Posted on Dec. 19: Crossing your hands confuses your mind until you can see them
[img_inline align=”right” src=”http://padnws01.mcmaster.ca/images/Shore.David_opt.jpg” caption=”David Shore”]Scratching your left knee with your right hand appears to be an effortless act. Not so for your brain.
An international research team including David Shore, an assistant professor of psychology at McMaster University and Donna Lloyd, Charles Spence and Gemma Calvert of the University of Oxford used functional magnetic resonance imaging (fMRI) to understand how the brain represents a limb placed across the body midline. The results showed profound changes in the way our brains process tactile stimulation to the right hand when it lies to the left of the body and that this is different when we can see the hand versus when we can't.
The new study shows the complex process the brain works through to ensure you can perform a movement that appears effortless. “There is a complexity involved that we take for granted,” said Shore, whose research specialty is multisensory temporal processing.
“This is the first examination of the fMRI-related cortical
consequences of placing a limb across the body midline in humans.”
Reaching for a glass at the dinner table is one example of the every day activities requiring the brain to combine information from different senses. “Visual information about the location of the glass, proprioceptive information about your body position, tactile
information about the feel of the glass and even auditory information as it slides along the table need to be integrated into a real-world' object,” Shore said.
“Your brain is constantly updating the representation of space,” Shore said. “With your eyes closed, it is the position of the hand (on the left) that determines the locus of brain activity (in the right hemisphere). With the addition of vision, processing shifts to the more appropriate' left hemisphere. This shift in activation (from right to left hemisphere) may account for improved performance previously observed when vision of the hand is possible.”
The researchers scanned 10 right-handed people while they passively received stimulation to the right thumb that was either on the right side of the body or across the body midline on the left side of the body. The study participants either kept their eyes closed throughout or had them open and fixated on the stimulated right hand.
The research study, Multisensory representation of limb position in human premotor cortex, is to be published in the online edition of the journal Nature Neuroscience on Dec. 16. The research was funded with a Network Grant from the University of Oxford McDonnell-Pew Centre for Cognitive Neuroscience.
