Who’s In Charge of Your Brain?

There has been a lot of discussion in the neuroscience community about the way in which different circuits in the brain are integrated. We know that the right and left sides of the brain normally operate together, and that most of the time the three major systems of the brain: reptilian, limbic and neocortical regions work together. However, we have also speculated that one of the causes for some neurological, psychological and psychiatric illnesses might be a result of “disconnections” between different regions of the brain. The idea that some brain regions may be uncoordinated goes back more than a hundred years, but was resurrected and developed quite brilliantly in the 1960s by one of my mentors, the late Norman Geschwind, who was one of the three smartest people that I ever met.

Now there is some new research that may have important implications for neurology and psychology.

Colleagues from Washington University School of Medicine in St. Louis have found strong evidence that there is not one but two complementary commanders in charge of the brain. It is rather like having two captains in charge of the same ship.

The two captains are networks of brain regions that do not consult each other but still work toward a common purpose: the control of voluntary, goal-oriented behavior. These behaviors include a vast range of activities from walking and talking, reading and deciding on a course of action. There are yet other systems that control behaviors that are usually involuntary such as control of the pulse rate or digestion.

Last year the researchers found that there are 39 brain regions that consistently became active before the brain goes to work on a task. They did this through functional magnetic resonance imaging (fMRI) scans that follow the oxygenation of the blood. As a region of the brain is activated, blood flow increases and we can work out which brain regions are contributing to a mental task. One of the keys to our mental capacity is the ability to recruit different parts of the brain as we need them. The previous research suggested that these brain regions create task sets: plans for using the specialized talents of various brain regions to achieve a goal. Let me give you an example.

Read the word: CAT

You can do many things with that word: make a mental image of a cat, read it aloud, make rhymes or lists of words and so on. And each of those activities involves a different set of circuits in the brain. The person with good powers of attention and concentration is able to mobilize and coordinate more of his or her mental resources than the person who is less focused on a task.

In this new study the researchers used a different brain scanning technique called “resting state functional connectivity MRI.” Volunteers were asked to relax while their brains are scanned instead of working on a task.

They then used graph theory, a branch of mathematics that visually graphs relationships between pairs of objects to work out how different brain regions are coordinated. This mathematical technique is rather like the party game Six Degrees of Kevin Bacon, in which you use paired connections to go from one actor or actress to another until you’ve identified a chain of connections linking Kevin Bacon and another actor, actress or movie that wasn’t immediately obvious.

They were able to identify pairs of brain regions where blood oxygen levels rose and fell roughly in synch with each other, implying that the regions most likely work together. What they found was two separate systems. Each system had multiple connections to other regions in its own team, but they never connected to regions on the opposite team.

Having established the existence of two control networks, the next task was to work out their roles. One network – the “cinguloopercular network” – was linked to a “sustain” signal. It turns on when you start doing a task and stays constant while you do it. When you are finished it switches off.

The second is the frontoparietal network that is consistently active at the start of mental tasks and during the correction of errors.

In some senses this is not too much of a surprise. Many systems of the body have multiple control systems. I have often talked about the scores of systems involved in the control of body weight, which means that a dietetic approach directed at only one system is doomed to failure. If the body thinks that it is starving other systems jump in to slow your metabolism, reduce your activity level and make you crave certain foods.

Another good example is body temperature. Your temperature is regulated by several independent factors including your sweat glands, metabolism and activity level. If one of them goes wrong, other systems will try and compensate. When one controlling factor goes awry, others can try to compensate. The controls of your weight and body temperature are known as complex adaptive systems, and they are found not only in biology, but also in ecology, economics and atmospheric dynamics. We study them using an approach called network dynamics.

The findings may help our efforts to understand the effects of brain injury and develop new strategies to treat such injuries.

They may also help us understand problems like goal-directed behavior and human motivation.

If only one of the two systems has agreed that you need to go out and exercise, it may help us design new strategies to help you and explain why some approaches to, say, diet and exercise, are more effective than others.

Groundbreaking stuff!