The location of a person's neural systems for emotion depends on whether they are left-handed or right-handed, a new study has suggested.
According to the radical new model, the traditional understanding that the neural system for emotions, that is, those linked to approaching and engaging with the world (happiness, pride and anger) lives in the left side of the brain, and those associated with avoidance (disgust and fear) live in the right - have been turned around.
This, according to Daniel Casasanto, associate professor of human development and of psychology at Cornell University, is because the older studies were done almost exclusively on right-handed people, giving a skewed understanding of how emotion works in the brain.
The findings could mean that current treatment for the most common mental health problems could be ineffective or even detrimental to a large chunk of the population, the professor said.
Older studies were done almost exclusively on right-handed people, giving a skewed understanding of how emotion works in the brain
"The old model suggests that each hemisphere is specialised for one type of emotion, but that's not true," Casasanto explained.
"Approach emotions are smeared over both hemispheres according to the direction and degree of your handedness. The big theoretical shift is, we're saying emotion in the brain isn't its own system. Emotion in the cerebral cortex is built upon neural systems for motor action."
The study is entitled Approach motivation in human cerebral cortex, appeared in Philosophical Transactions of the Royal Society B: Biological Sciences, and theorises research called the "sword and shield" hypothesis. This stems from Casasanto's observation that we use our dominant hands for approach-oriented actions, while nondominant hands are used for avoidance movements.
"You would wield the sword in your dominant hand to make approach-related actions like stabbing your enemy, and use the shield in your nondominant hand to fend off attack," he added. "Your dominant hand gets the thing you want and your nondominant hand pushes away the thing you don't."
The old model suggests that each hemisphere is specialised for one type of emotion, but that's not true
The researchers theorised that approach and avoidance emotions are built on neural systems for approach and avoidance actions.
"If this sword and shield hypothesis is correct," he said, "then three things should follow: Approach motivation should be mediated by the left hemisphere in strong right-handers, as it has been in tons of previous studies.
"But it should completely reverse in strong left-handers. For everyone in the middle of the handedness spectrum, approach emotions should depend on both hemispheres."
His theories looked to be proved accurate when the experiment worked, corroborating the researchers' first test of the sword and shield hypothesis using brain imaging. Strong righties who were zapped in the left hemisphere experienced a boost in positive emotions and strong lefties zapped in the right hemisphere.
But when lefties are zapped in the left hemisphere, or righties in the right, "you see either no change or a detriment in the experience of these emotions," Casasanto explained.
Nevertheless, Casasanto warned that his research studied only healthy participants and more work is needed to strengthen his findings to a clinical setting.
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