Where does the mind ‘meet’ the brain? While there’s no shortage of research into the effects of psychedelics, drugs like LSD still have much to teach us about the way the brain operates – and can shine a light on the mysterious interface between consciousness and neural physiology, research suggests.

In a new study investigating the effects of LSD on volunteers, scientists found that the psychedelic enables the brain to function in a way beyond what anatomy usually dictates, by altering states of dynamic integration and segregation in the human brain.

“The psychedelic compound LSD induces a profoundly altered state of consciousness,” explains first author and neuroscience researcher Andrea Luppi from the University of Cambridge.

“Combining pharmacological interventions with non-invasive brain imaging techniques such as functional MRI (fMRI) can provide insight into normal and abnormal brain function.”

The new research falls within the study of dynamic functional connectivity – the theory that brain phenomena demonstrate states of functional connectivity that change over time, much in the same way that our stream of consciousness is dynamic and always flowing.

As this happens, and the human brain processes information, it has to integrate that information into an amalgamated form of understanding – but at the same time segregate information as well, keeping distinct sensory streams separate from one another, so that they can be handled by particular neural systems.

This distinction – the dynamics of brain integration and segregation – is something that gets affected by psychedelic drugs, and with the advent of brain imaging technology, we can observe what happens when our regular functional connectivity gets disrupted.

In the study, a group of 20 healthy volunteers underwent brain scans in two separate sessions, a fortnight apart. In one of the sessions, the participants took a placebo before entering the fMRI scanner, while in the other slot, they were given an active dose of LSD.

In comparing the results from the two sessions, the researchers found that LSD untethers functional connectivity from the constraints of structural connectivity, while simultaneously altering the way that the brain handles the balancing act between integration and segregation of information.

“Our main finding is that the effects of LSD on brain function and subjective experience are not uniform in time,” Luppi says.

“In particular, the well-known feeling of ‘ego dissolution’ induced by LSD correlates with reorganisation of brain networks during a state of high global integration.”

In effect, the drug’s state of altered consciousness could be seen as an abnormal increase in the functional complexity of the brain – with the data showing moments where the brain revealed predominantly segregated patterns of functional connectivity.

In other words, the ‘ego dissolution’ of a psychedelic trip might be the subjective experience of your brain cranking up its segregation dynamics, decoupling the brain’s structure from its functioning – meaning your capacity to integrate and amalgamate separate streams of information into a unified whole becomes diminished.

“Thus, LSD appears to induce especially complex patterns of functional connectivity (FC) by inducing additional decoupling of FC from the underlying structural connectome, precisely during those times when structural-functional coupling is already at its lowest,” the authors explain in their paper.

“Due to the effects of LSD, the brain is free to explore a variety of functional connectivity patterns that go beyond those dictated by anatomy – presumably resulting in the unusual beliefs and experiences reported during the psychedelic state.”

The findings are reported in NeuroImage.