A brain may be the network of neurons integral to life in many organisms — a solid brain, located specifically in space. A brain might also be the liquid, amorphous cognitive networks guiding ant colonies and immune systems.

In a themed issue in Philosophical Transactions of the Royal Society B, a collection of papers explores the differences between "liquid" and "solid" brains, their varied abilities to perform computations, and their inherent limits. 

Edited by SFI External Professors Ricard Solé (Universitat Pompeu Fabra), Melanie Moses (University of New Mexico), and Stephanie Forrest (Arizona State University), this special issue is the result of the 2017 SFI Working Group "Liquid Brains, Solid Brains."

Below are links to articles within the issue, and to SFI-affiliated co-authors:

  1. Introduction: Liquid brains, solid brains
    Ricard Solé, Melanie Moses, and Stephanie Forrest
  2. The Cognitive Lens: a primer on conceptual tools for analysing information processing in developmental and regenerative morphogenesis
    Santosh Manicka and Michael Levin
  3. The brain: a concept in flux
    Oné R. Pagán
  4. Homeostasis as a fundamental principle for a coherent theory of brains
    J. Scott Turner
  5. Metabolic basis of brain-like electrical signalling in bacterial communities
    Rosa Martinez-Corral, Jintao Liu, Arthur Prindle, Gürol M. Süel, and Jordi Garcia-Ojalvo
  6. Memory inception and preservation in slime moulds: the quest for a common mechanism
    A. Boussard, J. Delescluse, A. Pérez-Escudero, and A. Dussutour
  7. Plant behaviour in response to the environment: information processing in the solid state
    Salva Duran-Nebreda and George W. Bassel
  8. The plant body as a network of semi-autonomous agents: a review
    Beata Oborny
  9. Statistical physics of liquid brains
    Jordi Piñero and Ricard Solé
  10. A brief history of liquid computers
    Andrew Adamatzky
  11. The computational stance in biology
    C. C. Wood
  12. How does mobility help distributed systems compute?
    William F. Vining, Fernando Esponda, Melanie E. Moses, and Stephanie Forrest
  13. Surface curvature guides early construction activity in mound-building termites
    Daniel S. Calovi, Paul Bardunias, Nicole Carey, J. Scott Turner, Radhika Nagpal, and Justin Werfel
  14. Evolutionary aspects of reservoir computing
    Luís F. Seoane
  15. Modular structure within groups causes information loss but can improve decision accuracy
    Albert B. Kao and Iain D. Couzin

Read the full issue, Liquid Brains, Solid Brains, in Philosophical Transactions of the Royal Society B (April 22, 2019)