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

How electroconvulsive therapy relieves depression per animal experiments

December 18, 2017
In a study using genetically engineered mice, Johns Hopkins researchers have uncovered some new molecular details that appear to explain how electroconvulsive therapy (ECT) rapidly relieves severe depression in mammals, presumably ...

'Simple, but powerful' model reveals mechanisms behind neuron development

December 18, 2017
All things must come to an end. This is particularly true for neurons, especially the extensions called axons that transmit electrochemical signals to other nerve cells. Without controlled termination of individual neuron ...

Restless leg syndrome risk factor for heart-related death

December 18, 2017
Restless leg syndrome (RLS) is associated with increased risk of cardiovascular disease (CVD)-related death among women, according to research published online today (Dec. 15) in the January 2018 issue of Neurology, the medical ...

Our memory shifts into high gear when we think about raising our children, new study shows

December 15, 2017
Human memory has evolved so people better recall events encountered while they are thinking about raising their offspring, according to a new study conducted by researchers at Binghamton University, State University of New ...

Offbeat brain rhythms during sleep make older adults forget

December 15, 2017
Like swinging a tennis racket during a ball toss to serve an ace, slow and speedy brainwaves during deep sleep must sync up at exactly the right moment to hit the save button on new memories, according to new UC Berkeley ...

Study finds graspable objects grab attention more than images of objects do

December 15, 2017
Does having the potential to act upon an object have a unique influence on behavior and brain responses to the object? That is the question Jacqueline Snow, assistant professor of psychology at the University of Nevada, Reno, ...

0 comments

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.