  Recordings of whole brain activity with single neuron resolution are now
feasible in simple organisms. Yet, it is still challenging to appropriately
simplify such complex, noisy, and multivariate data in order to reveal general
principles of nervous system function. Here, we develop a method that allows us
to extract global brain dynamics from pan-neuronal imaging. Success of this
method is rooted in a surprising mathematical connection between dimensionality
reduction and a general class of thermodynamic systems. Application of this
theoretical framework to the nervous system of C. elegans reveals the manifold
that sculpts global brain dynamics. This manifold allows us to predict switches
between worm behaviors across individuals, implying that macroscopic dynamics
embodied by the manifold are universal. In contrast, activation of individual
neurons differs consistently between worms. These findings suggest that brains
of genetically identical individuals express distinct microscopic neuronal
configurations which nonetheless yield equivalent macroscopic dynamics.
