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While scientists have long believed human behavior developed with the expanded cerebrum, a �������ϲ����� researcher has shown that our path diverged while our brains were still comparable in size to those of chimpanzees.

To help her further unravel this mystery, the National Science Foundation has awarded a three-year, $310,000 grant to Mary Ann Raghanti, PhD, professor and chair of the anthropology department in the College of Arts and Sciences, for her project, “Human Origins and Comparative Neurochemistry.” The project continues research she published last year.

“W���� Ardipithecus emerged (more than 4 million years ago), something changed her behavior that helped her and her descendants become very successful,” Raghanti says. What makes a species behave in a different way comes down to an ancient part of the brain, the striatum—a subcortical region that regulates behaviors involved with social reward and is involved in personality styles and modern human language.

“If a behavior is not plugging into the reward circuit, you’re not going to do it. That’s what makes every species unique,” says Raghanti,who studies the neurochemicals that modulate behavior, including dopamine, serotonin, acetylcholineand neuropeptide Y.

What makes a species behave in a different way comes down to an ancient part of the brain.

“Humans have high levels of dopamine within the striatum, which makes us more prosocial and probably feeds into our pair bonding, altruism and empathy. In addition, we have lower acetylcholine. In other species, high acetylcholine is associated with aggression and internally-motivated (read: selfish) behavior.”

The shift that occured millions of years ago led to more prosocial behavior, and social relationships became more complex, leading to even more complicated neurochemistry.

“It becomes a feedback loop: more complicated behavior increases intelligence, which leads to more complicated behavior and so on,” Raghanti says.

Her current project includes the study of additional species and brain regions. The study also may lead to better understanding of neurodegenerative diseases like Alzheimer’s, Huntington’s and Parkinson’s diseases and neuropathologies like autism, obsessive compulsive disorder and attention deficit hyperactivity disorder.

“By understanding how the human brain is different from those of all other species,” Raghanti says, “we can begin to identify the targets for neuropathological processes that have devastating cognitive effects.” 

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