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'Social Dementia' Decimates Special Neurons

Being human has its pluses and minuses. Our cognitive powers are superior to that of other animals, and we can act consciously to alter our destinies. On the other hand, our highly evolved brains are prone to serious malfunctions such as mental illness and dementia. Now a team of neuroscientists has found that some of these blessings and curses might be linked to the same specialized neural circuits.

In 1999, researchers discovered that the brains of humans and great apes such as chimpanzees and gorillas contain special elongated nerve cells called spindle neurons. These cells, also known as Von Economo neurons (VENs), are localized in two parts of the cerebral cortex known to be associated with social behavior, consciousness, and emotion. They are not found in other primates, although very recently they were discovered in some whales (ScienceNOW, 27 November).

William Seeley, a neurologist at the University of California, San Francisco, and colleagues set out to see whether VENs play a role in a type of dementia that causes people to lose inhibition in social situations. People with frontotemporal dementia (FTD) engage in inappropriate and impulsive behavior and sometimes even carry out criminal acts such as shoplifting. The team looked at the brains of 7 deceased patients with FTD and compared them to 7 controls who had died of causes unrelated to the brain, as well as 5 patients diagnosed with Alzheimer's disease, a very different type of dementia that mainly affects memory. The researchers found that one of the two brain areas that contain VENs, the anterior cingulate cortex, looked very different in FTD patients: There was a 74% reduction in the number of VENs compared to controls. In contrast, Alzheimer's patients had only a small and statistically insignificant reduction, they report online today in Annals of Neurology.

Seeley and his colleagues conclude that VENs may play a key role in making humans the social creatures that we are, but that they also expose us to a higher risk of degenerative neural diseases. Lary Walker, a neuroscientist at Emory University in Atlanta, Georgia, says that the authors make a "reasonably compelling case that the VENs are selectively vulnerable in FTD". Nevertheless, Walker cautions against ascribing complex behaviors to the action of specific cells or regions in the brain.

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