Everyday tasks like turning a key or writing with a pen involve detailed hand movements that the brain manages with ease. A recent study by researchers from Carnegie Mellon University and the University of Coimbra, published in PNAS, reveals how the brain organizes these actions in an orderly manner. Much like a language creates words by mixing letters from an alphabet, the brain forms a wide range of hand actions from a small set of basic movement parts.
The study used computational modeling on functional MRI data. This approach showed that a brain area called the supramarginal gyrus, found in the left inferior parietal lobe and known for helping plan actions with objects, builds complex actions by mixing limited sets of coordinated movements in fingers, hands, wrists, and arms.
For example, the hand position for scissors resembles that for pliers, even though the tools serve different purposes. But scissors and a knife, which might cut the same thing, require very different hand poses. Brain activity in the supramarginal gyrus was similar for objects needing alike hand positions.
Building actions like language
The supramarginal gyrus combines these basic elements much as sounds or phonemes combine to make words in speech. From these building blocks, the brain creates all possible hand actions.
This finding could improve robotics by helping create machines that move with human-like skill and efficiency. For brain-machine interfaces, mapping these synergies from brain signals might allow more natural control of artificial limbs.
The discovery also sheds light on apraxia, a brain disorder where people struggle to use objects correctly despite recognizing them, similar to trouble forming words from sounds. The supramarginal gyrus sits in a spot that blends visual, touch, movement, and idea-based information, making actions automatic without conscious thought, just as speaking feels effortless.
While people learn specific tool uses through experience and culture, all humans share this neural setup for hand actions, like the shared brain system for any language. This advances understanding of brain principles behind human tool use.