An invitation to understand the mindbrain
Cortex is the organ of mind.
The double-decker cortex, both the outer neocortex and the inner paleocortex, were proposed to be the “organ of mind,” as pioneering neurosurgeon Wilder Penfield wrote, based on 1,200 open brain-surgeries in conscious epileptic patients at the Montreal Neurological Institute from the 1920s to the 1950s. Speculation along those lines goes back more than two thousand years to the School of Hippocrates of Cos. But proof positive has been extremely difficult to obtain, and it has taken long-term research programs with advanced brain imaging to settle the question.
This image shows the physical stimulation of the fovea, the functional center of the retina, roughly a 1000x1000 array of dense receptors.
The retinal array is mirrored point-to-point in the visual thalamus (LGN), and again in the first visual projection region called V1.
Critically, the connectivity of LGN and V1 is bi-directional, with any minicolumn in LGN linking to a minicolumn in V1, and vice versa.
This would seem to risk an explosive feedback loop, but the waking cortex runs very well in the normal, healthy brain.
This puzzling wiring style led Gerald M. Edelman to propose that the cortex operates “near criticality,” so that it is ready for any sensory input or output. Perturbing the delicately oscillating cortex can ignite a rapid broadcast, corresponding reportable visual experiences. Global Workspace Dynamics (GWD) suggests this core idea for visual consciousness.
Labeled line coding implies that the relative locations of neurons are preserved in higher level retinotopic maps. Beyond V1 visuotopic maps preserve a sparser copy of the visual field, while cellular receptive fields increase in size and decrease in spatial resolution. Spatiotopic mapping is regular and systematic throughout the C-T complex.
For instance, there are tonotopic maps in auditory areas, body maps in the somatic regions, and similar such maps in the motor cortex. At higher levels C-T arrays project to self-centered and object-centered spaces, which must be coordinated with each other to support a coherent domain of action and perception. Multiple levels of inhibition serve to regulate and sculpt the excitatory activity of the cortex and its satellites. Cortical arrays therefore resemble the head-up cockpit display of a fighter jet, which may show a geometric frame for the plane itself, another frame for targets, and more for attackers and neutrals. When these floating spatial frames intersect, they may alert executive networks to make decisions.
Starting with LGN, all spatiotopic pathways become bidirectional. Successive arrays pick up visual features like spatial frequency, contrast, edge orientation, gestalt properties, hue, motion, and object identity. Higher level properties like object permanence, size constancy, color constancy, shape from shading, face and object recognition, scene analysis, movements, causality, and event organization, all require complex interactions among 40 or more spatiotopic arrays.
The sight of a red traffic light must remain stable in spite of differences in reflectance, observer motion, background clutter, and changes in sunlight.
To read more, order your copy of Baars’ latest book, On Consciousness: Science & Subjectivity – Updated Works on Global Workspace Theory.
Global Workspace Theory (GWT) began with this question: “How does a serial, integrated and very limited stream of consciousness emerge from a nervous system that is mostly unconscious, distributed, parallel and of enormous capacity?”
GWT is a widely used framework for the role of conscious and unconscious experiences in the functioning of the brain, as Baars first suggested in 1983.
A set of explicit assumptions that can be tested, as many of them have been. These updated works by Bernie Baars, the recipient of the 2019 Hermann von Helmholtz Life Contribution Award by International Neural Network Society form a coherent effort to organize a large and growing body of scientific evidence about conscious brains.
