In a nutshell: Supports idea that there are two stages to processing a planned arm movement, such as reaching for your mouse. First: consult your senses and motivations. Second: convert into an action plan.

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Here, CIBF researcher Marcello Rosa and his team examine brain connections at a level of detail that is only possible in a few laboratories across the world— the nerve cell level. They have traced the actual nerve cell connections from the brain’s cognitive centres to its motor centres, from one end of the brain to the other.

By tracing these fine connections in a tiny primate, the marmoset, the Rosa team infer the likelyfunction of two regions of the premotor cortex in the front part of the brain. The findings are also a good illustration of how the brain “chunks” tasks, with different regions responsible for different parts of a process.

They found that one region — called 6DR — connects to the visual system via the prefrontal cortex, which is responsible for complex thoughts such as decision making. 6DR also connected to regions that are suspected to relay information about internal states and motivations.

The other — called 6DC — has numerous connections to the primary motor cortex. The primary motor cortex controls voluntary movement. It’s the part of the brain that is represented as the iconic homunculus, the distorted human-like figure that illustrates the relationship of different parts of the cortex to body parts.

Finally, the Rosa team also found plenty of connections between the 6DR and 6DC, suggesting that those regions are working closely together.

The high resolution physical evidence supports Rosa’s working hypothesis that 6DR and 6DC form a communication bridge, carrying information from the brain’s cognitive centres to its motor centres.

So, first the brain, or more specifically 6DR, considers the sensory inputs and internal motivations. I am thirsty. The drink is in the glass over there. I want to pick up the glass and drink.

Then, the rough plan of action is forwarded to 6DC, which works out the precise movements needed, and sends instructions to the primary motor cortex to implement them.

“It’s a cascade of events and information,” says Rosa. “And it all happens in a split second.”

Next steps:
Efforts to map neural connections will continue, with the ultimate long-term aim for the brain research community being a complete map of all of the connections in the brain and nervous system—the Connectome.

Burman, K. J., Bakola, S., Richardson, K. E., Reser, D. H., & Rosa, M. G. (2014). Patterns of afferent input to the caudal and rostral areas of the dorsal premotor cortex (6DC and 6DR) in the marmoset monkey. Journal of Comparative Neurology, 522(16), 3683-3716.

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