The structure of the human brain is complex, reminiscent of a circuit diagram with countless connections. But what role does this architecture play in the functioning of the brain? To answer this question, researchers at the Max Planck Institute for Human Development in Berlin, in cooperation with colleagues at the Free University of Berlin and University Hospital Freiburg, have for the first time analysed 1.6 billion connections within the brain simultaneously. They found the highest agreement between structure and information flow in the “default mode network,” which is responsible for inward-focused thinking such as daydreaming.
Everybody’s been there: You’re sitting at your vdesk, staring out the window, your thoughts wandering. Instead of getting on with what you’re supposed to be doing, you start mentally planning your next holiday or find yourself lost in a thought or a memory. It’s only later that you realize what has happened: Your brain has simply “changed channels”—and switched to autopilot.
For some time now, experts have been interested in the competition among different networks of the brain, which are able to suppress one another’s activity. If one of these approximately 20 networks is active, the others remain more or less silent. So if you’re thinking about your next holiday, it is almost impossible to follow the content of a text at the same time.
To find out how the anatomical structure of the brain impacts its functional networks, a team of researchers at the Max Planck Institute for Human Development in Berlin, in cooperation with colleagues at the Free University of Berlin and the University Hospital Freiburg, have analysed the connections between a total of 40,000 tiny areas of the brain. Using functional magnetic resonance imaging, they examined a total of 1.6 billion possible anatomical connections between these different regions in 19 participants aged between 21 and 31 years. The research team compared these connections with the brain signals actually generated by the nerve cells.
Their results showed the highest agreement between brain structure and brain function in areas forming part of the “default mode network“, which is associated with daydreaming, imagination, and self-referential thought. “In comparison to other networks, the default mode network uses the most direct anatomical connections. We think that neuronal activity is automatically directed to level off at this network whenever there are no external influences on the brain,” says Andreas Horn, lead author of the study and researcher in the Center for Adaptive Rationality at the Max Planck Institute for Human Development in Berlin.
Similar study in US confirmed the findings.
Anyone who’s learned to ride a bike or touch type might have wondered how a task that is so arduous at first could be so seamlessly easy later. A new study reveals more about exactly what goes on in the brain as we form these habits, transitioning from intense concentration to autopilot.
The results, found in rats but thought to be analogous to humans, show that habitual learning, as it’s called, involves two brain circuits — one used for movement and the other for higher, cognitive thinking.
As a task is learned, these circuits trade off in terms of their engagement. The movement circuit, which involves a part of the brain called the dorsolateral striatum, becomes more active, while the cognitive circuit, which involves a region called the dorsomedial striatum, takes a dip.
If you imagine these two systems are competing, then at the end stages of training, activity in the dorsomedial striatum is fairly weak whereas activity in the dorsolateral striatum is fairly strong,” said study researcher Catherine Thorn, at MIT’s McGovern Institute for Brain Research. “And what we think that means is that the habit is taking over as training progresses,” she told LiveScience.
Competing brain circuits
While scientists had previously hypothesized these brain circuits were involved in habitual learning, the current work is the first to record the activity of the brain cells, or neurons, as the habits were formed. It is also the first to show that these two loops are active simultaneously.
The fact that these two circuits work together could potentially mean that one circuit might be able to compensate for the other. This would be useful in instances where one circuit is damaged, such as in Parkinson’s disease, where the dorsolateral striatum is affected.
“If we can learn how to tilt the competition in one direction or the other, we might help bring new focus to existing therapies, and possibly aid in the development of new therapies,” said lead researcher Ann Graybiel, also of MIT. However, the researchers emphasize these sorts of applications are a long way off.
And while rat brains are good models for studying this type of learning, studies on humans are needed before scientists can know if the results apply to us.
Rat habits
The researchers recorded the activity of thousands of neurons in the rats’ brains as they learned how to find a food reward in a maze. When they reached a specific T-junction, the rats were signaled to turn either right or left by either a sound or touch cue. Over many trials, the rats learned to associate the signal with turning in the correct direction for their reward. Eventually, this became routine.
The two brain circuits showed very different patterns of activity as the rats were learning. The dorsolateral striatal neurons (linked to motion control) were most active at specific points of action within the maze, such as a start, stop, or turn. And their activity steadily increased as the rats’ performance improved, and then remained fairly stable.
On the other hand, the dorsomedial neurons (involved in higher thinking) were most active when the rats had to make the “right or left” decision. The neuron activity in this region also declined once the rats got a handle on their task. Essentially, the thinking part of the brain wasn’t so necessary as the task became routine.
“The two systems are generally simultaneously engaged, and possibly competitive, but with extended training and repetition, as the habit takes over, the dorsolateral striatum becomes more strongly activated over the dorsomedial striatum,” Thorn said.
Another hypothetical implication of the findings is that a better understanding of how these circuits interact might lead to ways to help people avoid or unlearn bad habits. “It’s possible that if we could get a handle on the interaction between the two loops, we would be able to possibly suppress bad habits or encourage good ones,” Thorn said.
For more details visit : journal Neuron
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