Figure 1.

A family of different closed-loop designs to couple with brain state dynamics. (A) Traditional “black box” experiment where there is no environment that the brain can act on: the stimulation is predetermined by the experimenter, the experimental observable is the output from the brain. (B) The feedback loop triggers a stimulus based on a spontaneously occurring instantaneous brain state; here, the environment is static and without state. (C) This loop represents an agent-environment interaction where the environment has its own internal dynamics, consisting of state (which is fully observable) and the equations of motion (the laws that govern the behavior of the environment). The combined result is an interacting complex system. Areas shaded red indicate parts of the set-up under experimental control, white areas show the “observable behavior”. (D) Shows the relationship between “true” brain state trajectories and the projection onto the measured electroencephalogram (EEG) signal as well as the effect that a transcranial magnetic stimulation (TMS) pulse has shifting state to a new position (figure taken from Mutanen et al., 2013) (E). An experimental closed-loop EEG-TMS set-up configured to couple with cortical dynamics during a simultaneously executed motor-sensory task. Two conceptually different feedback loops can be distinguished, a “brain-state dynamics” loop that is designed to influence the trajectory of the brain state and a “task dynamics” loop that enables active interaction with a (real or computer simulated) environment through the motor and sensory system and the respective encoding stages.