From snail to man, one of the hallmarks of thebrain is the ease with which behavioral variants are generated--forexample, humans can easily walk with different stride lengths ordifferent speeds. By studying how a relatively simple motor network ofthe marine snail Aplysia produces variants of a particular feedingbehavior, researchers have found that the ability to generate a largenumber of behavioral variants stems from the elegant hierarchicalarchitecture of the brain's motor network.
Most motor systems are organized into a hierarchy of at leasttwo layers of neurons, with higher-order neurons acting on lower-orderneurons, which form a small number of building blocks or modules thatproduce a variety of behaviors. However, it was not clear how variantsof a single motor act are generated in such a hierarchical system.
In the new work, Jian Jing and Klaudiusz Weiss of the MountSinai School of Medicine in New York studied the feeding network ofAplysia, which exhibits a biting behavior in response to the presenceof food. The researchers showed that within the feeding network, twohigher-order neurons that are active during biting behavior employ acombinatorial mechanism to produce variations in one particularmovement parameter of the biting behavior. The researchers showed that,tellingly, these higher-order neurons accomplish their roles throughtheir specific actions on two groups of lower-order interneurons thatdirectly influence the particular biting-behavior movement parameter.Therefore, in this system, and likely others, the generation of largenumbers of behavioral variants is characterized by higher-order neuronsthat flexibly combine an "alphabet system" of outputs that aregenerated by lower-order modules within the brain's motor network.
The researchers included Jian Jing and Klaudiusz R. Weiss of MountSinai School of Medicine in New York, NY. This work was supported bygrants from National Institute of Mental Health.
Jing et al.: "Generation of Variants of a Motor Act in aModular and Hierarchical Motor Network." Publishing in Current Biology,Vol. 15, 1712-1721, October 11, 2005. DOI 10.1016/j.cub.2005.08.051 www.current-biology.com
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