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February 28, 2008

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Brain workings linked to parental instinct

Feb. 28, 2008
Courtesy Public Library of Science
and World Science staff

Why do we al­most in­stinc­tively treat ba­bies as spe­cial, pro­tect­ing them and help­ing to en­sure their sur­viv­al?

Charles Dar­win ar­gued that there’s some­thing about in­fants that prompts adults to care for them, al­low­ing our spe­cies to sur­vive. Nobel-Prize-winning zo­olo­g­ist Kon­rad Lo­renz lat­er pro­posed that what in­spires this re­sponse is the shape of the in­fant face—including the large head and fore­head, big eyes and bulging cheeks. But a bi­o­log­i­cal ba­sis for these claims has re­mained elu­sive.

Nobel-Prize-winning zo­olo­g­ist Kon­rad Lo­renz has pro­posed that what in­spires the pa­rent­al re­sponse is the shape of the in­fant face—including the large head and fore­head, big eyes and bulging cheeks.
Now, sci­en­tists have re­ported a pos­si­ble brain ba­sis for this pa­ren­tal in­s­tinct. They have found that a re­gion of the hu­man brain called the me­di­al or­bi­to­front­al cor­tex goes into a flurry of activity al­most im­me­diate­ly in re­sponse to un­fa­mil­iar in­fant—but not adult—faces.

The find­ing may be use­ful in iden­ti­fy­ing moth­ers at risk for post­na­tal de­pres­sion, the sci­en­tists said. The con­di­tion, which makes it hard for some new moth­ers to car­ry out daily ac­ti­vi­ties, af­fects an es­ti­mat­ed 13 per­cent of moth­ers, of­ten with­in six weeks af­ter giv­ing birth.

Led by Morten Kringel­bach and Al­an Stein of the Uni­ver­s­ity of Ox­ford, the re­search­ers used a brain im­ag­ing meth­od called mag­ne­to­en­ce­phal­o­gra­phy, or MEG. 

Be­cause they were mainly in­ter­est­ed in highly au­to­mat­ic, or in­stinctual, re­sponses to faces, they used a task that re­quired par­ti­ci­pants to mon­i­tor the colour of a small red cross on a screen and to press a but­ton as soon as the colour changed. This was in­ter­spersed by adult and in­fant faces that were shown for 300 millisec­onds, but weren’t needed for the task.

The sight of ba­by faces typ­ic­ally led to a wave of me­di­al or­bit­o­fron­tal cor­tex ac­ti­vity with­in a sev­enth of a sec­ond—re­sponses probably too fast to be con­sciously con­trolled and thus, per­haps, in­stinc­tive, the in­ves­ti­ga­tors said.

Lo­cat­ed just over the eye­balls, the me­di­al or­bitofrontal cor­tex is thought to be a key re­gion of the emo­tion­al brain in­volved in mon­i­toring reward-related stim­u­li. The re­gion may pro­vide the nec­es­sary “e­mo­tion­al tag­ging” of in­fant faces that pre­dis­poses us to treat them as spe­cial, the re­search­ers said. The find­ings were pub­lished in the re­search jour­nal PLoS One on Feb. 27.

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Why do we almost instinctively treat babies as special, protecting them and helping to ensure their survival? Charles Darwin argued that there’s something about infants that prompts adults to care for them, allowing our species to survive. Nobel-Prize-winning zoologist Konrad Lorenz later proposed that what inspires this response is the shape of the infant face-including the large head and forehead, big eyes and bulging cheeks. But a biological basis for these claims has remained elusive. Now, scientists have reported a possible brain basis for this parental instinct. Led by Morten Kringelbach and Alan Stein of the University of Oxford, researchers found that a region of the human brain called the medial orbitofrontal cortex is highly and specifically active within a seventh of a second in response to unfamiliar infant-but not adult-faces. The finding may be useful in identifying mothers at risk for postnatal depression, the scientists said. The condition, which makes it hard for some new mothers to carry out daily activities, affects an estimated 13% of mothers, often within six weeks after giving birth. The researchers used a brain imaging method called magnetoencephalography, or MEG. Because they were mainly interested in highly automatic, or instinctual, responses to faces, they used a task that required participants to monitor the colour of a small red cross on a screen and to press a button as soon as the colour changed. This was interspersed by adult and infant faces that were shown for 300 milliseconds, but weren’t needed for the task. The sight of baby faces typically led to a wave of medial orbitofrontal cortex activity within a seventh of a second-responses probably too fast to be consciously controlled and thus perhaps instinctive, the investigators said. Located just over the eyeballs, the medial orbitofrontal cortex is thought to be a key region of the emotional brain involved in monitoring reward-related stimuli. The region may provide the necessary “emotional tagging” of infant faces that predisposes us to treat infant faces as special, the researchers said. The findings were published in the research journal PLoS ONE on Feb. 27.