Entropic brain hypothesis
Tldr
Psychedelics increase brain entropy and experiential entropy, as the two are intimately related flip sides of the same system (mind/brain) Carhart-Harris2019a.
The qualia or subjective experience of any given conscious state, and specifically the ‘richness’ of its content, can be indexed by a quantitative measure of the magnitude of entropy (in the information-theoretic sense) in a given parameter of spontaneous brain activity, such as oscillations in electrical potentials recorded with EEG or MEG. Furthermore, entropy indexes simultaneously our uncertainty about the future behavior of a dynamic system and its information content. Uncertainty and information-content are near-equivalents, and entropic brain states are experienced as content-rich but unpredictable/uncertain (Carhart-Harris2018).
Mechanism
- Coupling within the DMN and especially between DMN and the medial temporal lobes is essential for ‘secondary consciousness’ (normal waking consciousness)
- Relative decoupling between DMN and specifically between medial temporal lobes and DMN occurs when secondary consciousness is suppressed and there is a reciprocal increase in the influence of ‘primary consciousness’
- Decreased MTL-DMN coupling allows MTLs to function more independently of the DMN and this can result in unusual activity, like has been recorded with depth electrodes in primary states (Grof1982, Bassett2008, Axmacher2010.
- Unconstrained MTL activity is a principal characteristic of primary states and the occurrence of these activities is consistent with a system at criticality
- Brain activity in primary consciousness is closer to criticality than it is during normal waking consciousness (slightly sub-critical rather than perfectly critical, or primary states are supercritical)
(Carhart-Harris2014)
- Introduced in 2014 Carhart-Harris2014 and revised in 2018 Carhart-Harris2018
- A breakdown in Hippocampus-DMN coupling is necessary for regression to primary consciousness (Carhart-Harris2014).
- It may be the case that entropy is just an index of arousal/stimulation, but until we compare psychedelics against stimulants (or another similar experiment), the world may never know (Mateos2018).