Social Memory Breakthrough

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According to a recent study, researchers at Columbia University discovered that a small region of the hippocampus, known as CA2, is essential for the ability of an animal to recognize another of the same species, also known as “social memory”.  A better grasp of the function of CA2 could be useful in understanding and treating disorders, such as autism, schizophrenia and bipolar disorder, that cause altered social behaviors.

Henry Molaison

In 1953, surgeons removed a large piece of the hippocampus Henry Molaison (pictured) in an effort to fix his chronic epilepsy. As a result of the procedure, Molaison was unable to form new memories.

It’s not news to anybody that the hippocampus region of the brain plays a critical role in memory.  Recent studies, though, have shown that the hippocampus’ different subregions serve unique functions.  For example, the dentate gyrus is essential for distinguishing between similar environments, while CA3 allows us to recall memories from partial cues.  The CA1 region is vital for all forms of memory.  However, scientists had yet to discover the purpose of CA2.  Some studies had hinted that CA2 might be involved with social memory, since the region has a high level of a receptor for vasopressin, a hormone linked to sexual motivation, bonding and other social behaviors.  To learn more about this, researchers created mice in which CA2 neurons could be inhibited in adult adult animals.  Once these neurons were inhibited, these mice were given a series of behavioral tests.  Until the tests focused on social memory, the mice looked completely normal.  While mice are usually curious about a mouse they’ve never met, the mice in this experiment showed no preference for a new mouse versus a familiar mouse, which indicated a lack of social memory.

In two separate novel-object recognition tests, CA2-deficient mice showed a preference for an object that they hadn’t encountered before, which proved that the mice didn’t lose complete interest in novelty.  In another test, mice showed no loss in ability to discriminate social or non-social odors.  Because several neuropsychiatric disorders are associated with altered social behaviors, these findings hint that CA2 could lead to these behavioral changes.  This theory is validated by the discovery that people with such disorders have a decreased number of CA2 inhibitory neurons.  Therefore, CA2 could provide a new method for therapeutic approaches to the treatment of social disorders.

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