A hormone known as the “love drug” because of its role in bonding between mother and child – as well as between lovers – has been shown to permanently alter the nerve pathways in the brain controlling certain social behaviour.
Studies on laboratory mice have found that oxytocin changes the behaviour of virgin females so that they are able to recognise and respond to the distress calls of baby mice despite never having given birth.
Scientists have shown oxytocin, a hormone that is also produced by women during childbirth and breastfeeding, irrevocably changes the why nerve cells communicate in the auditory cortex of the left side of the mouse’s brain. This area is responsible for processing the barely-audible distress sounds made by baby mice when separated from their mother.
The researchers said the findings demonstrate that oxytocin plays in important role in manipulating how the brain processes social information. They believe the results could lead to new ways of using the hormone as as drug to treat a range of psychological problems related to social behaviour.
“Our findings redefine oxytocin as something completely different from a 'love drug,' but more as an amplifier and suppressor of neural signals in the brain,” said Robert Froemke of New York University Langone and senior investigator on the study, published in the journal Nature.
“We found that oxytocin turns up the volume of social information processed in the brain. This suggests that it could one day be used to treat social anxiety, post-traumatic stress disorder, speech and language disorders, and even psychological issues stemming from child abuse,” Dr Froemke said.
“Our future research includes further experiments to understand the natural conditions, beyond childbirth, under which oxytocin is released in the brain,” he said.
The study investigated the natural instinct of mouse mothers to retrieve any of their pups that have strayed out of the nest. This behaviour is triggered by the high-pitched ultrasound calls made by mouse pups when they are in distress, but the sounds only works on females that have given birth and so have therefore already been exposed to high oxytocin levels.
Virgin female mice show no response to these distress calls, yet when injected with oxytocin they respond in the same manner as experienced mothers, quickly searching for stray pups and bringing them by the scruff of their neck back to the nest.
“It was remarkable to watch how adding oxytocin shifted animal behaviour, as mice that didn't know how to perform a social task could suddenly do it perfectly,” said Bianca Marlin, a postdoctoral researcher at NYU Langone and the study’s lead author.
The scientists found that this learned behaviour was permanent and when they mapped oxytocin’s effect in the brain of the mice, they found it was working on the left hemisphere of the auditory cortex. In other words they believe that oxytocin was controlling the volume of “social information” that was being processed by individual nerve cells, similar to the way a dimmer switch can turn a light up or down.
“This neuronal effect was long-lasting, suggesting that it might provide a key mechanism for establishing memories of socially relevant sounds in the auditory cortex,” said Robert Liu, an expert on oxytocin at Emory University in Atlanta Georgia, who was not involved in the study.
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