What is it about?
Using a corkscrew, writing a letter with a pen or unlocking a door by turning a key are actions that seem simple but actually require a complex orchestration of precise movements. So, how does the brain do it? According to a new study by researchers from Carnegie Mellon University and the University of Coimbra, the human brain has a specialized system that builds these actions in a surprisingly systematic way. Analogous to how all of the words in a language can be created by recombining the letters of its alphabet, the full repertoire of human hand actions can be built out of a small number of basic building block movements.
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Why is it important?
This study moves us one step closer to understanding the fundamental principles of brain organization that make human tool use possible. When we use our hands to grasp objects we don’t have to ‘think’ about building up actions out of their elemental parts — just like native speakers of a language don’t have to think about how to say the words they want to use. These processes are always running automatically in the background, behind what we are thinking about in any given moment. A key aspect of the system that supports complex hand actions is that its location – about one inch above and behind the left ear – is strategically located in the brain to receive and integrate many different types of information. These include visual, tactile, motor and conceptual information about the world and the status of the body. The structure and organization of the brain reflects the integration of each individual’s lived experience with evolutionarily constrained structures. We are not born knowing how to manipulate, for instance, a key, or a pen — the specific way to use objects must be learned, and is a type of cultural knowledge. Despite the very different kinds of interactions with objects that different people have, and despite differences in manual dexterity across individuals, all humans have a common neural system that supports complex object directed interactions. Similarly, by analogy, while human infants are not born speaking any particular language, human infants are able to become a native speaker of any language in the world — and all humans have a common neural system that supports language.
Perspectives
This study shows what is happening in the background, in our brain, every time we look at an object in our environment. Pause for a moment and notice the objects that happen to be around you--perhaps a cup, or a pen, or your phone or computer. Even though you may not have explicitly thought about the next action you will direct toward one of those objects, your brain's action system has already scoped out the parameters of those potential actions. For instance, imagine you reach out and take a sip from the cup on your desk. Before you start that movement of your hand to grasp the cup, your brain has already computed all kinds of properties about the cup and its contents, including its weight, how slippery it is, where its surface is likely to be hot, its location relative to your hand, and how big a sip you plan to take. This study shows that the final posture of the hand when grasping an object is built from a vocabulary of basic building blocks, and that vocabulary is the same across individuals.
Bradford Mahon
Carnegie Mellon University
Read the Original
This page is a summary of: Object-directed action representations are componentially built in parietal cortex, Proceedings of the National Academy of Sciences, August 2025, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2421032122.
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