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Why desire drives us mad?

Mammal brains have fewer mechanisms for pleasure than desire, finds a US study.

health and fitness Updated: Mar 12, 2007 14:20 IST

A new brain study has finally pointed out why most mammals, are often likely to be left wanting rather than satisfied.

According to a study recently published in the Journal of Neuroscience, wanting and liking are separate urges in the brain that are controlled by different circuits. When these urges occur in sync, the impact on the brain is very powerful. But there’s a catch. Mammal brains appear to have fewer mechanisms for pleasure than they do for desire.

"Our results suggest we all are inherently susceptible to wanting more than we’ll actually enjoy, at least in certain situations," co-author Kent Berridge told Discovery News.

Berridge, a University of Michigan psychology researcher, added, "If separable brain circuits exist for liking and wanting, then a person who had selective activation of the wanting circuit would want more without liking more." Such want/like dissociations can lead to addictions with drugs, sex, food, gambling and more, the researchers believe. Some people also appear to be prone to experiencing the out-of-sync phases.

For the study, Berridge and colleague Kyle Smith used a painless microinjection technique to deliver droplets of an opioid drug into a pleasure hotspot within the brains of rats. The drug caused the rats to want to eat three times their normal amount of food — in this case, sugar — while liking it twice as much as usual.

The scientists measured the "like" degree in rats by studying their facial expressions and behaviours while they ate. These included lip and paw licking. The researchers then turned off a rat pleasure circuit by microinjecting an opioid suppressant into another part of the rodent’s brain. The rats reacted by still wanting sugar, but exhibited no extra signs of liking it.