Signatures of Conscious Processing in the Human Brain

Understanding how brain activity leads to a conscious experience remains a major experimental challenge. I will describe a series of experiments that probe the signatures of conscious processing. In these experiments, my colleagues and I ask whether a specific type of brain activity can be detected when a person suddenly becomes aware of a piece of information. We create minimal contrasts whereby the very same visual stimulus is sometimes undetected, and sometimes consciously seen. We then use time-resolved methods of electro- and magnetoencephalography to follow the time course of brain activity. The results show that conscious access relates to a global burst of late synchronized activity (a cortical “ignition”), distributed through many cortical areas. We propose a theory of a global neuronal workspace, according to which what we experience as a consciousness is the global availability of information in a large-scale network of pyramidal neurons with long-distance axons. This knowledge is now being applied to the monitoring of conscious states in non-communicating patients. Using real-time signal processing techniques, we believe that a few minutes of testing with simple sounds and two recording electrodes might suffice to determine whether a person is conscious.