Tiny brain region better part of valor

March 9, 2009

Mice lose their fear of territorial rivals when a tiny piece of their brain is neutralized, a new study reports.

The study adds to evidence that primal responses do not depend on the amygdala - long a favored region of fear researchers - but on an obscure corner of the primeval .

A group of neuroscientists led by Larry Swanson of the University of Southern California studied the of rats and mice exposed to cats, or to rival rodents defending their territory.

Both experiences activated neurons in the dorsal premammillary nucleus, part of an ancient brain region called the hypothalamus.

Swanson's group then made tiny lesions in the same area. Those rodents behaved far differently.

"These animals are not afraid of a predator," Swanson said. "It's almost like they go up and shake hands with a predator."

Lost fear of cats in rodents with such lesions has been observed before. More important for studies of , the study replicated the finding for male rats that wandered into another male's territory.

Instead of adopting the usual passive pose, the intruder frequently stood upright and boxed with the resident male, avoided exposing his neck and back, and came back for more even when losing.

"It's amazing that these lesions appear to abolish responses," said Swanson, who added: "The same is found in primates and people that we find in rats and mice."

The study was slated for online publication the week of March 9 in .

Swanson predicted that his group's findings would shift some research away from the amygdala, a major target of fear studies for the past 30 years.

"This is a new perspective on what part of the brain controls fear," he said.

He explained that most amygdala studies have focused on a different type of fear, which might more accurately be called caution or risk aversion.

In those studies, animals receive an electric shock to their feet. When placed in the same environment a few days later, they display caution and increased activity of the amygdala.

But the emotion experienced in that case may differ from the response to a physical attack.

"We're not just dealing with one system that controls all fear," Swanson said.

Swanson and collaborators have been studying the role of the hypothalamus in the fear response since 1992.

Because of its role in basic survival functions such as feeding, reproduction and the sleep-wake cycle, the hypothalamus seems a plausible candidate for fear studies.

Yet, said Swanson, "nobody's paid any attention to it."

The PNAS study is the most recent of several by Swanson on fear and the hypothalamus. The few other researchers in the area include Newton Canteras of the University of Sao Paulo in Brazil, who collaborated with Swanson on the PNAS study, as well as Robert and Caroline Blanchard of the University of Hawaii.

Source: University of Southern California

Related Stories

Recommended for you

Neuro chip records brain cell activity

October 26, 2016

Brain functions are controlled by millions of brain cells. However, in order to understand how the brain controls functions, such as simple reflexes or learning and memory, we must be able to record the activity of large ...

After blindness, the adult brain can learn to see again

October 25, 2016

More than 40 million people worldwide are blind, and many of them reach this condition after many years of slow and progressive retinal degeneration. The development of sophisticated prostheses or new light-responsive elements, ...

The current state of psychobiotics

October 25, 2016

Now that we know that gut bacteria can speak to the brain—in ways that affect our mood, our appetite, and even our circadian rhythms—the next challenge for scientists is to control this communication. The science of psychobiotics, ...

Can a brain-computer interface convert your thoughts to text?

October 25, 2016

Ever wonder what it would be like if a device could decode your thoughts into actual speech or written words? While this might enhance the capabilities of already existing speech interfaces with devices, it could be a potential ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.