Large amygdalas, it seems, are social amygdalas.

These paired regions, typically referred to as almond-shaped (indeed their name comes from the Greek for almond), are known to be part of the brain responsible for sociability as well as fear and other deep-seated emotions. Lisa Feldman Barrett and colleagues sought to find out whether size matters in the amygdala, and according to their study in Nature Neuroscience, there is a connection between people having big amygdalas and having big, complex social networks.

The researchers measured two social network factors in 58 adults. First, they calculated the size of a participant’s network, which is simply the total number of people that are in regular contact with the participant. Second, they measured the network’s complexity, based on how many different groups a participant’s contacts can be divided into. … Linear regression revealed a positive correlation in amygdala size with both social network size and complexity. [Ars Technica]

The team’s MRI scans found a wide variation in amygdala size, from about 2.5 cubic millimeters to more than five. But other factors like a person’s happiness didn’t match up with amygdala size. And the subjects’ hippocampus, which the scientists used as a control, showed no variation when compared to a person’s social network. Only the amygdala size showed the connection, Barrett says.

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Whether your fear is panicked, like in a life-or-death situation, or deliberative, like a decision about whether to take a big risk on game show, it all comes back to the amygdala. And a new study of patients with lesions on the amygdala, reported by Caltech scientists in the Proceedings of the National Academy of Sciences, suggests that damage to our brain’s fear center might turn people into reckless gamblers.

The researchers found two women with Urbach-Wiethe disease, which results in damage to the almond-shaped amygdala. Benedetto De Martinoa and his team paired those two with 12 people with undamaged brains, and presented everyone with a series of gambling tests. The study found that healthy volunteers would only opt to gamble if the potential gains were one and a half to two times the size of the potential losses [BBC News]. The women with Urbach-Wiethe, however, would keep rolling the dice as the odds got worse, and in some cases would even play if the potential loss was greater than the potential gain.

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When people breathe in carbon dioxide, they start to panic. It happens in mice and other animals, too, as the body responds to the threat of suffocation. Now, in a study in Cell, researchers have connected a particular gene to that response in the brain.

The gene, called ASIC1a, is connected to a protein found in abundance in the amygdala, the area scientists believe to be the brain’s fear center. In their new study … the researchers show that mice lacking this gene don’t freeze in place–a commonly used indicator of rodent fear–to the extent that normal mice do when the team pumped CO2 into their enclosure. But when Wemmie and colleagues injected a virus containing the ASIC1a gene into the amygdala of the mice, they acted like normal mice, freezing up when exposed to elevated CO2 [ScienceNOW Daily News].

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