Brain-computer interfaces may help the paralyzed in the future to regain the ability to move. By directly reading what the brain intends on doing, muscles can be activated via electronic stimulation. The idea sounds easy enough, but reading the brain requires the ability to interpret complex neural physiology in real time. Researchers at UC Santa Barbara have been using functional MRI to study how the precuneus region inside the parietal lobe is involved with hand motion, and discovered that the brain uses different maps when moving the hand toward visible objects than when reaching toward expected but unseen targets like an itch at the back of the head.
Two UCSB scientists studied the brains of 18 individuals who made 400 distinct arm reaches as they lay in an MRI scanner.
The current scientific view is that all reaching movements –– those directed to visual targets or toward one’s own body –– are planned using a visual map. "Our findings suggest otherwise," said Pierre-Michel Bernier, first author and postdoctoral fellow. "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."
The researchers measured the "Blood Oxygen Level Dependent Signal," or BOLD signal, when looking at the MRI brain images. BOLD is an indirect way of looking at brain activity at a millimeter scale. They also used a methodology called "repetition suppression." This is what makes the study novel, according to the authors, as it is one of the first to identify where these maps are nested in the human brain. "We are a leader in the use of repetition suppression," said Grafton [Scott T. Grafton, professor of psychology].
Repetition suppression relies on the fact that when a brain region is involved in two similar activities in a row, it is less active the second time around. The team was able to pinpoint the brain’s use of body maps versus visual maps by isolating the location in the brain where the responses were less active with repeated, similar arm reaches.
Press release: UCSB Scientists Report Study of ‘Brain Maps’ for How Humans Reach; Robotics and Machine-Brain Interface for Paraplegics May Benefit …
Abstract in Neuron: Human Posterior Parietal Cortex Flexibly Determines Reference Frames for Reaching Based on Sensory Context
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