How the Brain Determines Its Thinking

When I was a college sophomore at the University of Tennessee, I decided to spend the summer with my fraternity buddy, Sam Harris, whose family had moved to Hollywood. I met the girl friend, Irene, of his girlfriend, and the four of us spent many date nights that quickly spawned love among us. Sam married his girl, but being a college student living in another state 2200 miles away made it too difficult to nurture my love relationship. On one date night, Irene said to me with some consternation, "You are always thinking. Why is that?" Well, I don't know why that is, but it is true. Surely, I am in the habit about thinking of all sorts of thinking.

One of the things I have been thinking about lately is how the human brain decides what it thinks about. Not all thoughts are chosen. Some are imposed from the outside, as for example, with thoughts being triggered by sensory input, spurious surfacing of memories, or thoughts triggered by something we read or heard from somebody else. There is also the fact that many, perhaps most, of our "thoughts" are unconscious.

Converting Unconscious Thought to Conscious Awareness

Unconscious thought is basically the consequence of neural processing of which we are unaware. The brain processes a great deal of information unconsciously, such as control over our viscera, our habits, our prejudices, our feelings, and so on. These processes surely influence our conscious thought and behavior in ways we do not consciously realize.

Conscious realization and thought involve at least two basic steps: 1) some kind of neural tagging to select which unconscious sensory or cognitive processes to make available for conscious processing, and 2) the process of conscious realization itself. Electrophysiological research reveals that these two processes are separated in time, and thus they may reflect two different processes. For my purposes here, I wish to focus on the tagging process that the brain might use to identify the various local circuit neural activity to make available for conscious awareness.

The brain is a global workspace of interacting modules. Processing is often parceled out to certain circuits. For example, bodily sensations are routed to the sensory cortex. Precise movements are handled by the motor cortex. Sound and vision have separate processing circuitry. There is a face-recognition area in the parietal cortex. There are executive controls handled by specific areas of neocortex. Religious thoughts are handled in different cortical areas depending on the nature of religious thought. And so on.

Brains are wired to constantly surveil sensations in need of conscious detection and interpretation, ideas to be understood, feelings to be accommodated, memories to be retrieved, problems to solve, and plans for future actions. The point is that the brain not only has some sort of mechanism for routing processing needs to specific cortical modules but also must have some way to scan its workspace to tag those modules that would benefit from conscious access. Of course, tagging is not necessary for situations where a stimulus so pronounced that it demands attention. For example, a sudden unexpected thunder clap is so pronounced that it triggers conscious attending by its own characteristics. But for routine thinking, whether mind wandering or intentional control over a sequence of thoughts, the brain must have some way to tag which modules need conscious access and in which sequence.

The basic idea is that the brain has a default mechanism for scanning its unconscious operations for momentarily novel or relevant information in widely distributed local networks that are specialized for certain kinds of thought. Such scanning could enable attentional focus, leading in turn to linking of diverse local networks through temporal coherence within and among local circuits, especially in high-frequency bands, that improves signal-to-noise ratio and sharing of information by those local networks.

Scanning via non-living systems. as in radar, commonly involves detecting reflection from targets that have been scanned by beams of light or sound. Cognitive scanning obviously cannot work that way, but an analogous mechanism would involve recursively re-entrant feedback between neural signals that are scanning the moment-to-moment neural activity in the local circuits of the global workspace. Re-entrant interactions can alter the timing and phase relationships within and among the various local circuits, which effectively tag those circuits that have sufficiently novel or relevant information that warrants conscious access.

If we knew how the brain achieves such scanning and tagging, it might help us develop training methods to make our conscious analysis more rigorous and effective. I am developing a scholarly paper for publication that suggests some possible mechanisms and ways to test them. We will have to see how those ideas evolve.