Pearson matrices as density operators: A test of the entropic brain hypothesis using the von Neumann entropy
entropy, correlation, brain, psychedelics
The entropic brain hypothesis states that key functional parameters should exhibit increased entropy during psychedelic
induced altered brain states. This hypothesis has gained significant support over the years, particularly via thresholding Pearson
correlation matrices of functional connectivity networks. However, the thresholding procedure is known to have drawbacks,
mainly its arbitrariness in the threshold value selection. In this work, we propose an entirely objective, threshold independent
method of entropy estimation. Let R be a generic N×N Pearson correlation matrix. We define ρ = R/N and prove that ρ
satisfies the necessary conditions for a density operator. Therefore, the von Neumann entropy S = –tr(ρlnρ ) can be directly
calculated from the Pearson matrix. We then calculate the entropy of functional correlations of the human brain. Consistent
with the entropic brain hypothesis, we find that entropy increases during the acute effects of the psychedelic indigenous
beverage ayahuasca.