In response to Bernardo Kastrup’s scathing criticisms of materialist explanations of the states of consciousness induced by psychedelics, David Nutt argues that we don’t need to adopt an untestable metaphysical worldview to explain the subjective richness of psychedelic experiences.

Let's start with where we agree. It doesn’t make intuitive sense that alterations in (increased) complexity of brain waves could explain the whole range of subjective experiences that are reported under the influence of psychedelics. I agree they probably don’t in a direct sense - it seems to me much more likely that they are correlated because they both derive from a common change in another system or systems. Despite Bernardo’s criticisms and scepticism, I think we can plausibly develop theories as a result of neuroscience and neuroimaging research coupled with simultaneous acquisition of subjective effects that help explain the altered state of consciousness produced by psychedelics.