The entropic brain: A theory of conscious states informed by neuroimaging research with psychedelic drugs
Carhart-Harris RL, Leech R, Hellyer PJ, Shanahan M, Feilding A, Tagliazucchi E, Chialvo DR, Nutt D.
Front Hum Neurosci. 2014 Feb 3;8:20. doi: 10.3389/fnhum.2014.00020. eCollection 2014.
PMID: 24550805
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Abstract:
Entropy is a dimensionless quantity that is used for measuring uncertainty about the state of a system
but it can also imply physical qualities, where high entropy is synonymous with high disorder.
Entropy is applied here in the context of states of consciousness and their associated neural dynamics,
with a particular focus on the psychedelic state. The psychedelic state is considered an exemplar of a
primitive or primary state of consciousness that preceded the development of modern, adult, human,
normal waking consciousness. Based on neuroimaging data with psilocybin, a classic psychedelic
drug, it is argued that the defining feature of ‘primary states’ is elevated entropy in certain aspects of
brain function, such as the repertoire of functional connectivity motifs that form and fragment across
time. It is noted that elevated entropy in this sense, is a characteristic of systems exhibiting ‘self-organised
criticality’, i.e., a property of systems that gravitate towards a ‘critical’ point in a transition
zone between order and disorder in which certain phenomena such as power-law scaling appear. This implies that entropy is suppressed in normal waking consciousness, meaning that the brain operates
just below criticality. It is argued that this entropy suppression furnishes consciousness with a
constrained quality and associated metacognitive functions, including reality-testing and self-awareness.
It is also proposed that entry into primary states depends on a collapse of the normally
highly organised activity within the default-mode network (DMN) and a decoupling between the
DMN and the medial temporal lobes (which are normally significantly coupled). These hypotheses
can be tested by examining brain activity and associated cognition in other candidate primary states
such as REM sleep and early psychosis and comparing these with non-primary states such as normal
waking consciousness and the anaesthetised state.
Comment from Wall Street Journal:
The
Psychedelic Road to Other Conscious States
