The reason behind how humans reach out for different things has been explained in a new study at UC Santa Barbara. It says that the brain uses different "maps" to plan for each of these movements.
In preparing for each of these reaching movements, the same part of the dancer's brain is activated, but it uses a different map to specify the action, according to the research.
Planning to hold hands is based on the visual map of space while the second plan, to reach for her calf, depends on the dancer's mental body map.
Two UCSB scientists studied the brains of 18 individuals who made 400 distinct arm reaches as they lay in an MRI scanner.
"Our results have two important applications. One is robotics. The other is in the area of machine-brain interface; for example, in developing machines to help paraplegics," said Scott T. Grafton, professor of psychology.
"A critical issue is to understand how movement-related information is represented in the brain if we're to decode it. We're interested in movement planning and movement control. We're looking at goal-directed behaviors, when we reach to grasp objects-visually defined objects in our environment. This forms the basis of our interactions with the world," he said.
"We found that when a target is visual, the posterior parietal cortex is activated, coding the movement using a visual map. However, if a movement is performed in darkness and the target is non-visual, the same brain region will use a fundamentally different map to plan the movement. It will use a body map," said Pierre-Michel Bernier.
Grafton explained, "The brain is trying to make a map of the world. One map is what you see, which is provided by the visual system. The other map is where the body is in space. This map is based on proprioception-the sense of limb position - which is derived from receptors in the skin, muscles, and joints. These maps are very different. How do you connect them? Either the visual map or the body map may be fixed, or neither may be fixed."
This flexibility underlies our ability to interact with the world with ease despite the ever-changing conditions in which our actions take place.
Their discovery is reported in the journal Neuron.