What is the amygdala?
We are hard-wired to respond emotionally to the sound of the human voice, Sometimes, that means grinning with YouTube’s laughing baby.

Or cringing at the sound of a movie drill sergeant.

Researchers are narrowing in on how the brain decides what makes speech pleasurable, or disturbing. Dr. Jeff Wenstrup heads a team studying sound and emotion at the Northeast Ohio Medical University.  

He says a variety of areas of the brain are affected by this interaction between speech and emotions and in particular a region of the brain called the amygdala, which is a center of emotional expression.

The amygdala, deep inside the brain is part of the limbic system, a set of brain structures that control emotion and memory.

No just for fear 
Wenstrup says the amygdala used to be thought of as mainly channeling fear in the brain. But a more complicated picture is emerging on how the amygdala orchestrates reactions to a variety of sounds.  He says, "They could be angry sounds, they could be pleasant sounds, but the key is that they’re important sounds, and that seems to be one of the jobs of the amygdala, to decide whether a sound is important or not.”

Wenstrup and his team are trying to figure out how the amygdala does this not in humans, but in creatures that live entirely in a world of sound: bats.

Inside the Wenstrup lab, graduate student Marie Gadziola measures the electrical output of amygdala neurons in bats.  She's learning to speak their language.  She says the neurons fire differently for different vocalizations. 

When Wenstrup pokes his head into a soundproof chamber holding a pair of bats fitted with electrodes, the electrodes measure the output of their amygdala neurons.

Gadziola says the neurons of the amygdala are very responsive to social vocalizations that the animals make.  She says, "they respond with these extremely long-lasting discharges of the neurons when the amygdala gets jazzed up and wants to show its response.”

Unlocking the amygdala code 
Wenstrup and his team believe that how long the amygdala neurons are firing helps the brain decide whether a sound is friendly or to be feared.

“The sound may only happen in tens or hundreds of milliseconds but the emotional response lasts much longer than that, so we think this prolonged activity of amygdala neurons is a way for it to orchestrate emotional responses.”

The implication of Wentrup’s research is that, for people with extreme emotional responses to sound, such as soldiers suffering from PTSD from battlefield blasts, the amygdala is too turned on, and, "hyper-responsive to any sound that comes in.”

Wenstrup’s research on bats may lead to an understanding of how people with a range of disorders can be helped.  Problems in the amygdala could affect people with autism, who have trouble interpreting emotion in speech, or people suffering from tinnitus -- a constant ringing in the ears.

Wenstrup says the problem of tinnitus in the military is extremely high.  Currently 1.5 million veterans are being treated for the condition at the cost of more than a billion dollars per year.

This month Jeff Wenstrup received a half million dollar grant from the National Institute on Deafness, part of $2.4 million in funding over the next five years, as he gradually pieces together an understanding of the mechanisms inside our brain linking sound and emotion.