Tiny brain region better part of valor

Mar 09, 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

Explore further: How nerve cells communicate with each other over long distances

add to favorites email to friend print save as pdf

Related Stories

Trust-building hormone found

Dec 08, 2005

Scientists at the National Institute of Mental Health have discovered how a brain chemical recently found to boost trust appears to work.

Altering a protein makes mice less fearful

Aug 01, 2007

A University of Iowa study shows that loss or chemical inhibition of a protein, known as acid sensing ion channel protein (ASIC1a), reduces innate fear behavior in lab animals, making normally timid mice relatively fearless. ...

Research identifies brain cells related to fear

Jul 11, 2008

The National Institute of Mental Health estimates that in any given year, about 40 million adults (18 or older) will suffer from some form of anxiety disorder, including debilitating conditions such as phobias, panic dis ...

Very young found to process fear memories in unique way

Feb 06, 2008

Very young brains process memories of fear differently than more mature ones, new research indicates. The findings appear in the Feb. 6 issue of The Journal of Neuroscience. The work significantly advances scientific unders ...

Researcher uncovers new gene for fear factor

Nov 17, 2005

Rutgers geneticist Gleb Shumyatsky has discovered a gene that controls both innate and learned forms of fear. The gene, known as Stathmin or Oncoprotein 18, is highly concentrated in the amygdala, a key region of the brain ...

Recommended for you

Why your favourite song takes you down memory lane

Aug 28, 2014

Music triggers different functions of the brain, which helps explain why listening to a song you like might be enjoyable but a favourite song may plunge you into nostalgia, scientists said on Thursday.

Transcranial Magnetic Stimulation of brain boosts memory

Aug 28, 2014

Stimulating a particular region in the brain via non-invasive delivery of electrical current using magnetic pulses, called Transcranial Magnetic Stimulation, improves memory, reports a new Northwestern Medicine ...

User comments : 0