed to effectively shut down the claustrum to observe what happens to consciousness when this "conductor" is not there to hold it all together. They suggest genetic modifications or multiple injections of inhibitors might be the only means of achieving this; but this is where Salvia presents a unique alternative…

Salvinorin A and the claustrum

Figure 2: Kappa-opioid receptors are highly expressed in the claustrum.

Figure 2: Kappa-opioid receptors are highly expressed in the claustrum. Here, KORs have been stained a dark colour, showing their high density in the claustrum (Cl), outlined in purple. Figure from Peckys & Landwehrmeyer (1999).

As we already know, the main action of Salvinorin A in the brain is the activation of the kappa-opioid receptor (KOR). It just so happens that one of the largest concentrations of KOR is found in the claustrum (Figure 2 (Peckys and Landwehrmeyer 1999)). Therefore Salvinorin A will be acting on these receptors and inhibiting the normal activity of the claustrum, releasing consciousness from its control and altering perception dramatically (Stiefel et al. 2014). Stiefel's group examined many Salvia trip reports on Erowid, finding that users lose their sense of body ownership and lose perception of the outside world. This can be attributed to Salvinorin A's inhibition of the claustrum; especially since there are many connections between the claustrum and the tempo-parietal cortical junction, an area of the brain strongly associated with the sense of body ownership and self-location (Ionta et al. 2011). Stiefel and his colleagues conclude that Salvinorin A shows us what happens when consciousness is released from the control of the claustrum.

Salvinorin A in other brain areas

Although the area of the brain with the highest concentration of KORs is the claustrum, it is by no means the only place they can be found. KORs are also found to be expressed in areas of the brain associated with movement (the cerebellum) and external perception (the thalamus), and have also been found in areas of the spinal cord linked to pain sensation (Simonin et al. 1995). KORs are also found in the hippocampus, an area of the brain important in memory, and these hippocampal KORs are found abnormally distributed in Schizophrenia, suggesting the involvement of the kappa-opioid system in the disease (Tejeda et al. 2012).

Conclusions

The role of the claustrum in consciousness is a relatively new theory and our understanding of how it organises our perception is still poor. Interestingly, the psychedelic effects of Salvinorin A consumption may give researchers vital clues about the importance of this brain area. Understanding how consciousness is generated in the brain will not only help us treat psychiatric disorders, it will also help us understand the nature of our existence.

References

Baggott MJ, Erowid E, Erowid F, Galloway GP, Mendelson J. (2010) Use patterns and self-reported effects of Salvia divinorum: an internet-based survey. Drug and alcohol dependence 111(3):250-256.

Crick FC, Koch C. (2005) What is the function of the claustrum? Philosophical transactions of the Royal Society of London Series B, Biological sciences 360(1458):1271-1279.

Ionta S, Heydrich L, Lenggenhager B, Mouthon M, Fornari E, Chapuis D, Gassert R, Blanke O. (2011) Multisensory mechanisms in temporo-parietal cortex support self-location and first-person perspective. Neuron 70(2):363-374.

Peckys D, Landwehrmeyer GB. (1999) Expression of mu, kappa, and delta opioid receptor messenger RNA in the human CNS: a 33P in situ hybridization study. Neuroscience 88(4):1093-1135.

Simonin F, Gaveriaux-Ruff C, Befort K, Matthes H, Lannes B, Micheletti G, Mattei MG, Charron G, Bloch B, Kieffer B. (1995) kappa-Opioid receptor in humans: cDNA and genomic cloning, chromosomal assignment, functional expression, pharmacology, and expression pattern in the central nervous system. Proceedings of the National Academy of Sciences of the United States of America 92(15):7006-7010.

Stiefel KM, Merrifield A, Holcombe AO. (2014) The claustrum's proposed role in consciousness is supported by the effect and target localization of Salvia divinorum. Frontiers in integrative neuroscience 8:20.

Tejeda HA, Shippenberg TS, Henriksson R. (2012) The dynorphin/kappa-opioid receptor system and its role in psychiatric disorders. Cellular and molecular life sciences : CMLS 69(6):857-896.

Valdes LJ, 3rd, Diaz JL, Paul AG. (1983) Ethnopharmacology of ska Maria Pastora (Salvia divinorum, Epling and Jativa-M.). Journal of ethnopharmacology 7(3):287-312.