Lefties and Righties use Opposite Brain Halves

Hemispheric dominance may require different treatment style in right handed vs left handed people

(RxWiki News) Whether a person is a righty or a lefty may affect how brain stimulation therapy should be targeted.  Hand dominance determines which side of the brain makes approach and defend decisions.

A new study takes a look at the brain waves of right- and left-handed people when they’re asked questions about their physical motivation. This could mean that brain stimulation should be tailored to people based on their dominant hand.

"Before brain-stimulation therapy, tell your doctor if you’re left-handed."

Under the direction of Dr. Daniel Casasanto PhD., assistant professor of psychology at The New School for Social Research in NYC, graduate student Geoffrey Brookshire set out to research emotional response differences between right and left handed people.

Previous research suggests that the left hemisphere of the brain sparks motivation and approach, while the right hemisphere supports withdrawal and avoidance. Most research has assumed the right hand to be dominant, disregarding the possibility of left hand dominance.

This notion forms the Sword and Shield Hypothesis, where the dominant hand (right) is the ‘sword hand’, and the defensive hand (left) is the ‘shield hand’. But what if there is a difference in the brain wiring for approach and avoidance for people who are left hand dominant?

Brookshire and Casasanto used electroencephalography (EEG) read outs to compare left and right hemisphere brain wave activity. Participants were then asked to take a survey to determine their approach motivation levels.

Agreeing with previous research the right-handed participants had greater activity in the left hemisphere of the brain with approach motivation. What Brookshire and Casasanto discovered is that the left-handed participants showed greater activity in the right hemisphere of the brain with approach motivation.

Casasanto states, “Approach motivation is computed by the hemisphere that controls the right hand in right-handers, and by the hemisphere that controls the left hand in left-handers. We don’t think this is a coincidence. Neural circuits for motivation may be functionally related to circuits that control hand actions – emotion may be built upon neural circuits for action, in evolutionary and developmental time.”

Does this knowledge have any real world application? According to the study authors, using left hemisphere brain stimulation to treat depression and anxiety disorders may not be appropriate for left-handed patients. It may even do more harm than good.

Further research will be needed to fully understand the differences in electro-stimulant therapies on patients with different hemispheric dominance. 

This study was published in the online journal PLoS ONE April 26, 2012. Research was funded by the Max Planck Gesellschaft, a Hass Fellowship from the University of California at Berkley to Geoffrey Brookshire, and a James S. McDonnell Foundation Scholar Award to Daniel Casasanto and no conflicts of interest were found.

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Review Date: 
May 7, 2012