UC Berkeley

The brain is a thermodynamic system operating far from equilibrium. Its function is to extract microscopic sensory information from the volleys of action potentials (pulses) that are delivered by immense arrays of sensory receptors, construct the macroscopic meaning of the information, and store, retrieve, and update that meaning by incorporating it into its knowledge base. The function is executed repetitively in the action-perception-assimilation cycle. Each cycle commences by a phase transition, in which the immense population comprising each sensory cortex condenses from a gas-like state to a liquid-like state. It ends with return of the cortex to the expectant gas-like state. We have modeled the microscopic thermodynamics of the cycle using quantum field theory. Our new result is modeling cortical macroscopic thermodynamics with the generalized Carnot cycle, in which the energy required for the construction of knowledge is supplied by brain metabolism and is dissipated as heat by the cerebral circulation. What makes the application possible is the unprecedented precision with which spatial patterns of ECoG are measured, thus providing precise state variables with which to represent energy vs. entropy. We present experimental evidence that these isothermal processes are coupled by adiabatic cooling and heating. We postulate that the action-perception-assimilation cycle comprises minimally three consecutive Carnot cycles required for basic perception, assimilation, and decision, and more cycles with greater complexity of cognitive tasks at hand.