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Discovery

Lopsided Brains

03.04.2014

In a nutshell: This finding helps explain why damage to the brain’s right side can be more harmful than damage to the left when it comes to perceiving space around you.

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Lopsided BrainsLopsided Brains

The big picture:

People who have had a stroke can end up with a condition called “spatial neglect”: their brain ignores objects and sounds on one side of the body. This can make everyday tasks like dressing or eating next to impossible.

Curiously, spatial neglect is far more common and severe following damage to the right side of the brain.

Why the brain behaves in this lopsided way has puzzled neuroscientists for decades.

According to one theory, the left side of the brain gets sight and sound inputs from the right side of the body, while the right side gets inputs from both sides. Because the right side is carrying more of the brain’s processing load, when it’s damaged, the outcome is worse.

To test whether this theory was correct, Marta Garrido and her colleagues recorded brain activity in 12 healthy people as they responded to sounds from their left and right sides. They used electroencephalography (EEG) – a way of monitoring rapid changes in electrical activity across the scalp.

Their observations strongly suggested that the theory was correct. “The right hemisphere seems to be interested in sounds coming from the left and the right, whereas the left hemisphere seems to be just interested in things coming from the right side of space,” says Garrido.

But EEG recordings only give a rough idea of where brain activity is occurring. So Garrido and her colleagues also used mathematical modelling to map the EEG activity onto discrete parts of the brain, confirming the finding.

“With modelling, we can tap into the networks and the mechanisms. We can really look at how information travels through different areas of the brain,” explains Garrido.

Next steps:
Studies like this are groundwork for investigating how the brain changes after injury and with recovery, which could lead to better treatments.


Reference:
Dietz, M. J., Friston, K. J., Mattingley, J. B., Roepstorff, A., & Garrido, M. I. (2014). Effective connectivity reveals right-hemisphere dominance in audiospatial perception: implications for models of spatial neglect. The Journal of Neuroscience, 34(14), 5003-5011.


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