How does the brain turn unconscious information into conscious thought?

Neuroscience tells us that most of the work done by our brains happens on an unconscious level, but when does that "a-ha!" moment occur? And what happens during it? New research investigates.

Many of us have noticed that we seem to get our best ideas when we're in the shower, or that we can find the answer to a difficult question when we least think about it.

A large body of neuroscientific studies has pointed out that the brain does a lot of work in its spare time, the so-called idle state - wherein the brain does not appear to be thinking about anything at all - and that this is the time when it works at its hardest to find solutions to complex problems.

With time and advances in neuroscience, it has become more and more clear to researchers that Freud was right and the mind, as well as the brain, do work unconsciously. In fact, it would be safe to say that what is consciously known to us is just the tip of a much larger iceberg, deeply submerged in unconscious waters.

But the exact moment at which information becomes known to us - or when the "tip of the iceberg" pierces through the water, and the unconscious becomes conscious - has been somewhat of a mystery, from a neuroscientific point of view.

In other words, we do not yet know when that intellectually satisfying "a-ha!" moment takes place, or what the biology is behind it. This is why a team of researchers at Columbia University in New York City, NY, set out to investigate this moment in more detail.

The scientists were led by Michael Shadlen, Ph.D., of Columbia University's Mortimer B. Zuckerman Mind Brain Behavior Institute, and the findings were published in the journal Current Biology.

The hypothesis

Dr. Shadlen and colleagues started out from an interesting hypothesis, one which they derived from previous research on the neurobiological processes involved in decision-making.

As the authors explain, research conducted in both monkeys and humans shows that many of our decisions take place at a point when the brain "feels" as though it has gathered enough information, or when a critical level of information has been accumulated.

This process of making a decision once the brain has accumulated enough evidence bears the name of "bounded evidence accumulation." Reaching this threshold is important because, although the brain does not use all of the information available, it uses as much as is necessary to make a speedy yet accurate decision.

The researchers wondered whether or not this threshold is also responsible for our "eureka!" moments.

In Dr. Shadlen's words, "Could the moment when the brain believes it has accumulated enough evidence be tied to the person's awareness of having decided - that important 'a-ha!' moment?"

Examining the 'a-ha!' moment

To answer this question, the scientists asked five people to perform a "direction discrimination" task. In it, the participants looked at dots on a computer screen. The dots moved randomly, as grains of sand would when blown by the wind. The participants were asked to say in which direction the dots had moved.

The moment they "decided" which direction the dots seemed to be taking was considered to be the equivalent of the "a-ha!" moment.

In the center of the screen, there was a fixed point and a clock. The display also had two "choice targets" - namely, left or right - and these were the directions in which the participants had to decide that the dots had moved.

Shortly after the dots had stopped moving, the participants used an electronic, hand-held stylus to move the cursor in the direction that they thought the dots had moved.

To determine when the decision was made, the researchers used the technique called "mental chronometry" - that is, after they made their decision, the participants were asked to move the clock backward to the point when they felt that they had consciously done so.

"The moment in time indicated by the participants - this mental chronometry - was entirely subjective; it relied solely on their own estimation of how long it took them to make that decision," Dr. Shadlen says. "And because it was purely subjective, in principle it ought to be unverifiable."

'A-ha' moment similar to making a decision

However, by applying a mathematical model, the scientists were able to match these subjective decision times to the bounded evidence accumulation process.

The subjective decision times fit so well with what the scientists determined as the evidence accumulation threshold that they were able to predict the choices of four of the five participants.

"If the time reported to us by the participants was valid, we reasoned that it might be possible to predict the accuracy of the decision," explains Dr. Shadlen.

"We incorporated a kind of mathematical trick, based on earlier studies, which showed that the speed and accuracy of decisions were tied together by the same brain function." This "mathematical trick" was the evidence accumulation model.

"Essentially, the act of becoming consciously aware of a decision conforms to the same process that the brain goes through to complete a decision, even a simple one - such as whether to turn left or right."

Michael Shadlen, Ph.D.

In other words, the study shows that the conscious awareness of the "a-ha!" moment takes place precisely when the brain has reached that threshold of evidence accumulation.

The findings provide unique insights into the biology of consciousness, say the researchers, and they bring us closer to understanding the biological basis of decisions, ethics, and, generally, the human mind.